The overall objectives of the proposal are to analyze the factors which regulate renal medullary prostaglandin E2 receptor binding and to demonstrate that changes in the receptor are determinants of the action of PGE2. PGE2 increases renal water excretion by antagonizing the activity of antidiuretic hormone (ADH) - stimulated adenylate cyclase. PQE2 initiates its actions by first binding to specific plasma membrane receptors. We have developed methods to measure PGE2 receptor number and affinity in rat renal medullary membranes and also methods to measure PGE2 inhibition of ADH-stimulated adenylate cyclases. The specific aims are: (1) to assess the effect of in vitro manipulations of sodium, divalent cations, and guanyl nucleotide concentration on the binding of 3H-PGE2 to medullary membranes and to define the chemical constitution (protein, lipid, oligosaccharide) of the receptor; (2) to determine the potential factors (changes in ambient PGE2 concentration, changes in salt and water balance) which regulate PGE2 receptor number and affinity in vivo; and (3) to correlate both in vivo and in vitro changes in the receptor with changes in PGE2 inhibition of adenylate cyclase. Prostaglandins are important regulators and protectors of kidney function particularly under conditions of renal compromise such as volume depletion and intrinsic renal disease. Although we have a general view of what PGE2 does and the factors which regulate its synthesis, we know very little of the factors which regulate the interaction of PGE2 with its target cell receptors and how this interaction might be manipulated. The objective of this proposal is to begin to understand this fundamentally important aspect of the action of prostaglandins within the kidney.