title: Luteinizing hormone responses to repeated injections of luteinizing hormone releasing hormone in the rat during the oestrous cycle and after ovariectomy with or without oestrogen treatment.
abstract: In order to characterize the nature of the LH response to exogenous LH releasing hormone (LH-RH) in female rats during the oestrous cycle and after ovariectomy with or without oestrogen treatment, serum LH levels were determined after repeated LH-RH injections (300 ng/kg body wt, six times with 30-min intervals). The LH response to the first LH-RH stimulation was greatest on the days of pro-oestrus and oestrus followed by dioestrus 2 and dioestrus 1. Second and subsequent LH-RH challenges enhanced the LH response only on pro-oestrus and dioestrus 2. Larger doses of LH-RH (3 microgram/kg body wt) induced a small self-priming effect on dioestrus 1 and oestrus. The LH response to the first LH-RH administration increased with time up to 30 days after ovariectomy and then reached a plateau. A small self-priming effect was present in rats ovariectomized for 30 and 60 days, but absent in rats ovariectomized for 5, 10 and 120 days. Oestrogen treatment increased the self-priming effect in rats ovariectomized for 5 days, with little sensitization of the pituitary gland to the first LH-RH injection on the next day. In rats ovariectomized for 120 days, oestrogen treatment enhanced responsiveness to the first and successive LH-RH stimulations on the next day, and further enhancement to the first response only was induced 3 days after oestrogen treatment.
mesh_terms: D000818:Animals; D002369:Castration; D004958:Estradiol / Q000494:pharmacology; D004971:Estrus; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism*; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism; D011247:Pregnancy; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D007987:Gonadotropin-Releasing Hormone; D004958:Estradiol; D007986:Luteinizing Hormone