Thyroid function during growth hormone therapy

Treatment of Isolated Idiopathic Growth Hormone Deficiency in Children and Thyroid Function: Is the Need for LT4 Supplementation a Concern in Long-Term Therapy?

Introduction

Recombinant human growth hormone (rhGH) replacement therapy might be able to induce hypothyroidism, but this is a controversial issue. Previous studies evaluated the effects of rhGH replacement therapy on thyroid function, but little information is available in the subset of children with isolated idiopathic growth hormone deficiency (GHD). Our aim was to assess the effects of rhGH replacement therapy on thyroid function in children with isolated idiopathic GHD.

Methods

Retrospective analysis of the medical files of 64 children with confirmed GHD treated with rhGH. After review, 56 children with isolated idiopathic GHD and treated with rhGH for at least one year were included. Auxological (weight standard deviation score [SDS], height SDS, growth velocity [GV] SDS) and biochemical (free thyroxine [FT4], thyroid-stimulating hormone [TSH], and insulin-like growth factor 1 [IGF-1]) parameters were recorded before, during, and after treatment with rhGH.

Results

FT4 and TSH levels decreased significantly during rhGH therapy in children with isolated idiopathic GHD. Twenty-one percent (n=12) of the children developed hypothyroidism, on average 47 months after initiation of rhGH. Higher baseline FT4 levels were protective against the need for levothyroxine (LT4) (OR=0.8, CI 0.592-0.983; p=0.036). Hypothyroidism was reversed after interruption of rhGH, except in one patient; FT4 levels returned to baseline in the first year after completing the treatment. Final height SDS of the children who developed hypothyroidism was not different from their counterparts without hypothyroidism (-1.24 [-1.52 to -1.10] vs -1.13 [-1.78 to -0.74], p=1.000). Predicted adult height (PAH) SDS in patients who completed rhGH treatment was similar in both LT4 supplemented (n=7; final Ht SDS -1.16 [-1.31 to -1.10] vs PAH -1.00 [-1.42 to -0.48]; p=0.398) and not supplemented patients (n=25; final Ht SDS -1.46 [-1.83 to -0.78] vs PAH SDS -0.88 [-1.35 to -0.56]; p=0.074).

Conclusions

Our results show that patients with isolated idiopathic GHD may transiently need LT4 during GH treatment. Properly supplemented patients achieved PAH.

Decreased Thyroxine Levels during rhGH Therapy in Children with Growth Hormone Deficiency

Background: Hypothyroidism in children leads to growth retardation. However, there is some evidence that recombinant human growth hormone (rhGH) therapy could suppress thyroid function. The most common observation in rhGH-treated patients is a decrease in thyroxine levels, which is reported as transient, but the studies in the field are inconsistent. We aimed to evaluate thyroid function in initially euthyroid children with idiopathic isolated GH deficiency during long-term rhGH therapy and to determine who is at a higher risk of thyroid function alterations during the therapy. Methods: The study group consisted of 101 children treated with rhGH for at least three years. Serum TSH and fT4 levels were determined at baseline, after the first six months and after each full year of therapy. The associations between changes in thyroid hormone levels during rhGH therapy and GH deficit, insulin-like growth factor-1 levels and growth response were investigated. Results: A significant decrease in fT4 levels (p = 0.01) was found as early as after the first six months of rhGH therapy. This effect persisted in the subsequent years of treatment without any significant changes in TSH values and tended to be rhGH dose related. Children with a greater fT4 decrease after the initiation of rhGH therapy were older, had higher bone age and responded to that therapy worse than children with lower fT4 changes. Conclusions: Our study revealed a long-term decrease in fT4 levels during rhGH therapy in initially euthyroid GHD children. The decrease in fT4 levels was associated with a lower growth response to rhGH therapy.

