Pituitary in Vitro LH and FSH Secretion after Administration of the Antiprogesterone RU486 in Vivo

Abstract

This chapter explores pituitary in vitro follicle-stimulating hormone (FSH) and luteinizing hormone (LH) secretion after administration of the antiprogesterone RU486 in vivo. When RU486 is administered on the afternoon of proestrus, the pattern of basal LH and FSH pituitary secretion is remarkably different the next morning. The secretion of LH and FSH during the 4-day rat estrous cycle is remarkably similar except following the preovulatory gonadotropin surges on the afternoon of proestrus. Although levels of serum LH drop immediately following the proestrous surge, serum FSH remains elevated throughout the evening of proestrus until noon on the day of estrus, a phenomenon known as the secondary FSH surge. The primary surges of LH and FSH and the secondary FSH surge can be completely abolished by administration of a GnRH antagonist before the primary surges have taken place. The data on pituitary FSH secretion, either basal or GnRH-stimulated secretion, suggest a role for progesterone, at the pituitary level, in maintaining FSH secretion, which may have implications for the producing the secondary FSH surge.