The effect of acute and chronic captopril therapy on baroreflex function in man

1. The effect of captopril 12.5 mg three times daily for 14 days on baroreflex sensitivity was investigated in six normotensive salt-replete male subjects. 2. Baroreflex sensitivity [delta R-R interval ms/mmHg systolic blood pressure (SBP)] was assessed following decreases and increases in SBP with glyceryl trinitrate and phenylephrine respectively and during Valsalva's manoeuvre. 3. Captopril had no effect on supine intra-arterial SBP or R-R interval on days 1 and 15 compared with placebo. However decreases (P less than 0.05) which occurred in plasma angiotensin II on day 1 (12.3 +/- 0.8 to 7.6 +/- 1.5 pg ml-1) and on day 15 (14.5 +/- 1.5 to 6.3 +/- 0.5 pg ml-1) and increases (P less than 0.02) in plasma renin activity on day 1 (1.2 +/- 0.7 to 4.8 +/- 0.8 ng A I ml-1 h-1) and on day 15 (1.1 +/- 0.2 to 5.4 +/- 0.9 ng A I ml-1 h-1) compared with placebo, indicated angiotensin-converting enzyme inhibition. 4. Baroreflex sensitivity was unchanged by captopril on day 1 and day 15 compared with placebo following the use of glyceryl trinitrate and phenylephrine to deactivate and activate respectively the baroreceptors, and during the strain and release phases of Valsalva's manoeuvre.