help button home button Endocrine Society JCEM JCEM Call for Nominations for EIC
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
Journal of Clinical Endocrinology & Metabolism, doi:10.1210/jc.2005-1013
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
90/12/6498    most recent
Author Manuscript (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 Peeters, R. P.
Right arrow Articles by Van den Berghe, G.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Peeters, R. P.
Right arrow Articles by Van den Berghe, G.
Related Collections
Right arrow Thyroid
The Journal of Clinical Endocrinology & Metabolism Vol. 90, No. 12 6498-6507
Copyright © 2005 by The Endocrine Society

Tissue Thyroid Hormone Levels in Critical Illness

Robin P. Peeters, Serge van der Geyten, Pieter J. Wouters, Veerle M. Darras, Hans van Toor, Ellen Kaptein, Theo J. Visser and Greet Van den Berghe

Department of Internal Medicine (R.P.P., H.v.T., E.K., T.J.V.), Erasmus University Medical Center, Rotterdam, The Netherlands; and Laboratory of Comparative Endocrinology, Zoological Institute (S.v.d.G., V.M.D.) and Department of Intensive Care Medicine (P.J.W., G.V.d.B.), Katholieke Universiteit Leuven, B-3000 Leuven, Belgium

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


   Abstract
Top
 Abstract
Introduction
 Patients and Methods
 Results
 Discussion
 References
 
Context: Pronounced alterations in serum thyroid hormone levels occur during critical illness. T3 decreases and rT3 increases, the magnitudes of which are related to the severity of disease. It is unclear whether these changes are associated with decreased tissue T3 concentrations and, thus, reduced thyroid hormone bioactivity.

Patients and Study Questions: We therefore investigated, in 79 patients who died after intensive care and who did or did not receive thyroid hormone treatment, whether total serum thyroid hormone levels correspond to tissue levels in liver and muscle. Furthermore, we investigated the relationship between tissue thyroid hormone levels, deiodinase activities, and monocarboxylate transporter 8 expression.

Results: Tissue iodothyronine levels were positively correlated with serum levels, indicating that the decrease in serum T3 during illness is associated with decreased levels of tissue T3. Higher serum T3 levels in patients who received thyroid hormone treatment were accompanied by higher levels of liver and muscle T3, with evidence for tissue-specific regulation. Tissue rT3 and the T3/rT3 ratio were correlated with tissue deiodinase activities. Monocarboxylate transporter 8 expression was not related to the ratio of the serum over tissue concentration of the different iodothyronines.

Conclusion: Our results suggest that, in addition to changes in the hypothalamus-pituitary-thyroid axis, tissue-specific mechanisms are involved in the reduced supply of bioactive thyroid hormone in critical illness.


   Introduction
Top
 Abstract
 Introduction
Patients and Methods
 Results
 Discussion
 References
 
PRONOUNCED ALTERATIONS IN the hypothalamus-pituitary-thyroid axis occur during critical illness without any evidence for thyroid disease (1, 2). Total plasma T3 decreases and plasma rT3 increases within a few hours after the onset of disease, and the magnitude of these changes is related to the severity of the disease (2, 3, 4, 5). In severely ill patients, T4 decreases, and both T4 and T3 are inversely correlated with mortality rate (2, 6). Hardly any data are available in humans on whether these changes in serum thyroid hormone levels also result in changes in (free) tissue concentrations (7) and thus in a decreased bioactivity of thyroid hormone.

It is still controversial whether the reduction in serum T3 is a beneficial adaptation resulting in a protection against catabolism or whether it is a maladaptation contributing to a worsening of the disease (2, 8, 9). It has not been clearly demonstrated that substitution of critically ill patients with thyroid hormone has a positive effect on clinical outcome (10, 11, 12), and it is unclear whether thyroid hormone is taken up and metabolized in tissues when patients are treated with T4 and/or T3.

The decrease in serum T3 and the increase in rT3 levels can (partially) be explained by a reduced activation of T4 by type I deiodinase (D1) or type II deiodinase (D2) but also by an increased inactivation by type III deiodinase (D3) (1, 13). There is also evidence that, next to the regulation of D1, D2, and D3, a diminished transport of thyroid hormone into D1-expressing tissues plays a role in the changes in serum iodothyronines levels during critical illness (5, 14).

In this study, we investigated in a group of patients who died after intensive care whether local thyroid hormone levels in liver and skeletal muscle correspond to serum thyroid hormone levels. Furthermore, we investigated the relationship between tissue thyroid hormone levels, deiodinase activities, and monocarboxylate transporter 8 (MCT8), a recently identified thyroid hormone-specific transporter (15), expression in liver and skeletal muscle. All patients in this study had been randomized for insulin treatment as part of a large clinical trial that was recently described (16).


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

This study was part of a large randomized controlled study on intensive insulin treatment in intensive care unit (ICU) patients (n = 1548), of which the major clinical outcomes have been published in detail previously (16). All mechanically ventilated adult patients were eligible for inclusion in this trial after informed consent from the closest family member. The study protocol has been approved by the Ethical Review Board of the Catholic University of Leuven School of Medicine.

A total of 79 patients were included in the current study. All of these patients had died in the ICU, and the cause of death was determined both clinically by the attending ICU physician and by postmortem examination. Eleven patients died of a cardiovascular collapse, 36 died of multiorgan failure with sepsis, 26 died of multiorgan failure with systemic inflammatory response syndrome, and six died of severe brain damage. Relevant patients’ characteristics are summarized in Table 1Go.


