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The Journal of Clinical Endocrinology & Metabolism Vol. 89, No. 3 1402-1409
Copyright © 2004 by The Endocrine Society

Urocortin-1 Infusion in Normal Humans

Mark E. Davis, Chris J. Pemberton, Timothy G. Yandle, John G. Lainchbury, Miriam T. Rademaker, M. Gary Nicholls, Christopher M. Frampton and A. Mark Richards

Christchurch Cardioendocrine Research Group, Christchurch School of Medicine and Health Sciences, University of Otago (M.E.D., C.J.P., T.G.Y., J.G.L., M.T.R., C.M.F., A.M.R.), Christchurch 8001, New Zealand; and Department of Medicine, University of the United Arab Emirates (M.G.N.), Al Ain, United Arab Emirates

Address all correspondence and requests for reprints to: Dr. Mark E. Davis, Research Fellow, Christchurch Cardioendocrine Research Group, Department of Medicine, Christchurch School of Medicine and Health Sciences, P.O. Box 4345, Christchurch, New Zealand. E-mail: mark.davis{at}chmeds.ac.nz.


   Abstract
Top
 Abstract
Introduction
 Subjects and Methods
 Results
 Discussion
 References
 
Urocortin-1 (Ucn-1), a member of the corticotropin-releasing factor family, has been shown in animal studies to have effects on the pituitary-adrenal axis, the cardiovascular system, circulating neurohormones, and renal function and to suppress appetite. For the first time in man we have evaluated these effects of infused Ucn-1 as well as actions on plasma ghrelin, a hormone known to increase appetite. We also assessed Ucn-1 pharmacokinetics. Eight healthy male volunteers consuming a diet of constant sodium and potassium content received 50 µg Ucn-1 iv over 1 h in a placebo-controlled, randomized, time-matched, cross-over study. Ucn-1 infusion compared with placebo increased plasma levels of corticotropin [44.6 ± 7.7 vs. 19.1 ± 3.2 pg/ml (9.5 ± 1.7 vs. 4.2 ± 0.7 pmol/liter); P < 0.001], cortisol [15.6 ± 1.6 vs. 7.7 ± 1.4 µg/dl (432 ± 43 vs. 213 ± 40 nmol/liter); P < 0.001], and atrial natriuretic peptide [26.2 ± 3.4 vs. 21.3 ± 2.2 pg/ml [8.5 ± 1.1 vs. 6.9 ± 0.7 pmol/liter); P = 0.019] while suppressing plasma ghrelin (P = 0.008). No hemodynamic or renal effects were observed at the dose used. The plasma Ucn-1 t1/2 was 52 min based on a one-compartment model. In conclusion, a brief iv infusion of 50 µg Ucn-1 stimulates plasma ACTH, cortisol, and atrial natriuretic peptide secretion and suppresses plasma ghrelin in healthy male volunteers. The latter effect might contribute to the anorexic action of Ucn-1.


   Introduction
Top
 Abstract
 Introduction
Subjects and Methods
 Results
 Discussion
 References
 
UROCORTIN-1 (Ucn-1) is a 40-amino acid peptide belonging to the corticotropin-releasing factor (CRF) family and acting via CRF receptor type 1 (CRF-R1) and CRF-R2 with cAMP as second messenger (1). The name is derived from its structural homology to urotensin and CRF. The amino acid sequence is highly conserved across species; rat and ovine sequences are identical and have 95% homology with the human peptide (2). Ucn-1 immunoreactivity has been found in anterior pituitary cells, various hypothalamic loci, Purkinje cells of the cerebellum, anterior horn cells of the spinal column, human cardiac myocytes and nonmyocytes in all four chambers (highest concentration in the left ventricle), parietal cells of the stomach, myenteric and submucosal plexuses, as well as cells in Lieberkuhn crypts of the small and large intestine, placental and fetal membranes, synovial tissue, skin, and lymphocytes (3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15). In animals, its actions include elevation of CRF, ACTH, and cortisol secretion and suppression of appetite (16, 17, 18, 19, 20). Cardiovascular actions include augmentation of cardiac output and an increase in mean arterial pressure in normal sheep, whereas in experimental heart failure, Ucn-1 decreased calculated total peripheral resistance and left atrial pressure and increased cardiac output, all in association with marked attenuation of vasopressor hormone systems and enhancement of renal function (21). Ucn-1 may protect against cardiac ischemic insult (by direct effects on cellular trafficking and up-regulation of the p42/p44 MAPK signaling pathway and via protein kinase C- and ATP-sensitive potassium channels) and induce endothelium-dependent vasodilatation, as seen in coronary arteries (21, 22, 23, 24, 25, 26, 27, 28). Ucn-1 is also capable of stimulating cardiac natriuretic peptide secretion (29).

