title: Regulation of the preovulatory gonadotropin surge by endogenous steroids.
abstract: Estradiol secreted by growing ovarian follicle(s) has been considered classically to be the neural trigger for the preovulatory surge of gonadotropins. The observation that the estradiol-induced gonadotropin surge in ovariectomized rats is of lesser magnitude and duration than that found in the cycling rat at proestrus has resulted in a search for other steroid regulators. Progesterone is a major regulator of the preovulatory gonadotropin surge. It can only act in the presence of an estrogen background, which is necessary for the synthesis of progesterone receptors. In the estrogen-primed ovariectomized rat, progesterone is able to initiate and enhance the gonadotropin surge to the magnitude observed on the day of proestrus and limit it to 1 day. The physiological role of progresterone in the induction of the preovulatory gonadotropin surge has been demonstrated by the attenuation of the progesterone-induced surge and the endogenous proestrus surge by progesterone receptor antagonist RU486 and the progesterone synthesis inhibitor trilostane. The promoter region of the follicle-stimulating hormone (FHS)-beta gene contains multiple progesterone response elements and progesterone brings about FSH release as well. The reduction of progesterone in the 5 alpha-position appears to be important for the regulation of progesterone secretion. Corticosteroids appear to play a significant role in the secondary FSH surge on late proestrus and early estrus.
authors.affiliation: Department of Physiology and Endocrinology, Medical College of Georgia, Augusta 30912-3000, USA. vmahesh@mail.mcg.edu
authors.forename: V B
authors.initials: VB
authors.lastname: Mahesh
authors.forename: D W
authors.initials: DW
authors.lastname: Brann
mesh_terms: D000311:Adrenal Glands / Q000378:metabolism; D000818:Animals; D005260:Female; D005640:Follicle Stimulating Hormone / Q000378:metabolism; D005498:Follicular Phase / Q000502:physiology*; D007987:Gonadotropin-Releasing Hormone / Q000502:physiology; D006062:Gonadotropins / Q000378:metabolism*; D051381:Rats; D013256:Steroids / Q000502:physiology*
chemical_list: D006062:Gonadotropins; D013256:Steroids; D007987:Gonadotropin-Releasing Hormone; D005640:Follicle Stimulating Hormone