View this table:
[in this window]
[in a new window]
  		TABLE 1. Descriptive statistics of the population used in this study

 
Blood samples were obtained from 64 patients, open liver biopsies from 65 patients, and open skeletal muscle (rectus abdominis) biopsies from 65 patients within minutes after death. The time between death and obtaining the tissue was 20 (12–31) min [median (interquartile range) (IQR)] for liver and 17 (8–25) min for skeletal muscle. From 49 patients blood, liver as well as skeletal muscle samples were available. Thirty-one patients had been treated with thyroid hormone during the course of their critical illness. Treatment was initiated when they had a serum T4 concentration less than 50 nmol/liter in the face of a normal T4-binding globulin and concomitantly clinical signs of hypothyroidism. The latter was defined as coma or central nervous system suppression, failure to wean from the ventilator, or hemodynamic instability, which were unexplained and resistant to conventional supportive therapy. In these cases, thyroid hormone treatment consisted of an iv bolus of 150 µg T4 daily plus 0.6 µg T3 per kilogram of body weight per 24 h as a continuous iv infusion. The median treatment was 11 d (6–23 IQR).

Serum analyses

The care of patients in the ICU often comprises infusion of heparin either systemically or locally to prevent clotting of vascular access, which substantially interferes with the assay used to quantify free concentrations of thyroid hormone (17). Therefore, we refrained from measuring serum free T4 and free T3 in this study. Serum total T4, T3, rT3, and TSH were measured as described previously (13, 18). Normal values for TSH (0.4–4.3 µU/dl), T4 (4.51–9.95 µg/dl), T3 (92.8–162.9 ng/dl), and rT3 (9.1–22.1 ng/dl) were determined in 270 healthy individuals. T4-binding globulin levels were measured using a commercially available RIA (Schering-CIS Biointernational, Gif-sur-Yvette, France).

Determination of T4, T3, and rT3 concentrations in human liver and skeletal muscle samples

T4, T3, and rT3 were determined by highly sensitive and specific RIAs after extraction and purification of the iodothyronines from tissues, as described previously (19, 20). Two thousand counts per minute [131I]T4 and [125I]T3 were added to each sample as internal tracers for recovery calculations. Average recovery was 50.6 and 55.4% for [131I]T4 in liver and skeletal muscle, respectively, and 69.0 and 72.3% for [125I]T3. Due to the limited amount of available tissue, [125I]T4 was also used as a recovery tracer for the determination of rT3, because previous experiments in our laboratory have shown that recovery of T4 and rT3 is similar. No corrections for the amounts of iodothyronines contributed by the blood trapped in the tissue aliquot were performed.

Tissue deiodinase activities

Human liver and skeletal muscle samples were homogenized on ice in 10 vol of PE buffer (0.1 M phosphate and 2 mM EDTA, pH 7.2) using a Polytron (Kinematica, Lucerne, Switzerland). Homogenates were snap frozen in aliquots and stored at –80 C until additional analysis. Liver and skeletal muscle deiodinase activities were determined as described previously (13).

RNA isolation and RT

RNA was isolated from liver samples using the High Pure RNA Tissue kit (Roche Diagnostics, Almere, The Netherlands) according to the protocol of the manufacturer. With this method, RNA is bound to a glass fiber fleece and eluted with distilled water. RNA isolation from skeletal muscle failed, because skeletal muscle tissue obstructed the fleece. Therefore, skeletal muscle RNA was isolated using Trizol reagent (Invitrogen, Breda, The Netherlands) as an initial isolation step, with an additional purification of the RNA using the High Pure RNA Tissue kit. RNA concentrations were determined using the RiboGreen RNA Quantitation kit (Molecular Probes, Leiden, The Netherlands). All samples were diluted to 0.1 µg/µl, and 1 µg was used for cDNA synthesis using the TaqMan Reverse Transcription kit (Roche Diagnostics).

Real-time RT-PCR

MCT8 mRNA levels were determined in 57 liver samples and 65 skeletal muscle samples using the ABI PRISM 7700 Sequence Detection System (Applied Biosystems, Nieuwerkerk aan den IJssel, The Netherlands), which uses TaqMan chemistry for highly accurate quantitation of mRNA levels, as described previously (13). Sequences and concentrations of the primers and probes are given in Table 2Go. mRNA levels are expressed relative to those of the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) housekeeping gene. The GAPDH probe and primers were provided as preoptimized control system (Applied Biosystems).


View this table:
[in this window]
[in a new window]
  		TABLE 2. Sequences and concentrations of the primers and probes that were used for determination of MCT8 mRNA levels by quantitative real-time PCR

 
Data were expressed as CT values, which represent the cycle number at which probe-derived dye absorbance reaches the calculated threshold value. Data are expressed relative to the housekeeping gene as (2{Delta}CT) x 1000. {Delta}CT is the CT value of the housekeeping gene minus the CT value of the target gene.

Statistical analysis

Data were analyzed using the statistical program SPSS 10.0.7 for Windows (SPSS, Chicago, IL). Logarithmic transformations were applied to normalize variables and to minimize the influence of outliers, when appropriate. All analyses were done on the whole group, as well as on subgroups treated or not treated with thyroid hormone. Data were analyzed using one-way ANOVA tests, with a post hoc Fisher’s least significant difference test for multiple comparisons, Mann-Whitney U tests, and linear regression analyses, when appropriate. Correlation coefficients represent Spearman’s correlation coefficients. Statistical significance was assumed for P < 0.05.


