Pituitary Responsiveness to LH-RH in Post-partum Ewes Treated With Oestradiol-17ß and Failing to Show a Plasma LH Surge

Abstract
Estradiol-17.beta. (40 .mu.g i.v.) failed to elicit a surge in plasma LH [luteinizing hormone, lutropin] levels by 13 h after administration in 64% (16 of 25) Merino ewes, .apprx. 30 days post partum in the anestrous season. LH-RH [luteinizing hormone-releasing hormone, luliberin] responsiveness and LH-RH priming effect was significantly greater in these ewes than in similar post partum (no. = 9) and non-parturient ewes (no. = 3) not treated with estradiol. Apparently, the failure of the estrogen-positive feedback effect on LH release in post partum ewes is not due to a failure of estradiol 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.