help button home button Endocrine Society JCEM JCEM Call for Nominations for EIC
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Submit a related Letter to the Editor
Right arrow Purchase Article
Right arrow View Shopping Cart
Right arrow Alert me when this article is cited
Right arrow Alert me when eLetters are posted
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow Request Copyright Permission
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Van den Berghe, G.
Right arrow Articles by Bouillon, R.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Van den Berghe, G.
Right arrow Articles by Bouillon, R.
The Journal of Clinical Endocrinology & Metabolism Vol. 84, No. 4 1311-1323
Copyright © 1999 by The Endocrine Society

Original Studies

Reactivation of Pituitary Hormone Release and Metabolic Improvement by Infusion of Growth Hormone-Releasing Peptide and Thyrotropin-Releasing Hormone in Patients with Protracted Critical Illness1

Greet Van den Berghe, Pieter Wouters, Frank Weekers, Subburaman Mohan, Robert C. Baxter, Johannes D. Veldhuis, Cyril Y. Bowers and Roger Bouillon

Department of Intensive Care Medicine (G.V.d.B., P.W., F.W.) and Laboratory for Experimental Medicine and Endocrinology (R.B.), University Hospital Gasthuisberg, University of Leuven, B-3000 Leuven, Belgium; Loma Linda University, Jerry L. Pettis Veterans Administration Medical Center (S.M.), Loma Linda, California 92357; Kolling Institute of Medical Research, Royal North Shore Hospital, Sydney University (R.C.B.), St. Leonards, New South Wales 2065, Australia; the Department of Medicine, Division of Endocrinology, University of Virginia Health Sciences Center (J.D.V.), Charlottesville, Virginia 29908; and the Department of Medicine, Division of Endocrinology, Tulane University Medical Center (C.Y.B.), New Orleans, Louisiana 70112-2699

Address all correspondence and requests for reprints to: Greet Van den Berghe, M.D., Ph.D., Department of Intensive Care Medicine, University Hospital Gasthuisberg, University of Leuven, B-3000 Leuven, Belgium. E-mail: greta.vandenberghe{at}uz.kuleuven.ac.be


   Abstract
Top
 Abstract
Introduction
 Subjects and Methods
 Results
 Discussion
 References
 
Protracted critical illness is marked by protein wasting resistant to feeding, by accumulation of fat stores, and by suppressed pulsatile release of GH and TSH. We previously showed that the latter can be reactivated by brief infusion of GH-releasing peptide (GHRP-2) and TRH. Here, we studied combined GHRP-2 and TRH infusion for 5 days, which allowed a limited evaluation of the metabolic effectiveness of this novel trophic endocrine strategy.

Fourteen patients (mean ± SD age, 68 ± 11 yr), critically ill for 40 ± 28 days, were compared to a matched group of community-living control subjects at baseline and subsequently received 5 days of placebo and 5 days of GHRP-2 plus TRH (1+1 µg/kg·h) infusion in random order.

At baseline, impaired anabolism, as indicated by biochemical markers (osteocalcin and leptin), was linked to hyposomatotropism [reduced pulsatile GH secretion, as determined by deconvolution analysis, and low GH-dependent insulin-like growth factor and binding protein (IGFBP) levels]. Biochemical markers of accelerated catabolism (increased protein degradation and bone resorption) were related to tertiary hypothyroidism and the serum concentration of IGFBP-1, but not to hyposomatotropism. Metabolic markers were independent of elevated serum cortisol.

After 5 days of GHRP-2 plus TRH infusion, osteocalcin concentrations increased 19% vs. -6% with placebo, and leptin had rose 32% vs. -15% with placebo. These anabolic effects were linked to increased IGF-I and GH-dependent IGFBP, which reached near-normal levels from day 2 onward. In addition, protein degradation was reduced, as indicated by a drop in the urea/creatinine ratio, an effect that was related to the correction of tertiary hypothyroidism, with near-normal thyroid hormone levels reached and maintained from day 2 onward. Concomitantly, a spontaneous tendency of IGFBP-1 to rise and of insulin to decrease was reversed. Cortisol concentrations were not detectably altered.

In conclusion, 5-day infusion of GHRP-2 plus TRH in protracted critical illness reactivates blunted GH and TSH secretion, with preserved pulsatility, peripheral responsiveness, and feedback inhibition and without affecting serum cortisol, and induces a shift toward anabolic metabolism. This provides the first evidence of the metabolic effectiveness of short term GHRP-2 plus TRH agonism in this particular wasting condition.


   Introduction
Top
 Abstract
 Introduction
Subjects and Methods
 Results
 Discussion
 References
 
CRITICALLY ill patients supported by intensive medical care for weeks or months present with feeding-resistant loss of protein, whereas fat stores are paradoxically preserved or even accrue (1, 2). The consequences of this wasting are skeletal muscle weakness, deficient healing of wounds and fractures, osteoporosis, and impaired recovery of failing organ systems, which together further prolong the dependency on intensive care support.

From a neuroendocrine perspective, the chronic phase of severe illness treated with intensive care for several weeks is different from the first few days after resuscitation (3, 4, 5, 6). Within hours after the onset of acute illness or trauma, anterior pituitary function is activated, which contributes to the metabolic adaptation essential for survival. In contrast, protracted critical illness is characterized by a uniformly suppressed pulsatile secretion of GH, TSH, and PRL and is accompanied by low serum levels of insulin-like growth factor I (IGF-I), thyroid hormones, and leptin (3, 4, 5, 6). We previously reported that pulsatile secretion of GH and TSH in this condition can be reactivated acutely by the continuous and combined infusion of GH-releasing peptide-2 (GHRP-2) (7) and TRH for 21–45 h, which elicits a proportionate rise in circulating IGF-I and thyroid hormones (3, 4, 5, 6). This suggested that the relative impairment of pulsatile GH and TSH release in protracted critical illness is at least partly due to a reduced content or activity of hypothalamic TRH and of the putative endogenous ligand for the GH secretagogue receptor (3, 4, 5, 6, 8).

In the current study, we hypothesized that impaired hypothalamic stimulation of anterior pituitary hormone secretion, as evident distinctively in the chronic phase of critical illness, contributes to the development and maintenance of the wasting syndrome. We tested this hypothesis by extending the infusion time of GHRP-2 plus TRH to 5 days, which allowed a limited evaluation of the metabolic effectiveness of this novel endocrine strategy. As we postulated a deficiency of endogenous hypothalamic releasing factors, we anticipated exogenous GHRP-2 plus TRH to reinstate pulsatile anterior pituitary hormone secretion, in turn maintained within physiological ranges by active feedback inhibition loops. To assess the metabolic effectiveness of releasing peptides in this wasting condition, we studied selected biochemical markers of catabolism (urea production and urinary excretion of collagen cross-links) and markers of anabolism [serum concentrations of osteocalcin (OC), skeletal alkaline phosphatase (sALP), carboxyl-terminal extension peptide of type I procollagen (PICP), and leptin].


   Subjects and Methods
Top
 Abstract
 Introduction
 Subjects and Methods
Results
 Discussion
 References
 
Patients and concomitant treatment

As the particular wasting syndrome present in protracted critical illness is determined by the duration, rather than the type, of critical condition (2), patients depending on intensive care (including mechanical ventilatory support) for at least 2 weeks and with an expected stay in the intensive care unit (ICU) of at least another 2 weeks were eligible for participation in this study. Further inclusion criteria were a stable condition without dopamine treatment for at least 72 h, in view of the pronounced suppressive effect dopamine exerts on pituitary function in this type of patient (9, 10, 11, 12). Exclusion criteria were age less than 18 yr; preexisting neurological, psychiatric, metabolic, or endocrine disease; intracranial lesions; clinically significant liver failure (prothrombin time, <30%); renal failure requiring replacement therapy; concomitant treatment with glucocorticoids, estrogens, somatostatin, thyroid hormones, Ca2+ reentry blockers, clonidine, amiodarone, etomidate, dopamine agonists, or antagonists; and the use of iodine in antiseptic dressings or as iv contrast agents.

