EFFECTS OF ANGIOTENSIN-II ON ELECTROLYTE TRANSPORT IN THE EARLY AND LATE DISTAL TUBULE IN RAT-KIDNEY

We have demonstrated in previous studies that luminal administration o f low doses of angiotensin II (ANG II) stimulate and high doses of ANG II inhibit fluid and HCO3- transport in proximal tubules of rat kidne y. However, the role of ANG II on Na+ and HCO3- transport in the dista l nephron has not yet been fully elucidated. The superficial early and late distal tubules (DT) of the nephron segments correspond to the di stal convoluted tubule and initial collecting tubule. Accordingly, we investigated the effects of ANG II on Na+, HCO3-, and K+ transport in the early and late DT by separate perfusion of these tubule segments i n vivo. [H-3]inulin, Na+, K+, and total CO2 concentrations were measur ed in the perfusate and collected fluid, and transport of sodium (J(Na )), bicarbonate (J(HCO3)), potassium (J(K)), and fluid (J(v)) were ana lyzed as an index of the hormone effect. Intravenous infusion of the A NG II receptor antagonist [Sar(1),Ile(8)]ANG II (1 mu g . kg(-1). min( -1)) decreased J(v), J(Na), and J(HCO3) in the early DT and decreased J(v) and J(Na) in the late DT. Addition of ANG II (10(-11) M) to the t ubular perfusate significantly increased the J(v), J(Na), and J(HCO3) in the early DT. Similar studies in late DT demonstrated an increase i n J(v) and J(Na), decrease in J(K), but no effect on J(HCO3) The effec ts of ANG II on fluid and ion transport were abolished by the luminal application of amiloride (10(-3) M) and of the angiotensin-receptor bl ocker [Sar1,Ile(8)]ANG II (10(-6) M). These results suggest that ANG I I stimulates Na+/H+ exchange in the early DT (distal convoluted tubule ) and amiloride-sensitive Na+ transport (Na+ channels) in the late DT (initial collecting tubule) of cortical nephrons.