Thyrotropic Function Research Articles

The influence of insulin-induced hypoglycemia on copeptin concentrations

Plasma copeptin is a biomarker that reflects arginine vasopressin (AVP) secretion. In this study we measured copeptin during insulin tolerance test (ITT) in 65 patients referred to our department for evaluation of anterior pituitary function. Plasma for measurements of copeptin were collected at the start of the test and regurarly up to 120 minutes thereafter. Of 60 patients who developed significant hypoglycemia and were included in the analyses, 13 (22%) had corticotropic deficiency, 11 (18%) had thyreotropic deficiency, 33 (55%) had growth hormone deficiency and 4 (6%) had AVP deficieny (AVPD). Thirty-seven (62%) patients had at least one anterior pituitary deficiency. In patients without AVPD, median (range) copeptin increased from 4.5 pmol/L (1.3–33.0) to a maximum of 6.2 pmol/L (2.0–34.4; p<0.001). Baseline copeptin was similar in men and women, but maximal copeptin during ITT was higher in men. Copeptin concentrations were not affected by age, BMI, somatotropic, or corticotropic function. Copeptin concentrations were lower in patients with AVPD than patiets without AVPD, and in patients with thyrotropic deficiency, compared to patients with intact thyrotropic function, both at baseline and during ITT. In conclusion, copeptin increases significantly during insulin induced hypoglycemia but is of limited value in predicting anterior pituitary hormonal function.

Associations between paraben exposure, thyroid capacity, homeostasis and pituitary thyrotropic function in the general Taiwanese: Taiwan Environmental Survey for Toxicants (TEST) 2013.

Several studies have suggested that some endocrine disruptors such as synthetic phenols, parabens and phthalates may disrupt thyroid hormone signaling and associated negative feed-backs with the central hypothalamic-pituitary-thyroid (HPT) axis. Therefore, we investigated urinary paraben and blood thyroid hormone levels in the Taiwanese population. Our sample comprised 264 adults (aged 18-97 years) and 75 minors (aged 7-17 years) from Taiwan Environmental Survey for Toxicants 2013. Urinary levels of methylparaben (MeP), ethylparaben (EtP), propylparaben (PrP), and butylparaben (BuP) were assessed. Hormones of particular interest include: thyroid-stimulating hormone (TSH), triiodothyronine (T3), and thyroxine (T4). We sought integrated parameters to describe the transfer of thyroid hormones in homeostatic models. The geometric mean urinary paraben levels of the adults were higher than those of the minors (adults vs. minors; MeP: 383 vs. 62.4 ng/mL; PrP: 109 vs. 8.00 ng/mL; EtP: 39.5 vs. 2.38 ng/mL, and BuP: 6.36 vs. 2.13 ng/mL). In the male adults, we discovered that 0.253% (p = 0.032), 0.256% (p = 0.041) and 0.257% (p = 0.037) decreases in the TSH, TSH/T4 and TSH/FreeT4 ratio was associated with 1% EtP increases, respectively. In the female minors, 0.093% (p = 0.044), 0.072% (p = 0.047) and 0.156 (p = 0.004) increases in the TSH ratios were associated with a 1% MeP, EtP and BuP increase, respectively. Moreover, 0.151% (p = 0.008) and 0.177% (p = 0.001) increases in TSH/T4 and TSH/free T4 ratios were associated with a BuP 1% increase, respectively. Finally, EtP was positively associated with SPINA-GT (β: 15.66, p = 0.036) in the male adults. By contrast, EtP were positively associated with Jostel's TSH index and sTSHI (β: 0.072, p = 0.049; β: 0.107, p = 0.049) in the female minors. The Taiwanese population is commonly exposed to parabens, which can potentially lead to alteration of thyroid hormone homeostasis.

The association between thyroid homeostasis parameters and obesity in subjects with euthyroidism.