Ghrelin, a 28-amino acid GH secretagogue isolated from the stomach (30), enhances appetite in humans (31). In that Ucn-1 has a marked anorectic effect in animals, we considered the possibility that it might interact with ghrelin.

We hypothesized that Ucn-1, administered to man, would 1) reproduce the cardiovascular effects seen in animals, and 2) inhibit ghrelin production. We report the first controlled study of Ucn-1 infusion in humans, examining effects on ghrelin, anterior pituitary and cardiovascular hormones, as well as hemodynamics and renal function.


   Subjects and Methods
Top
 Abstract
 Introduction
 Subjects and Methods
Results
 Discussion
 References
 
Subjects

We studied eight healthy males, aged 24–45 yr (mean ± SEM age, 36.3 ± 2.2). Their mean weight was 81.7 ± 4.8 kg, mean body mass index was 24.8 ± 1.0, and mean plasma creatinine was 0.9 ± 0.1 mg/dl (0.08 ± 0.01 mmol/liter). Subjects were not taking any medications.

Study protocol

Participants gave informed consent to the study. The protocol was approved by the ethics committee of the Ministry of Health (Canterbury, New Zealand). Human Ucn-1 for infusion was purchased from Clinalfa AG (Weidenmattweg, Switzerland). Subjects were studied on two occasions, 2 wk apart, receiving Ucn-1 and placebo in a balanced, randomized, single-blind, cross-over design. On the morning of the third day of a controlled metabolic diet (sodium, 80 mmol/d; potassium, 100 mmol/d), participants ate breakfast by 0730 h, presented to the study room, and completed a 24-h urine collection at 0800 h. The subjects fasted until lunch at 1400 h. Participants were weighed, and 10 ml/kg water were given orally, followed by 200 ml water/h between 0900 and 1800 h. Subjects remained seated throughout the day, except when standing to urinate. At 0815 h venous cannulas were placed in each forearm, one for infusion of Ucn-1 and placebo, and the other for blood sampling. All subjects received 50 µg Ucn-1 [dissolved in 1 ml normal saline, ultrasonicated, and made up to 1 µg/ml with Hemaccel (Hoechst Marion Roussel, Lane Cove, New South Wales, Australia), i.e. total infusate volume was 50 ml] or matching placebo vehicle infusion (50 ml Hemaccel) over 1 h commencing at 0900 h. The Ucn-1 dose was based on that which achieved hemodynamic, neurohormonal, and renal effects in sheep. Ucn-1 was infused rather than given as a bolus for safety reasons. Venous samples were drawn from the opposite arm at 0830, 0900, 0930, 1000, 1030, 1100, 1200, 1400, and 1800 h. Blood was collected into chilled tubes containing EDTA and centrifuged at 4 C, and plasma was stored at -80 C before assay for Ucn-1 (detailed below), cAMP (Biotrak, Amersham Pharmacia Biotech, Arlington Heights, IL), cGMP (32), ghrelin (detailed below), ACTH (Nichols Institute Diagnostics, San Juan Capistrano, CA), cortisol (33), GH (Bioclone, Marrackville, Australia), LH, FSH, prolactin (PRL), and TSH (LH, FSH, PRL, and TSH were assayed by Access 2, Beckman Coulter, Fullerton, CA), arginine vasopressin (AVP) (34), brain natriuretic peptide (BNP) (35), atrial natriuretic peptide (ANP) (36), N-terminal BNP (37), plasma renin activity (PRA) (38), aldosterone (39), adrenaline (40), noradrenaline (40), endothelin (ET) (41), and adrenomedullin (ADM) (42). At the conclusion of infusions, further plasma Ucn-1 sampling was conducted at 1005, 1010, 1015, and 1020 h for kinetic calculations.