A total of 14 patients (4 women and 10 men) were included in this study (Table 1Go). The mean ± SD age was 68 ± 11 yr (range, 44–81 yr). The Apache II score, an indicator of severity of illness, with higher values reflecting a more critical condition (13), was 15.5 ± 6.4 (range, 7–33) on the ICU admission day and 14.1 ± 4.1 (range, 8–23) on the day of inclusion in the study. Body mass index was 24.5 ± 4.6 kg/m2 (range, 19–38 kg/m2). Patients were critically ill for 40 ± 28 days (range, 14–92 days) at the time of inclusion in the study. Concomitant treatment included standardized, continuously administered feeding: total parenteral nutrition (n = 8), combined parenteral and enteral nutrition (n = 3), or full enteral feeding (n = 3). Caloric intake (a mean of 29 nonprotein kilocalories per kg/day; range, 23–35 Cal/kg·day) and composition (0.8–1.6 g amino acids/kg·day; 2.8–4.0 g glucose/kg·day, and 1–1.5 g fat/kg·day covering 25–40% of nonprotein calories) were adequate (14). Other concomitant therapies consisted of standardized vitamin supplements, including 220 IU cholecalciferol/day (n = 14), inotropic support with exogenous nondopaminergic catecholamines (n = 4), antibiotics (n = 10), analgesia and sedation with continuously infused opioids (n = 10), and/or benzodiazepines (n = 3). Blood glucose levels were monitored every 4 h and clamped between 5–9 mmol/L with continuous insulin infusion if necessary (n = 8) (15). At the start of the study, the blood glucose level was 7.5 ± 1.3 mmol/L (range, 4.9–8.6 mmol/L). Human albumin was continuously infused when serum levels were very low (mean serum albumin concentration at inclusion, 2.5 ± 0.4 g/dL). The mean serum level of triglycerides was 159 ± 70 mg/dL (range, 54–278 mg/dL), and the C reactive protein concentration was elevated (136 ± 8 mg/L). Continuous hemodynamic monitoring always included electrocardiogram, intraarterial blood pressure, central venous pressure, fluid balance, and core and peripheral temperatures. During the entire study period, the concomitant ICU therapy, including the feeding regimen, remained virtually unaltered, allowing for optimization of and eventually partial weaning from ventilatory and hemodynamic support.


View this table:
[in this window]
[in a new window]
  		Table 1. Clinical patient data

 
The ultimate outcome of the studied patients was a total ICU stay of 69 ± 40 (range, 23–146) days. One patient died from intercurrent sepsis during the course of the study (on day 5 of the GHRP-2 plus TRH infusion). Three patients died in the ICU, respectively 35, 27, and 11 days after inclusion in the study. Ten patients were discharged to the ward, subsequently left the hospital, and are known to be well 4–9 months after the end of the study. The observed mortality in this study (28%) was not significantly different from the expected mortality (37%), as determined in a group of patients (n = 111) matched for age, duration of stay in the ICU, and underlying diseases, treated in the ICU during the 12 months preceding the study.

The study was approved by the institutional review board of the University of Leuven School of Medicine. Informed consent from a first degree relative was obtained before patient inclusion in the study.

Study design and peptide administration

For selected parameters, the baseline condition of the study group was compared to that of an age- and gender-matched sample of 65 community-living control subjects (15 women and 50 men; mean ± SD age, 68 ± 8 yr) previously recruited and studied with the same assays for an independent study (16, 17).

Patients were studied during a total period of 10 days and received an overnight (2100–0006 h) sampling (every 20 min) on nights 0, 5, and 10. Additional blood samples were taken daily at 0600 h. In 7 of 14 patients, a complete 24-h urine collection on HCl was obtained on days 0, 5, and 10.

Patients were randomized to receive one of two cross-over treatment schedules, which were initiated after a baseline overnight sampling every 20 min: group 1 (n = 6) started with a placebo infusion for 5 days, followed by a continuous infusion of GHRP-2 plus TRH (1 µg/kg GHRP-2 plus 1 µg/kg TRH bolus at 0600 h preceding a continuous infusion of 1 µg/kg·h GHRP-2 plus 1 µg/kg·h TRH) for the next 5 days; and group 2 (n = 8) received GHRP-2 plus TRH (1 µg/kg GHRP-2 plus 1 µg/kg TRH bolus at 0600 h preceding a continuous infusion of 1 µg/kg·h GHRP-2 and 1 µg/kg·h TRH) for 5 days followed by a placebo infusion for the next 5 days.

Placebo (0.9% NaCl), TRH (200 µg/mL 0.9% NaCl; Ferring, Kiel, Germany) and GHRP-2 (50 µg/mL 0.9% NaCl; Kaken Pharmaceutical Co. Ltd., Tokyo, Japan) infusions were given through a separate lumen of a central venous catheter, inserted for clinical purposes. A PERFUSOR Secura FT pump with a 50-mL PERFUSOR syringe (B. Braun, Melsungen, Germany) permitted precise infusions of small volumes at a constant rate. Inadvertent interruption of the infusion or unanticipated bolus injections of the peptides were thereby avoided.

Serum concentrations of GH, TSH, and PRL were measured in each sample of the nocturnal time series, and serum cortisol levels were measured every hour. At 2100 h on nights 0, 5, and 10, serum IGF-I and IGF-binding protein-1 (IGFBP-1) were determined. Daily at 0600 h, serum concentrations of IGF-I, IGFBP-1, IGFBP-3, the acid-labile subunit (ALS), IGFBP-4, IGFBP-5, insulin, leptin, T4, T3, rT3, and 25OHD3 were determined. Serum concentrations of OC, PICP, sALP, were determined at 2100 and 0600 h on study nights 0 and 5.

Urinary excretion of collagen cross-links [pyridinoline and deoxypyridinoline (PYD and DPD) normalized for urinary creatinine in an acidified (HCl) 24-h urine collection] was determined when a complete 24-h urine collection was available. Serum concentrations of urea and creatinine were determined at 0600 h on a daily clinical basis.

Blood sampling

All blood samples were collected through an arterial line inserted for clinical purposes independently of this study. The Edwards VAMP system (Baxter Healthcare Corp., Irvine, CA) was used, permitting withdrawal of undiluted blood samples from an indwelling catheter without undue blood loss. The total amount of blood sampled per patient over 10 days was 270 mL. Blood was collected into Vacutainer tubes (Becton Dickinson Vacutainer Systems, Meylan Cedex, France); after clotting and centrifugation, the serum was kept frozen at -20 C until assay.

Assays

All samples from each patient were processed in the same assay run. All samples had detectable values for each of the determinations (see assays below). Normal ranges for the assay, mean ± SD values, and range of the control population for each measurement are listed in Table 2Go.


View this table:
[in this window]
[in a new window]
  		Table 2. Endocrine and metabolic measurements at baseline

 
Serum concentrations of GH were measured by RIA, using the Nichols Institute Diagnostics HGH immunoassay 100T kit (40-2155, San Juan Capistrano, CA). The intraassay coefficient of variation was 4.2% at 1.4 µg/L and 2.8% at 12.2 µg/L. The serum concentrations of total IGF-I were measured by RIA after acid-ethanol extraction. The intraassay coefficient of variation was 10.1% at 95 µg/L and 5.5% at 474 µg/L. The between-assay coefficient of variation was 14.8% at 109 µg/L and 10.1% at 389 µg/L. IGFBP-1 was purified from amniotic fluid as previously described (18) using an IGF-I affinity column. The measurements were performed by RIA, using 125I-labeled IGFBP-1 as radiolabel (SA, 284 mCi/mg) and a rabbit polyclonal antiserum. The intraassay coefficient of variation ranged from 2.4–4.0% (n = 10 for 6 samples), and the interassay coefficient of variation ranged from 6.2–9.7% (for 2 samples; n = 15 and 14, respectively). The normal value for a gender-matched control population (n = 114; aged 18–60 yr) was 11.6 ± 9.0 µg/L, ranging from 0–52.4 µg/L. The serum IGFBP-3 concentrations were measured by RIA as previously described (19), using antiserum R-100. The intraassay coefficient of variation was 6.2% at 2.5 mg/L and 5.5% at 5.7 mg/L, and the between-assay coefficient of variation was 11.9% at 2.9 mg/L and 14.5% at 6.3 mg/L. The serum ALS concentrations were assessed by RIA, as previously described (20). The intraassay coefficient of variation was 3.4%, and the between-assay coefficient of variation was 10.5% at 5.3 mg/L and 5.4% at 24 mg/L. Circulating levels of IGFBP-4 and IGFBP-5 were measured by specific RIAs using guinea pig antisera and recombinant IGFBP standard and tracer as described previously (21, 22). The intra- and interassay coefficients of variation for both of these assays were less than 10%. None of the other purified IGFBPs produced significant cross-reactivity in either of these two assays.