The hypothalamus-pituitary-thyroid (HPT)-axis and its role in physiology and pathophysiology of other hypothalamus-pituitary functions

The hypothalamus-pituitary-thyroid axis is one of several hormone regulatory systems from the hypothalamus to the pituitary and ultimately to the peripheral target organs. The hypothalamus and the pituitary gland are in close anatomical proximity at the base of the brain and extended through the pituitary stalk to the sella turcica. The pituitary stalk allows passage of stimulatory and inhibitory hormones and other signal molecules. The target organs are placed in the periphery and function through stimulation/inhibition by the circulating pituitary hormones. The several hypothalamus-pituitary-target organ axis systems interact in very sophisticated and complicated ways and for many of them the interactive and integrated mechanisms are still not quite clear. The diagnosis of central hypothyroidism is complicated by itself but challenged further by concomitant affection of other hypothalamus-pituitary-hormone axes, the dysfunction of which influences the diagnosis of central hypothyroidism. Treatment of both the central hypothyroidism and the other hypothalamus-pituitary axes also influence the function of the others by complex mechanisms involving both central and peripheral mechanisms. Clinicians managing patients with neuroendocrine disorders should become aware of the strong integrative influence from each hypothalamus-pituitary-hormone axis on the physiology and pathophysiology of central hypothyroidism. As an aid in this direction the present review summarizes and highlights the importance of the hypothalamus-pituitary-thyroid axis, pitfalls in diagnosing central hypothyroidism, diagnosing/testing central hypothyroidism in relation to panhypopituitarism, pointing at interactions of the thyroid function with other pituitary hormones, as well as local hypothalamic neurotransmitters and gut-brain hormones. Furthermore, the treatment effect of each axis on the regulation of the others is described. Finally, these complicating aspects require stringent diagnostic testing, particularly in clinical settings with lower or at least altered à priori likelihood of hypopituitarism than in former obvious clinical patient presentations.

Correlation between severity of growth hormone deficiency and thyroid metabolism and effects of long-term growth hormone treatment on thyroid function in children with idiopathic growth hormone deficiency

BACKGROUND/AIM

The significance of changes in thyroid function in children during growth hormone (GH) treatment remains uncertain. We aimed to evaluate the impact of GH replacement on thyroid status in children with idiopathic GH deficiency (GHD).

METHODS

Data of 105 GHD children (82 M, 23 F; aged 11.13 years) during a 36-month follow-up were analyzed. At diagnosis the areas under the curve of GH (AUCGH) were calculated during a GH-releasing hormone + arginine (GHRH-Arg) and insulin tolerance test.

RESULTS

A significant ΔfT3 (p < 0.001) was documented at 12 months, without any further change at 24 and 36 months and without fT4 and TSH modifications. Grouping patients according to ΔfT3 at 12 months into those with lower (n = 80, 76%) or greater values than the 75th percentile (n = 25, 24%), the latter showed lower AUCGH and GH peak during a GHRH-Arg (p = 0.018 and 0.014, respectively) and insulin tolerance test (p = 0.023 and 0.020, respectively) at diagnosis. In addition, children with lower GH at diagnosis showed a greater ΔfT3 at 12 months (p = 0.030).

CONCLUSIONS

In GHD children, GH treatment is associated with a significant increase in fT3 in the first 12 months, more pronounced in patients with more severe GHD, highlighting the strong correlation between severity of GHD and thyroid metabolism.

Serum thyroid hormone levels in healthy children from birth to adulthood and in short children born small for gestational age

CONTEXT

Age-appropriate reference ranges for thyroid hormones are required for detecting pediatric thyroid dysfunction. Data on thyroid hormones and peripheral thyroid metabolism in short children born small for gestational age (SGA) before and during GH treatment are lacking.

OBJECTIVES

Our objectives were to obtain pediatric thyroid hormone reference ranges; to investigate thyroid hormones in short SGA children before puberty, during puberty, and during postponement of puberty by GnRH analog; and to evaluate thyroid hormones during GH treatment.

