title: Pituitary responsiveness to synthetic LH-RH and pituitary LH content at various reproductive stages in the sheep.
abstract: In sheep the basal concentration of LH in jugular vein plasma was significantly higher during the first 50 days of gestation in late pregnancy or at parturition. The pituitary response to a single i.v. injection of 200 microng synthetic LH-RH was determined at different stages of gestation and compared with that of anoestrous and cyclic sheep. Pituitary response to LH-RH decreased progressively with advancing gestation: by 56 days after mating the response had declined to 35% and by parturition to 14% of the value in anoestrous sheep. The pituitary response to LH-RH increased after parturition and the pattern of recovery differed in non-lactating and lactating sheep. By 63 days postpartum the response to LH-RH in non-lactating and lactating animals had returned to values similar to those in sheep during anoestrus and sheep during the luteal phase of the oestrous cycle. A decrease in pituitary responsiveness during pregnancy was associated with a decrease in pituitary content of LH. The quantity of LH released in response to a standard injection of LH-RH was linearly related to pituitary LH content.
mesh_terms: D000818:Animals; D004971:Estrus; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology; D007774:Lactation; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism*; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism*; D011247:Pregnancy; D011270:Pregnancy, Animal; D012756:Sheep / Q000502:physiology*
chemical_list: D007987:Gonadotropin-Releasing Hormone; D007986:Luteinizing Hormone