Serum insulin levels were determined by a human insulin immunoradiometric assay (Medgenix INS-IRMA, BioSource, Fleurus, Belgium). The intraassay coefficient of variation was 4.5% at 6.6 µIU/mL and 2.1% at 53 µIU/mL.

All serum leptin concentrations were determined by a human leptin RIA (Linco Research, Inc., St. Charles, MO) using a single assay run. The intraassay coefficient of variation was 6.3% at a leptin concentration of 15.6 µg/L.

Serum concentrations of TSH were measured by immunoradiometric assay using the TSH Riabead II (Abbott Laboratories, North Chicago, IL). The intraassay coefficient of variation was 4.3% at 1.2 mIU/L and 2.2% at 7.0 mIU/L. The detection limit was less than 0.02 mIU/L. From two patients presenting with undetectable values using this assay, all samples were reassayed using the TSH electrochemiluminescence assay (Elecsys, Boehringer Mannheim, Mannheim, Germany), which has a sensitivity of 0.005 mIU/L. The intraassay coefficient of variation was 6.7% at 0.03 mIU/L and 1.7% at 0.1 mIU/L. Serum concentrations of T4 were measured by RIA using the Tetrabead-125 Diagnostic Kit (Abbott Laboratories). The intraassay coefficient of variation was 4.6% at 59 nmol/L and 4.4% at 102 nmol/L. Serum concentrations of T3 were measured by RIA using the T3 Riabead Kit (Abbott Laboratories). The intraassay coefficient of variation was 5.9% at 1.1 nmol/L and 4.4% at 2.8 nmol/L. Serum concentrations of rT3 were measured by RIA using the rT3 Kit (Techland SA, Liege, Belgium). The intraassay coefficient of variation was 10.5% at 0.8 nmol/L and 10.3% at 4 nmol/L.

Serum concentrations of PRL were measured by immunoradiometric assay using the PRL-IRMA Kit (Medgenix, Fleurus, Belgium). The intraassay coefficient of variation was 6.2% at 6.6 µg/L and 4.7% at 46.4 µg/L.

Serum concentrations of cortisol were measured by RIA after extraction with dichloromethane. The intraassay coefficient of variation was 3.1% at 417 nmol/L.

Serum OC was measured by a homologous human osteocalcin RIA. The within- and between-assay variation coefficients were 5% and 7%, respectively (23). Serum levels of carboxyl-terminal extension peptide of PICP were measured by RIA (Orion Diagnostica, Espoo, Finland). The between-assay variation coefficient was 6.6% at 216 µg/L and 4.0% at 435 µg/L. The within-assay coefficient of variation was 2.7% at 214 µg/L and 3.2% at 451 µg/L. Serum sALP was determined by immunoradiometric assay (Tandem-R Ostase, Hybritech, Inc., San Diego, CA). The intraassay CV was 6.7% at 13.2 µg/L, and the interassay CV was 8.1% at 11.7 µg/L. Urinary pyridinolines (PYD and DPD) were measured in 24-h urine collections acidified with hydrochloric acid, as previously described (16, 17, 24). Values are expressed as nanomoles per mmol creatinine, and urinary creatinine was measured colorimetrically (25). Interassay coefficients of variation were 11.5% and 13.3% for PYD and DPD, respectively (n = 12), and within-assay coefficients of variation were 10.2% and 12.5% (n = 9). Serum 25OHD3 was measured by competitive binding assay as previously described (26).

The urea concentration was measured in serum on a routine clinical basis using a kinetic UV test (Boehringer Mannheim Systems, Germany/Hitachi 737). The total inaccuracy was 3.15% at 50 mg/dL and 1.76% at 158 mg/dL. The creatinine concentration was measured daily in serum using the Jaffé method (Boehringer Mannheim Systems, Mannheim, Germany/Hitachi 737). The total inaccuracy was 3% at 1.9 mg/dL and 1.5% at 4.1 mg/dL.

Data analysis

The time series of sequential serum GH concentrations measured overnight was transformed into pituitary secretion profiles by adjusting for endogenous GH half-life using multiple parameter deconvolution analysis (27). This method is designed to compute hormonal half-life and the number, amplitude, and mass of underlying pituitary secretory bursts and to estimate tonic (basal or nonpulsatile) secretion (27).

Individual GH half-lives were estimated on each of the 3 study nights and were not different; hence, they were averaged before application to the data series. Besides mean serum concentrations, the following parameters were calculated for each hormonal profile in each subject: basal secretion rate (estimated as the amount of hormone continuously released from the pituitary to achieve serum concentrations approximating the mean of the lowest 5% of all values observed [micrograms per liter of distribution volume (Lv)] and per min), amplitudes (maximal secretory rate, micrograms per Lv and per min) and temporal positions of all secretory bursts, the mass of hormone secreted per burst (estimated as the area of the resolved secretion burst, micrograms per Lv), and the mean pulsatile production (calculated as the product of the number of secretory bursts and the mean secretory burst mass over the time interval considered, micrograms per Lv over 9 h). The total nocturnal GH production (micrograms per Lv) was calculated as the sum of pulsatile GH production (micrograms per Lv) over 9 h and the nonpulsatile GH secretion over 9 h [basal GH secretion rate (micrograms per Lv/min) x 540 min]. The proportion of pulsatile secretion (percentage) was calculated as the pulsatile production over 9 h divided by the total nocturnal GH production, multiplied by 100.

TSH, PRL, and cortisol profiles were quantified by determining area under the curve, calculated using the trapezoid rule, and by mean nocturnal serum concentrations.

We used the changes in the serum urea/creatinine ratio (UCR) as a marker of alterations in overall protein degradation, which is appropriate in the absence of prerenal kidney failure and with normal and constant protein and fluid intake, as present in this study (28). The UCR of matched controls was 28.9 ± 4.6 (range, 21.5–38.3).

At inclusion in the study, groups were compared using two-tailed unpaired t test, Mann-Whitney U test, and {chi}2 test. Comparison with literature reference values for pulsatile fraction of GH release was performed using the two-tailed, one-sample t test. The effect of intervention was analyzed using repeated measures ANOVA or two-tailed paired and unpaired t tests, as appropriate. Results are expressed as the mean ± SD unless indicated otherwise. P < 0.05 was construed as significant.


   Results
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
Discussion
 References
 
Baseline patient characteristics are shown in Tables 1Go and 2Go and were statistically identical in both study groups.

Infusing the releasing peptides was well tolerated. No side-effects were noted, apart from an increased insulin requirement to maintain the blood glucose level below the preset upper limit of 9 mmol/L in those patients already receiving exogenous insulin infusion (Table 1Go). Serum concentrations of triglycerides did not change significantly throughout the study (data not shown).

Somatotropic axis

Pulsatile GH secretion and GH-dependent IGF-I and IGFBPs were jointly reduced at baseline as shown in Table 2Go, positively interrelated as shown in Fig. 1Go, and similar in both study groups. The IGFBPs known to be GH independent (IGFBP-1 and IGFBP-4) were elevated (Table 2Go) and comparable in both study groups. Baseline serum IGF-I correlated positively with IGFBP-3 (r2 = 0.78; P < 0.0001), ALS (r2 = 0.73; P = 0.0001), and IGFBP-5 (r2 = 0.74; P < 0.0001). Serum levels of IGFBP-1 correlated inversely with IGFBP-3 (r2 = 0.33; P = 0.03), but not significantly with IGF-I (r2 = 0.25; P = 0.07). IGFBP-4 concentrations were independent of GH and GH-regulated proteins.



