Preliminary observations indicate that acute expansion of the extracellular fluid volume (ECVE) with saline is accompanied by increased urinary excretion and nephrogenous production of cyclic AMP in dogs previously subjected to thyroparathyroidectomy. The proposed research is designed to evaluate some of the mechanisms which may be responsible for the increased renal production of cyclic AMP during ECVE. Renal production of cyclic AMP will be measured during acute and chronic volume expansion, during experimental sodium retaining states and while manipulating renal hemodynamic factors . Specifically, during excretion of cyclic AMP, renal clearance of cyclic AMP will be measured in T-PTX dogs in the following conditions: 1) acute ECVE with saline with and without aortic constriction between the renal arteries, 2) during acute ECVE with saline after administration of indomethacin, 3) during acute and chronic thoracic inferior vena cava constriction and ECVE with saline, 4) during unilateral renal vasodilatation and also the addition of increased arterial pressure, 5) during chronic ECVE with DOCA and high salt intake, 6) after production of sodium retention in dogs with chronic ligation of the common bile duct, 7) we will also examine the existence of an additive effect of cyclic AMP infusion over the natriuretic effect of renal arterial bradykinin or protaglandins E2 which do not depress proximal reabsorption.