For each hormone all samples from an individual were analyzed in a single assay. Intra- and interassay coefficients of variation (CVs), measured at concentrations similar to those extant during these experiments, were all less than 16.2%, except interassay CVs for BNP (21.5%) and ET (17.4%). Plasma sodium (Na+), potassium (K+), creatinine, glucose, hemoglobin, and hematocrit were also measured at 0900, 1000, 1100, and 1400 h. After blood sampling, the subjects stood to pass urine at 0900, 1000, 1100, 1400, and 1800 h for measurement of volume and urinary cAMP, sodium, potassium, and creatinine.

Systolic and diastolic blood pressures and heart rate were recorded in duplicate at 30-min intervals until 4 h postinfusion and then hourly with an automatic sphygmomanometer (PRO 300 monitor, Dinamap, Critikon, Tampa, FL). Cardiac output was measured by the thoracic impedance method at the same time intervals (Minnesota impedance cardiograph, model 304B, Surcom Inc., Minneapolis, MN).

Echocardiography was undertaken pre- and postinfusion using standard techniques with a Vivid 3 echocardiogram (General Electric, Fairfield, CT). Left ventricular volume was measured in the four-chamber view using the modified Simpson’s Rule. Transmitral flow was measured by pulse Doppler at the mitral valve leaflet tips in the four chamber view. Tissue Doppler velocities at the medial and lateral mitral valve annulus were measured using the machine presets.

Ucn-1 RIA

Plasma samples were extracted using a method previously employed to extract total CRF (bound plus free) from human plasma (42). One milliliter of plasma was mixed with 2 ml methanol and centrifuged. The supernatant was adjusted to contain 0.003% Triton X-100, dried under an air stream at room temperature, and reconstituted in 0.5 ml assay buffer. For assay, 100 µl plasma extract or standard plus 100 µl antiserum PBL#5779 diluted 1:165,000 were incubated at 4 C for 24 h before addition of 100 µl radiolabeled [125I]Tyr0-Ucn-1 (prepared by the chloramine T method and purified by reverse phase HPLC) containing 10,000 cpm. The assay was incubated an additional 24 h at 4 C after which bound and free labels were separated by a solid phase second antibody (donkey antirabbit Sac-Cell, IDS, Bolden, UK). The RIA characteristics (mean ± SD): zero binding, 35.5 ± 6.3% (n = 25); standard curve 50% effective concentration, 414 ± 69 pg/ml (88.1 ± 14.6 pmol/liter); detection limit, 12.7 ± 6.6 pg/ml [2.7 ± 1.4 pmol/liter; 6.6 pg/ml (1.4 pmol/liter) in plasma after 2-fold concentration during extraction; n = 25]. Cross-reactivity with human [Tyr0]Ucn-II was less than 0.0034% (human stresscopin-related peptide has the same amino acid sequence as Ucn-II, but with the addition of five amino acids at the C-terminal end of the peptide), less than 0.026% with mouse Ucn-II, <0.07% with human Ucn-III (human stresscopin has the same amino acid sequence as Ucn-III but with the addition of 2 amino acids at the C-terminal end of the peptide), less than 0.0016% with human CRF, and less than 0.0014% with human urotensin II. Within-assay CVs calculated from variance between assay duplicates were 13.4% over 0–52 pg/ml (0–11 pmol/liter), 10.3% over 56–239 pg/ml (12–51 pmol/liter), and 3.3% over 239-1490 pg/ml (51–317 pmol/liter). Between-assay CV was 17.5% at 63 pg/ml (13.5 pmol/liter; n = 23), 16.2% at 111 pg/ml (23.7 pmol/liter; n = 20), and 13.3% at 145 pg/ml (30.9 pmol/liter; n = 23). Recovery of Ucn-1 added to plasma was 61.2% at 141 pg/ml (30 pmol/liter), 60.9% at 329 pg/ml (70 pmol/liter), and 59.3% at 470 pg/ml (100 pmol/liter). The Ucn-1 reference range encompassing 95% of results for healthy subjects [25.8 to 176.1 pg/ml (5.5 to 37.5 pmol/liter)] was determined in 88 subjects drawn at random from the Christchurch, New Zealand, electoral role.