View larger version (30K):
[in this window]
[in a new window]
  		Figure 1. At baseline as well as after 5 days of infusion with GHRP-2 plus TRH (1+1 µg/kg·h), GH secretory pulse amplitude was positively related to circulating levels of IGF-I, IGFBP-3, and ALS in protracted critical illness.

 
The changes observed in GH secretion and in levels of IGF-I and its binding proteins during the infusion of placebo and GHRP-2 plus TRH are presented in Fig. 2Go. After 5 days of continuous GHRP-2 plus TRH infusion, the mean GH concentration, basal (nonpulsatile) GH secretion rate, GH pulse amplitude, and pulsatile GH production were increased in both groups to means that were 3.3-, 5.4-, 3-, and 3.3-fold higher than pretreatment values, respectively. All parameters decreased again after 5 days of subsequent placebo treatment in group 2.



View larger version (34K):
[in this window]
[in a new window]
  		Figure 2. Responses (mean ± SEM) to a randomized treatment with either 5 days of GHRP-2 plus TRH infusion (1+1 µg/kg·h) followed by 5 days of placebo (filled symbols) or 5 days of placebo followed by 5 days of GHRP-2 plus TRH infusion (1+1 µg/kg·h; open symbols) of deconvolution-derived GH secretion and serum levels of IGF-I, IGFBP-1, IGFBP-3, ALS, IGFBP-4, IGFBP-5, insulin, and leptin.

 
Placebo infusion during the first 5 days decreased or did not alter serum levels of IGF-I, IGFBP-3, ALS, and IGFBP-5. In both groups, infusion of GHRP-2 plus TRH evoked an immediate rise in IGF-I, ALS, IGFBP-3, and IGFBP-5, reaching a maximum after 2–3 days. Thereafter, serum concentrations of IGF-I, IGFBP-3, ALS, and IGFBP-5 remained stable at normal or near-normal levels until day 5. Five days of placebo after GHRP-2 plus TRH infusion returned IGF-I and ALS levels to pretreatment values, whereas IGFBP-3 and IGFBP-5 remained slightly elevated. Calculated half-lives after withdrawal of the GHRP-2 plus TRH infusion were, respectively, 31.6, 31.2, and 41.3 h for IGF-I, ALS, and IGFBP-3. Infusion of GHRP-2 plus TRH counteracted a spontaneous increase in the serum IGFBP-1 concentration during placebo and left IGFBP-4 levels unaltered.

Insulin

Baseline insulin levels in the fed state are shown in Table 2Go. Insulin concentrations were comparable in both groups and independent of whether patients needed exogenous insulin infusion to keep the blood glucose level below the preset value of 9.0 mmol/L. Serum insulin concentrations were unrelated to GH secretion, IGF-I, IGFBP-1 and IGFBP-3 levels, but correlated positively with serum ALS concentration (r2 = 0.28; P = 0.05).

During placebo infusion during the first 5 days, serum insulin concentrations further decreased (Fig. 2Go). In both groups, infusion of GHRP-2 plus TRH evoked an immediate rise in insulin, reaching a maximum within 1–2 days, after which levels remained stable until day 5. Five days of placebo treatment after GHRP-2 plus TRH infusion returned insulin levels to pretreatment values within 2 days.

Thyroid axis

Table 2Go shows baseline thyroid status, which was similar in both study groups. At baseline, serum concentrations of T4 correlated inversely with serum levels of IGFBP-1 (r2 = 0.27; P = 0.05); serum concentrations of T3 tended to follow a similar inverse correlation (r2 = 0.20; P = 0.1).

During infusion of placebo in group 1, there was no significant change in the mean nocturnal TSH concentration. After 5 days of GHRP-2 plus TRH infusion, mean nocturnal TSH was elevated compared to the pretreatment level in both groups, whereas it dropped below the pretreatment level after 5 subsequent days of placebo infusion in group 2 (Fig. 3Go).



View larger version (19K):
[in this window]
[in a new window]
  		Figure 3. Responses (mean ± SEM) to a randomized treatment with either 5 days of GHRP-2 plus TRH infusion (1+1 µg/kg·h) followed by 5 days of placebo (filled symbols) or 5 days of placebo followed by 5 days GHRP-2 plus TRH infusion (1+1 µg/kg·h; open symbols) of mean nocturnal TSH concentrations and serum levels of T4, T3, and rT3.

 
During the infusion of placebo in group 1, T4 levels remained unaltered. Upon treatment with GHRP-2 plus TRH there was an immediate rise in circulating T4, reaching a plateau after 2 or 3 days in both groups. During 5 days of subsequent placebo infusion in group 2, T4 levels decreased again to values not significantly different from pretreatment levels.

Comparable changes were documented for circulating T3 levels. Five days after GHRP-2 plus TRH interruption, T3 levels were not different from pretreatment levels.

In contrast, rT3 was not significantly altered by GHRP-2 plus TRH infusion.

PRL

During the infusion of placebo in group 1, mean nocturnal PRL levels decreased slightly from a mean ± SD of 11.1 ± 1.9 to 9.0 ± 1.9 µg/L. Upon treatment with GHRP-2 plus TRH, PRL levels increased in both groups (from 9.0 ± 1.9 to 13.1 ± 5.7 µg/L and from 9.0 ± 3.9 to 16.2 ± 15.5 µg/L, respectively), and after 5 subsequent days of placebo infusion in group 2, PRL concentrations decreased again to 9.5 ± 6.9 µg/L (P = 0.001, by ANOVA).

Cortisol

Nocturnal cortisol levels were elevated (Table 2Go) continuously between 2100–0600 h without circadian variation (data not shown), but were not evidently linked to any of the other studied endocrine or metabolic parameters. Nocturnal serum cortisol levels were not detectably altered by the infusion of either placebo or GHRP-2 plus TRH in both groups (data not shown).

Leptin

Baseline leptin levels are shown in Table 2Go. Leptin concentrations were similar in both groups and appeared to be independent of body mass index, age, caloric intake, C reactive protein, serum cortisol level, or thyroid status. In contrast, baseline leptin concentrations correlated positively with serum insulin (r2 = 0.41; P = 0.02), IGF-I (r2 = 0.39; P = 0.02), and ALS (r2 = 0.37; P = 0.03) concentrations (Fig. 4Go).



View larger version (20K):
[in this window]
[in a new window]
  		Figure 4. At baseline, markers of anabolism during protracted critical illness, such as serum concentrations of osteocalcin and leptin, were positively correlated with serum levels of the GH-dependent IGF-I and IGFBPs.

 
During placebo infusion, serum leptin concentrations decreased (Fig. 2Go). In both groups, infusion of GHRP-2 plus TRH evoked a rise in leptin concentrations, reaching a maximum within 1 day. Placebo infusion after GHRP-2 plus TRH treatment returned leptin levels to pretreatment values within 1 day.

After 1 day of GHRP-2 plus TRH infusion, concentrations of leptin correlated positively with insulin (r2 = 0.49; P = 0.008) and IGF-I (r2 = 0.36; P = 0.03). This relationship was maintained after 5 days of infusion of GHRP-2 plus TRH (r2 = 0.42; P = 0.02 and r2 = 0.36; P = 0.03, respectively, for insulin and IGF-I).

Protein degradation

At baseline, protein degradation was accelerated, as indicated by the elevated serum urea concentration (78 ± 34 vs. 31.4 ± 7.9 mg/dL in matched controls; P < 0.0001) and UCR (84 ± 39 vs. 29 ± 5; P < 0.0001) in the presence of normal serum creatinine (1.01 ± 0.45 vs. 1.08 ± 0.18 mg/dL; P = 0.5). The UCR was inversely correlated with serum concentrations of T4 and positively related to serum IGFBP-1 levels (Fig. 5Go), but otherwise was independent of the somatotropic axis, serum cortisol, and C reactive protein.



