Cardiac and vascular beta-adrenoceptor-mediated responses before and during treatment with bisoprolol or atenolol.

The degree of cardiac and vascular beta-adrenoceptor blockade of bisoprolol and atenolol was determined by the chronotropic dose 25 (CD25) of isoproterenol (the dose of an intravenous isoproterenol bolus required to increase resting heart rate by 25 beats/min) and by the increase in forearm blood flow (venous occlusion plethysmography) to intrabrachial artery infusions of increasing doses of isoproterenol (0.12, 1.2, 4, 12, and 20 ng/min/100 ml forearm tissue). Measurements were taken following placebo and after one week's treatment with atenolol or bisoprolol under double-blind conditions using a within-patient crossover design. Two patients received 10 mg bisoprolol and 50 mg atenolol daily, and three patients 20 and 100 mg daily, respectively. Both beta-blockers produced a similar fall in blood pressure, heart rate, and plasma renin activity. While CD25 of isoproterenol was comparable for both drugs, forearm blood flow to intra-arterial infusion of isoproterenol increased to a greater extent following bisoprolol (20 mg) than during atenolol (100 mg) treatment. Equieffective cardiac beta-blockade with bisoprolol and atenolol was associated with a lesser degree of vascular beta-adrenoceptor blockade during treatment with the more cardioselective beta-blocker bisoprolol.