   Results
Top
 Abstract
 Introduction
 Patients and Methods
 Results
Discussion
 References
 
The effect of insulin and thyroid hormone therapy on serum and/or tissue thyroid parameters

The baseline characteristics of the two insulin treatment groups are shown in Table 1Go. There was no difference in age, gender, length of intensive care, need for thyroid hormone treatment, or any of the serum or tissue thyroid parameters between the two treatment groups. In both groups, iodothyronine concentrations in liver were substantially higher than in skeletal muscle. Table 3Go shows the same characteristics for the patients who did and those who did not receive thyroid hormone treatment. No distinction can be made in this study between primary and illness-induced (central) hypothyroidism, but presumably most thyroid hormone-treated patients belonged to the latter category (1, 2, 9). Patients who were treated with thyroid hormone stayed longer in the ICU [25 (18–42) vs. 9 (3–16)], received glucocorticoid treatment more often, and had a significantly lower TSH [0.01 (0.002–0.08) vs. 0.61 (0.13–0.96)] and higher T3 [1.41 (0.98–2.03) vs. 0.79 (0.61–1.11)] than patients who did not receive thyroid hormone treatment. T3 levels in patients who were treated with thyroid hormone were still in the low or low-normal range (Table 3Go). Higher serum T3 levels in these patients were accompanied by higher levels of liver T3 and rT3, higher levels of muscle T4, T3, and rT3, and by a higher muscle D3 activity. The increased liver T3 concentration in patients who received thyroid hormone treatment was remarkable, because it was disproportional compared with the increased serum and muscle T3 concentrations (approximately four times higher in liver compared with approximately two times higher in serum and skeletal muscle).


View this table:
[in this window]
[in a new window]
  		TABLE 3. Differences between the patients who were treated with thyroid hormone and the patients who were not

 
Correlation analysis of serum and tissue iodothyronine levels

Serum T4, T3, and rT3 levels showed a strong positive correlation with the respective hormone concentrations in liver (r = 0.31, P = 0.03; r = 0.81, P < 0.001; r = 0.58, P < 0.001 for T4, T3, and rT3, respectively), independent of thyroid hormone treatment (Table 4Go and Fig. 1Go). Similarly, skeletal muscle iodothyronine concentrations were positively correlated with serum iodothyronine concentrations (r = 0.67, P < 0.001; r = 0.72, P < 0.001; r = 0.71, P < 0.001) (Table 4Go and Fig. 2Go). The relationship between serum and tissue iodothyronine concentrations was weakest for liver T4 compared with the other iodothyronines in liver and skeletal muscle.


View this table:
[in this window]
[in a new window]
  		TABLE 4. Correlation analysis of serum and tissue (liver and skeletal muscle) iodothyronine levels

 


View larger version (15K):
[in this window]
[in a new window]
  		FIG. 1. Correlation analysis of serum T4, T3, and rT3 levels with local T4, T3, and rT3 concentrations in liver. Patients who did not receive thyroid hormone treatment are represented by gray circles, and patients who received thyroid hormone therapy are represented by black triangles. R represents Spearman’s correlation coefficient. To convert values for serum T4 to micrograms per deciliter, multiply by 0.0777; to convert values for serum T3 and rT3 to nanograms per deciliter, multiply by 65.1. Liver concentrations of T4, T3, and rT3 are shown in picomoles per gram wet weight. To convert values for liver T4 to nanograms per gram, multiply by 0.777; to convert values for liver T3 and rT3 to nanograms per gram, multiply by 0.651.

 


View larger version (14K):
[in this window]
[in a new window]
  		FIG. 2. Correlation analysis of serum T4, T3, and rT3 levels with local T4, T3, and rT3 concentrations in skeletal muscle. Patients who did not receive thyroid hormone treatment are represented by gray circles, and patients who received thyroid hormone therapy are represented by black triangles. R represents Spearman’s correlation coefficient. To convert values for serum T4 to micrograms per deciliter, multiply by 0.0777; to convert values for serum T3 and rT3 to nanograms per deciliter, multiply by 65.1. Muscle concentrations of T4, T3, and rT3 are shown in picomoles per gram wet weight. To convert values for muscle T4 to nanograms per gram, multiply by 0.777; to convert values for muscle T3 and rT3 to nanograms per gram, multiply by 0.651.

 
Correlation of tissue deiodinase activities and tissue iodothyronine levels

As described previously, we were not able to measure any D2 activity in the liver and skeletal muscle samples of these patients, whereas D3 activity was induced in both liver and skeletal muscle (13). Liver D1 was negatively correlated with serum rT3 levels and positively with the serum T3/rT3 ratio. Liver D3 was positively correlated with serum rT3 levels, whereas muscle D3 activity was not correlated to serum rT3 levels in these patients (13). No significant correlation was observed between deiodinase activities and postmortem time.

In this study, liver D1 activity showed a strong negative correlation with liver rT3 levels (r = –0.54, P < 0.001) and a positive correlation with the liver T3/rT3 ratio (r = 0.57, P < 0.001) but no relationship with liver T4 or T3 levels (Table 5Go and Fig. 3Go). After exclusion of all patients who were treated with thyroid hormone, liver T3 levels tended to be higher in patients with higher liver D1 activity (r = 0.28, P = 0.07). D3 activity in liver was positively correlated with the liver rT3 concentration (r = 0.28, P = 0.03), and D3 activity in skeletal muscle showed a significant correlation with both skeletal muscle rT3 (r = 0.57, P < 0.001) and the T3/rT3 ratio (r = –0.53, P < 0.001) (Table 5Go and Fig. 3Go). In patients who did not receive thyroid hormone therapy, skeletal muscle T3 levels tended to be lower in patients with a higher muscle D3 activity (r = –0.28, P = 0.07).


