Stimulation of Chinese hamster ovary cells expressing human thyrotropin receptors by serum human chorionic gonadotropin of patients with hydatidiform mole

Inhibitory effect of thyroid blocking antibody (TBAb) on the thyroid stimulatory effect of human chorionic gonadotropin (HCG) and equine chorionic gonadotropin (ECG)

We examined the inhibitory effect of thyroid blocking antibody (TBAb) on the thyroid stimulating activity of human chorionic gonadotropin (HCG) and equine CG (ECG). Five TBAb positive sera obtained from patients who had been hypothyroid but were currently on T4 treatment. The TSH binding inhibitory immunoglobulin (TBII) activities of the sera were 60-160 IU/L. Inhibition of TSH binding to the TSH receptor (TSHR) [TSH binding inhibition (TBI) activity] of HCG or ECG, and inhibition of TBAb on HCG or ECG-stimulated cAMP production were examined. Both HCG and ECG preparations showed weak TBI activity in the presence of small amounts of protein [bovine serum albumin (BSA)] but were negative in the presence of large amounts of protein [normal human serum (NHS) or BSA]. Four thousand IU/mL of HCG and ECG preparation caused cAMP production similar to 100 microU/mL of bovine (b) TSH. The inhibitory effect of TBAb on cAMP production by this amount of HCG or ECG was then examined. The inhibitory effect of TBAb on cAMP production by HCG and ECG was similar to bTSH, and TBAb positive sera with more than 40 IU/L TBII activity completely blocked cAMP production by HCG, ECG and bTSH. This suggests that common alpha -subunit of both HCG and TSH are involved in the inhibitory effect of TBAb. Previous reports demonstrated that the thyroid stimulating activity of thyroid stimulating antibody (TSAb) was blocked by deglycosylated HCG (competitive antagonist of TSH binding to TSHR). The fact and our present study suggest that TSH, HCG ECG, TSAb and TBAb have a similar binding site (alpha-subunit-mimicking binding site) on the TSH receptor.

Thyreotropic effect of human Chorionic Gonadotropin (hCG) in mares at estrus

The beta-subunits of thyroid stimulating hormone (TSH) and human chorionic gonadotropin (hCG) share a high homology, just like the ectodomains of their receptors, do. As a consequence, hCG was shown to exert a thyrotropic action in humans and hamsters. This study aimed to investigate whether hCG, used to induce ovulation, displays a thyrotropic effect in the equine species too. Forty mares at estrus were divided in two groups; 20 were intravenously treated with sterile saline solution (NaCl 0.9%) (group A); 20 were intravenously treated with 4000 I.U. of hCG (group B). All the mares were artificially inseminated 24 hours after the administration of the drugs and underwent blood collection at estrus detection (T1), 2, 6, 24 hours later (T2, T3, T4), and 3 and 6 days later (T5, T6), in order to detect serum fT3 and fT4 concentrations. fT3 concentrations gave rise to similar and constant trends in the two groups, without any statistically significant difference, whereas fT4 concentrations declined in both groups, remaining statistically higher in group B than in group A for 48 hours (p < 0.05), thus accounting for a thyrotropic effect of hCG. Pregnancy rate was 70% in group B and 40% in group A, respectively. The higher success in the outcome of pregnancy may result from the immunomodulating and steroidogenic effects of hCG and from the higher levels of thyroid hormones observed in the hCG treated group.

Thyrotropin receptors in brown adipose tissue: thyrotropin stimulates type II iodothyronine deiodinase and uncoupling protein-1 in brown adipocytes

It has been demonstrated that TSH receptors are expressed not only in thyroid gland but also in extrathyroidal tissues. Brown adipose tissue of guinea pig has been reported to express TSH receptor messenger RNA (mRNA), but the physiological roles of TSH receptors in brown adipose tissue have not been understood. We studied the expression and function of TSH receptors in rat brown adipose tissue and cultured rat brown adipocytes. Northern analysis demonstrated the expression of TSH receptor mRNA in rat brown adipose tissue and cultured rat brown adipocytes. TSH receptor mRNA in rat brown adipose tissue was decreased by cold exposure of the rat, and its mRNA in cultured rat brown adipocytes was also decreased by incubation with TSH or (Bu)(2)cAMP. TSH increased the intracellular cAMP concentration in cultured rat brown adipocytes in a dose dependent manner. Type II iodothyronine deiodinase mRNA, its activity, and uncoupling protein-1 mRNA in cultured rat brown adipocytes were significantly increased by incubation with TSH in a dose-dependent manner. These results suggest the expression of functional TSH receptors in brown adipose tissue, which may be involved in regulation of the expression of type II iodothyronine deiodinase and uncoupling protein-1.

Thyrotoxicosis in a male patient associated with excess human chorionic gonadotropin production by germ cell tumor

We report a case of a man with thyrotoxicosis due to excess production of human chorionic gonadotropin (hCG) by metastatic choriocarcinoma, followed by alterations of his thyroid function tests by nonthyroidal illness. All reported cases of thyrotoxicosis due to high hCG levels in male patients are reviewed. Patients with this syndrome usually have widespread choriocarcinoma and relatively few symptoms of thyrotoxicosis. Typically, if the patient survives the metastatic germ cell tumor, the thyrotoxicosis resolves as the hCG levels decrease after chemotherapy directed at the choriocarcinoma. Only rarely are specific antithyroid medications required. The hCG molecule directly stimulates the thyroid gland, and these patients appear to have in the serum a predominance of acidic variants of hCG with greater intrinsic thyroid-stimulating activity than the hCG secreted during a normal pregnancy. In general, these patients have a poor prognosis due to the usually widespread nature of the germ cell tumor at the time of diagnosis.