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PubMed1994

A region on the human thyrotropin receptor which can induce antibodies that inhibit thyrotropin-mediated activation of in vitro thyroid cell function also contains a highly immunogenic epitope.

Autoantibodies to the thyrotropin receptor (TSHr) bind to the extracellular domain of the TSHr (ETSHr) and either stimulate or inhibit thyroid cell function and/or growth. In order to investigate the regulation and the specificity of the immune response to the TSHr, our laboratory recently produced recombinant human ETSHr protein by using the baculovirus expression system. In the present study, we used the recombinant ETSHr protein, a panel of overlapping synthetic peptides derived from the TSHr, and polyclonal rabbit antibodies produced against recombinant ETSHr and synthetic peptides to define a highly immunogenic region (aa 352-388) of the TSHr. Moreover, we used competitive inhibition studies to identify a dominant epitope (aa 367-372) within this region to which ETSHr antibodies react. This immunodominant epitope lies within a region unique to the TSHr when compared to the other glycoprotein hormone receptors. These data, together with the earlier observation that antibodies against aa region 357-372 can inhibit thyrotropin (TSH)-mediated activation of thyroid cells in culture, show that aa 367-372 represents, an immunodominant epitope within a functionally important region which is unique to the TSHr. Therefore, this region may play an important role in the induction or modulation of the specific immune response against the TSHr.

Amino Acid Sequence↗

PubMed1985

Exaggerated response of thyrotropin to thyrotropin-releasing hormone in patients resected for Crohn's ileitis.

We have studied the response of thyrotropin to exogenous thyrotropin-releasing hormone in 13 patients who had previous intestinal resection for Crohn's disease, and in 42 healthy controls. An exaggerated and prolonged response curve was found in eight of the patients and one control (P less than 0.01), while baseline hormone levels were normal in all. These results may be related to the state of iodine deficiency known to develop in inflammatory bowel disease, but the pathophysiology requires further elucidation.

Adult↗

PubMed1988

The influence of diabetes mellitus on thyrotropin response to thyrotropin-releasing hormone in untreated acromegalic patients.

Impairment of thyrotropin (TSH) response to thyrotropin-releasing hormone (TRH) has been documented in patients with uncontrolled diabetes mellitus (DM). In acromegalic patients, however, there have been no data regarding TSH secretion studied taking the existence of DM into consideration. Therefore, we investigated the TSH response to TRH [expressed as TSH increment (delta TSH)] in 14 untreated acromegalic patients, who did not show the suprasellar extension of adenoma, divided into two groups on the basis of either presence or absence of uncontrolled DM, and in 28 normal subjects. The mean max delta TSH was significantly reduced (p less than 0.02) in acromegalic patients despite similar mean serum T4 and free T4 index (FT4l) levels. Furthermore, the mean basal and max delta TSH in 7 patients with DM (FBS, 120-300 mg/dl; HbA1, 8.8-15.2%) were significantly lower than those in 7 patients without DM (p less than 0.05 and p less than 0.02, respectively) despite similar the mean serum T3, T4, FT4l, growth hormone (GH) and prolactin (PRL) levels and sellar volume. In 4 patients with DM the TSH response to TRH 6-8 weeks after insulin therapy, when their HbA1 levels were normal, increased compared to that before insulin therapy. The mean max delta TSH after selective adenomectomy in 8 patients (3 in DM group and 5 in non-DM group), whose fasting basal GH fell to less than 5 ng/ml, was almost identical to that in normal subjects. In conclusion, the present study suggests that the abnormality in TSH secretion in acromegalic patients may be increased by the existence of uncontrolled DM.

Acromegaly↗

PubMed1987

Further studies on the covalent crosslinking of thyrotropin to its receptor: evidence that both the alpha and beta subunits of thyrotropin are crosslinked to the receptor.

