Pituitary responsiveness to LH-RH in post-partum ewes treated with oestradiol-17 beta and failing to show a plasma LH surge.
Oestradiol-17 beta (40 micrograms intravenously) failed to elicit a surge in plasma LH levels by 13 h after administration in 64% (16 out of 25) Merino ewes about 30 days post partum in the anoestrous season. LH-RH responsiveness and LH-RH priming effect were significantly greater in these ewes than in similar post-partum (n = 9) and non-parturient ewes (n = 3) not treated with oestradiol. This suggests that the failure of the oestrogen-positive feedback effect on LH release in post-partum ewes is not due to a failure of oestradiol action on the pituitary increasing pituitary responsiveness to LH-RH and LH-RH priming effect, but could be due to inadequate release of LH-RH from the hypothalamus.
D000818:Animals; D004958:Estradiol / Q000494:pharmacology*; D005246:Feedback; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D007031:Hypothalamus / Q000502:physiology; D007986:Luteinizing Hormone / Q000097:blood*; D010902:Pituitary Gland / Q000187:drug effects / Q000502:physiology*; D049590:Postpartum Period; D011247:Pregnancy; D012756:Sheep
D007987:Gonadotropin-Releasing Hormone; D004958:Estradiol; D007986:Luteinizing Hormone