The relationship between thyroid homeostasis parameters and obesity remains poorly understood in subjects with euthyroidism. This retrospective study aimed to investigate the association between the thyroid homeostasis and obesity in a population with euthyroidism. A total of 201 adult participants with euthyroidism (age range: 27-85 years) were enrolled. Clinical measurements, including obesity indices and biochemical analyses, were conducted. Thyroid homeostasis parameters were calculated. Multiple linear regression analysis was used to analyze the associations between thyroid function, thyroid homeostasis parameters, and obesity measurements. There was a positive correlation between thyroid-stimulating hormone (TSH), free triiodothyronine (fT3), Jostel's thyrotropin index (TSHI), standard TSH index (sTSHI), thyrotroph thyroid hormone sensitivity index (TTSI), sum activity of peripheral deiodinase (SPINA-GD), and body mass index (BMI) in participants with euthyroidism and a negative correlation between thyroid's secretory capacity (SPINA-GT) and BMI (all P<0.05). Only the fT3, TSHI, and sTSHI had a positive correlation with waist circumference (all P<0.05). We concluded that BMI was positively associated with pituitary thyrotropic function parameters and SPINA-GD, and negatively correlated with SPINA-GT in adults with euthyroidism.

The association between thyroid homeostasis parameters and obesity in subjects with euthyroidism.

The relationship between thyroid homeostasis parameters and obesity remains poorly understood in subjects with euthyroidism. This retrospective study aimed to investigate the association between the thyroid homeostasis and obesity in a population with euthyroidism. A total of 201 adult participants with euthyroidism (age range: 27-85 years) were enrolled. Clinical measurements, including obesity indices and biochemical analyses, were conducted. Thyroid homeostasis parameters were calculated. Multiple linear regression analysis was used to analyze the associations between thyroid function, thyroid homeostasis parameters, and obesity measurements. There was a positive correlation between thyroid-stimulating hormone (TSH), free triiodothyronine (fT3), Jostel's thyrotropin index (TSHI), standard TSH index (sTSHI), thyrotroph thyroid hormone sensitivity index (TTSI), sum activity of peripheral deiodinase (SPINA-GD), and body mass index (BMI) in participants with euthyroidism and a negative correlation between thyroid's secretory capacity (SPINA-GT) and BMI (all P<0.05). Only the fT3, TSHI, and sTSHI had a positive correlation with waist circumference (all P<0.05). We concluded that BMI was positively associated with pituitary thyrotropic function parameters and SPINA-GD, and negatively correlated with SPINA-GT in adults with euthyroidism.

Somatostatin receptor ligands induce TSH deficiency in thyrotropin-secreting pituitary adenoma.

Somatostatin receptor ligands (SRL) are useful to control central hyperthyroidism in patients with thyrotropin-secreting pituitary adenoma (TSH pituitary adenoma). The aim of this study was to describe the frequency of thyrotropin deficiency (TSH deficiency) in patients with TSH pituitary adenoma treated by SRL. Retrospective study. Patients with central hyperthyroidism due to TSH pituitary adenoma treated by short or long-acting SRL were retrospectively included. TSH deficiency was defined by a low FT4 associated with non-elevated TSH concentrations during SRL therapy. We analysed the frequency of TSH deficiency and the characteristics of patients with or without TSH deficiency. Forty-six patients were included. SRL were used as the first-line therapy in 21 of 46 patients (46%). Central hyperthyroidism was controlled in 36 of 46 patients (78%). TSH deficiency appeared in 7 of 46 patients (15%) after a median time of 4 weeks (4-7) and for a median duration of 3 months (2.5-3). The TSH deficiency occurred after one to three injections of long-acting SRL used as first-line therapy in 6/7 cases. There were no differences in terms of clinical and hormonal features, size of adenomas or doses of SRL between patients with or without TSH deficiency. SRL can induce TSH deficiency in patients with central hyperthyroidism due to TSH pituitary adenoma. Thyrotropic function should be assessed before the first three injections of SRL in order to track TSH deficiency and reduce the frequency of injections when control of thyrotoxicosis rather than tumour reduction is the aim of the treatment.

