The proposed studies are designed to evaluate the effects of progesterone and its 20 Alpha-reduction product on the secretion of the gonadotropins LH and FSH andof prolactin by the pituitary of rats under conditions whereby progesterone is a positive stimulus for gonadotropin secretion (i.e., on the day before proestrus in normally cycling rats and after estrogen priming of ovariectomized rats), and under conditions whereby progesterone appears to suppress gonadotropin secretion (i.e., during pseudopregnancy induced by cervical stimulation and after pituitary autotransplantation). Because of the many phjysiological factors that influence gonadotropin secretion, it is necessary to be able to control more than the time of exposure of an animal to hormones in order to contribute to the understanding of correlated phenomena. For this purpose we have available antiprogesterone (APA) and anti-20 Alpha-dihydroprogsterone (APD) antisera that have been produced in large quantity; these antisera have been purified and characterized for their binding affinity and specificity in vitro and in vivo. With these antisera we can achieve rapid depletion of the respective progestins regardless of their source in animals that have been prepared in such a way that the time of onset and rate of progestin depletion represents second and third controlled variables. In addition to studies utilizing these antisera in vivo pituitaries of pseudopregnant rats, some of which will receive estrogen, will be incubted with combinations of APA, APD, and LH-releasing hormone or thyrotropin-releasing hormone in vitro; gonadotropins and prolactin measured in the media will help characterizet the direct relationship bebween progestins and gonadotropin secretion within the pituitary. The influence of progesterone depletion within the oary on its own biosynthesis will also be examined by similar methods. Inadeuqate progestrone secretion by the ovary (inadequate luteal phase) is an important cause of infertility/ in womenm. These studies willcontribute to a better understanding of the relationships between ovarian secretion of progesterone and factors that promote or inhibit its continued secretion.