Highly purified alpha- and beta-subunits of thyrotropin were individually radioiodinated and, subsequently, recombined with their unlabeled complementary subunits. This procedure resulted in the formation of [125I]thyrotropin(TSH) hybrid molecules which were labeled on only one hormone subunit. Characterization of the binding properties of these two hybrid molecules demonstrated that both yielded nonlinear Scatchard plots with Kd and Bmax values similar to those obtained with radioiodinated native TSH and that both were capable of interaction with the high- and low-affinity binding components of the TSH receptor. The recombined [125I]TSH molecules were then crosslinked to the TSH receptor using disuccinimidyl suberate. Following electrophoresis and autoradiography, two labeled TSH-receptor complexes with Mr of 68,000 and 80,000 were observed. These two complexes exhibited hormone specificity and electrophoretic mobility identical to those previously observed using native [125I]TSH. Crosslinking with increasing concentrations of disuccinimidyl suberate suggested that the formation of the 68,000 and 80,000 complexes was sequential with the 68,000 appearing before the 80,000. Furthermore, the two bands were labeled regardless of which TSH subunit of the hybrid TSH was radioiodinated. These data strongly suggest that the 68,000 and 80,000 TSH-receptor complexes are the result of crosslinking to the TSH alpha-beta dimer and not to one subunit in the case of the 68,000 complex and to the TSH alpha-beta dimer in the case of the 80,000 complex, as had been hypothesized previously.

Animals↗

PubMed1992

Biological activities of rabbit antibodies against synthetic human thyrotropin receptor peptides representing thyrotropin binding regions.

Recently, we have shown that the thyrotropin (TSH) binding regions of human thyrotropin receptor (TSHR) reside in two areas within residues 12-44 and 308-344. Serial antisera were raised against four overlapping synthetic peptides representing these two regions of TSHR (peptides 12-30, 24-44, 308-328, and 324-344) and were investigated for their ability to stimulate or block the cultured porcine thyroid cells. In addition, serum concentrations of triiodothyronine (T3) and thyroxine (T4) in serial sera obtained from each rabbit were examined. It was shown that residues of 12-30 and 324-344 of TSHR, respectively, are the site (at least a part of the site) where stimulating (TSAb) and blocking type (TSBAb) immunoglobulins are directed.

Amino Acid Sequence↗

PubMed1986

Human corticotropin-releasing hormone in depression--correlation with thyrotropin secretion following thyrotropin-releasing hormone.

Twenty-two subjects (11 patients with major endogenous depression and 11 controls) received an intravenous test dose of 100 micrograms human corticotropin-releasing hormone (h-CRH). Corticotropin (ACTH), but not cortisol, responses were blunted in depressives. Basal cortisol secretion was higher in depressives than in controls and was negatively correlated to the corticotropin response following h-CRH. This finding indicates the integrity of the glucocorticoid-dependent negative feedback regulation in depression and supports the view that hypercortisolism in depression is primarily due to a suprapituitary disturbance. Comparison of ACTH responses after h-CRH with thyrotropin (TSH) output following thyrotropin-releasing hormone (TRH) revealed a positive correlation (r = 0.65, p less than 0.001). The concordance between ACTH and TSH responses after specific challenges suggests that regulation of both systems is at least in part under a common control.

Adrenocorticotropic Hormone↗

PubMed1987

Thyrotropin, prolactin, and growth hormone responses to thyrotropin-releasing hormone in anorexia nervosa and bulimia.

Serum thyrotropin (TSH), prolactin (PRL), and growth hormone (GH) levels were measured before and after stimulation with thyrotropin-releasing hormone (TRH) in 10 patients with bulimia, 7 with features of the restricting subtype of anorexia nervosa, and 6 with bulimic subtype of anorexia nervosa. The mean basal levels of TSH, PRL, and GH did not differ among the three groups. A delayed TSH response was found in 86% of the restricting anorectics, 80% of the bulimic anorectics, and 22% of the bulimics. The PRL response was normal in all patients, with no significant difference among the three groups. Elevated basal GH levels were found in 29% of the restricting anorectics, 33% of the bulimic anorectics, and 33% of the bulimics. An abnormal GH increase after TRH stimulation was observed in 50% of the restricting anorectics, 20% of the bulimic anorectics, and 13% of the bulimics. These results suggest that some patients with bulimia, and some with anorexia nervosa, have a hypothalamic dysfunction. These neuroendocrine abnormalities do not appear to be due solely to low weight or to metabolic changes resulting from binge eating and are not associated with depressive symptoms.