MON-288 TSH Deficiency in Patients on Somatostatin Analog for TSH-PitNET

Background: Somatostatin analogs (SSA) are efficiently used to control central hyperthyroidism in patients with thyrotropin-secreting pituitary neuroendocrine tumor (TSH-PitNET). The aim of this study was to describe the frequency of thyrotropin (TSH) deficiency under SSA in patients with TSH-PitNET. Methods: We retrospectively recruited patients presenting a central hyperthyroidism due to TSH-PitNET. Inclusion criteria were patients treated in first, second or third line by short or long-acting SSA, with central hyperthyroidism before SSA. Patients treated by radiotherapy or dopamine agonist were excluded. TSH deficiency was defined by either a low FT4 or low FT4 and FT3, associated with non-elevated TSH concentrations during SSA therapy. We analyzed the frequency of TSH deficiency and the characteristics of patients with or without TSH deficiency. Results: 46 patients were included in the study. SSA were used as the first-line therapy in 21 of 46 patients (46%). Central hyperthyroidism was controlled in 36 of 46 patients (78%). TSH deficiency appeared in 7 of 46 patients (15%), after a median time of 4 weeks (4–7) after the starting of SSA, and for a median duration of 3 months (2.5–3). The TSH deficiency occurred after 1 to 3 injections of long-acting SSA. There were no differences in terms of clinical and hormonal features and size of adenomas between patients with or without TSH deficiency. Conclusions: In patients with central hyperthyroidism due to TSH-PitNET, SSA can induce TSH deficiency. Thyrotropic function should be assessed before each injection of SSA in order to adapt the frequency of injection when control of thyrotoxicosis rather than tumor reduction is purpose of the treatment.

Thyroid Parameters and Kidney Disorder in Type 2 Diabetes: Results from the METAL Study.

Objective Diabetic kidney disease is one of the most common microvascular complications of diabetes mellitus. We aimed to analyze the association of thyroid parameters with kidney disorders, especially in euthyroid participants. Methods The data were obtained from a cross-sectional study, the METAL study. Thyroid parameters, including thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), free thyroxine (FT4), triiodothyronine (T3), thyroxin (T4), thyroid peroxidase antibody (TPOAb), and thyroglobulin antibody (TgAb), of 4136 participants with type 2 diabetes were measured. Two structure parameters of thyroid homeostasis, including the sum activity of step-up deiodinases (SPINA-GD) and thyroid secretory capacity (SPINA-GT), and two pituitary thyrotropic function indices, including Jostel's TSH index (TSHI) and the thyrotroph thyroid hormone resistance index (TTSI), were also calculated. Kidney disorders were described according to the presence of reduced estimated glomerular filtration rate (eGFR) and/or higher urinary albumin to creatinine ratio (UACR). Results The prevalence of kidney disorders increased with decreasing FT3 or T3 and increasing FT4 or T4 quartile levels (all P < 0.05). After full adjustment, linear regression showed that UACR levels were negatively associated with FT3 and T3 (P < 0.001). In addition, eGFR was positively associated with FT3 and T3 and was negatively associated with TSH and FT4 levels and TgAb positivity (all P < 0.05). By using binary logistic regression, higher TSH and FT4 and lower FT3 and T3 were associated with kidney disorders (all P < 0.05). Similar results were seen in sensitivity analyses, which were performed in 3035 euthyroid diabetic participants; however, TSH was no longer related to them. The area under the receiver operating characteristic curve (AUROC) of lower FT3 for existing kidney disorder was greater than that for any other thyroid hormones (all P < 0.001). The cutoff value of FT3 for reduced eGFR was 4.39 pmol/L. Regarding thyroid homeostasis parameters, SPINA-GD was negatively associated with three statuses of kidney disorders, and TSHI and TTSI were positively associated with reduced eGFR (all P < 0.05). Conclusions Among patients with type 2 diabetes, elevated TSH and FT4 (or T4), lower FT3 (or T3), TgAb positivity, lower SPINA-GD, and higher TSHI and TTSI were associated with kidney disorders. The lower FT3, even within the normal range (<4.38 pmol/L), may be the factor most related to reduced eGFR compared with other thyroid hormones in diabetic patients.

The Impact of Testosterone on Metformin Action on Hypothalamic-Pituitary-Thyroid Axis Activity in Men: A Pilot Study.