PATIENTS AND DESIGN

In 512 healthy children (225 females; 0-18 yr), free T(4) (FT(4)), TSH, total T(4), T(3), rT(3), and T(4)-binding globulin were determined. Reference ranges were calculated using the linearity, median, and skewness method. In 125 short SGA children (62 females; mean age 11.3 yr), thyroid hormones were analyzed before and after 2 yr of GH treatment and additional GnRH analog.

RESULTS

Thyroid references showed wide ranges postnatally and age-specific patterns thereafter, similar in boys and girls. Untreated short SGA children had similar FT(4) and T(4) levels as the reference population but significantly higher T(3), rT(3), and T(4)-binding globulin levels. During puberty and during GH treatment, FT(4) and rT(3) significantly decreased, whereas T(3) significantly increased.

CONCLUSION

Age-specific thyroid reference ranges are presented. Puberty and GH treatment both induce changes in peripheral thyroid metabolism, resulting in more biologically active T(3) at the expense of less inactive rT(3), possibly mediated by IGF-I. GH treatment induces altered peripheral thyroid metabolism but does not result in thyroid dysfunction.

Effects of depot growth hormone replacement on thyroid function and volume in adults with congenital isolated growth hormone deficiency

BACKGROUND

Conflicting data exist on the effects of GH replacement therapy (GHRT) on thyroid function and thyroid volume (TV) in GH-deficient (GHD) patients.

AIM

The aim of this study was to assess the effects of GHRT on thyroid function and TV in adults with congenital lifetime isolated GHD (IGHD).

SUBJECTS AND METHODS

We studied 20 GH-naïve adults with IGHD due to a homozygous mutation of the GHRH-receptor gene at baseline, after 6-month depot- GH replacement therapy (pGH), and 6-month washout (6mo). Total T(3), free T(4) (FT(4)), reverse T(3) (rT(3)), TSH, IGF-I, SHBG, and TV were measured; body surface area-corrected TV (CTV) was calculated.

RESULTS

IGF-I and T(3) increased pGH. T(3) levels remained elevated at 6mo. GHRT did not significantly change FT(4), rT(3), TSH, and SHBG. TV and CTV increased pGH and remained elevated at 6mo.

CONCLUSIONS

GHRT in IGHD adults caused an increase in serum T(3) levels and TV, suggesting an important role of the GH-IGF-I axis in thyroid function.

Do IGF-I concentrations better reflect growth hormone (GH) action in children with short stature than the results of GH stimulating tests? Evidence from the simultaneous assessment of thyroid function

Background

The diagnosis of growth hormone (GH) deficiency (GHD) in short children seems unquestionable when both GH peak in stimulating tests (GHST) and IGF-I concentration are decreased. However, the discrepancies between the results of GHST and IGF-I secretion are observed. It seems purposeful to determine the significance of GHST and IGF-I assessment in diagnosing GHD. The relationship between GH secretion and thyroid function, as well as GH influence on the peripheral thyroxine (T₄) to triiodothyronine (T₃) deiodination, mediated by IGF-I, were identified. Thus, clear differences in thyroid function between GH-deficient and non-GH-deficient subjects should exist.

Methods

Analysis comprised 800 children (541 boys), age 11.6 ± 3.1 years (mean ± SD), with short stature, in whom two (2) standard GHST (with clonidine and with glucagon) were performed and IGF-I, free T₄ (FT₄), free T₃ (FT₃) and TSH serum concentrations were assessed. The patients were qualified to the following groups: GHD - decreased GH peak in GHST and IGF-I SDS (n = 81), ISS - normal GH peak and IGF-I SDS (n = 347), low GH - normal IGF-I SDS, and decreased GH peak (n = 212), low IGF - decreased IGF-I SDS, and normal GH peak (n = 160). The relationships among the results of particular tests were evaluated.