Anorexia Nervosa↗

PubMed1993

Thyrotropin response to thyrotropin-releasing hormone in patients with dementia of the Alzheimer type.

Eleven patients with senile dementia of the Alzheimer type and 11 age-matched control subjects were given the thyrotropin-releasing hormone (TRH) test. The two groups did not differ with respect to peak thyrotropin (TSH) response or TSH levels at baseline, 20, 30, and 45 min after TRH injection. There were significant differences between the groups on Hamilton Depression Rating Scale scores (p < 0.03), although neither group met clinical criteria for depression. Items that were significantly different pertained to depressed mood, loss of interest, loss of insight, suicidal ideation, and obsessional symptoms.

Aged↗

PubMed1993

The effect of dietary protein on thyrotropin-releasing hormone and thyrotropin gene expression.

In the rat, 48 h of food deprivation significantly reduces hypothalamic paraventricular nucleus (PVN) thyrotropin-releasing hormone (TRH) gene expression, anterior pituitary thyrotropin (TSH) gene expression and circulating triiodothyronine (T3). Using in situ hybridization histochemistry, we have now assessed the effect of selective nutritional deprivation, by comparing protein-free and protein and fat-free diets with a normal diet matched for total energy content. As previously demonstrated, fasting markedly reduced PVN TRH transcripts, pituitary TSB beta transcripts, circulating T3 and body weight. Compared to rats fed a control diet, rats fed a protein-free or a protein and fat-free diet of similar energy content showed a highly significant decrease in PVN TRH transcripts, pituitary TSB beta transcripts and circulating T3 levels. The exclusion of fat from the protein-free diet did not produce any further decline in the parameters measured. This indicates that variations in the protein composition alone of the diet are sufficient to reduce hypothalamic TRH mRNA, pituitary TSB beta mRNA and plasma T3, and are the predominant factors in the TRH response to starvation.

Animals↗

PubMed1987

Effects of thyrotropin-releasing hormone in vitro on thyrotropin and prolactin release from the turtle pituitary.

Effects of synthetic thyrotropin-releasing hormone (TRH) on thyrotropin (TSH) and prolactin (PRL) release by hemipituitaries of adult turtles, Chrysemys picta, were studied in an in vitro superfusion system. Significant increases in the rates of secretion of both immuno-reactive TSH and PRL occurred at doses between 0.01 and 10 ng/ml TRH. TSH secretion increased acutely by two-, to sixfold over nonstimulated secretion levels; responses tended to decline after many hours of continual stimulation, but output remained elevated above baseline in most cases. PRL secretion increased, parallel to TSH secretion during TRH stimulation. No significant difference was found in secretion rates between males and females, and no clear relationship between TRH responsiveness and reproductive stage was evident. These data provide the first direct evidence for the stimulation of TSH secretion by TRH in a reptile and confirm earlier reports that TRH stimulates the release of PRL in the turtle. Although previous in vivo studies indicated that TSH secretion was not affected by TRH in turtles, the present data indicate that the dose sensitivity of the chelonian gland is comparable with that of mammalian and avian pituitaries. Evidence for the role of TRH in endogenous TSH regulation is still lacking in reptiles but the present data provide evidence for functional TRH receptors on the chelonian thyrotrope and, hence, argue against the hypothesis that TSH stimulating activity of TRH evolved relatively recently in association with endothermy.

Animals↗

PubMed1995

Effect of substance P on basal and thyrotropin-releasing hormone-stimulated thyrotropin release in humans.