View this table:
[in this window]
[in a new window]
  		TABLE 5. Correlation analysis of tissue (liver or skeletal muscle) iodothyronine levels and liver or muscle deiodinase activities

 


View larger version (16K):
[in this window]
[in a new window]
  		FIG. 3. Correlation analysis of liver D1, liver D3, and muscle D3 activity with local rT3 concentrations in liver or skeletal muscle. Patients who did not receive thyroid hormone treatment are represented by gray triangles, and patients who received thyroid hormone therapy are represented by black triangles. R represents Spearman’s correlation coefficient. Tissue concentrations of T4, T3, and rT3 are shown in picomoles per gram wet weight. To convert values for tissue T4 to nanograms per gram, multiply by 0.777; to convert values for tissue T3 and rT3 to nanograms per gram, multiply by 0.651.

 
MCT8 expression and different thyroid parameters

MCT8 expression in liver showed a positive correlation with liver D1 activity (r = 0.34, P = 0.01) and a negative correlation with liver D3 activity (r = –0.52, P < 0.001) (Table 6Go and Fig. 4Go). MCT8 expression in skeletal muscle showed a positive relationship with muscle D3 activity (r = 0.32, P = 0.006) (Table 6Go and Fig. 4Go).


View this table:
[in this window]
[in a new window]
  		TABLE 6. Correlation analysis of liver or skeletal muscle MCT8 expression, the serum/tissue ratio of the different iodothyronines, and tissue deiodinase activities

 


View larger version (16K):
[in this window]
[in a new window]
  		FIG. 4. Correlation analysis of liver D1 and liver D3 activity with liver MCT8 expression and of muscle D3 activity with muscle MCT8 expression. MCT8 mRNA levels are expressed relative to the housekeeping gene GAPDH (see Patients and Methods). Patients who did not receive thyroid hormone treatment are represented by gray circles, and patients who received thyroid hormone therapy are represented by black triangles. R represents Spearman’s correlation coefficient.

 
Liver MCT8 expression was negatively correlated with serum and liver rT3 concentrations (P < 0.001 and P = 0.004) and positively with the serum and liver T3/rT3 ratio (P < 0.001 and P = 0.003) but not with the other iodothyronines. Multiple linear regression analysis showed that the relationship of liver MCT8 expression and liver iodothyronine levels was due to the positive relationship of liver MCT8 expression with liver D1 activity, because the relationship of MCT8 with liver rT3 and the T3/rT3 ratio disappeared completely when liver D1 was added to the regression model (P = 0.11 and P = 0.40). However, after adjustment for liver D1, the relationship of liver MCT8 with serum rT3 and T3/rT3 remained significant (P = 0.02 and P = 0.02). Muscle MCT8 expression was positively correlated with muscle rT3 concentrations and negatively with the muscle T3/rT3 ratio (P = 0.01 and P = 0.03), which was due to the positive relationship of muscle MCT8 expression and muscle D3 activity (P = 0.34 and P = 0.33, after addition of muscle D3 to the regression model).

If MCT8 expression would play an important role in transmembrane transport of iodothyronines, an effect of MCT8 expression on the ratio of the serum over tissue concentrations of the different iodothyronines would be expected. However, in neither liver nor skeletal muscle was MCT8 expression related to the ratio of the serum over tissue concentration of the different iodothyronines (Table 6Go).


   Discussion
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Discussion
References
 
Plasma T3 decreases and plasma rT3 increases during critical illness, and the magnitude of these changes is related to the severity of the disease (2, 3, 4, 5). Although intensive insulin therapy has been shown to result in a decreased morbidity and mortality in intensive care patients (16, 21), no differences in liver and skeletal muscle iodothyronine levels were found between the two insulin treatment groups. This is in line with previous studies, in which we found no effect of insulin treatment on serum thyroid parameters and/or deiodinase activities (13, 22). It should be noted, however, that all patients in this study died in the ICU. Because insulin therapy has a beneficial effect on survival, the possibility of a selection bias (sicker patients in the group receiving intensive insulin therapy) cannot be excluded.

Whether the reduction in serum T3 is a maladaptation that should be treated or whether it is a beneficial adaptation is still a controversial issue (2, 8, 9). A positive effect on clinical outcome of thyroid hormone substitution during critical illness has so far not been demonstrated (10, 11, 12). When patients are treated with T4 or T3, it is unclear whether thyroid hormone is taken up by tissues and metabolized. In this study, patients were treated with a combination of T4 and T3 if they had a serum T4 concentration less than 50 nmol/liter and concomitantly strictly defined clinical signs suggestive of hypothyroidism (13). Patients who received glucocorticoids, which are known to inhibit TSH secretion, received thyroid hormone substitution more often. It cannot be ascertained to what extent the requirement for thyroid hormone replacement is caused by administration of the glucocorticoids or by the underlying illness. Due to the lack of a good control group, no conclusions about the possible beneficial or negative effects of thyroid hormone substitution can be drawn from this study. It can be concluded, however, that the higher serum T3 levels, although still in the low-normal range, in patients who received thyroid hormone substitution therapy were accompanied by higher levels of T3 in liver and skeletal muscle, with a 2-fold greater increase in liver T3 than in serum T3. These data indicate different effects of thyroid hormone treatment on T3 levels in different tissues, which is in line with studies in thyroidectomized rats, demonstrating tissue-specific regulation of tissue thyroid hormone concentrations (23, 24, 25). In these studies, it was also shown that substitution with neither T4 nor T3 was able to restore T3 in plasma and all tissues of these thyroidectomized rats to similar levels as in euthyroid rats (23, 24, 25).

