Dose-dependent stimulation and inhibition of proximal tubular sodium reabsorption by angiotensin II in the rat kidney.

The effect of val5-angiotensin II on steady-state sodium concentration gradients (deltacNa) was studied in rat proximal tubules by stationary micro-perfusion combined with perfusion of the peritubular capillaries. Angiotensin added to the peritubular perfusion fluid had a biphasic action with stimulation of sodium reabsorption at low doses (10(-12)-10(-10)M) and inhibition at high doses (3 X 10(-7) - 3 X 10(-6)M). Stimulation of transport was also observed with intraluminal angiotensin but only at a dose of 10(-9)M. Transepithelial potential difference was calculated from the steady-state chloride distribution; no significant change was observed at low (10(-11)M) or high (10(-6)M) concentrations and a direct action on sodium transport is postulated. This biphasic effect is discussed in relation to the responses of the intact kidney to intra-renal infusion of angiotensin, and to the control of tubulo-glomerular feed-back.