Results

In the groups with decreased IGF-I concentrations (GHD Group and low IGF Group), the more severe deficit of height was observed, together with higher TSH and FT₄ but lower FT₃ levels than in groups with normal IGF-I concentrations (ISS Group and low GH Group), independently of the results of GHST. TSH, FT₄ and FT₃ concentrations were - respectively - similar in two groups with decreased IGF-I secretion, as well as in two groups with normal IGF-I levels. Significant correlations were found between patients' height SDS and IGF-I SDS, between FT₃ and IGF-I SDS (positive), and between FT₄ and IGF-I SDS (negative), with no correlation between GH peak and any of the parameters analyzed.

Conclusion

The assessment of thyroid function in children with short stature provides the evidence that measurement of IGF-I concentration may be a procedure reliable at least to the some degree in diagnosing GHD as the results of GHST.

Thyroid function in children with growth hormone (GH) deficiency during the initial phase of GH replacement therapy - clinical implications

Background

Normal thyroid hormone secretion or appropriate L-thyroxine (L-T₄) substitution is necessary for the optimal effect of the growth hormone (GH) administration on growth rate. The decrease of free thyroxine (FT₄) levels at recombinant human GH (rhGH) therapy onset has been reported in several studies. The aim of the present study was to evaluate the effect of rhGH administration on thyrotropin (TSH) and FT₄ serum concentrations in children with GH deficiency (GHD) during the 1st year of therapy, as well as to assess potential indications to thyroid hormone supplementation in them.

Patients and methods

The analysis involved data of 75 children (59 boys, 16 girls) with disorders of GH secretion (GHD, neurosecretory dysfunction - NSD) and partial GH inactivity (inactGH), who were treated with rhGH for - at least - one year. In all the children, body height and height velocity (HV) were assessed before and after 1 year of therapy, while TSH, FT₄, IGF-I and IGFBP-3 before treatment and after 3-6 months and 1 year of treatment. In the patients, who revealed hypothyroidism (HypoT), an appropriate L-T₄ substitution was introduced immediately. The incidence of HypoT, occurring during the initial phase of rhGH therapy, was assessed, as well as its influence on the therapy effectiveness.

Results

Before rhGH substitution, there were no significant differences in either auxological indices or TSH and FT₄ secretion, or IGF-I concentration and its bioavailability among the groups of patients. During the initial 3-6 months of rhGH administration, a significant decrease of FT₄ serum concentration, together with a significant increase of IGF-I SDS and IGF-I/IGFBP-3 molar ratio was observed in all the studied groups. In 17 children, HypoT was diagnosed and L-T₄ substitution was administered. Despite similar IGF-I secretion increase, the improvement of HV presented significantly lower in children with HypoT than in those who remained euthyroid all the time.

Conclusions

The incidence of HypoT during the initial phase of GH treatment in children with GHD and the negative effect of even transient thyroid hormone deficiency on the growth rate should be taken into account.

The growth hormone/insulin-like growth factor-I axis in exercise and sport

The syndrome of adult GH deficiency and the effects of GH replacement therapy provide a useful model with which to study the effects of the GH/IGF-I axis on exercise physiology. Measures of exercise performance including maximal oxygen uptake and ventilatory threshold are impaired in adult GH deficiency and improved by GH replacement, probably through some combination of increased oxygen delivery to exercising muscle, increased fatty acid availability with glycogen sparing, increased muscle strength, improved body composition, and improved thermoregulation. In normal subjects, in addition to the long-term effects of GH/IGF-I status, there is evidence that the acute GH response to exercise is important in regulating substrate metabolism after exercise. Administration of supraphysiological doses of GH to athletes increases fatty acid availability and reduces oxidative protein loss, particularly during exercise, and increases lean body mass. Despite a lack of evidence that these metabolic effects translate to improved performance, GH abuse by athletes is widespread. Tests to detect GH abuse have been developed based on measurement in serum of 1) indirect markers of GH action, and 2) the relative proportions of the two major naturally occurring isoforms (20 and 22kDa) of GH. There is evidence that exercise performance and strength are improved by administration of GH and testosterone in combination to elderly subjects. The potential benefits of GH in these situations must be weighed against potential adverse effects.

