The project is designed to gather data which will test the hypothesis that hypothalamic releasing factors provide a final regulatory stimulus for the release of pituitary gonadotrophins, especially LH and FSH. The experiments will provide an analysis of the dynamics of LH secretion in proestrous and castrated rats and the quantitative adjustments of these systems in response to steroid induced alterations of LH release. In so far as possible, newly developed radioimmunoassays for LH releasing hormone will be used to measure any changes in the serum concentrations of LH-RH, both in rats and in sheep. Some emphasis will be given to the concepts of differential control of LH and FSH secretion especially in regard to the ability of some androgenic steroids to modulate the effects of exogenous releasing factors.