The influence of sodium intake on physiological responses to angiotensin II in conscious dogs.

The renin-angiotensin system (RAS) is suppressed either by high sodium intake or by high levels of angiotensin II (A II). Therefore in prior studies it has been difficult to sort out the influence on the cardiovascular homeostases of different levels of A II and different levels of sodium in the diet respectively. The present study examines the quantitative effects of A II on mean arterial blood pressure (MABP), electrolyte excretion and hormone secretion in conscious dogs on low, normal and high sodium intake with the endogenous RAS blocked with continuous intravenous infusion of enalapril (MK-421). Fourteen dogs on three different Na diets, low, normal and high (5, 30 and 250 mmol/day), were infused continuously with enalapril, 4 mg/kg/day and studied with superinfused A II at rates of 0, 1, 3, 6 and 12 ng/kg/min., each period lasting one week. Converting enzyme inhibitor (CEI) decreased MABP equally in dogs on low and normal sodium intake to about 80% of control, but did not have a significant effect in dogs on high sodium intake. The initial infusion of angiotensin II at the lowest rate had a pronounced effect on MABP in the normal and high sodium states, but had no effect on MABP in the sodium depleted dogs. However, at the higher rates of infusion, the angiotensin II increased the pressure to a similar degree at all levels of sodium intake.(ABSTRACT TRUNCATED AT 250 WORDS)