Estrogen-induced luteolysis in the ewe: possible sites of action.

Abstract

To investigate the site(s) and mechanism(s) by which estrogen is luteolytic in cyclic ewes, estradiol cyclopentylpropionate (ECP) (20,40 and 100 µg/ewe) was injected directly into corpora lutea (CL) on day 10 after estrus. By day 14, progesterone concentration in CL had fallen to undetectable levels, whereas luteal weight was unaffected. These data support the hypothesis that increased secretion of ovarian estrogens during the preovulatory period promotes functional luteolysis in cyclic ewes. In a second experiment, continuous infusion of LH (600 µg/day), starting on day 10 after estrus. prolonged luteal life span to day 20 in ewes whose ovarian follicles were destroyed to minimize endogenous estrogen secretion. Injection of ECP (but not oil vehicle) directly into CL of such ewes caused luteal regression, whereas injection of ECP into the contralateral ovary did not. Since circulating LH concentrations were maintained by continuous infusion of the gonadotropin, a negative feedback suppression of LH secret...