Long-term captopril therapy: evolving hemodynamic effects

Nine patients with resistant hypertension received captopril for 12 months. Five received captopril alone, four required additional therapy. In the former, mean blood pressure fell from 109 +/- 4.2 mm Hg to 84 +/- 7.5 mm Hg (P less than 0.025) after seven days. A rise to 101 +/- 19 mm Hg was noted at six and 12 months. Total peripheral resistance fell at seven days but returned to levels above control at six and 12 months. Cardiac index was 3.21 +/- 0.55 liters/min/m2 before treatment, 3.27 +/- 0.56 liters/min/m2 at seven days, and 2.17 +/- 4.0 liters/min/m2 (P less than 0.025) at 12 months. However, forearm blood flow rose from subnormal levels during the 12 months of observation, suggesting a persistent effect on the arterioles of the extremities. Plasma converting enzyme activity was significantly reduced at seven days but was above control levels at six and 12 months. However, plasma renin activity remained elevated, and plasma aldosterone concentration was significantly reduced. The fall in mean blood pressure was not related to the change in plasma converting enzyme activity in patients receiving captopril alone (five patients) or with diuretic (two patients). In the presence of beta-adrenergic blockade and volume depletion (two patients), changes in mean blood pressure appeared to be related to changes in converting enzyme activity. The data suggest that patients with essential hypertension whose blood pressure was not adequately controlled by previous medications may initially respond to captopril with a fall in blood pressure and total peripheral resistance. However, in certain individuals, these effects diminish with time despite addition of diuretics and beta-adrenergic receptor blocking agents.