Effect of acute administration of propranolol and atenolol on baroreflex function in normal man

The acute administration of the beta-adrenoceptor antagonists propranolol (80 mg) and atenolol (50 mg) on baroreflex function were investigated in healthy volunteers. Two h after administration both propranolol and atenolol significantly prolonged the supine R-R interval (1126, 1128 ms respectively) compared to placebo (1012 ms); systolic arterial pressure also fell (102.9, 102.0 mm Hg respectively) compared to placebo (112.6 mm Hg). Baroreflex function, assessed using glyceryl trinitrate to deactivate the baroreceptors was unchanged by these drugs compared to placebo. Baroreflex sensitivity (slope of the linear regression line relating R-R interval to systolic blood pressure) using phenylephrine to activate the baroreceptors, was also unchanged (17.2, 17.9 ms/mm Hg respectively) compared to placebo (19.9 ms/mm Hg). However both regression lines were shifted (p less than 0.05) to the left compared to placebo.