Effects of single doses of quinapril and atenolol on autonomic nervous function and exercise capacity in healthy volunteers

Abstract

The effects of single oral doses of the angiotensin converting enzyme (ACE) inhibitor quinapril (CI-906) 40 mg and the cardioselective beta-adrenoceptor blocker atenolol 100 mg on sympathetic and parasympathetic function and on exercise capacity have been studied in 8 healthy young men. The trial followed a double-blind, placebo controlled, randomized cross-over design, with at least one week between treatments. Blood pressure (BP) and heart rate (HR) at rest were slightly reduced by atenolol but were not affected by quinapril. Atenolol impaired the sympathetically mediated increases in HR and BP caused by standing, immersion of the hand into melting ice, the Valsalva manoeuvre and isometric forearm exercise. Quinapril did not influence those responses nor the vagally mediated bradycardia of the diving reflex. Atenolol, however, augmented the vagal bradycardia, presumably by sympathetic inhibition. In a dynamic bicycle ergometer test with a stepwise increasing work load, exercise performance was decreased by atenolol but not by quinapril. Inhibition of the renin-angiotensin system by quinapril was shown by a marked decrease in serum ACE activity and a several-fold increase in plasma renin activity (PRA). Atenolol produced a moderate reduction in PRA. Before or during exercise, plasma noradrenaline and adrenaline were not influenced by either drug. The results indicate that, unlike the atenolol-induced beta-adrenoceptor blockade, ACE inhibition by a single dose of quinapril had no clear effect on autonomic nervous function or exercise capacity.