Aldosterone as a Mediator in Cardiovascular Injury :

Endothelial cells produce a number of substances, collectively termed endothelium-derived relaxing factor (EDRF), that promote local relaxation of vascular smooth muscle. Although studies have demonstrated defects in endothelium-dependent vasodilation in animal models of hypertension, atherosclerosis, and heart failure, there are only limited data from human subjects because of the difficulty in obtaining fresh vascular segments. To address the hypothesis that endothelium-dependent vasodilation is attenuated in patients with heart failure, we measured forearm blood flow responses to the intra-arterial administration of methacholine, a known stimulus of EDRF release through muscarinic receptors. In 14 normal subjects, a dosage range of methacholine increased forearm blood flow by 5.26 +/- 0.63, 10.50 +/- 0.63, and 13.22 +/- 0.86 ml/min/100 ml forearm volume (FAV); these responses were 1.98 +/- 0.46, 5.48 +/- 0.79, and 8.50 +/- 1.53 ml/min/100 ml FAV in 14 patients with heart failure. When pooled over all doses, the responses were strikingly less in the patients with heart failure (5.32 +/- 0.31 versus 9.52 +/- 0.60 ml/min/100 ml FAV; p = 0.0003). In a second study, the average difference in forearm blood flow responses between patients with heart failure and normal subjects with methacholine was significantly greater than the average difference between the groups with nitroprusside (4.04 +/- 1.10 versus 2.20 +/- 0.71 ml/min/100 ml FAV; p = 0.04). The decreased methacholine responses in the patients with heart failure were not related to age (r = 0.39; p = NS) or etiology because there was no difference in the responses between patients with ischemic heart disease and those with idiopathic cardiomyopathy. These data suggest that endothelium-dependent vasodilation is attenuated in patients with heart failure. Although the mechanisms of the decreased endothelium-dependent responses in heart failure are not known, this impaired local vasodilation may contribute to abnormalities in vasoconstriction that are characteristic of heart failure.

The RALES study showed that spironolactone, added to conventional therapy for chronic heart failure, dramatically reduced mortality. We tested the hypothesis that this benefit was partially due to improvement in endothelial function and/or to amplified suppression of the vascular renin-angiotensin axis. We performed a randomized, placebo-controlled, double-blind crossover study on 10 patients with NYHA class II to III chronic heart failure on standard diuretic/ACE inhibitor therapy, comparing 50 mg/d spironolactone (1 month) versus placebo. Forearm vasculature endothelial function was assessed by bilateral forearm venous occlusion plethysmography using acetylcholine and N-monomethyl-L-arginine (L-NMMA), with sodium nitroprusside as a control vasodilator. Also, vascular ACE activity was assessed by use of angiotensin (Ang) I, with Ang II as a control vasoconstrictor. Spironolactone significantly increased the forearm blood flow response to acetylcholine (percentage change in forearm blood flow [mean+/-SEM], 177+/-29% versus 95+/-20%, spironolactone versus placebo; P<0.001), with an associated increase in vasoconstriction due to L-NMMA (-35+/-6% versus -18+/-4%; P<0.05). The Ang I response was also significantly reduced with spironolactone (P<0.05), with Ang II responses unaltered. Spironolactone improves endothelial dysfunction, increases NO bioactivity, and inhibits vascular Ang I/Ang II conversion in patients with heart failure, providing novel mechanisms for its beneficial effect on cardiovascular mortality.