Dietary sodium and the renal responses to Angiotensin1–7 (ANG1–7)

Abstract

This study investigated how the renal excretory actions of ANG1–7 were altered when the renin‐angiotensin system (RAS) was activated or suppressed following a period of low or high dietary sodium intake. Male Wistar rats were fed a low (0.03%), normal (0.3%) or a high (3.0%) sodium diet for 2 weeks. The animals were anaesthetised with chloralose/urethane and prepared for the measurement of blood pressure (BP), iv infusion of saline (0.9%NaCl, 3.0 ml/h). Cannulae were placed in the left ureter for urine collection and at the cortico‐medullary border for saline or ANG1–7 infusion at 1.0ml/h. Four 20 min clearances were taken, two before and two 45min after either saline or ANG1–7 (9×10−7M) infusion. Data, means ±SEM were analysed using Student's t test. Infusion of saline had no effect on BP or any renal functional parameter. ANG1–7 infusion in rats on the normal diet did not change BP, at 99±4mmHg, but urine flow, at 18.1±1.3μl/min/kg, and fractional sodium excretion (FENa), at 0.6±0.1, were increased by 24 and 25% (both P<0.05). In the low salt rats, ANG1–7 caused a greater response in FENa, of some 2–3 fold (P<0.05) whereas in the high salt rats, it was blunted, being only 60% of the response in normal rats. These findings demonstrate a dependency of the excretory responses to ANG1–7 on the endogenous levels of RAS.