The overall objectives of this proposal is to determine the cellular mechanism by which gonadotropins regulate ovarian function. More specifically, the work to be carried out during the current project period would involve studies on the characterization of the functional groups of the receptor involved in the hormone receptor interaction by selective modification of the reactive groups on membrane. This will be accomplished by in vitro techniques and by the use of a collagenase dispersed cell suspension from highly luteinized rat ovaries. The effect of cell surface gonadotropin receptor modification will be tested on the responsiveness of ovarian cells on hCG and LH-stimulated progesterone synthesis. We are also proposing to investigate the extent of utilization of endogenous and exogenous cholesterol sources for steroidogenesis and the effect of gonadotropin on this process. In this connection, we are proposing to investigate LDL and HDL receptor on ovarian plasma membranes and their regulation by gonadotropins.