View larger version (30K):
[in this window]
[in a new window]
  		Figure 5. Low levels of T4 and high levels of IGFBP-1 at baseline are associated with markers of protein hypercatabolism, such as high serum UCR and increased urinary excretion of DPD. The response of urea production (mean ± SEM) to a randomized treatment with either 5 days of GHRP-2 plus TRH infusion (1+1 µg/kg·h) followed by 5 days of placebo (filled symbols) or 5 days of placebo followed by 5 days of GHRP-2 plus TRH infusion (1+1 µg/kg·h; open symbols) is depicted, indicating reduction of protein hypercatabolism by treatment.

 
The first 5 days of placebo infusion did not significantly alter UCR (Fig. 5Go). In both groups, infusion of GHRP-2 plus TRH evoked a drop in UCR (mean, -19% and -15%, respectively), which became significant from day 2 onward. The more pronounced catabolism at baseline, the more this was reduced by GHRP-2 plus TRH treatment [inverse correlation between baseline UCR and maximum change ({Delta}) in UCR; P = 0.01]. Five days of placebo treatment after GHRP-2 plus TRH infusion allowed UCR to rise again.

After 5 days of treatment, UCR remained inversely correlated with circulating levels of thyroid hormones (r2 = 0.27; P = 0.06 for T4 and r2 = 0.37; P = 0.02 for T3) and positively correlated with IGFBP-1 (r2 = 0.56; P = 0.005).

Bone turnover markers

At baseline, urinary excretion of collagen cross-links (DPD; nanomoles of deoxypyridinoline per nanomoles of creatinine in 24-h acidified urine collections) was more than 9-fold higher than that in healthy controls (Table 2Go) and to be positively correlated with the leptin concentration (r2 = 0.73; P = 0.01), and the mean nocturnal IGFBP-1 concentration (Fig. 5Go), UCR (r2 = 0.61; P = 0.03) and inversely correlated with T3 (r2 = 0.52; P = 0.05). The same trend of inverse correlation between DPD and serum T4 (Fig. 5Go) was documented. DPD was independent of other studied parameters, including serum cortisol and C reactive protein.

Serum levels of PICP at baseline were 5-fold higher than those in healthy controls (Table 2Go) and were independent of DPD and PYD. Serum sALP levels were normal (Table 2Go) and independent of DPD and PYD. Serum OC levels were lower than those in healthy controls and correlated positively with circulating levels of IGF-I (r2 = 0.69; P = 0.0002), ALS (r2 = 0.63; P = 0.0007), IGFBP-3 (r2 = 0.71; P = 0.0001), IGFBP-5 (r2 = 0.58; P = 0.001; Fig. 4Go), and leptin (r2 = 0.40; P = 0.02), whereas they were independent of DPD in 24-h urine, thyroid status, and serum cortisol.

Urinary excretion of DPD was not significantly altered by either placebo or GHRP-2 plus TRH infusion. In contrast, serum OC was increased by a mean of 19% after 5 days of GHRP-2 plus TRH infusion compared to a decrease of 6% with placebo (P = 0.03; Fig. 6Go). Five-day infusion of GHRP-2 plus TRH restored a positive correlation between OC and DPD (r2 = 0.83; P = 0.004). The decreases in PICP and sALP after 5 days of GHRP-2 plus TRH infusion did not reach significance (P = 0.1; Fig. 6Go). However, {Delta}%OC - ({Delta}%PICP + {Delta}%sALP), an indicator of osteoblast maturation (29, 30), increased by a mean of 34% vs. a mean decrease of -52% with placebo (P = 0.01; Fig. 6Go). Moreover, after 5 days of secretagogue infusion, serum OC remained positively correlated with serum levels of IGF-I (r2 = 0.60; P = 0.002) and leptin (r2 = 0.49; P = 0.008), and DPD remained positively correlated with circulating levels of leptin (r2 = 0.61; P = 0.04).



View larger version (17K):
[in this window]
[in a new window]
  		Figure 6. Random assignment to GHRP-2 plus TRH (1+1 µg/kg·h) or placebo infusion during the first 5 days of the study revealed that GHRP-2 plus TRH treatment increased serum OC concentrations after 5 days, whereas it did not significantly alter, but had a tendency to decrease, concentrations of PICP and sALP. Box plots represent medians, interquartiles, and interdecile ranges.

 
At baseline and despite a daily cholecalciferol supplement of 220 IU, serum levels of 25OHD3 were lower than those in controls (Table 2Go), but were unrelated to any of the above-mentioned parameters. Serum 25OHD3 levels were not detectably altered by the infusion of either placebo or GHRP-2 plus TRH (data not shown).

Endocrine changes in relation to severity of illness

At baseline, ultimate survivors and nonsurvivors were only distinguishable by age (respectively, 65 ± 11 vs. 78 ± 3 yr; P = 0.04), IGFBP-1 levels (respectively, 7.3 ± 3.8 vs. 16.1 ± 3.1 µg/L; P = 0.002; both variables were positively interrelated, r2 = 0.39; P = 0.01), and serum insulin concentrations (45 ± 41 vs. 16 ± 3 µIU/mL; P = 0.04), whereas blood glucose levels were comparable (7.4 ± 0.8 vs. 7.6 ± 2.2 mmol/L; P = 0.8). Even after correction for age, a high IGFBP-1 level remained predictive of fatal outcome (P = 0.0009), with a cut-off value of 2.0 µg/L·yr being discriminative. In contrast, the overall Apache II severity of illness score (13), calculated either at the time of admission to ICU or at study inclusion, could not predict ultimate outcome.

The responsiveness to 5 days of GHRP-2 plus TRH infusion was not detectably different between survivors and nonsurvivors for the studied variables, except for the increase in circulating levels of ALS, which was lower in nonsurvivors (mean ± SD, 25 ± 21% vs. 108 ± 50%; P = 0.009); the increase in rT3, which was higher in nonsurvivors (86 ± 99% vs. 5 ± 42%; P = 0.04); and IGFBP-1 levels, which tended to increase in response to GHRP-2 plus TRH treatment only in the nonsurvivors (P = 0.08),

The Apache II score, calculated at time of study inclusion, was positively correlated with the change in rT3 obtained after 5 days of infusion of GHRP-2 plus TRH and was inversely related to the change in ALS (Fig. 7Go). The change in rT3 and the change in ALS after 5 days of secretagogue infusion were inversely interrelated (Fig. 7Go).



View larger version (14K):
[in this window]
[in a new window]
  		Figure 7. Apache II score, reflecting severity of illness, calculated at study inclusion correlated positively with the percent change in rT3 and inversely with the percent change in ALS observed after 5 days of GHRP-2 plus TRH infusion. Both latter parameters were inversely interrelated. The two patients presenting with a substantial increase in rT3 and an absent ALS rise in response to treatment subsequently died.

 

   Discussion
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
References
 
Whether the endocrine changes observed during the course of critical illness reflect beneficial adaptations or harmful disorders has been highly controversial. The current study reveals that, selectively in protracted critically ill patients supported with intensive medical care for several weeks, at least part of the wasting syndrome is brought about by relatively insufficient release of GH and TSH and thereby reduced trophic activity of target organs and can be reversed by continuous infusion of the presumably deficient hypothalamic releasing factors.

Increased urea production at baseline reflected overall activated protein degradation in protracted critical illness. Skeletal muscle in particular is subject to proteolysis as evoked by acute illness or trauma (2, 31). In prolonged critical illness, other vital organ systems also participate in the wasting (32). Bone appeared to be one of the latter, with resorption being dramatically accelerated, in many cases here more than in cancer patients, metabolic bone disease, osteoporosis (33, 34, 35), or during the acute phase of critical illness (36). The two markers of hypercatabolism, increased collagen cross-link excretion and urea production, were statistically related to tertiary hypothyroidism and IGFBP-1 concentrations, whereas they were independent of hyposomatotropism and hypercortisolism. The extent to which this correlation reflects a causal relationship between hypothyroidism and hypercatabolism remains unclear, as other associated endocrine abnormalities, such as depletion of gonadal steroids (24, 37), may also contribute. Moreover, the impact of elevated free cortisol levels might have been underestimated, as transcortin was not measured. Inflammatory mediators, known to activate bone resorption in vitro (38), could also be involved. However, their role in the chronic phase of critical illness remains unclear, because at least circulating levels of cytokines are no longer elevated substantially if at all (39), and the increased C reactive protein levels reflecting inflammation in the current study were independent of hypercatabolism markers. Finally, immobilization for several weeks undoubtedly favored bone resorption.

