Role of thyroid hormone in controlling the concentration of luteinizing hormone/human chorionic gonadotropin receptors in rat ovaries.

Little is known about the mechanism by which thyroid hormones influence ovarian function, especially in gonadotropin receptor formation. In this study the concentration of luteinizing hormone (LH)/human chorionic gonadotropin (hCG) receptors in the ovaries of hypo- and hyperthyroid rats was estimated. Rats were made experimentally hypothyroid by thyroidectomy (N = 10) and hyperthyroid by injections of 40 micrograms of L-thyroxine daily for 21 days (N = 14). After 3 weeks the ovaries were excised, weighed, immersed in liquid nitrogen and then, after 24 h of incubation with 125I-labeled hCG (CR-121), the concentration of receptors (cpm) for one ovary and 1 mg of tissue was counted in their respective homogenates. The ovaries of the hyperthyroid group were diminished in size and consequently the level of receptors per ovary also was reduced when compared with control animals. The number of receptors per ovary and per milligram of tissue of hypothyroid rats was three times higher than in the control. In hyperthyroid animals a significant decrease in these values was noted when compared with hypothyroid rats, especially in the calculation of receptor concentration per ovary. It may be concluded that thyroid function may affect the size of the gland and also the number of LH/hCG-binding sites in rat ovaries. These data may be useful for interpretation of the pathophysiology of polycystic ovary syndrome in women and animals.