A major disadvantage of substitution with thyroid hormone itself is that the hypothalamus-pituitary-thyroid axis is bypassed. This may result in overtreatment and TSH suppression, whereas an increase in serum TSH marks the onset of recovery and concomitantly drives the increase in serum T4 (2, 26, 27). If a combination of T4 and T3 is given, the local regulation of thyroid hormone bioactivity by T4 to T3 conversion is also bypassed, which may be an argument against giving a combination of T4 and T3. Conversely, a randomized prospective study in hypothyroxinemic critically ill patients showed an increase in serum T4, but not in serum T3, after T4 treatment (10), which can be explained by the decreased D1 and D2 activity during critical illness (13, 22). It is unclear from our study whether substitution therapy with T4 alone would have resulted in higher levels of serum and/or tissue T3. Intervention with hypothalamic releasing factors, which restores pulsatile pituitary hormone secretion, normalizes peripheral hormone levels, and keeps the negative feedback loop intact, might be a more successful approach (28, 29, 30).

Serum iodothyronine levels showed a strong positive correlation with both liver and skeletal muscle iodothyronine levels. It should be noted that we do not have any data on the free concentrations of T4 and T3 in the sera and tissues of these patients, nor do we have data on the (intracellular) localization of thyroid hormone. However, liver T4 and tissue T3 in general are predominantly located intracellularly, in contrast to muscle T4, which is predominantly located in plasma and interstitial fluids (31, 32). Our data indicate that the decrease in serum T4 and T3 levels during critical illness also results in decreased levels of T4 and T3 in liver and skeletal muscle. The decreased expression of liver D1 during critical illness supports this (1, 13), because D1 is a very sensitive marker of tissue thyroid hormone status (33). An autopsy study, in which 12 patients who died of severe nonthyroidal illnesses were compared with 10 patients who died acutely from trauma, showed significantly decreased levels of T4 and T3 in liver, but not in skeletal muscle, of the severely ill patients (7). In our study, however, the relationship between serum and tissue iodothyronine levels was weakest for liver T4 compared with the other iodothyronines in liver and muscle. This might suggest that other factors than serum concentrations, such as deiodination and regulation of transport, are more important in the regulation of liver T4 concentration than in the regulation of liver T3 or muscle iodothyronine concentration.

A low D1 activity results in a reduced T3 production and rT3 clearance (5). The negative correlation of liver D1 activity with the local rT3 concentration in liver and the positive correlation with the liver T3/rT3 ratio are in line with this. An induction of D3 activity enhances the clearance of T3 and the production of rT3 (5, 13). The positive correlation of tissue D3 activity with rT3 levels in both liver and skeletal muscle and the negative correlation of muscle D3 with the local T3/rT3 ratio are also in agreement with this. Furthermore, in patients who did not receive thyroid hormone substitution, liver D1 activity showed a trend with higher levels of liver T3, whereas muscle D3 activity showed a trend with lower levels of muscle T3. The complete absence of muscle D2 activity in these patients is remarkable and must have resulted in a decreased local T3 production, because D2 activity is present in skeletal muscle of normal subjects (5, 34, 35). A possible explanation for the lack of D2 activity is the short half-life of functional D2 protein. D2 has an approximately 45-min half-life in euthyroid conditions due to selective ubiquitin-mediated endoplasmatic reticulum-associated degradation (36). This short half-life may cause rapid postmortem D2 inactivation. However, because muscle biopsies were taken within 45 min after death, postmortem decay of D2 cannot solely explain the lack of D2 activity in skeletal muscle samples of these patients. The shortest interval between entry in the ICU and isolation of tissue samples was between 24 and 48 h. Thus, in view of the short half-life of the D2 protein, it may well have disappeared from skeletal muscle if its expression is acutely suppressed in severe illness. These data indicate an important role during critical illness for liver D1 and D3 and skeletal muscle D2 and D3 activity in the regulation of local concentrations of thyroid hormone and thus of local thyroid hormone bioactivity.

In addition to serum iodothyronine levels and tissue deiodinase expression, transmembrane transport of iodothyronines is also important in the regulation of thyroid hormone bioactivity (14). Uptake of T4 by human hepatocytes is temperature, Na, and energy dependent (37), and kinetic analyses indicate that T4 and T3 cross the plasma membrane by different transporters (38, 39). Recently, human MCT8 was identified as the first known thyroid hormone-specific transporter, with a preference for T3 over T4 in humans (Friesema, E. C. H., and T. J. Visser, unpublished data). Although MCT8 transport activity is not Na and/or energy dependent, MCT8 is expressed in, among other tissues, liver and skeletal muscle (15). An effect of MCT8 expression on the ratio of the serum over tissue concentration of the iodothyronines would be expected if MCT8 expression is important in transmembrane transport of iodothyronines in a certain tissue. In this study, neither liver nor skeletal muscle MCT8 expression were related to the ratio of the serum over tissue concentration of T4, T3, or rT3, suggesting that MCT8 is not crucial in the transport of these iodothyronines over the plasma membrane in liver and skeletal muscle. This is supported by the fact that inactivating mutations in MCT8 result in elevated levels of T3, low levels of rT3, and a phenotype of severe mental retardation, but that there is currently no evidence for liver or muscle hypothyroidism in these patients (40). Alternatively, MCT8 may facilitate both influx and efflux, without having a net effect on intracellular iodothyronine levels in liver and skeletal muscle. A relationship between MCT8 activity and the tissue vs. serum ratio of the different iodothyronines can obviously not be excluded by these data, because we only looked at mRNA expression of MCT8.

