The aim of the research proposed is to investigate the mechanisms by which estrogen (E) and progesterone (P) interact with GnRH at the level of the pituitary gonadotrope to stimulate and inhibit the secretion of LH and FSH in rats and monkeys. The specific question to be addressed is whether there are subtypes of gonadotropes in adult monkey and rat pituitary glands, and whether these subtypes change in functional capacity during menstrula and estrous cycles so as to account for the preovulatory LH and FSH surges and for the differential secretion of LH and FSH. The specific aims are based on this question: 1. To investigate the morphological and functional characteristics of gonadotropes in rat and monkey pituitaries. a. To separate gonadotropes according to size using isokinetic Ficoll gradient centrifugation; ICC will be used to detect gonadotropes in the fractions. b. To measure the functional and morphological characteristics of the separated gondotropes by: 1) measuring LH and FSH contents using RIA: 2) measuring GnRH stimulation of LH and FSH secretion using static incubations and perifusions; 3) measuring the stimulatory and inhibitory effects of E and P on GnRH-stimulated gonadotropin secretion; 4) measuring GnRH receptor numbers and; 5) studying their electron microscopic-ICC characteristics. c. To investigate quantitative changes in the morphological and functional characteristics of gonadotrope subtypes according to stages of the estrous and menstrual cycles or after E and P treatment of ovariectomized animals. 2. To investigate the differential secretion of LH and FSH by individual gonadotropes. a. To determine what % of the gonadotropes contain only LH or only FSH using double-stain, light-microscopic ICC, and whether this varies according to subtypes of gonadotrope or stage of the estrous or menstrual cycle. b. To determine the secretory product (LH or FSH) of individual gonadtropes in culture using an agar "overlay" technique which traps the secteted hormone around each gonadodtrope for subsequent identification by ICC.