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

Abstract

The effect of val⁵-angiotensin II on steady-state sodium concentration gradients (Δc_Na) 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 (3×10⁻⁷–3×10⁻⁶ M). Stimulation of transport was also observed with intraluminal angiotensin but only at a dose of 10⁻⁹M. Transepithelial potential difference was calculated from the steady-state chloride distribution; no significant change was observed at low (10⁻¹¹M) or high (10⁻⁶M) 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.