title: Characterization of estrogen stimuli sufficient to initiate cyclic luteinizing hormone release in acutely ovariectomized rats.
abstract: Estradiol (E)-filled Silastic capsules were implanted subcutaneously to characterize the estrogen stimulus sufficient to initiate cyclic LH secretion in female rats ovariectomized on diestrus 1 of the estrous cycle. Such capsules elevate preoptic area, hypothalamic and hypophysial cell nuclear estrogen receptor levels to proestrous values within 1/2 h following insertion; upon removal of the capsules, nuclear receptor levels decline monotonically to ovariectomized control levels by 8 h in brain and 12 h in pituitary. Three parameters of the E stimulus were studied: latent period, duration, and continuity. E stimuli, short in duration (7-12 h) and discontinuous in nature (3 h pulses 12 or 15 h apart), effectively stimulated LH surges on "proestrus'. However, these stimuli had to begin 30 h prior to the onset of LH release. Such a latent period for estrogen action was not observed when we monitored the ability of the same E stimuli to enhance pituitary responsiveness to GnRH. These studies demonstrate that the "rate-limiting step' for estrogen's positive feedback action is located within the estrogen-sensitive brain circuits controlling GnRH release and defines the temporal characteristics of E stimuli activating these circuits.
mesh_terms: D000818:Animals; D002369:Castration; D004343:Drug Implants; D004958:Estradiol / Q000097:blood / Q000494:pharmacology*; D004971:Estrus; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology; D007031:Hypothalamus / Q000378:metabolism; D007986:Luteinizing Hormone / Q000378:metabolism*; D010903:Pituitary Gland, Anterior / Q000378:metabolism; D011247:Pregnancy; D011301:Preoptic Area / Q000378:metabolism; D011374:Progesterone / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011960:Receptors, Estrogen / Q000378:metabolism*
chemical_list: D004343:Drug Implants; D011960:Receptors, Estrogen; D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D004958:Estradiol; D007986:Luteinizing Hormone