The effect ofmetforminon thyrotrope function seems to be sex dependent. The aim of this study was to determine the role of endogenous testosterone in the impact of metformin on hypothalamic-pituitary-thyroidaxis activity. The study population consisted of 2 groups of men with nonautoimmune hypothyroidism matched for age, weight, insulin sensitivity, and thyrotropin levels. The first group (n = 11) included subjects with low serum testosterone levels, while the second (n = 12) men with testosterone levels within the reference range. Because of concomitant type 2 diabetes, all men were treated withmetformin(2550-3000 mg daily). Circulating levels of glucose, prolactin, testosterone, gonadotropins, thyrotropin, and freethyroidhormones were measured, while thestructure parameters of thyroid homeostasisand the degree of insulin sensitivity were calculated at baseline and 16 weeks later. In both study groups, metformindecreased plasma glucose levels and improved insulin sensitivity. However, only in men with low testosterone levels, the drug decreased thyrotropin levels, reduced Jostel's thyrotropin index, and increased SPINA-GT. Metformin-induced changes in thyrotropin and Jostel's index correlated with their baseline values, baseline levels of testosterone, and with the effect of treatment on insulin sensitivity. In men with neither low or normal testosterone levels, metformin affected free thyroid hormones, prolactin, testosterone, gonadotropins, and SPINA-GD. The obtained results suggest that the impact of metformin on thyrotrope function depends on the androgen status of a patient.

Influence of recombinant growth hormone treatment on the state of pituitary-thyroid and pituitary-adrenal systems in children with syndrome of biologically inactive growth hormone

Combined insufficiency of adenohypophysis such as thyrotropic and adrenocorticotropic, especially during treatment with recombinant growth hormone, were often observed among children with somatotropic insufficiency.Aim. To evaluate the adaptation mechanisms of the organism based on studying the peculiarities of pituitary-thyroid and pituitary-adrenal functions in patients with syndrome of biologically inactive growth hormone on the background of recombinant growth hormone treatment.Materials and methods. There were examined 158 patients with syndrome of biologically inactive GH (49 girls and 109 boys); the mean age of patients was 8.3 ± 0.24 years. The levels of thyrotropic hormone, thyroxine, triiodothyronine, thyroid peroxidase antibody, adrenocorticotropic hormone, and cortisol were determined. The examinations were performed before and against the recombinant growth hormone treatment for 6 months. The control group consisted of 42 healthy children (12 girls and 30 boys), the age was from 5 to 16 years.Results. The levels of thyrotropic hormone in blood plasma of children with syndrome of biologically inactive growth hormone were increased but remained within the normal range during therapy with recombinant growth hormone. Peripheral indices of thyroid function in patients with syndrome of biologically inactive growth hormone, according to free thyroxine, before treatment and against the background of the recombinant growth hormone use almost had no differences and did not reach a significant difference, although they tended to decrease compared with the control group. The levels of adrenocorticotropic hormone and cortisol in blood plasma of children with syndrome of biologically inactive growth hormone before recombinant growth hormone treatment comparing to the control group did not have significant differences. Recombinant growth hormone therapy for 6 months resulted in an increase in the values of adrenocorticotropic hormone (p<0.01) and cortisol (p <0.01) compared with those of children with syndrome of biologically inactive growth hormone before the use of recombinant growth hormone and practically consistent with the reference values.Conclusions. Syndrome of biologically inactive growth hormone is not accompanied by disorder of the thyrotropic and adenocorticotropic functions of the pituitary gland. Reserve adaptive mechanisms of pituitary-thyroid gland and pituitary-adrenal gland systems have an adequate response to long-term treatment with recombinant growth hormone drugs

Gene Expression in Mouse Thyrotrope Adenoma: Transcription Elongation Factor Stimulates Proliferation.

Thyrotrope hyperplasia and hypertrophy are common responses to primary hypothyroidism. To understand the genetic regulation of these processes, we studied gene expression changes in the pituitaries of Cga(-/-) mice, which are deficient in the common α-subunit of TSH, LH, and FSH. These mice have thyrotrope hypertrophy and hyperplasia and develop thyrotrope adenoma. We report that cell proliferation is increased, but the expression of most stem cell markers is unchanged. The α-subunit is required for secretion of the glycoprotein hormone β-subunits, and mutants exhibit elevated expression of many genes involved in the unfolded protein response, consistent with dilation and stress of the endoplasmic reticulum. Mutants have elevated expression of transcription factors that are important in thyrotrope function, such as Gata2 and Islet 1, and those that stimulate proliferation, including Nupr1, E2f1, and Etv5. We characterized the expression and function of a novel, overexpressed gene, transcription elongation factor A (SII)-like 5 (Tceal5). Stable expression of Tceal5 in a pituitary progenitor cell line is sufficient to increase cell proliferation. Thus, Tceal5 may act as a proto-oncogene. This study provides a rich resource for comparing pituitary transcriptomes and an analysis of gene expression networks.