Ghrelin RIA method

Ghrelin assay. Aliquots of plasma (1 ml) were extracted on Sep-Pak C18 cartridges as previously described (35). The mean extraction recovery of synthetic ghrelin added to human plasma by this method was 80 ± 3% (n = 5). Synthetic human (n-octanoyl) ghrelin and purified IgG recognizing total ghrelin were purchased from Phoenix Pharmaceuticals (Belmont, CA). The antibody binds an epitope within the amino acid 15–28 region of ghrelin and thus recognizes total circulating ghrelin (i.e. both octanoyl and nonoctanoyl forms). Ghrelin (5 µg) was iodinated through His9 using 0.5 mCi Na125I in the presence of 2.5 µg chloramine T in 5 µl of 0.5 M phosphate buffer, pH 7.3, for 2 min. The reaction was halted by addition of 50 µg cysteine HCl in a further 5 µl phosphate buffer. The resulting iodinate was loaded onto a 10 cm RP300 Brownlee HPLC column (PE Applied Biosystems, San Jose, CA) and eluted with a gradient of 0–60% acetonitrile in 49 mM phosphate buffer (pH 2.9) over 30 min at a flow rate of 1 ml/min. Fractions (0.5 ml) were collected, with one major peak eluting at 34% acetonitrile, and contained more than 50% of the total radioactivity.

Antihuman ghrelin IgG was used in the RIA at a final dilution of 1:1500. The cross-reactivities of this IgG with the synthetic human peptides, vasointestinal peptide, PRL, galanin, GHRH, neuropeptide Y, BNP, ANP, ET, and angiotensin II were all less than 0.03%. All sample extracts, radioactive trace, standard, and antiserum solutions were diluted in RIA buffer (35). The assay incubate consisted of 100 µl extracted sample or standard (0–1078.7 pg/ml (0–320 pmol/liter)] combined with 100 µl antiserum. Tubes were vortexed and incubated for 24 h at 4 C. Then 100 µl radioactive trace (4000–6000 cpm) was added, the tubes were vortexed and incubated for a further 24 h at 4 C. Free and bound ghrelin were separated by solid phase second antibody method (donkey antirabbit Sac-Cell). Sac-Cell (1 ml) diluted in 5% dextran solution (final Sac-Cell concentration, 5%) was added to each tube, the solution was vortexed and incubated at room temperature for 30 min. The tubes were then centrifuged at 2800 x g for 10 min at 20 C and decanted, with the resulting pellet counted in a Gammamaster (LKB, Uppsala, Sweden). Under these conditions the RIA had a mean zero binding of 24 ± 2%, a mean detection limit of 36.4 ± 2.7 pg/ml (10.8 ± 0.8 pmol/liter), and a mean 50% effective concentration of 459.1 ± 33.7 pg/ml (136.2 ± 10.0 pmol/liter) over 23 consecutive assays.

