Converting
enzyme inhibition of the renin-angiotensin system has proved a valuable therapeutic approach in patients with severe chronic
congestive heart failure. In the present study, a new long-acting converting
enzyme inhibitor (
enalapril) was evaluated with acute single dose testing (10, 20 or 40 mg) in nine patients with severe chronic
congestive heart failure. Four hours after administration, there was a significant reduction of systemic vascular resistance (-19%) and pulmonary wedge pressure (-19%); in addition, there were related increases of cardiac index (+16%) and
stroke index (+19%) (probability [p] less than or equal to 0.05 for all changes). This was associated with an increase of plasma
renin activity (9 +/- 3 to 35 +/- 11 ng/ml per hour) and a decrease of plasma
aldosterone (19 +/- 4 to 9 +/- 2 ng/100 ml) (p less than 0.02 for both). With long-term
therapy (1 month), there was improvement of exercise tolerance time and lessening of symptoms based on the New York Heart Association classification. Hemodynamic improvement was maintained in most, but not all, patients. There was no
orthostatic hypotension during head-up tilt and hemodynamic values in the upright position were associated with normalization of intracardiac pressures. Long-term converting
enzyme inhibition was indicated by a persistent increase of plasma
renin activity (16 +/- 2 ng/ml per hour) and a decrease of plasma
aldosterone (8 +/- 3 ng/100 ml). In addition, relative
angiotensin II receptor occupancy was decreased as judged by the pharmacodynamic response to infusion of the
angiotensin II analog
saralasin. In conclusion, the long-acting converting
enzyme inhibitor,
enalapril, was effective in patients with chronic
congestive heart failure; however, additional studies will be necessary to further delineate the optimal dose range and identify those patients who are most likely to respond to the
drug.