Time course of the luteolytic action of LH in 4-day estrous cyclic rats.

In 4-day estrous cyclic rats the neutralization of postovulatory biological activity of LH (by means of a single 0.5 ml sc injection of an anti-LH serum) (LHAS) at any time between 12.00 h on estrus and 12.00 h on metestrus prolongs the estrous cycle corpus luteum (CL) progesterone secretion for almost 24 hours. Injection of LHAS later on during the estrous cycle has no effect on CL progesterone secretion. It is concluded that postovulatory LH secreted up to time of CL maximum capacity to produce progesterone (metestrus afternoon) accelerates the intrinsic luteolytic mechanism, and that once the intrinsic luteolytic process has been switched on (shortly after noon of metestrus), it will lead to the CL functional demise regardless of the luteolytic action of LH.