The direct renal tubular effect of angiotensin II in chicken

Taking advantage of the particular renal vascular arrangement in cocks, angiotensin II was injected (0.12-0.96 microgram/min) into the portal system of one kidney in order to increase the angiotensin II concentration in the physiological nanomolar range at the level of the renal tubules. Angiotensin II induced an increase in blood pressure of 5% and a bilateral rise in glomerular filtration rate and effective renal plasma flow of 28 and 22%, respectively. The urine volume increased five times on the infused side and three times on the control side. The Na+ excretion increased 14 times on the infused side and only seven times on the control side. During angiotensin infusion, the fractional water excretion was 4.9% on the infused side and 2.9% on the control side versus 1.1 and 1.2% during the control period. For the fractional Na+ excretion, the respective values were 2 and 1.2% versus 0.2 and 0.2% during the control period. The differences between the two kidneys demonstrate the direct tubular action of angiotensin II, inhibiting the tubular Na+ and water reabsorption at physiological nanomolar concentrations. Angiotensin seems thus to play an important intrarenal role.