ISL1 Is Necessary for Maximal Thyrotrope Response to Hypothyroidism.

ISLET1 is a homeodomain transcription factor necessary for development of the pituitary, retina, motor neurons, heart, and pancreas. Isl1-deficient mice (Isl1(-/-)) die early during embryogenesis at embryonic day 10.5 due to heart defects, and at that time, they have an undersized pituitary primordium. ISL1 is expressed in differentiating pituitary cells in early embryogenesis. Here, we report the cell-specific expression of ISL1 and assessment of its role in gonadotropes and thyrotropes. Isl1 expression is elevated in pituitaries of Cga(-/-) mice, a model of hypothyroidism with thyrotrope hypertrophy and hyperplasia. Thyrotrope-specific disruption of Isl1 with Tshb-cre is permissive for normal serum TSH, but T4 levels are decreased, suggesting decreased thyrotrope function. Inducing hypothyroidism in normal mice causes a reduction in T4 levels and dramatically elevated TSH response, but mice with thyrotrope-specific disruption of Isl1 have a blunted TSH response. In contrast, deletion of Isl1 in gonadotropes with an Lhb-cre transgene has no obvious effect on gonadotrope function or fertility. These results show that ISL1 is necessary for maximal thyrotrope response to hypothyroidism, in addition to its role in development of Rathke's pouch.

Functional activity of the thyroid gland, the thyrotropic function of the hypophysis and the level of cortisol in patients with new-onset pulmonary tuberculosis depending on the clinical forms

The degree of disbalance of interleukin-6, depending on the functional activity of the thyroid gland, has been studied on the basis of a survey of 55 patients with newly diagnosed pulmonary tuberculosis with preserved sensitivity to anti-TB drugs and 36 patients with drugresistent pulmonary tuberculosis (case-control) using ELISA research. Results of the study showed that patients with preserved thyroid secretion, regardless of the variant of the sensitivity an increase of interleukin-6 can be observed, and in patients with disorder of thyroyid homeostasis its level is significantly lower (p&lt;0,05) than in the group with preserved thyroid activity.

Multiple thyrotropin β-subunit and thyrotropin receptor-related genes arose during vertebrate evolution.

Thyroid-stimulating hormone (TSH) is composed of a specific β subunit and an α subunit that is shared with the two pituitary gonadotropins. The three β subunits derive from a common ancestral gene through two genome duplications (1R and 2R) that took place before the radiation of vertebrates. Analysis of genomic data from phylogenetically relevant species allowed us to identify an additional Tshβ subunit-related gene that was generated through 2R. This gene, named Tshβ2, present in cartilaginous fish, little skate and elephant shark, and in early lobe-finned fish, coelacanth and lungfish, was lost in ray-finned fish and tetrapods. The absence of a second type of TSH receptor (Tshr) gene in these species suggests that both TSHs act through the same receptor. A novel Tshβ sister gene, named Tshβ3, was generated through the third genomic duplication (3R) that occurred early in the teleost lineage. Tshβ3 is present in most teleost groups but was lostin tedraodontiforms. The 3R also generated a second Tshr, named Tshrb. Interestingly, the new Tshrb was translocated from its original chromosomic position after the emergence of eels and was then maintained in its new position. Tshrb was lost in tetraodontiforms and in ostariophysians including zebrafish although the latter species have two TSHs, suggesting that TSHRb may be dispensable. The tissue distribution of duplicated Tshβs and Tshrs was studied in the European eel. The endocrine thyrotropic function in the eel would be essentially mediated by the classical Tshβ and Tshra, which are mainly expressed in the pituitary and thyroid, respectively. Tshβ3 and Tshrb showed a similar distribution pattern in the brain, pituitary, ovary and adipose tissue, suggesting a possible paracrine/autocrine mode of action in these non-thyroidal tissues. Further studies will be needed to determine the binding specificity of the two receptors and how these two TSH systems are interrelated.

