The overall objective of this research proposal is to establish subcellular distribution, biochemical nature and the physiological significance of the receptors for prostaglandin (PG) Es, PGF2 alpha and human chorionic gonadotropin-luteinizing hormone (HCG-LH). To this end, experiments are being conducted 1) to assess the subcellular distribution of the receptors with the aid of marker enzymes to establish the purity of the fractions, 2) the functional relevance of the intracellular receptors, 3) search for the mediators of PGF2 alpha action, 4) solubilize and purify the receptors to study their true biochemical nature as well as to raise antibodies against them, 5) assess the physiological significance of the receptors by the use of antibodies to receptors and by measuring hormone binding and consequences of this interaction in various reproductive states, and 6) to establish quantitative and qualitative relationships between hormone binding and the consequences of this phenomenon. The luteal tissue from cows throughout pregnancy and from superovulated rats in various reproductive states will be used because this will provide us with greater flexibility and convenience in accomplishing the stated goals of this proposal. It is becoming increasingly clear that hormones once believed to bind exclusively to the cell surface, do bind to various intracellular membranous organelles. It is perhaps the single most important challenge to unravel the relevance of these receptors in overall action of hormones. Such a goal is a part of this proposal. Despite tremendous advances made by us and others in identifying PGF2 alpha receptors, nothing is known on what signal follows receptor-PGF2 alpha interaction. The task of identifying mediator(s) will be undertaken as a part of this research proposal. The solubilization and purification studies, besides giving information on the true biochemical nature of the receptors, can also easily test the possibility whether PGE1, PGF2 alpha and hCG bind to different sites on the same macromolecule or to sites on different macromolecules. Raising antibodies to pure receptors and using specific antibodies in physiological studies would be a novel approach towards understanding several potentially important biological phenomena. It would be an equally novel approach to try and block luteal function at will using specific antibodies to receptors.