Statistics

The effects of Ucn-1 infusion were analyzed using repeated measures ANOVA. Associations between measured and derived variables were analyzed using Pearson’s correlation coefficient. Areas under the curve were calculated using the standard trapezoidal rule.

The Ucn-1 plasma half-life (t1/2) was calculated using a one-compartment model during and after the infusion period (WinNonLin Professional 3.1, Pharsight Corp., Mountain View, CA). P < 0.05 was taken to indicate statistical significance. Results are presented as the mean ± SEM.


   Results
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
Discussion
 References
 
There were no significant differences in baseline hormone, plasma, or urine biochemical or hemodynamic variables between the 2 experimental d (placebo vs. Ucn-1). No hypotension or other adverse effects were noted for the duration of the infusion period or for the subsequent monitoring period (until 1800 h). The mean (±SEM) baseline plasma Ucn-1 levels were 45.1 ± 4.2 pg/ml (9.6 ± 0.9 pmol/liter) and 43.2 ± 3.3 pg/ml (9.2 ± 0.7 pmol/liter) before Ucn-1 and placebo infusions, respectively. With Ucn-1 infusion, plasma Ucn-1 concentrations were significantly increased compared with placebo (Fig. 1Go). The peak plasma concentration (bound and free) of the peptide [940 ± 136 pg/ml (200 ± 29 pmol/liter)] was achieved at the end of the 60-min infusion period. Compared with placebo, Ucn-1 infusion induced a significant increase in plasma ACTH and cortisol levels (P < 0.001 for both). Plasma ACTH and cortisol were sequentially elevated; the peak increment in ACTH occurred at the end of the infusion period [18.2 ± 3.2 pg/ml (4.0 ± 0.7 pmol/liter) at baseline to 43.1 ± 7.7 pg/ml (9.5 ± 1.7 pmol/liter); P = 0.008 compared with placebo], whereas maximum cortisol levels were achieved 30 min later [8.7 ± 0.8 µg/dl (241 ± 22 nmol/liter) at baseline to 15.6 ± 1.6 µg/dl (432 ± 43 pmol/liter); P = 0.009 compared with placebo; Fig. 1Go]. On the control day, plasma ghrelin levels increased steadily to peak levels at 180 min and declined thereafter. ANOVA demonstrated that the Ucn-1 infusion significantly suppressed plasma ghrelin levels from the 180 min point onward (P = 0.008; Fig. 2Go). Plasma ANP concentrations were increased subtly, but significantly (P = 0.019), with peak levels achieved at the end of the Ucn-1 infusion [24.3 ± 2.5 ng/ml (7.9 ± 0.8 pmol/liter) at baseline to 26.2 ± 3.4 ng/ml (8.5 ± 1.1 pmol/liter); P = 0.034 compared with placebo]. ANP second messenger cGMP showed a concurrent rise that did not achieve significance (Fig. 3Go).



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  		FIG. 1. Plasma Ucn, ACTH, and cortisol concentrations with 50 µg human Ucn (•) or placebo ({circ}) infusions over 1 h in eight normal men. Sequential elevation in ACTH and cortisol was seen with significant peak increments (P < 0.001 for both) compared with control. Values are displayed as units ± SEM. The factors for conversion to Systeme International (SI) units are: Ucn-I: pg/ml to pmol/liter, multiply by 0.2129; ACTH: pg/ml to pmol/liter, multiply by 0.2202; cortisol: pg/dl to nmol/liter, multiply by 27.59.

 


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  		FIG. 2. Plasma ghrelin concentration response to 50 µg human Ucn (•) or placebo ({circ}) infusions over 1 h in eight normal men. Ghrelin was suppressed from 120 min post-infusion (P < 0.008). Values are displayed as units ± SEM. The factor for conversion to SI units is: ghrelin: pg/ml to pmol/liter, multiply by 0.2966.

