Effect of progesterone and estradiol on the regulation of pulsatile secretion of LH in the various phases of the estrous cycle of rats

: The normal changes on LH pulse amplitude and frequency throughout the estrous cycle and the specific role of Progesterone (P) and Estradiol (E) on pulsatile LH release have been determined in rats at the different stages of the estrous cycle. The effects on pulsatile LH release 24 h after ovariectomy (OVX), have been studied, as well as the way the normal values of the pulsatile release was re-established, when the physiological levels of P and/or E were restored by implantation of either P, E, or both Silastic capsules in OVX rats 24 h early. Our data during the rat estrous cycle, have confirmed that the lowest pulsatile LH release was on estrus, and the largest LH pulses were obtained on diestrus day 1, when the plasmatic levels of both P and E were lowest. Moreover, a variable ovarian steroid effect has been found at the different stages of the cycle. In estrus and diestrus day 2, both steroids were necessary to restore the normal values of the pulsatile LH release in OVX rats 24 h before, while in proestrus, the main steroid was Estradiol, although a non steroidal ovarian factor was also necessary to restore the normal pulse amplitude. Finally, in diestrus day 1 there was an absence of an ovarian steroid negative feedback on pulsatile LH release, because the levels of both steroids were too low in this stage, to exert a regulatory role on pulsatile LH release.