Effects of converting-enzyme inhibitor on hemodynamic actions of ANP in renal hypertensive rats

Abstract

In the present study, we have evaluated whether the hemodynamic effects of atrial natriuretic peptide (ANP) infusion in two-kidney, one-clip (2K, 1C) hypertensive rats are mediated by inhibition of the renin-angiotensin system (RAS). Hemodynamic determinations were performed by thermodilution in conscious, chronically instrumented animals. ANP (1.5 micrograms.kg-1.min-1) and converting-enzyme (CE) inhibitor captopril (1 mg/kg plus 1 mg.kg-1.h-1), produced a similar fall of blood pressure through different hemodynamic mechanisms. ANP induced hypotension by decreasing cardiac index (CI; from 337.3 +/- 24.9 to 255.1 +/- 21.3 ml.min-1.kg-1, P less than 0.001), whereas a fall in total peripheral resistance (TPR) was observed during CE inhibition (from 0.568 +/- 0.02 to 0.488 +/- 0.02 mmHg.min.ml-1.kg, P less than 0.05). In addition, the ANP-induced decrease in CI was not significantly modified by previous CE inhibition. Furthermore, the decrease in TPR induced by CE inhibition did not change when CE inhibitor was administered during ANP treatment. The results of the present study indicate that the acute hemodynamic responses to ANP in 2K, 1C hypertensive rats are not mediated through antagonism of the vasoconstrictor actions of the RAS.