Concomitantly with evident hypercatabolism of bone, serum levels of OC, a marker of mature osteoblast function and of bone formation, were low. At the same time, circulating levels of an early osteoblast marker, the carboxyl-terminal extension peptide of PICP, were 5-fold increased, which points to a maturation defect underlying impaired bone acquisition and mineralization despite activation of the osteoblastic cell line (29, 30). The latter could be expected in the presence of stimulated osteoclastic activity. The lack of anabolism in bone tissue was linked exclusively to hyposomatotropism, which consisted of a reduction of the pulsatile fraction of GH secretion and low IGF-I, IGFBP-3, and ALS concentrations. Here, we also measured low circulating levels of IGFBP-5, which extends the spectrum of reduced somatotropism in protracted critical illness. IGFBP-5 is a GH-regulated binding protein that, like IGFBP-3, is carried in the circulation in complexes with ALS (40) and can potentiate IGF actions in osteoblasts (41, 42). In addition, levels of IGFBP-4, a binding protein known to inhibit the effects of IGF on osteoblasts, were elevated, which may have contributed to impairment of bone formation. Although IGFBP-4 is not regulated by GH, its degradation is accelerated by IGF-I, which may in part explain the elevated serum levels (43).

After 5 days of combined and continuous infusion of GHRP-2 and TRH, the tertiary hyposomatotropism and hypothyroidism of protracted critical illness were to a large extent reversed. Pulsatile GH secretion was 3-fold the baseline level after 5 days of treatment, but lower than previously observed after 1–2 days of secretagogue infusion (3, 4, 6), and remained positively correlated with serum levels of IGF-I and GH-dependent IGFBPs. The latter had all reached (near) normal levels from day 2 onward and were stable thereafter. This observation strongly favors the presence of active feedback inhibition preventing overcorrection of the somatotropic axis. Treatment with high doses of recombinant human GH during critical illness has recently shown to increase morbidity and mortality.2 The self-limiting effect of GH secretagogues, which avoids overtreatment, may offer an important advantage over exogenous GH, especially in vulnerable, critically ill elderly. GHRP-2 plus TRH infusion also reversed a spontaneous insulin decrease and IGFBP-1 rise. Whether this should be considered a diabetogenic effect of GH secretagogues is not clear. Given the expected insulin resistance (15), it was indeed surprising to find baseline insulin levels not to be substantially elevated, if at all, taking into account the fed state and blood glucose levels, and to observe a spontaneous decrease over time. That the latter does not reflect some improvement in the patient’s condition is suggested by the lower insulin concentrations and the higher IGFBP-1 levels for the same blood glucose observed in the ultimate nonsurvivors compared to survivors. Apparently, in the chronic phase of critical illness, impaired glucose metabolism or disposal is caused by relative insulin deficiency rather than insulin resistance. The effects of GHRP-2 plus TRH infusion on the somatotropic axis and insulin were reversible within a few days. This full reversibility could indicate that any presumed deficiency of the endogenous GHRP-like ligand was not restored, but only circumvented during GHRP-2 infusions.

The mean nocturnal TSH concentrations observed after 5 days of infusion of GHRP-2 plus TRH were elevated compared to baseline levels, but were lower than those previously observed after 1 day (4), in the presence of increased and stable T4 and T3 levels, both of which approached normal values. Again, this constellation favors active endogenous feedback loops preventing overstimulation of the thyroid gland. In addition, coinfusing a GH secretagogue with TRH appeared to overcome the impaired peripheral conversion of thyroid hormones in the majority of critically ill patients, as suggested by unaltered serum rT3. Only the sickest individuals, the ones who ultimately did not survive, presented with an increase in rT3, which was linked statistically to absent ALS increment in response to the GH secretagogue. This observation implies that the combined secretagogue infusion is capable of stimulating the thyroid gland while allowing for peripheral shifts in thyroid hormone activity determined by the metabolic needs of the disease process. The possibility of individualized (endogenously governed) peripheral hormonal responses to GHRP-2 plus TRH infusion may reflect an important safety aspect for an endocrine treatment at a time when it is difficult, if not impossible, to determine the optimal patient-specific level of peripherally active hormones. The effect of 5 days of GHRP-2 plus TRH infusion on peripheral thyroid hormone levels was reversible, also suggesting that the presumably deficient endogenous TRH production (6, 44) was not restored. Although this finding may advocate a longer treatment time, the slightly lower than baseline nocturnal TSH levels observed 5 days after treatment withdrawal may also reflect inhibition of endogenous TRH production or down-regulation of the TRH receptor. The latter possibility warrants more extended monitoring of thyroid function in future studies.

The feedback-controlled endocrine responses to 5 days of GHRP-2 plus TRH treatment were associated with beneficial changes at the peripheral tissue level. The leptin rise provides evidence that adipose tissue was affected by the secretagogues. In a previous study, we found that infusion of TRH alone is unable to alter leptin concentrations (45). Moreover, we exclude a direct effect of GHRP-2 on human adipocytes in culture (46) (Brichard S., Van den Berghe G., unpublished observations). Consequently, the release of leptin by adipose tissue may be GH induced, which is in line with some reports of an acute leptin-stimulating effect of exogenous GH in human GH deficiency (47), and/or related to the concomitant increase in insulin (48). Leptin remained elevated throughout the 5-day treatment, although a slight, but progressive, decline started on day 2, which might be explained by the concomitant IGF-I increment (49). Metabolic changes evoked by the treatment could hypothetically have contributed, but the clamped blood glucose and unaltered circulating levels of triglycerides do not support such a mechanism. Finally, as leptin is a hormone with the ability to increase utilization of fat as metabolic substrate (50), the initial leptin rise in itself may have evoked the subsequent decrease, in turn reflecting reduced fat storage. In wasting conditions, a rise in circulating leptin reflects anabolism (51).

Bone also responded to GHRP-2 plus TRH treatment. Serum OC increased, and circulating levels of PICP and sALP tended to decrease, a constellation reflecting maturation of osteoblast function. In view of the positive correlation with the IGF(BP) response, this anabolic effect on bone was most likely mediated, either directly or indirectly, by reactivation of the somatotropic axis (52). In addition, as a stimulatory effect of leptin on osteoblast differentiation in vitro has been reported (53), the concomitant rise in leptin may have contributed. In contrast, GHRP-2 plus TRH treatment did not detectably alter the rate of cross-link excretion within 5 days. This apparent lack of effect on osteoclasts could be explained by an already maximally activated state of these cells. Alternatively, the small number of subjects and the relatively short treatment time may have played a role. Although preliminary, the positive correlation between OC and DPD documented within 5 days of treatment might suggest that communication between osteoblasts and osteoclasts was at least partially restored. Activating bone formation without further increasing breakdown in a wasting condition, known to be complicated by osteoporosis and impaired healing of surgical and traumatic bone injury, is likely to be beneficial.

Skeletal muscle and/or other organ systems subjected to proteolysis during critical illness also apparently responded to treatment with GHRP-2 plus TRH for 5 days, as protein degradation was found to be reduced as early as after 2 days of treatment. The counteraction of protein hypercatabolism was independent of hypercortisolism and insulin variations and was not related to the changes observed within the somatotropic axis, but was exclusively linked to the normalization of thyroid hormone levels. This intriguing finding seems to challenge the general assumption that low thyroid hormone levels in protracted critical illness reflect an adaptive mechanism to limit hypercatabolism.

In conclusion, the wasting syndrome of protracted critical illness appears to be at least in part brought about by impaired pulsatile GH and TSH release and reduced secretory activity of the respective target organs. Markers of increased catabolism were related specifically to tertiary hypothyroidism and circulating levels of IGFBP-1, whereas impaired anabolism was linked to hyposomatotropism. The continuous infusion of GHRP-2 and TRH jointly for 5 days reactivated both axes, with preserved pulsatility and peripheral tissue responsiveness that were self-limited by apparently intact feedback inhibition loops that avoided overtreatment. Secretagogue infusion did not affect cortisol release. This novel endocrine trophic strategy evoked a shift toward anabolic metabolism, as indicated by multiple biochemical markers, and thus offers the first evidence of the effectiveness of secretagogues for treatment of this particular clinical wasting condition.