Thyroid hormone levels in children with Prader-Willi syndrome before and during growth hormone treatment

BACKGROUND

Prader-Willi syndrome (PWS) is a neurogenetic disorder characterized by muscular hypotonia, psychomotor delay, obesity and short stature. Several endocrine abnormalities have been described, including GH deficiency and hypogonadotrophic hypogonadism. Published data on thyroid hormone levels in PWS children are very limited.

OBJECTIVE

To evaluate thyroid function in children with PWS, before and during GH treatment.

DESIGN/PATIENTS

At baseline, serum levels of T4, free T4 (fT4), T3, reverse T3 (rT3) and TSH were assessed in 75 PWS children. After 1 year, assessments were repeated in 57 of the them. These children participated in a randomized study with two groups: group A (n = 34) treated with 1 mg GH/m(2)/day and group B (n = 23) as controls.

RESULTS

Median age (interquartile range, IQR) of the total group at baseline was 4.7 (2.7-7.6) years. Median (IQR) TSH level was -0.1 SDS (-0.5 to 0.5), T4 level -0.6 SDS (-1.7 to 0.0) and fT4 level -0.8 SDS (-1.3 to -0.3), the latter two being significantly lower than 0 SDS. T3 level, at 0.3 SDS (-0.3 to 0.9), was significantly higher than 0 SDS. After 1 year of GH treatment, fT4 decreased significantly from -0.8 SDS (-1.5 to -0.2) to -1.4 SDS (-1.6 to -0.7), compared to no change in untreated PWS children. However, T3 did not change, at 0.3 SDS (-0.1 to 0.8).

CONCLUSIONS

We found normal fT4 levels in most PWS children. During GH treatment, fT4 decreased significantly to low-normal levels. TSH levels remained normal. T3 levels were relatively high or normal, both before and during GH treatment, indicating that PWS children have increased T4 to T3 conversion.

Unmasking of central hypothyroidism following growth hormone replacement in adult hypopituitary patients

BACKGROUND

The effect of GH replacement on thyroid function in hypopituitary patients has hitherto been studied in small groups of children and adults with conflicting results.

OBJECTIVE

We aimed to define the effect and clinical significance of adult GH replacement on thyroid status in a large cohort of GH-deficient patients.

PATIENTS AND METHOD

We studied 243 patients with severe GH deficiency due to various hypothalamo-pituitary disorders. Before GH treatment, 159 patients had treated central hypothyroidism (treated group) while 84 patients were considered euthyroid (untreated group). GH dose was titrated over 3 months to achieve serum IGF-1 concentration in the upper half of the age-adjusted normal range. Serial measurements of serum T4, T3, TSH and quality of life were made at baseline and at 3 and 6 months after commencing GH replacement.

RESULTS

In the untreated group, we observed a significant reduction in serum T4 concentration without a significant increase in serum T3 or TSH concentration; 30/84 patients (36%) became hypothyroid and needed initiation of T4 therapy. Similar but lesser changes were seen in the treated group, 25 of whom (16%) required an increase in T4 dose. Patients who became hypothyroid after GH replacement had lower baseline serum T4 concentration, were more likely to have multiple pituitary hormone deficiencies and showed less improvement in quality of life compared with patients who remained euthyroid.

CONCLUSION

GH deficiency masks central hypothyroidism in a significant proportion of hypopituitary patients and this is exposed after GH replacement. We recommend that hypopituitary patients with GH deficiency and low normal serum T4 concentration should be considered for T4 replacement prior to commencement of GH in order to provide a robust baseline from which to judge the clinical effects of GH replacement.

Recombinant Human Growth Hormone Treatment after Liver Transplantation in Childhood: The 5-year Outcome

BACKGROUND

Because the results of short-term recombinant human growth hormone (rhGH) treatment in children with growth impairment after liver transplantation (LTx) have been promising, we have studied the long-term effects of rhGH on growth and graft function after LTx.

