The proposed work will investigate the effects of endogenous and exogenous prostaglandins on Na and water flow across the isolated perfused rabbit cortical collecting tubule. Arachidonic acid and meclofenamate will be used to stimulate and inhibit respectively prostaglandin production in cells during perfusion. The effects of prostaglandin E2 and F2 alpha on Na and C1 transport across the medullary thick ascending limb of Henle's loop will also be evaluated.