Nitric Oxide Regulates Renin Release During Salt Depletion but Does Not Alter Angiotensin Responses in Normal Humans

NO Synthase Inhibition Increases Aldosterone in Humans

To test the hypothesis that NO influences aldosterone production in humans, we examined the effect of N G -nitro- l -arginine methyl ester ( l -NAME) on aldosterone concentrations in the presence and absence of the NO precursor l -arginine (3 g TID) and the angiotensin-converting enzyme inhibitor ramipril (10 mg QD). Ten normal subjects were given l -NAME (66 μg/kg per min for 30 minutes) or vehicle in random order on separate days during placebo and after randomized, double-blind treatment with l -arginine, ramipril, or l -arginine plus ramipril. Infusion of l -NAME significantly increased systolic blood pressure (all P <0.05) and decreased heart rate (all P ≤0.02) during all 4 treatment arms. After placebo pretreatment, serum aldosterone was significantly higher during l -NAME infusion than during vehicle (6.6±1.7 versus 3.3±0.5 ng/dL; P =0.045). Combined treatment with l -arginine plus ramipril abolished this effect. There was no effect of l -NAME on plasma renin activity (PRA; P =0.297) or angiotensin II concentrations ( P =0.537). However, there was a significant interactive effect of l -NAME and time on serum potassium ( P =0.039). There was a significant linear relationship between PRA and aldosterone concentration after vehicle infusion ([aldosterone]=3.9·PRA+1.9; r 2 =0.476; P =0.027) and l -NAME infusion ([aldosterone]=7.2·PRA+3.1; r 2 =0.457; P =0.032), and the intercepts of these lines were different ( P =0.029). There was a significant linear relationship between serum potassium and aldosterone during l -NAME ([aldosterone]=8.2 · [potassium]−28.9; r 2 =0.609; P =0.008) but not during vehicle ( P =0.313). These data suggest that endogenous NO modulates aldosterone synthesis in humans.

Spironolactone increases nitric oxide bioactivity, improves endothelial vasodilator dysfunction, and suppresses vascular angiotensin I/angiotensin II conversion in patients with chronic heart failure

BACKGROUND

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.

METHODS AND RESULTS

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.

CONCLUSIONS

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.