METHODS

Indications for rhGH treatment were height standard deviation score (hSDS) below -2.0 or growth velocity SDS below 0 and LTx at least 18 months before inclusion. Eight growth-retarded children were treated with rhGH for more than 5 years.

RESULTS

During the first year, median growth rate improved from 3.3 to 7.0 cm/year. In the second and third year, growth velocity remained high at 6.6 cm/year and 6.2 cm/year, respectively (P=0.008). In the fourth year, median growth velocity started to decline but still remained above baseline during the fifth year of treatment (4.2 cm/year). The median hSDS improved from -3.6 to -2.7. During the rhGH treatment, no acute rejection episodes were detected, and graft function remained stable in all except one patient. She was diagnosed with chronic rejection in the third year of rhGH treatment. The patient had elevated liver enzymes and abnormal liver function tests already before rhGH treatment.

CONCLUSIONS

The efficacy of rhGH treatment is sustained after the first year in liver-transplant children with non-GH-deficient growth retardation. Because of a potential risk of side effects, close monitoring of these patients is required.

High dose growth hormone exerts an anabolic effect at rest and during exercise in endurance-trained athletes

The anabolic actions of GH in GH-deficient adults and children are well documented. Replacement with GH in such individuals promotes protein synthesis and reduces irreversible loss of protein through oxidation. Although GH is known to be self-administered by athletes, its protein metabolic effects in this context are unknown. This study was designed to determine whether 4 wk of high dose recombinant human GH (r-hGH) administration altered whole body leucine kinetics in endurance-trained athletes at rest and during and after 30 min of exercise at 60% of maximal oxygen uptake. Eleven endurance-trained male athletes were studied, six randomized to receive r-hGH (0.067 mg/kg.d), and five to receive placebo. Whole body leucine turnover was measured at rest and during and after exercise, using a 5-h primed constant infusion of 1-[(13)C]leucine, from which rates of leucine appearance (an index of protein breakdown), leucine oxidation, and nonoxidative leucine disposal (an index of protein synthesis) were estimated. Under resting conditions, r-hGH administration increased rate of leucine appearance and nonoxidative leucine disposal, and reduced leucine oxidation (P < 0.01). This effect was apparent after 1 wk, and was accentuated after 4 wk, of r-hGH administration (P < 0.05). During and after exercise, GH attenuated the exercise-induced increase in leucine oxidation (P < 0.05). There were no changes observed in placebo-treated subjects compared with the baseline study. We conclude that GH administration to endurance-trained male athletes has a net anabolic effect on whole body protein metabolism at rest and during and after exercise.

Pharmacological and toxicological effects of chronic porcine growth hormone administration in dogs

