Abnormal renal vasodilation to an amino acid infusion in congestive heart failure: Normalization by enalapril

In congestive heart failure (CHF), the neurohormonal mechanisms that cause renal vasoconstriction, particularly those depending on the renin-angiotens in system, could interfere with renal vasodilating mechanisms. To elucidate this issue, we studied the kidney response to an amino acid infusion (know n to cause renal vasodilation in healthy individuals) in eight patients wit h CHF. We found that the amino acid infusion (0.7 mL/kg/h of a 10% solution ) elicited no renal hemodynamic response, in marked contrast to healthy sub jects, We next hypothesized that the renin-angiotensin system (known to be activated in heart failure) has a role in the lack of response to the amino acid infusion. To test this hypothesis, we repeated the study after two 5- mg doses of enalapril, an inhibitor of the angiotensin-converting enzyme, a dministered 12 hours apart. After enalapril treatment, the amino acid infus ion caused a 45% increase in mean renal blood flow (RBF) from 383 +/- 55 to 557 +/- 51 mL/min at the fifth hour (P < 0.05), This normalization of the renal response to the amino acid infusion occurred without changes in cardi ac output or in systemic vascular resistance. Hence, the renal fraction of the cardiac output increased during the amino acid infusion. The recovery o f the renal vascular response was not accompanied by an increase in glomeru lar filtration rate (GFR; filtration fraction decreased), suggesting a pred ominant efferent arteriole dilatation, Our study shows that, in heart failu re, the kidney loses its ability to increase RBF in response to an amino ac id load. This lack of renal vascular response can be restored by inhibiting the renin-angiotensin system and is unrelated to changes in systemic hemod ynamics. (C) 1999 by the National Kidney Foundation, Inc.