1. Recent animal evidence suggests that aldosterone, like angiotensin II, may possess detrimental autonomic modulating properties. Aldosterone has been shown to impair the baroreflex response in animal models. This study is designed to test the hypothesis that aldosterone directly attenuates the baroreflex in vivo in man.

2. Fourteen healthy male volunteers [mean age (S.D.) 25 (9) years] received intravenous d-aldosterone (12 pmol·min-1·kg-1) and 5% dextrose (vehicle) in a double-blind crossover fashion, co-infused with incremental doses of intravenous phenylephrine and sodium nitroprusside. Aldosterone had no significant effect on resting blood pressure, heart rate or baroreflex response to sodium nitroprusside. However, reflex responses to phenylephrine were impaired with aldosterone (P< 0.01) while blood pressure responses were unaltered. Baroreflex sensitivity was significantly blunted in the aldosterone group [8.36±2.19 versus 10.12±2.27 ms/mmHg; P< 0.04].

3. This study confirms previous observations from animal models that aldosterone impairs the baroreflex response. High aldosterone levels may contribute to the baroreflex dysfunction in cardiovascular diseases such as hypertension and heart failure.

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