 


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  		FIG. 3. Plasma ANP and cGMP concentration response to 50 µg human Ucn (•) or placebo ({circ}) infusions over 1 h in eight normal men. ANP was subtly elevated (P = 0.019). Values are displayed as units ± SEM. The factors for conversion to SI units are: ANP: pg/ml to pmol/liter, multiply by 0.3244; cGMP: ng/ml to nmol/liter, multiply by 2.723.

 
Ucn-1 kinetics were consistent with a one-compartment model. The t1/2 for immunoreactive Ucn-1 was 52.1 ± 3.0 min. Metabolic clearance rate and volume of distribution were not calculated as steady state was not achieved for plasma Ucn (Fig. 1Go).

Ucn did not alter plasma levels of cAMP, BNP, N-terminal BNP, adrenaline, noradrenaline, ADM, GH, LH, FSH, PRL, AVP, ET, PRA, or aldosterone (Table 1Go). Hemodynamics (heart rate, cardiac output, systolic blood pressure, and diastolic blood pressure; Table 2Go), echocardiographic parameters [left ventricular volumes (diastolic and systolic)], ejection fraction and mitral valve Doppler indexes (E, A, E/A ratio, and E), plasma Na+, K+, creatinine, hemoglobin, hematocrit, glucose, and urinary excretion of Na+, K+, creatinine, and cAMP (Table 3Go) were also unchanged.


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  		TABLE 1. Plasma hormones, second messengers, and biochemistry upon infusion of 50 µg human urocortin over 1 h

 

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  		TABLE 2. Hemodynamic measurements during urocortin infusion

 

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  		TABLE 3. Urine analyses during urocortin infusion

 

   Discussion
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
References
 
The biological effects of Ucn-1 infused in man have not previously been documented. Ucn-1 infusion in healthy male volunteers increased plasma levels of ACTH, cortisol, and ANP, while suppressing plasma ghrelin. In contrast to earlier studies in sheep, there were no hemodynamic or renal effects observed at the dose used.

The sequential pattern of ACTH and cortisol responses suggests that Ucn-1 increased ACTH release, which, in turn, stimulated cortisol secretion. Effects on ACTH are most likely due to Ucn-1’s CRF-like activity via pituitary CRF-R1s. This is in keeping with previous work showing Ucn-1-induced release of ACTH from isolated pituitary cells (1) and increased plasma ACTH and cortisol in animals (21, 22, 44).

The effect of Ucn-1 on plasma ghrelin, not previously reported, is of particular interest. Our subjects had eaten breakfast before commencement of the infusions (Ucn-1 and placebo) and had their next food soon after the 1400 h venous sampling. Plasma ghrelin showed the expected rise in the fasted state. This rise in plasma ghrelin toward provision of lunch was attenuated by Ucn-1, the onset apparent 2 h after cessation of the Ucn-1 infusion. The mechanism by which Ucn-1 suppressed plasma ghrelin levels remains to be determined. Perhaps Ucn-1, like somatostatin, has a direct inhibitory effect on secretion of ghrelin from the stomach (45). Alternatively, given the delayed effect, an indirect action of Ucn-1 is possible, via insulin (46), neuropeptide Y, or an orexin, for example. A third possibility is that there might be a feedback mechanism through ACTH and/or cortisol to inhibit ghrelin production (47, 48). However, we are not aware of data supporting such a link between ACTH and ghrelin. Finally, an action on clearance, rather than secretion, of ghrelin cannot be excluded.

Ucn-1 increased plasma ANP concentrations in the present study, a finding consistent with Ucn-1’s actions to stimulate ANP secretion from neonatal rat cardiomyocytes (29). Both the mechanism underlying this effect and its physiological relevance are currently uncertain, but subtle changes in plasma ANP, if sustained, can produce important biological effects (49, 50).