Although our data suggest that MCT8 expression does not play a major role in iodothyronine uptake in liver and skeletal muscle, there was a close relationship between MCT8 expression and deiodinase activities. Liver D1 activity was positively associated with liver MCT8 expression, whereas liver D3 activity showed a negative relationship. This relationship was opposite in skeletal muscle, because muscle D3 activity was positively correlated with muscle MCT8 expression. This might suggest a different role for these tissues during critical illness. The liver plays a major role in serum T3 production (5), and the decreased T3 production during critical illness may not only be explained by a decreased D1 activity but also by a decreased transport of T4 into D1-containing tissues (14). Muscle D2 activity, which is present in skeletal muscle of normal subjects (5, 34, 35), was completely absent in these patients, whereas muscle D3 activity was induced. The positive relationship between muscle D3 activity and muscle MCT8 expression suggests an increased uptake of iodothyronines in skeletal muscle under conditions when D3 activity is high. This might result in an increased substrate availability for muscle D3, suggesting that, during critical illness, skeletal muscle is more important for the inactivation than for the activation of thyroid hormone. However, this is highly speculative, especially because our data also suggest that transporters other than MCT8 are more important in the regulation of thyroid hormone uptake in liver and skeletal muscle.

In conclusion, this is the first study on the relationship between serum and tissue iodothyronine levels in a large group of critically ill patients. Serum iodothyronine levels were positively correlated with both liver and muscle iodothyronine levels, indicating that the decrease in serum T4 and T3 levels during critical illness also results in decreased levels of tissue T4 and T3. Higher serum T3 levels in patients who received thyroid hormone therapy were accompanied by higher levels of liver T3 and rT3 and by higher levels of muscle T4, T3, and rT3, indicating tissue-specific effects of thyroid hormone treatment. Furthermore, tissue rT3 and T3/rT3 were correlated with tissue deiodinase activities, whereas MCT8 expression was not related to the ratios of the serum over tissue concentrations of the different iodothyronines.


   Acknowledgments
 
We acknowledge the medical and nursing staff of the Leuven Intensive Care Unit for their help in completing this study and Monique Kester for the development of the MCT8 TaqMan probes and primers.


   Footnotes
 
This work was supported by Zorg Onderzoek Nederland en Medische Wetenschappen Grant 920-03-146 (to R.P.P.) and the Fund for Scientific Research-Flanders (to S.v.d.G.), and by Belgian Fund for Scientific Research Grants G.0144.00 and G.3C05.95N, Research Council of the University of Leuven Grant OT 99/33, and the Belgian Foundation for Research in Congenital Heart Diseases (to G.V.d.B.). G.V.d.B. is the holder of an unrestrictive Novo Nordisk Chair of Research on Insulin in Critical Illness.

First Published Online September 20, 2005

Abbreviations: CT, Cycle threshold; D1–D3, types I–III deiodinase; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; ICU, intensive care unit; IQR, interquartile range; MCT8, monocarboxylate transporter 8.

Received May 6, 2005.

Accepted September 9, 2005.


   References
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Discussion
 References
 

