The overall goals of the project are to elucidate some of the physiological and biochemical mechanisms which govern the function of the corpus luteum in a representative primate, the rhesus monkey. Specifically, we propose to continue our investigation of the factors which initiate luteolysis during the menstrual cycle, with particular emphasis on the role of estrogens in this regard. Further, we will examine the intraovarian sites and mechanisms whereby estrogens act to induce luteolysis, and whether the intraovarian events associated with estradiol-induced luteolysis are similar to those which occur during normal luteolysis. Radioimmunoassays are available for measurement of circulating levels of LH, estradiol, and progesterone and techniques include methods for chronic delivery of small quantities of estradiol directly into the corpus luteum, and procedures for quantitation of receptor activity for LH and estradiol in ovarian tissues.