The purpose of this study was to evaluate the pharmacological and toxicological effects of exogenous GH administration in normal adult dogs. Because porcine GH (pGH) is structurally identical to canine GH, pGH was selected for a 14-wk study in dogs. Thirty-two dogs (< 2 yr) were randomized to 4 groups (4 dogs/sex/group); 1 group was treated with the vehicle and 3 groups received pGH at 0.025, 0.1, or 1.0 IU/kg/day subcutaneously. Daily clinical signs and weekly body weights were recorded. Hematology, serum biochemistry, urinalyses, electrocardiograms, and ophthalmoscopic examinations were done. Serum GH, insulin-like growth factor-1 (IGF-1), insulin, thyroxine (T4), triiodothyronine (T3), and cortisol levels were determined. Necropsies were performed, organs weighed, and tissues were fixed and processed for light microscopic examination. Porcine GH caused increased body weight gain (p < or = 0.05) through the mid dose; the mean weight gains at study termination in mid- and high-dose groups were 2.8 kg and 4.7 kg, respectively, compared to 0.4 kg and 0.8 kg in control and low-dose groups, respectively. Dose-related increased weights of liver, kidney, thyroid, pituitary gland, skeletal muscle, and adrenal gland were noted. In pGH-treated dogs, increased skin thickness seen grossly correlated histologically with increased dermal collagen. There was no gross or histomorphological evidence of edema. There were dose-related increased serum IGF-1 levels (approximately 2-10-fold; p < or = 0.05) that correlated with the elevated serum GH levels in pGH-treated dogs. Also, increased serum insulin levels (p < or = 0.05) through the mid dose were seen throughout the study. In high-dose dogs, the insulin levels remained elevated over 24 hr postdose. The serum glucose levels in fasted dogs remained within the control range and there was no chronic hyperglycemia based on glycosylated hemoglobin levels. Renal glomerular changes, significant polyuria with decreased urine specific gravity, and increased serum insulin levels suggested that the dogs had early insulin-resistant diabetes. There was minimal or no biologically significant effect of pGH on serum T3, T4, and cortisol levels in dogs. Other serum biochemical changes in pGH-treated dogs included decreased urea nitrogen and creatinine, and increased potassium, cholesterol, and triglycerides. Significant increases in serum calcium and phosphorous levels and alkaline phosphatase activity (bone isozyme) correlated with the histological changes in bone. In pGH-treated dogs, there was a dose-related normochromic, normocytic, nonregenerative anemia. The changes described above, except for the anemia, are related to either anabolic or catabolic effects of high doses of GH. Based on this study, it is concluded that the dog is a good model in which to evaluate the safety of GH secretagogues as well as compounds with GH-like activity.

Recombinant human growth hormone treatment at low doses does not significantly change thyroid function in growth hormone deficient adults

Pituitary-thyroid changes have been reported during recombinant human growth hormone (rhGH) therapy at the dose commonly used in prepuberty. We have previously demonstrated that low doses of rhGH were able to normalize body composition and both cardiac structure and function in growth hormone deficient adults (GHDA), without causing any of the side effects described when the GHDA were treated with doses commonly employed in the GHD children. The aim of this study was to evaluate the behaviour of pituitary-thyroid parameters in GHDA undergoing such a low dose of rhGH treatment. We studied 9 (2 females and 7 males, 25-34 yr) GHDA, 7 congenital and 2 acquired GH deficiency, before, during and after a 12-month rhGH treatment of dose of 10 micrograms/kg/day (= 70 micrograms/kg/week) divided in 3 injections, administered sc at 20:00 h on Monday, Wednesday and Friday, respectively. Thyroid deficiency and other hormonal deficiencies, when present, had been adequately corrected with replacement therapy. Serum IGF1, T3, T4, free-T3, free-T4, TSH, reverse-T3, T3/T4 and FT3/FT4 ratios were studied basally, every 3 months during the 12-month rhGH treatment and every 3 months for a period of 12 months off therapy. Analysis of variance (ANOVA) was performed as statistical method. All parameters (except IGF1) did not show any variation during and after rhGH treatment at low doses. The alterations of T3 and T4 metabolism, in the sense of a T3 increase and a T4 reduction, caused sometimes by rhGH treatment, could be due to the higher doses used and therefore should be considered another side effect, like artrhalgia, fluid retention, carpal tunnel syndrome, etc.

Growth hormone deficiency in adults: a review

For more than 35 years, growth hormone (GH) has been used to promote linear growth in GH-deficient children. Previously, GH replacement in adults was limited to the supply of human pituitary-derived GH. In addition, until recently, GH replacement was not deemed clinically indicated. With the introduction of recombinant human prion-free GH, replacement therapy in GH-deficient adults has become feasible, and its use has burgeoned. In this review, recent studies on GH therapy in healthy and GH-deficient adults are evaluated to provide a rational basis for the widened scope of its clinical application.