To test the possible effects of intravenous administration of substance P (SP) on basal and thyrotropin-releasing hormone (TRH)-stimulated thyrotropin (TSH) release, SP was infused alone (0.5 or 1.5 pmol/kg-1/min-1 for 60 minutes) or after TRH (20 or 400 micrograms in an intravenous bolus) in 21 normal male subjects (aged 26 to 36 years) and in 18 normal women (aged 25 to 32 years). Women were studied during follicular (day 6 to 8) and luteal (day 21 to 23) phases of following regular menstrual cycles. In addition, plasma cortisol levels during SP infusion were measured. In agreement with previous findings, significant increments in plasma cortisol levels were observed in men and women when the higher (1.5 pmol/kg-1/min-1) but not the lower (0.5 pmol/kg-1/min-1) amount of SP was administered. In contrast, in both men and women basal and TRH (20 or 400 mg)-induced TSH releases were not modified by SP at any tested amount. Results in the follicular and luteal phase were similar. These data suggest that in normal men and women plasma SP is not involved in the control of TSH release, at least not outside the blood-brain barrier.

Adult↗

PubMedDate not supplied

The effects of dieting and weight loss upon the stimulation of thyrotropin (TSH) by thyrotropin-releasing hormone (TRH) and suppression of cortisol secretion by dexamethasone in men and women.

The effects upon basal hormone levels and neuroendocrine responses of a weight reducing diet allowing 1200 kcal daily were determined in male and female volunteers. Thyrotropin (TSH) responses to thyrotropin-releasing hormone (TRH) were unchanged in men but attenuated in women; this effect was associated with a fall in basal TSH in women, not in men. Rates of non-suppression of cortisol in response to oral dexamethasone (1 mg) were unchanged during dieting although basal morning cortisol levels rose in males and females. The implications for the use of the TRH test and the dexamethasone suppression test (DST) in depressive illness are discussed.

Adult↗

PubMed1985

Effect of amitriptyline on the thyrotropin response to thyrotropin-releasing hormone in endogenous depression.

Patients with endogenous depression whose depressive episodes were clinically resolved after electroconvulsive therapy were divided into two groups: one in which patients remained well (n = 16) and another in which patients relapsed within 6 months (n = 11). Treatment with amitriptyline for 3 weeks did not affect the median thyrotropin (thyroid-stimulating hormone; TSH) response to thyrotropin-releasing hormone (TRH) in recovered patients, whereas that in relapsed patients was significantly enhanced. The data suggest that amitriptyline affects the TSH response to TRH differently in stably recovered and relapsed patients. If this effect is maintained beyond the 3-week period studied, treatment with amitriptyline will invalidate the predictive value of the TRH test.

Aged↗

PubMed1986

Effects of age and diagnosis on thyrotropin response to thyrotropin-releasing hormone in psychiatric patients.

The thyrotropin (thyroid-stimulating hormone; TSH) response to thyrotropin-releasing hormone (TRH) was studied in 64 age-matched healthy volunteers, 44 patients with endogenous depression, and 21 patients with schizophrenia. A significant negative correlation between delta TSH and age was found both in healthy subjects and in depressed patients. We based our comparison on normal ranges for delta TSH calculated from the delta TSH values in the healthy subjects related to age. It was then seen that blunted TSH response to TRH does not occur significantly more often in depression (13.6%) than in healthy controls (4.7%). Blunted TRH test results were also found in a considerable number of severely ill schizophrenic patients (19%). Application of an improved radioimmunoassay revealed a highly significant correlation between TSH values at baseline and after stimulation, and showed decreased baseline TSH levels in subjects with blunted TRH test results.

Adult↗

PubMed1987

Serum thyrotropin (TSH) responses to thyrotropin-releasing hormone (TRH) in patients with anorexia nervosa and bulimia: influence of changes in body weight and eating disorders.