  1. Wiersinga WM 2000 Nonthyroidal illness. In: Braverman LE, Utiger RD, eds. The thyroid. Philadelphia: Lippincott; 281–292
  2. Docter R, Krenning EP, de Jong M, Hennemann G 1993 The sick euthyroid syndrome: changes in thyroid hormone serum parameters and hormone metabolism. Clin Endocrinol (Oxf) 39:499–518[Medline]
  3. Wartofsky L, Burman KD 1982 Alterations in thyroid function in patients with systemic illness: the "euthyroid sick syndrome." Endocr Rev 3:164–217[Medline]
  4. Rothwell PM, Lawler PG 1995 Prediction of outcome in intensive care patients using endocrine parameters. Crit Care Med 23:78–83[CrossRef][Medline]
  5. Bianco AC, Salvatore D, Gereben B, Berry MJ, Larsen PR 2002 Biochemistry, cellular and molecular biology, and physiological roles of the iodothyronine selenodeiodinases. Endocr Rev 23:38–89[Abstract/Free Full Text]
  6. McIver B, Gorman CA 1997 Euthyroid sick syndrome: an overview. Thyroid 7:125–132[Medline]
  7. Arem R, Wiener GJ, Kaplan SG, Kim HS, Reichlin S, Kaplan MM 1993 Reduced tissue thyroid hormone levels in fatal illness. Metabolism 42:1102–1108[CrossRef][Medline]
  8. De Groot LJ 1999 Dangerous dogmas in medicine: the nonthyroidal illness syndrome. J Clin Endocrinol Metab 84:151–164[Free Full Text]
  9. Van den Berghe G 2002 Dynamic neuroendocrine responses to critical illness. Front Neuroendocrinol 23:370–391[CrossRef][Medline]
  10. Brent GA, Hershman JM 1986 Thyroxine therapy in patients with severe nonthyroidal illnesses and low serum thyroxine concentration. J Clin Endocrinol Metab 63:1–8[Abstract]
  11. Bettendorf M, Schmidt KG, Grulich-Henn J, Ulmer HE, Heinrich UE 2000 Tri-iodothyronine treatment in children after cardiac surgery: a double-blind, randomised, placebo-controlled study. Lancet 356:529–534[CrossRef][Medline]
  12. Becker RA, Vaughan GM, Ziegler MG, Seraile LG, Goldfarb IW, Mansour EH, McManus WF, Pruitt Jr BA, Mason Jr AD 1982 Hypermetabolic low triiodothyronine syndrome of burn injury. Crit Care Med 10:870–875.[Medline]
  13. Peeters RP, Wouters PJ, Kaptein E, van Toor H, Visser TJ, Van den Berghe G 2003 Reduced activation and increased inactivation of thyroid hormone in tissues of critically ill patients. J Clin Endocrinol Metab 88:3202–3211[Abstract/Free Full Text]
  14. Hennemann G, Docter R, Friesema EC, de Jong M, Krenning EP, Visser TJ 2001 Plasma membrane transport of thyroid hormones and its role in thyroid hormone metabolism and bioavailability. Endocr Rev 22:451–476[Abstract/Free Full Text]
  15. Friesema EC, Ganguly S, Abdalla A, Manning Fox JE, Halestrap AP, Visser TJ 2003 Identification of monocarboxylate transporter 8 as a specific thyroid hormone transporter. J Biol Chem 278:40128–40135[Abstract/Free Full Text]
  16. Van den Berghe G, Wouters P, Weekers F, Verwaest C, Bruyninckx F, Schetz M, Vlasselaers D, Ferdinande P, Lauwers P, Bouillon R 2001 Intensive insulin therapy in the critically ill patients. N Engl J Med 345:1359–1367[Abstract/Free Full Text]
  17. Mendel CM, Frost PH, Kunitake ST, Cavalieri RR 1987 Mechanism of the heparin-induced increase in the concentration of free thyroxine in plasma. J Clin Endocrinol Metab 65:1259–1264[Abstract]
  18. Visser TJ, Docter R, Hennemann G 1977 Radioimmunoassay of reverse tri-iodothyronine. J Endocrinol 73:395–396[Medline]
  19. Morreale de Escobar G, Calvo R, Escobar del Rey F, Obregon MJ 1994 Thyroid hormones in tissues from fetal and adult rats. Endocrinology 134:2410–2415[Abstract]
  20. Morreale de Escobar G, Pastor R, Obregon MJ, Escobar del Rey F 1985 Effects of maternal hypothyroidism on the weight and thyroid hormone content of rat embryonic tissues, before and after onset of fetal thyroid function. Endocrinology 117:1890–1900[Abstract]
  21. Van den Berghe G 2004 How does blood glucose control with insulin save lives in intensive care? J Clin Invest 114:1187–1195[CrossRef][Medline]
  22. Peeters RP, Wouters PJ, van Toor H, Kaptein E, Visser TJ, Van den Berghe G 2005 Serum 3,3',5'-triiodothyronine (rT3) and 3,5,3'-triiodothyronine/rT3 are prognostic markers in critically ill patients and are associated with post-mortem tissue deiodinase activities. J Clin Endocrinol Metab 90:4559–4565[Abstract/Free Full Text]
  23. Escobar-Morreale HF, Obregon MJ, Escobar del Rey F, Morreale de Escobar G 1995 Replacement therapy for hypothyroidism with thyroxine alone does not ensure euthyroidism in all tissues, as studied in thyroidectomized rats. J Clin Invest 96:2828–2838
  24. Escobar-Morreale HF, Obregon MJ, Hernandez A, Escobar del Rey F, Morreale de Escobar G 1997 Regulation of iodothyronine deiodinase activity as studied in thyroidectomized rats infused with thyroxine or triiodothyronine. Endocrinology 138:2559–2568[Abstract/Free Full Text]
  25. Escobar-Morreale HF, Obregon MJ, Escobar del Rey F, Morreale de Escobar G 1999 Tissue-specific patterns of changes in 3,5,3'-triiodo-L-thyronine concentrations in thyroidectomized rats infused with increasing doses of the hormone. Which are the regulatory mechanisms? Biochimie (Paris) 81:453–462
  26. Hamblin PS, Dyer SA, Mohr VS, Le Grand BA, Lim CF, Tuxen DV, Topliss DJ, Stockigt JR 1986 Relationship between thyrotropin and thyroxine changes during recovery from severe hypothyroxinemia of critical illness. J Clin Endocrinol Metab 62:717–722[Abstract]
  27. Bacci V, Schussler GC, Kaplan TB 1982 The relationship between serum triiodothyronine and thyrotropin during systemic illness. J Clin Endocrinol Metab 54:1229–1235[Abstract]
  28. Weekers F, Michalaki M, Coopmans W, Van Herck E, Veldhuis JD, Darras VM, Van den Berghe G 2004 Endocrine and metabolic effects of growth hormone (GH) compared with GH-releasing peptide, thyrotropin-releasing hormone, and insulin infusion in a rabbit model of prolonged critical illness. Endocrinology 145:205–213[Abstract/Free Full Text]
  29. Van den Berghe G, Baxter RC, Weekers F, Wouters P, Bowers CY, Iranmanesh A, Veldhuis JD, Bouillon R 2002 The combined administration of GH-releasing peptide-2 (GHRP-2), TRH and GnRH to men with prolonged critical illness evokes superior endocrine and metabolic effects compared to treatment with GHRP-2 alone. Clin Endocrinol (Oxf) 56:655–669[CrossRef][Medline]
  30. Van den Berghe G, Wouters P, Bowers CY, de Zegher F, Bouillon R, Veldhuis JD 1999 Growth hormone-releasing peptide-2 infusion synchronizes growth hormone, thyrotrophin and prolactin release in prolonged critical illness. Eur J Endocrinol 140:17–22[Abstract]
  31. Irvine CH 1974 Concentration of thyroxine in cellular and extracellular tissues of the sheep and the rate of equilibration of labeled thyroxine. Endocrinology 94:1060–1071[Medline]
  32. Hennemann G 1986 Thyroid hormone deiodination in healthy man. In: Hennemann G, ed. Thyroid hormone metabolism. New York: Marcel Dekker; 277–295
  33. Zavacki AM, Ying H, Christoffolete MA, Aerts G, So E, Harney JW, Cheng SY, Larsen PR, Bianco AC 2005 Type 1 iodothyronine deiodinase is a sensitive marker of peripheral thyroid status in the mouse. Endocrinology 146:1568–1575[Abstract/Free Full Text]
  34. Canani LH, Capp C, Dora JM, Souza Meyer EL, Wagner MS, Harney JW, Larsen PR, Gross JL, Bianco AC, Maia AL 2005 The type 2 deiodinase A/G (Thr92Ala) polymorphism is associated with decreased enzyme velocity and increased insulin resistance in patients with type 2 diabetes mellitus. J Clin Endocrinol Metab 90:3472–3478[Abstract/Free Full Text]
  35. Salvatore D, Bartha T, Harney JW, Larsen PR 1996 Molecular biological and biochemical characterization of the human type 2 selenodeiodinase. Endocrinology 137:3308–3315[Abstract]
  36. Kim BW, Zavacki AM, Curcio-Morelli C, Dentice M, Harney JW, Larsen PR, Bianco AC 2003 Endoplasmic reticulum-associated degradation of the human type 2 iodothyronine deiodinase (D2) is mediated via an association between mammalian UBC7 and the carboxyl region of D2. Mol Endocrinol 17:2603–2612[Abstract/Free Full Text]
  37. de Jong M, Visser TJ, Bernard BF, Docter R, Vos RA, Hennemann G, Krenning EP 1993 Transport and metabolism of iodothyronines in cultured human hepatocytes. J Clin Endocrinol Metab 77:139–143[Abstract]
  38. Riley Jr WW, Eales JG 1994 Characterization of 3,5,3'-triiodo-L-thyronine transport into hepatocytes isolated from juvenile rainbow trout (Oncorhynchus mykiss), and comparison with L-thyroxine transport. Gen Comp Endocrinol 95:301–309[CrossRef][Medline]
  39. Krenning E, Docter R, Bernard B, Visser T, Hennemann G 1981 Characteristics of active transport of thyroid hormone into rat hepatocytes. Biochim Biophys Acta 676:314–320[Medline]
  40. Friesema EC, Grueters A, Biebermann H, Krude H, von Moers A, Reeser M, Barrett TG, Mancilla EE, Svensson J, Kester MH, Kuiper GG, Balkassmi S, Uitterlinden AG, Koehrle J, Rodien P, Halestrap AP, Visser TJ 2004 Association between mutations in a thyroid hormone transporter and severe X-linked psychomotor retardation. Lancet 364:1435–1437[CrossRef][Medline]