Dopamine and the sick euthyroid syndrome in critical illness

OBJECTIVE

The sick euthyroid syndrome is a poorly understood hallmark of critical illness. Dopamine is a natural catecholamine with hypophysiotrophic properties, that is used as an inotropic agent of first choice in intensive care medicine. We explored the effect of dopamine infusion (5 micrograms/kg/min) on the sick euthyroid syndrome of critically ill patients.

PATIENTS AND DESIGN

In a prospective, randomized, controlled and open-labelled study of critically ill, adult polytrauma patients (n = 12), we evaluated the effect of prolonged (83-296 hours) dopamine infusion (5 micrograms/kg/min i.v.) on the thyroid axis. The effect of brief (15-21 hours) dopamine administration was documented in an additional randomized, controlled, cross-over study involving 10 patients. The median age of the studied patients was 29 (16-83) years.

MEASUREMENTS

Serum TSH concentrations were measured by IRMA. The TSH profiles were obtained by blood sampling every 20 minutes for 9 hours during two consecutive nights. Serum T4, T3 and reverse T3 concentrations were measured by RIA once per study night.

RESULTS

Withdrawal of prolonged dopamine infusion was found to elicit a tenfold increase of serum thyrotrophin concentrations, a 57 and 82% rise of T4 and T3 respectively, and an increase of the T3/rT3 ratio, resulting in virtual normalization of the thyroid axis within 24 hours. The brief dopamine infusion was documented to have a suppressive effect on the thyroid axis within 24 hours.

CONCLUSIONS

Dopamine infusion appears to induce or aggravate the sick euthyroid syndrome in critical illness. As a consequence, the sick euthyroid syndrome of severely ill patients receiving dopamine may be not an adaptive mechanism, but a condition of iatrogenic hypothyroidism.

Growth hormone administration stimulates energy expenditure and extrathyroidal conversion of thyroxine to triiodothyronine in a dose-dependent manner and suppresses circadian thyrotrophin levels: studies in GH-deficient adults

OBJECTIVE

The impact of exogenous GH on thyroid function remains controversial although most data add support to a stimulation of peripheral T4 to T3 conversion. For further elucidation we evaluated iodothyronine and circadian TSH levels in GH-deficient patients as part of a GH dose-response study.

PATIENTS

Eight GH-deficient adults, who received stable T4 substitution due to central hypothyroidism; two patients, who were euthyroid without T4 supplementation were studied separately.

DESIGN

All patients were initially studied after at least 4 weeks without GH followed by 3 consecutive 4-week periods in fixed order during which they received daily doses of 1, 2 and 4 IU of GH/m2 body surface area. The patients were hospitalized for 24 hours at the end of each period.

MEASUREMENTS

Circulating total and free concentrations of T4 and T3, total rT3 and TSH were measured once at the end of each study period. Circadian TSH levels were recorded during the period without GH and during GH treatment with 2 IU GH.

RESULTS

Highly significant GH dose-dependent increases in total and free T3 and a reduction in rT3 were observed. The T3/T4 ratio also increased with increasing GH dosages (P < 0.001). In seven patients subnormal T3 levels were recorded in the period off GH, despite T4 levels well within the normal range. Resting energy expenditure also increased and correlated with free T3 levels (r = 0.47, P < 0.05). The circadian TSH levels exhibited a significant nocturnal increase during the period without GH, whereas GH therapy significantly suppressed the TSH levels and blunted the circadian rhythm (mean TSH levels (mU/l) 0.546 +/- 0.246 (no GH) vs 0.066 +/- 0.031 (2 IU GH) (P < 0.05)). The two euthyroid non-T4 substituted patients exhibited qualitatively similar changes in all parameters.

CONCLUSIONS

GH administration stimulated peripheral T4 to T3 conversion in a dose-dependent manner. Serum T3 levels were subnormal despite T4 substitution when the patients were off GH but normalized with GH therapy. Energy expenditure increased with GH and correlated with free T3 levels. GH caused a significant blunting of serum TSH. These findings suggest that GH plays a distinct role in the physiological regulation of thyroid function in general, and of peripheral T4 metabolism in particular.