Physiological responses to angiotensin II infusion during chronic angiotensin converting enzyme inhibition in dogs on normal, low and high sodium intake.

The function of the renin-angiotensin system (RAS) is influenced by changes in sodium balance and angiotensin II (ANG II) levels. In previous studies it has been difficult to assess the physiological effects on blood pressure homeostasis of different rates of ANG II infusion and of different levels of sodium in the diet. The present study examined the quantitative effects of ANG II in conscious dogs on low, normal and high sodium intake with the endogenous RAS blocked by continuous intravenous infusion of enalapril [MK-421,N-(1(S)-carbethoxy-3-phenyl propyl)-L-alanyl-L-proline maleate]. Conscious dogs on three different sodium diets, low, normal and high (5, 30 and 250 mmol/day), were infused continuously with enalapril, 4 mg/kg/day, and studied with superinfused ANG II at rates of 0, 1, 3, 6 and 12 ng/kg/min, each period lasting 1 week. Converting enzyme inhibitor (CEI) decreased mean arterial blood pressure (MAP) equally in dogs on low and normal sodium intake by 20 mmHg, but did not have a significant effect in dogs on high sodium intake. The initial infusion of ANG II at the lowest rate had a pronounced effect on MAP in dogs on normal and high sodium, but had no effect in the sodium depleted dogs. However, at the higher rates of infusion, the angiotensin increased the pressure equally at all levels of sodium intake.(ABSTRACT TRUNCATED AT 250 WORDS)