This article has been cited by other articles:


Home page
 EndocrinologyHome page
Y. Debaveye, B. Ellger, L. Mebis, T. J. Visser, V. M. Darras, and G. Van den Berghe
Effects of Substitution and High-Dose Thyroid Hormone Therapy on Deiodination, Sulfoconjugation, and Tissue Thyroid Hormone Levels in Prolonged Critically Ill Rabbits
Endocrinology, August 1, 2008; 149(8): 4218 - 4228.
[Abstract] [Full Text] [PDF]

Home page
 Eur J EndocrinolHome page
P. H Bisschop, A. W Toorians, E. Endert, W. M Wiersinga, L. J Gooren, and E. Fliers
The effects of sex-steroid administration on the pituitary-thyroid axis in transsexuals.
Eur. J. Endocrinol., July 1, 2006; 155(1): 11 - 16.
[Abstract] [Full Text] [PDF]

Home page
 EndocrinologyHome page
J. Yu and R. J. Koenig
Induction of Type 1 Iodothyronine Deiodinase to Prevent the Nonthyroidal Illness Syndrome in Mice
Endocrinology, July 1, 2006; 147(7): 3580 - 3585.
[Abstract] [Full Text] [PDF]

Home page
 EndocrinologyHome page
T. J. Visser
The elemental importance of sufficient iodine intake: a trace is not enough.
Endocrinology, May 1, 2006; 147(5): 2095 - 2097.
[Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
90/12/6498    most recent
Author Manuscript (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 Peeters, R. P.
Right arrow Articles by Van den Berghe, G.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Peeters, R. P.
Right arrow Articles by Van den Berghe, G.
Related Collections
Right arrow Thyroid

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
Endocrinology Endocrine Reviews J. Clin. End. & Metab.
Molecular Endocrinology Recent Prog. Horm. Res. All Endocrine Journals