Embryonic exposure to excess thyroid hormone causes thyrotrope cell death

Central congenital hypothyroidism (CCH) is more prevalent in children born to women with hyperthyroidism during pregnancy, suggesting a role for thyroid hormone (TH) in the development of central thyroid regulation. Using the zebrafish embryo as a model for thyroid axis development, we have characterized the ontogeny of negative feedback regulation of thyrotrope function and examined the effect of excess TH on thyrotrope development. We found that thyroid-stimulating hormone β subunit (tshb) and type 2 deiodinase (dio2) are coexpressed in zebrafish thyrotropes by 48 hours after fertilization and that TH-driven negative feedback regulation of tshb transcription appears in the thyroid axis by 96 hours after fertilization. Negative feedback regulation correlated with increased systemic TH levels from the developing thyroid follicles. We used a transgenic zebrafish that expresses GFP under the control of the tshb promoter to follow thyrotrope fates in vivo. Time-lapse imaging revealed that early exposure to elevated TH leads to thyrotrope cell death. Thyrotrope numbers slowly recovered following the removal of excess TH. These data demonstrate that transient TH exposure profoundly impacts the thyrotrope population during a critical period of pituitary development and may have long-term implications for the functional reserve of thyroid-stimulating hormone (TSH) production and the TSH set point later in life.

Central neuropeptide Y infusion and melanocortin 4 receptor antagonism inhibit thyrotropic function by divergent pathways

Weight loss inhibits thyrotropic function and reduces metabolic rate, thereby contributing to weight regain. Under negative energy balance there is an increase in the hypothalamic expression of both neuropeptide Y (NPY) and agouti related peptide (AgRP), the endogenous antagonist of melanocortin 4 (MC4) receptors. Both NPY and MC4 receptor antagonism reduce thyrotropic function centrally, but it is not known whether these pathways operate by similar or distinct mechanisms. We compared the time-course of effects of acute or chronic intracerebroventricular (ICV) administration of NPY (1.2 nmol acute bolus, or 3.5 nmol/day for 6 days) or the MC4 receptor antagonist HS014 (1.5 nmol bolus, or 4.8 nmol/day) on plasma concentrations of thyroid stimulating hormone (TSH) or free thyroxine (T4) in male rats pair-fed with vehicle-infused controls. These doses equipotently induced hyperphagia in acute studies, reduced latency to feed, and increased white adipose tissue mass after 6 days of infusion. Acute central NPY but not HS014 administration significantly reduced plasma TSH concentrations within 30-60 min and plasma free T4 levels within 90-120 min. These inhibitory effects were sustained for up to 5-6 days of continuous NPY infusion. HS014 induced a transient decrease in plasma free T4 levels that was observed only after 1-2 days of continuous ICV infusion. While both NPY and HS014 significantly increased corticosteronemia within an hour after ICV injection, the effect of NPY was significantly more pronounced and was sustained for up to 4 days of administration. Both NPY and HS014 significantly decreased the brown adipose tissue protein levels of uncoupling protein-3. We conclude that central NPY and MC4 antagonism decrease thyrotropic function via partially distinct mechanisms with different time courses, possibly involving glucocorticoid effects of NPY. MC4 receptor antagonism increases adiposity via pathways independent of increased food intake or changes in circulating concentrations of TSH, free T4 or corticosterone.

A rexinoid antagonist increases the hypothalamic–pituitary–thyroid set point in mice and thyrotrope cells

Retinoid X receptor (RXR) signaling influences thyrotrope function. Synthetic RXR agonists, rexinoids, can cause central hypothyroidism. To test the hypothesis that endogenous rexinoids contribute to the TSH ‘set point’, TαT1 mouse thyrotrope cells were treated with a rexinoid antagonist, LG101208. Increasing concentrations of LG101208 significantly increased TSHβ mRNA levels, indicating that the rexinoid antagonist may interfere with RXR-signaling by an endogenous rexinoid in thyrotropes. When the same experiments were repeated in the presence of charcoal-stripped serum the effect of the rexinoid antagonist was lost. Pretreatment with the transcription inhibitor DRB blocked the increase of TSHβ mRNA levels by rexinoid antagonist, indicating the primary effect is at the level of gene transcription. Mice treated with LG101208 had higher levels of serum T4, T4/TSH ratios as well as pituitary α-subunit and TSHβ mRNA compared with vehicle treated mice. Hypothalamic TRH levels were unchanged. In summary, the rexinoid antagonist, LG101208, increases TSH subunit mRNA levels in thyrotrope cells and mouse pituitaries, primarily at the level of gene transcription. These data suggest that an “endogenous rexinoid” contributes to the TSH ‘set point’ in thyrotropes.

