Estradiol involvement in the luteolytic action of LH during the estrous cycle in the rat

The study was undertaken to examine LH, prolactin (Prl) and estradiol involvement in the control of corpus luteum function during 4-day cycle in the female rat. A potent LHRH antagonist (Antag) and bromocriptine (BRC) were used to induce LH and Prl deprivation in 4-day cyclic rats. Both drugs were administered after the occurrence of LH and Prl release on the afternoon of proestrus. Blood progesterone (P) concentration on diestrus 1 at 24:00 hr was similar in Antag, Antag + BRC and BRC-treated animals and did not differ from P values in control females. It was then concluded that neither LH nor Prl were necessary for the corpus luteum to achieve its stage of maximal activity during the night from diestrus 1 to diestrus 2. By contrast higher P values were observed on diestrus 2 at 12:00 hr in Antag-treated rats than in those given Antag + BRC, BRC or in the controls. When given on diestrus 1 evening estradiol benzoate completely prevented this effect of Antag to occur in LH and Prl deprived females. These results allow to hypothesize that LH exerts luteolytic effects during the diestrous period of the cycle and also suggest a possible involvement of estradiol in the regression phase of the corpus luteum.