Correlation between angiotensin converting enzyme inhibition and the acute hypotensive response to MK 421 in...

1. The acute hormonal and hypotensive effects of MK 421 (10 mg p.o.) were assessed by a double-blind randomized trial in twelve subjects with essential hypertension. The study was performed during a normal and low salt intake. 2. Plasma angiotensin converting enzyme (ACE) activity was maximally inhibited by 57 (s.e.m. = 4)% of control activity at 4-8 h. Plasma ACE was still depressed at 24 h by 10% of control activity but had returned to normal by 32 h. 3. Sodium depletion did not alter basal plasma ACE activity, nor change the degree of inhibition of MK 421. 4. Plasma angiotensin II was depressed during ACE inhibition, but no change in circulating bradykinin was detected. Reciprocal rises occurred in plasma renin and angiotensin I levels with a time course similar to ACE inhibition. 5. All subjects showed a fall in their blood pressure, maximal between 6-8 h. Mean arterial pressure fell 12 (s.e.m. = 5) mmHg on the normal sale intake and 16 (s.e.m. = 3) mmHg on the low salt diet, at 8 h. 6. Blood pressure and angiotensin converting enzyme activity changes were significantly correlated (r = 0.86, n = 12).