The overall objective is to determine the intraovarian and extraovarian endocrine relationships which govern ovarian function during pregancy in the rabbit and rat. The functional significance of aromatization in the rat corpus luteum will be investigated with particular attention to the role of intraluteal estradiol in the regulation of progesterone synthesis, cyclic AMP concentrations, and 20 alpha-hydroxysteroid dehydrogenase activity in the corpus luteum. The mechanism of lutenization of Graafian follicles will be investigated using a procedure in which follicles are incubated in vitro and autotransplanted beneath the kidney capsule where they develop into ectopic corporea lutea. Follicles will be incubated with 125I-hCG to determine the site of binding of labeled hormone and the role of hormone binding in subsequent luteinization. The contribution and functional significance of theca interna cells during luteinization will be studied by histologic and autoradiographic analysis of corpora lutea derived from follicles with "tagged" thecal cells and by transplantation of isolated follicular cells. The requirement for non-luteal ovarian tissues during pregnancy will be determined in relation to 1) survival of pregnancy, 2) maintenance of the corpus luteum and 3) maintenance of normal serum levels of progesterone, 17 beta-estradiol, 20 alpha-dihydroprogesterone, LH and prolactin which are measured by radioimmunoassay. Ectopic Graafian follicles will be established in pregnant animals to study their longevity, their ability to synthesize and secrete 17 beta-estradiol, their ability to luteinize in response to LH and their histological fate upon degeneration.