Although ovulation and luteinization of the ovarian follicle are essential components of the reproductive cycle, very little is known regarding the control of these processes in primates. The interval from the gonadotropin surge to ovulation in primates is 37-42 hours, during which time the follicle ruptures, the oocyte is extruded, and the follicle is remodeled into a functional corpus luteum. Periovulatory events, therefore, are critical for fertilization and pregnancy maintenance. In the rhesus monkey, progesterone ablation prevents ovulation and luteinization, although the mechanism(s) by which progesterone mediates these processes are unknown. The proposed studies will investigate events occurring during the periovulatory period in rhesus monkeys and, using progesterone albation/replacement, will elucidate the role of progesterone in regulating these processes in the monkey model. Data will be collected on molecular and biochemical indices relating to steroidogenesis, vascularization, proliferation/cell death, and ovulation. Granulosa cells, follicular fluid, and tissue sections will be utilized to determine levels of messenger RNA and protein. These studies will provide the first detailed characterization of the periovulatory period in the primate, and will enhance our understanding of progesterone action in ovulation and luteinization of the primate follicle.