   Acknowledgments
 
The authors thank the medical and nursing staff of the Intensive Care Unit for their cooperation, in particular Drs. Ph. Lampaert, C. Van Riel, V. Swinnen, M. Schetz, C. Verwaest, D. Vlasselaers, and P. Ferdinande for the clinical patient management. Dr. J. Billen and Prof. Ph. de Nayer are acknowledged for the TSH and thyroid hormone determinations, and Dr. L. Carlsson for the leptin measurements. We thank Sri Devi, Kevin Hardman, Paula Azimi, Ulla Karlsson, Viviane Celis, Tina Schreurs, Myriam Smets, Christiane Eyletten, Marianne Aerts, Marleen Foriers, Ivo Jans, Erik Van Herck, Willy Coopmans, and Koen Vermeiren for expert technical assistance. We thank Dr. S. Boonen for providing the data from the matched control group, and Dr. S. Brochard for the in vitro data on the effect of GH secretagogues on ob gene expression by human adipocytes in culture. Mr. J. Hellers (Baxter, Belgium) is acknowledged for generously providing the Vamp systems.


   Footnotes
 
1 Presented in part at the 80th Annual Meeting of The Endocrine Society, New Orleans, LA, and the 3rd International Conference of the Growth Hormone Research Society, San Francisco, CA. This work was supported by the NSF Center for Biological Timing and NIH Grant ROI-AG-14799 (to J.D.V.); the National Health and Research Council, Australia (Grant 940447; to R.C.B.); NIH Grant AR-31062 (to S.M.); the Fund for Scientific Research Flanders, Belgium (Grants G.0162.96 and G.3C05.95N; to G.V.d.B.); and Research Council of the University of Leuven Grant OT 95/24 (to G.V.d.B.). Back

2 Takala, J. 1998 Outcome of growth hormone trials in critically ill patients. Oral presentation, 3rd International Conference of Growth Hormone Research Society, San Francisco, CA. Back

Received November 6, 1998.

Revised January 8, 1999.

Accepted January 19, 1999.