CUSP Catastrophe Model of Pituitary Thyrotropic Function Stimulatably Protirelin

Article CUSP Catastrophe Model of Pituitary Thyrotropic Function Stimulatably Protirelin was published on January 1, 1978 in the journal Biomedical Engineering / Biomedizinische Technik (volume 23, issue s1).

Effect of thymus on the thyroid and pituitary thyrotropic function.

Thymus inflammation induced in infantile guinea pigs and rabbits by administration of melted paraffin drops into the thymic parenchyma resulted in enhancement of the thyroid functional activity. Thymosin injections provoked an identical effect. In both variants of these experiments the pituitary thyrotropin level remained within the norm. Hence, the pituitary thyrotropic function as in thyrotoxicosis lost the ability of response to enhancement of the thyroid hormone production. This result suggests that the cause of disorganization of the negative feedback between the thyroid and the pituitary thyrotropic function might be attributed to enforcement of the stimulated thymus secretory activity.

Blunted nocturnal TSH surge does not indicate central hypothyroidism in patients after pituitary surgery.

The thyrotropin-releasing hormone stimulation test (TRH test) is commonly used as part of the endocrine evaluation after pituitary surgery. However, some patients with a normal thyrotropin (TSH) response to TRH after pituitary surgery develop central hypothyroidism during follow-up. On the other hand, hypothyroidism does not necessarily ensue in patients with a blunted TSH response. As TSH is secreted in a pulsatile fashion with maximum secretion in the early morning, we investigated whether measurement of the nocturnal TSH surge is useful for predicting development of thyrotropic function after pituitary surgery. Serum TSH concentrations were measured at hourly intervals from 16.00 h to 06.00 h in 13 healthy volunteers and in 10 patients within 2 weeks after pituitary surgery. A standard TRH test using i.v. injection of 200 microg synthetic TRH was performed the next morning. Three and six months later thyroid function was reassessed in all patients by measuring thyroid hormones and TSH. Healthy volunteers showed a clear nocturnal TSH surge from a nadir of 0.55 +/- 0.27 microIU/ml at 18.00 h to a peak concentration of 1.82 +/- 0.97 microU/ml at 06.00 h (p = 0.0015). DeltaTSH during TRH test was 6.31 +/- 2.27 microIU/ml. In contrast, following pituitary surgery, patients invariably showed a blunted nocturnal increase in TSH concentration, which was 0.27 +/- 0.20 microIU/ml at 18.00 h and 0.33 +/- 0.26 microIU/ml at 06.00 h (p = 0.044). DeltaTSH during TRH test was 1.99 +/- 2.51 microIU/ml and was subnormal in 8 out of 10 patients. Levothyroxine supplementation was initiated in two of these patients, because free T4 levels were also subnormal and clinical hypothyroidism was present. In the remaining patients with subnormal TRH response, no case of central hypothyroidism was identified at the follow-up visits after 3 and 6 months. We conclude from these data that both nocturnal TSH surge and TRH test are subnormal after pituitary surgery and do not indicate that central hypothyroidism will develop.

The thyrotropic function of the hypophysis and peripheral thyroid hormones after removal of bland and autonomous nodular goiters

Bilateral subtotal resection or enucleation or unilateral resection was performed in 60 patients (36 with bland nodular goitre, 24 with autonomic adenoma). The thyrotropic pituitary activity and the peripheral thyroid function were examined in all patients preoperatively and followed up for 12 months postoperatively. The results show that all patients with bilaterally resected bland nodular goitre require postoperative administration of thyroid hormone, since enhanced thyrotropic activity is seen not later than three months after surgery. Since thyrotropic function remains normal in unilaterally operated nodular goitre, thyroid hormone administration does not appear generally necessary. In patients with autonomic adenoma there is postoperatively variability of function, independent of the surgical method employed. In view of possible functional recompensation, final decision on the administration of thyroid hormones should not be made before the end of the sixth postoperative month. These results can be considered as guidelines for a differentiated postoperative management.