It has been proposed that des-aspartyl angiotensin II (angiotensin III) plays an important role in the regulation of aldosterone production. We will examine the effects of an analogue of angiotensin III, isoleucine-7 angiotensin III on aldosterone production in the conscious rabbit subjected to dietary sodium depletion. Previous studies in our laboratory suggest that isoleucine-7 angiotensin III acts as a non-competitive inhibitor of angiotensin III-induced adrenal steroidogenesis. A significant decrease in aldosterone secretion during infusion of isoleucine-7 angiotensin III in the sodium-deplete animal, would led support to the proposed role of angiotensin III in mediating the aldosterone response to sodium depletion. An assay for aspartyl-aminopeptidase (angiotensinase) activity will be developed using 3H angiotensin II (20-40 Cu/m mole) as substrate. The effects of dietary sodium depletion on plasma and tissue angiotensinase activity will be examined. BIBLIOGRAPHIC REFERENCES: Steele, J.M. Jr., Neusy, A.J., and Lowenstein, J. The effects of Des-1-Asp Angiotensin II on Blood Pressure, Plasma Aldosterone Concentration and Plasma Renin Activity in the Rabbit. Circ. Res. 38 Suppl II II 113-116, 1976. Lowenstein, J., and Steele, J.M. Jr. Aldosterone Production During Sodium Restriction and Beta Adrenergic Blockade. Kidney Int. 11, 128-135, 1977.