   References
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
 References
 

  1. Streat SJ, Beddoe AH, Hill GL. 1987 Aggressive nutritional support does not prevent protein loss despite fat gain in septic intensive care patients. J Trauma. 27:262–266.[Medline]
  2. Gamrin L, Essén P, Forsberg AM, Hultman E, Wernerman J. 1996 A descriptive study of skeletal muscle metabolism in critically ill patients: free amino acids, energy-rich phosphates, protein, nucleic acids, fat, water, and electrolytes. Crit Care Med. 24:575–583.[CrossRef][Medline]
  3. Van den Berghe G, de Zegher F, Veldhuis JD, et al. 1997 The somatotropic axis in critical illness: effect of continuous GHRH and GHRP-2 infusion. J Clin Endocrinol Metab. 82:590–599.[Abstract/Free Full Text]
  4. Van den Berghe G, de Zegher F, Baxter RC, et al. 1998 Neuroendocrinology of critical illness: effect of continuous thyrotropin-releasing hormone infusion and its combination with growth hormone-secretagogues. J Clin Endocrinol Metab. 83:309–319.[Abstract/Free Full Text]
  5. Van den Berghe G, de Zegher F, Bouillon R. 1998 Acute and chronic critical illness as different neuroendocrine paradigms. J Clin Endocrinol Metab. 83:1827–1834.[Free Full Text]
  6. Van den Berghe G, de Zegher F, Bowers CY, et al. 1996 Pituitary responsiveness to growth hormone (GH) releasing hormone, GH-releasing peptide-2 and thyrotropin releasing hormone in critical illness. Clin Endocrinol (Oxf). 45:341–351.[CrossRef][Medline]
  7. Bowers CY, Momany FA, Reynolds GA, Hong A. 1984 On the in vitro and in vivo activity of a new synthetic hexapeptide that acts on the pituitary to specifically release growth hormone. Endocrinology. 114:1537–1545.[Abstract]
  8. Howard AD, Feighner SD, Cully DF, et al. 1996 A receptor in pituitary and hypothalamus that functions in growth hormone release. Science. 273:974–977.[Abstract]
  9. Van den Berghe G, de Zegher F, Veldhuis JD, et al. 1997 Thyrotropin and prolactin release in prolonged critical illness: dynamics of sponaneous secretion and effects of growth hormone secretagogues. Clin Endocrinol (Oxf). 47:599–612.[CrossRef][Medline]
  10. Van den Berghe G, de Zegher F, Lauwers P, Veldhuis JD. 1994 Growth hormone secretion in critical illness: effect of dopamine. J Clin Endocrinol Metab. 79:1141–1146.[Abstract]
  11. Van den Berghe G, de Zegher F, Lauwers P. 1994 Dopamine and the sick euthyroid syndrome in critical illness. Clin Endocrinol (Oxf). 41:731–737.[Medline]
  12. Van den Berghe G, de Zegher F. 1996 Anterior pituitary function during critical illness and dopamine treatment. Crit Care Med. 24:1580–1590.[CrossRef][Medline]
  13. Knaus WA, Draper EA, Wagner DP, Zimmerman JE. 1985 APACHE II: a severity of disease classification system. Crit Care Med. 13:818–829.[Medline]
  14. Souba WW. 1997 Nutritional support. N Engl J Med. 336:41–48.[Free Full Text]
  15. Mizock BA. 1995 Alterations in carbohydrate metabolism during stress: a review of the literature. Am J Med. 98:75–84.[CrossRef][Medline]
  16. Boonen S, Lesaffre E, Dequeker J, et al. 1996 Relationship between baseline insulin-like growth factor-I (IGF-I) and femoral bone density in women aged over 70 years: potential implications for the prevention of age-related bone loss. J Am Geriatr Soc. 44:1301–1306.[Medline]
  17. Boonen S, Vanderschueren D, Cheng XG, et al. 1997 Age-related (type II) femoral neck osteoporosis in men: biochemical evidence for both hypovitaminosis D- and androgen deficiency-induced bone resorption. J Bone Miner Res. 12:2119–2126.[CrossRef][Medline]
  18. Baxter RC, Cowell CT. 1987 Diurnal rhythm of growth hormone-independent binding protein for insulin-like growth factors in human plasma. J Clin Endocrinol Metab. 65:423–431.[Abstract]
  19. Baxter RC, Martin JL. 1986 Radioimmunoassay of growth hormone-dependent insulin-like growth factor binding protein in human plasma. J Clin Invest. 78:1504–1512.
  20. Baxter RC. 1990 Circulating levels and molecular distribution of the acid-labile ({alpha}) subunit of the high molecular weight insulin-like growth factor-binding protein complex in normal subjects. J Clin Endocrinol Metab. 70:1347–1353.[Abstract]
  21. Honda Y, Landale E, Strong D, Baylink D, Mohan S. 1996 Recombinant synthesis insulin-like growth factor binding protein-4 (IGFBP-4): development, validation and application of a radioimmunoassay for IGFBP-4 in human serum and other biological fluids. J Clin Endocrinol Metab. 81:1389–1396.[Abstract]
  22. Mohan S, Libanati C, Dony C, Lang K, Srinivasan N, Baylink D. 1995 Development, validation and application of a radioimmunoassay for insulin-like growth factor binding protein-5 in human serum and other biological fluids. J Clin Endocrinol Metab. 80:2638–2645.[Abstract]
  23. Bouillon R, Vanderschueren D, Van Herck E, et al. 1992 Homologous radioimmunoassay of human osteocalcin. Clin Chem. 38:2055–2060.[Abstract]
  24. Vanderschueren D, Jans I, Van Herck E, Moermans K, Verhaeghe J, Bouillon R. 1994 Time-related increase of biochemical markers of bone turnover in androgen-deficient male rats. Bone Miner. 26:123–131.[Medline]
  25. Heinegard D, Tiderstrom G. 1973 Determination of serum creatinine by a direct colometric method. Clin Chim Acta. 43:305–307.[CrossRef][Medline]
  26. Bouillon R, Van Assche F, Van Baelen H, Heyns W, De Moor P. 1981 Influence of the vitamin D-binding protein on the serum concentration of 1,25-dihydroxyvitamin D3: significance of the free 1,25-dihydroxyvitamin D3concentration. J Clin Invest. 67:589–596.
  27. Veldhuis JD, Johnson ML. 1992 Deconvolution analysis of pulsatile hormone data. Methods Enzymol. 210:539–575.[Medline]
  28. Beck C. 1988 Disordered renal function: diagnosis. In: Civetta JM, Taylor RW, Kirby RR, eds. Critical care. Philadelphia: Lippincott; 1315–1322.
  29. Stein GS, Lian JB, Owen TA. 1990 Relationship of cell growth to regulation of tissue-specific gene expression during osteoblast differentiation. FASEB J. 4:3111–3123.[Abstract]
  30. Bouillon R, Bex M, Van Herck E, et al. 1995 Influence of age, sex, and insulin on osteoblast function: osteoblast dysfunction in diabetes mellitus. J Clin Endocrinol Metab. 80:1194–1202.[Abstract]
  31. Kinney JM, Elwyn DH. 1985 Protein metabolism in the traumatized patient. Acta Chir Scand. 522(Suppl):45–56.
  32. Greene HL. 1983 Response of the bowel to the injury and the transition from parenteral to enteral feedings. Acta Chir Scand. 517(Suppl):21–27.
  33. Lipman A, Demers L, Daniloff Y, et al. 1993 Increased urinary excretion of pyridinium cross-links in cancer patients. Clin Chem. 39:614–618.[Abstract/Free Full Text]
  34. Robins SP, Black D, Paterson CR. 1991 Evaluation of urinary hydroxypyridium crosslink measurement as resorption markerts in metabolic bone diseases. Eur J Clin Invest. 21:310–315.[Medline]
  35. Seibel MJ, Woitege H, Scheidt-Nave C, et al. 1994 Urinary hydroxypyridinium crosslinks of collagen in pomulation-based screening for overt vertebral osteoporosis: results of a pilot study. J Bone Miner Res. 9:1433–1440.[Medline]
  36. Shapses SA, Weissman C, Seibel MJ, Chowdhury HA. 1997 Urinary pyridinium cross-link excretion is increased in critically ill surgical patients. Crit Care Med. 25:85–90.[CrossRef][Medline]
  37. Van den Berghe G, de Zegher F, Lauwers P, Veldhuis JD. 1994 Luteinizing hormone secretion and hypoandrogenemia in critically ill men: effect of dopamine. Clin Endocrinol (Oxf). 41:563–569.[Medline]
  38. Abu-Amer Y, Ross FP, Edwards J, Teitelbaum SL. 1997 Lipopolysaccharide-stimulated osteoclastogenesis is mediated by tumor-necrosis factor via its P55 receptor. J Clin Invest. 100:1557–1565.[Medline]
  39. Damas P, Reuter A, Gysen P, Demonty J, Lamy M, Franchimont P. 1989 Tumor necrosis factor and interleukin-1 serum levels during severe sepsis in humans. Crit Care Med. 17:975–978.[Medline]
  40. Twigg SM, Baxter RC. 1998 Insulin-like growth factor (IGF)-binding protein-5 forms an alternative ternary complex with IGF’s and the acid-labile subunit. J Biol Chem. 273:6074–6079.[Abstract/Free Full Text]
  41. Mohan S, Nakao Y, Honda Y, et al. 1995 Studies on the mechanisms by which insulin-like growth factor binding protein-4 (IGFBP-4) and IGFBP-5 modulate IGF actions in bone cells. J Biol Chem. 270:20424–20431.[Abstract/Free Full Text]
  42. Thoren M, Hilding A, Brismar T, et al. 1998 Serum levels of insulin-like growth factor binding proteins (IGFBP)-4 and -5 correlate with bone mineral density in growth hormone (GH)-deficient adults and increase with GH replacement therapy. J Bone Miner Res. 13:891–899.[CrossRef][Medline]
  43. Fowlkes J, Freemark M. 1992 Evidence for a novel insulin-like growth factor (IGF)-dependent protease regulating IGF-binding protein-4 in dermal fibroblasts. Endocrinology. 131:2071–2076.[Abstract]
  44. Fliers E, Guldenaar SEF, Wiersinga WM, Swaab DF. 1997 Decreased hypothalamic thyrotropin-releasing hormone gene expression in patients with nonthyroidal illness. J Clin Endocrinol Metab. 82:4032–4036.[Abstract/Free Full Text]
  45. Van den Berghe G, Wouters P, Carlsson L, Baxter RC, Bouillon R, Bowers CY. 1998 Leptin levels in protracted critical illness: effects of growth hormone-secretagogues and thyrotropin-releasing hormone. J Clin Endocrinol Metab. 83:3062–3070.[Abstract/Free Full Text]
  46. Halleux CM, Servais I, Reul BA, Detry R, Brichard SM. 1998 Multihormonal control of ob gene expression and leptin secretion from cultured human visceral adipose tissue: increased responsiveness to glucocorticoids in obesity. J Clin Endocrinol Metab. 83:902–910.[Abstract/Free Full Text]
  47. Gill MS, Toogood AA, Adams JE, Clayton PE, Shalet SM. The acute and chronic effect of growth hormone (GH) treatment on leptin in GH deficiency: relationship to bodycomposition, IGF-I and insulin [Abstract P1–222]. Proc of the 80th Annual Meet of The Endocrine Soc. 1998; 167.
  48. Boden G, Chen X, Kolaczynski JW, Polansky M. 1997 Effects of prolonged hyperinsulinemia on serum leptin in normal human subjects. J Clin Invest. 100:1107–1113.[Medline]
  49. Askari H, Franklin SC, Vijayan A, Liu SB, Miller J, Dagago-Jack S. Effect of recombinant human IGF-I therapy on plasma leptin [Abstract P2–552]. Proc of the 80th Annual Meet of The Endocrine Soc. 1998; 365.
  50. Shimabukuro M, Koyama K, Chen G, et al. 1997 Direct antidiabetic effect of leptin through triglyceride depletion of tissues. Proc Natl Acad Sci USA. 94:4637–4641.[Abstract/Free Full Text]
  51. Eckert ED, Pomeroy C, Raymond N, Kohler PF, Thuras P, Bowers CY. 1998 Leptin in anorexia nervosa. J Clin Endocrinol Metab. 83:791–795.[Abstract/Free Full Text]
  52. Ohlsson C, Bengtsson BA, Isaksson OGP, Andreassen TT, Slootweg MC. 1998 Growth hormone and bone. Endocr Rev. 19:55–79.[Abstract/Free Full Text]
  53. Thomas T, Gori F, Burguera B, Spelsberg TC, Jensen MD, Riggs BL. Leptin acts on human marrow stromal precursor cells to enhance osteoblast differentiation and to inhibit adipocyte differentiation: a potential mechanism for increased bone mass in obesity [Abstract OR29–1]. Proc of the 80th Annual Meet of The Endocrine Soc. 1998; 90.
  54. Veldhuis JD, Iranmanesh A, Wilkowski MJ, Samojlik E. 1994 Neuroendocrine alterations in the somatotropic and lactotropic axes in uremic men. Eur J Endocrinol. 131:489–498.[Abstract]



This article has been cited by other articles:


Home page
 Nutr Clin PractHome page
J. M. Hollander and J. I. Mechanick
Nutrition Support and the Chronic Critical Illness Syndrome
Nutr Clin Pract, December 1, 2006; 21(6): 587 - 604.
[Abstract] [Full Text] [PDF]

Home page
 Endocr. Rev.Home page
J. Kohrle, F. Jakob, B. Contempre, and J. E. Dumont
Selenium, the Thyroid, and the Endocrine System
Endocr. Rev., December 1, 2005; 26(7): 944 - 984.
[Abstract] [Full Text] [PDF]

Home page