It is notable that the achieved plasma immunoreactive Ucn-1 concentrations in the present study were far lower than for the equivalent dose in sheep, and the pharmacokinetics differed markedly between the species. The calculated half-life for Ucn-1 in man was shorter at 52 min than in normal sheep, in which two compartment kinetics prevail (t1/2{alpha} and t1/2ß of ~90 min and ~18 h, respectively). CRF-binding protein (CRF-BP), present in human plasma, but not in sheep or rats (51), binds Ucn-1 and CRF with similar high affinity (52). It has been suggested that CRF-BP acts as a clearance mechanism, with the bound CRF-BP-ligand complex being endocytosed (53, 54). This has not yet been substantiated. Peripheral CRF-BP binding to Ucn-1 may be an explanation for the short half-life, if the complex is rapidly removed from plasma (or is not detected by our Ucn-1 assay). It might also explain the lower peak achieved concentrations compared with previous ovine experiments (21).

The metabolism of Ucn-1 is not well defined. Preliminary work suggests that urinary excretion is not major, as the change in urinary Ucn-1 with infusion is small (our unpublished observations). However, metabolism within the kidney (and in other tissues) is possible. Without information about levels of free vs. bound Ucn-1, we cannot define the relevance of CRF-BP to Ucn-1 pharmacokinetics, and it is also unknown whether the Ucn-1-CRF-BP complex is physiologically active.

Although we have demonstrated biological effects with the currently studied dose, higher concentrations of plasma Ucn-1 may be needed to elicit its full range of actions. The levels of Ucn-1 we obtained in plasma peaked at approximately 940 pg/ml (200 pmol/liter). Whether these levels are within the physiological or pathophysiological range remains to be determined. Our study used only a brief (60-min) period of Ucn-1 administration. The responses to more sustained infusion also remain to be defined and would also allow estimation of metabolic clearance rate and volume of distribution. The clear-cut rise in plasma levels of ACTH and cortisol without hemodynamic response suggest a differing threshold of plasma concentrations of Ucn for pituitary and cardiovascular effects. The presence of Ucn-1 and CRF-R2, but not CRF, immunoreactivity within the human heart raises the possibility of an independent role for Ucn-1 within the heart in man.

In summary, we present the first Ucn-1 infusion study in humans. In healthy male volunteers, we have demonstrated that Ucn-1 significantly elevates circulating levels of ACTH, cortisol, and, to a minor degree, plasma ANP. Ucn-1 depresses plasma ghrelin levels, which may reflect one mechanism underlying the anorexic action of Ucn-1. Ucn-1 had no demonstrable hemodynamic effects, nor did it alter circulating levels of second messenger cAMP, BNP, PRA, aldosterone, or AVP. The pharmacokinetics of infused Ucn-1 differ markedly between man and sheep. Future directions for research include elucidating physiological and pathophysiological levels of Ucn-1 in human plasma, dose-response relationships between plasma Ucn-1 and its assorted biological effects, the role (or otherwise) of CRF-BP in modifying the clearance and/or biochemistry of Ucn-1, and the bioactivity and metabolism of Ucn-II and Ucn-III.


   Acknowledgments
 
We gratefully acknowledge the provision of Ucn-1 antiserum by Prof. Wylie Vale and Joan Vaughn of The Salk Institute for Biological Studies (La Jolla, CA). We thank the technical staff at Endolab, in particular Steve Fisher and Greg Hammond, and the nurses from the Endocrine Special Test Center. Barbara Griffin provided secretarial assistance.


   Footnotes
 
This work was supported by the National Heart Foundation and Health Research Council of New Zealand.

Abbreviations: ADM, Adrenomedullin; ANP, atrial natriuretic peptide; AVP, arginine vasopressin; BNP, brain natriuretic peptide; CRF, corticotropin-releasing factor; CRF-BP, corticotropin-releasing factor-binding protein; CRF-RI, corticotropin-releasing factor receptor type 1; CV, coefficient of variation; ET, endothelin; PRA, plasma renin activity; PRL, prolactin.

Received July 16, 2003.

Accepted December 8, 2003.


   References
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
 References
 

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