Dual control of secretion of the gonadotropic hormones of the anterior pituitary gland
Our laboratory pioneered in demonstrating that estradiol and progesterone are inadequate negative feedbacks for suppression of the gonadotropic follicle-stimulating hormone (FSH) in the female lacking ovaries and discovered a gonadal peptide called inhibin, necessary for proper suppression of FSH. We have employed antagonists to gonadotropin-releasing hormone (GnRH) - a well-established and necessary signal from the hypothalamus - to demonstrate relative lack of dependence on endogenous GnRH of FSH in males and females. We are investigating, in an in vitro perifusion system, sex differences in hypothalamic and pituitary secretion. Another discovery is that glucocorticoid hormones from the adrenal differentially affect the gonadotropins luteinizing hormone (LH) and FSH in vivo or in vitro, suppressing LH secretion and enhancing FSH synthesis and secretion. We have expanded these studies to measurement of mRNA for the gonadotropin subunits and to direct testing of glucocorticoid action on the rat FSH▀ gene. Finally, we are studying the regulation of FSH secretion by RU486, which antagonizes progesterone. These studies have led us to measurements of mRNA for the progesterone receptor forms A and B in the pituitary during the cycle. All of these in vivo and in vitro studies are directed toward understanding the neuroendocrinology of the hypothalamic-pituitary-gonadal axis.