Serum thyrotropin (TSH) responses to thyrotropin-releasing hormone (TRH) were studied in 47 women with anorexia nervosa (AN) (group I) and in 11 bulimic patients of normal weight (group II). In group I, TSH responses were low in nine patients, delayed in 32 and normal in six. Patients with a normal TSH response had a lesser degree of anorexia than those with a delayed TSH response. Bulimia and vomiting were more frequently observed in the low response group. The maximum increase in TSH concentrations following TRH administration in the group I patients with vomiting (4.0 +/- 0.90 microU/ml, mean +/- S.E.) was significantly lower than that in the group I patients without vomiting or in normal controls (11.2 +/- 0.82 microU/ml and 11.1 +/- 2.34 microU/ml, respectively). Twenty-five patients with abnormal TSH responses in group I were retested after weight gain. Initially, TSH responses were low in six and delayed in 19. Following weight recovery, responses continued to be abnormal in five of the six and in eight of the 19, respectively. The symptoms of eating disorders continued in all patients with abnormal TSH responses even after weight recovery, whereas patients with normal responses after weight gain recovered from all symptoms. Of 11 patients in group II, six had abnormal TSH responses to TRH; the responses were delayed in four and low in two. Patients with normal responses had a lesser degree of eating disorder, compared with abnormal responders. These observations suggest that abnormal TSH responses in patients with AN were not necessarily due to weight loss alone; rather, they may be related to the eating disorder itself.

Adolescent↗

PubMed1978

Suppression of serum thyrotropin (TSH) concentrations following thyroidectomy and cold exposure by passive immunization with antiserum to thyrotropin-releasing hormone (TRH) in rats.

Administration of antiserum to synthetic thyrotropin-releasing hormone (TRH) to thyroidectomized rats caused a significant depression of serum thyrotropin (TSH). Serum TSH and triiodothyronine (T3) responses to cold exposure (4 +/- 1 C) were abolished by administration of anti-TRH serum. In addition, synthetic TRH lost its biological activity when bound to the gamma globulin fraction from the anti-TRH serum. These observations provide evidence that TRH is involved in the mechanism of enhanced TSH secretion from the pituitary following thyroidectomy and cold exposure.

Animals↗

PubMed2003

Involvement of thyrotropin-releasing hormone receptor, somatostatin receptor subtype 2 and corticotropin-releasing hormone receptor type 1 in the control of chicken thyrotropin secretion.

Thyrotropin or thyroid-stimulating hormone (TSH) secretion in the chicken is controlled by several hypothalamic hormones. It is stimulated by thyrotropin-releasing hormone (TRH) and corticotropin-releasing hormone (CRH), whereas somatostatin (SRIH) exerts an inhibitory effect. In order to determine the mechanism by which these hypothalamic hormones modulate chicken TSH release, we examined the cellular localization of TRH receptors (TRH-R), CRH receptors type 1 (CRH-R1) and somatostatin subtype 2 receptors (SSTR2) in the chicken pars distalis by in situ hybridization (ISH), combined with immunological staining of thyrotropes. We show that thyrotropes express TRH-Rs and SSTR2s, allowing a direct action of TRH and SRIH at the level of the thyrotropes. CRH-R1 expression is virtually confined to corticotropes, suggesting that CRH-induced adrenocorticotropin release is the result of a direct stimulation of corticotropes, whereas CRH-stimulated TSH release is not directly mediated by the known chicken CRH-R1. Possibly CRH-induced TSH secretion is mediated by a yet unknown type of CRH-R in the chicken. Alternatively, a pro-opiomelanocortin (POMC)-derived peptide, secreted by the corticotropes following CRH stimulation, could act as an activator of TSH secretion in a paracrine way.

Animals↗

PubMed1999

Thyrotropin stimulating hormone response to thyrotropin releasing hormone in patients with panic disorder.

OBJECTIVE: The aim of this study is to assess thyrotropin stimulating hormone (TSH) response to thyrotropin releasing hormone (TRH) in patients with panic disorder (PD). METHOD: The effects of TRH administration on the release of TSH were examined in 15 patients who met DSM-III-R criteria for PD and compared their test results with those of 15 normal control subjects. Blood samples were taken before TRH administration (baseline values) and at 15, 30 and 60 min. RESULTS: delta max TSH values were lower in the panic disorder patients than in the control subjects. Using the criterion of delta max TSH < or = 7 mlU/l, nine of the 15 panic disorder patients and four of the 15 control subjects had a blunted TSH response to TRH. CONCLUSIONS: These results confirm the findings from earlier reports that patients with PD show blunted TSH response to TRH which is similar to that seen in depressed patients.

Adult↗