Double-blind comparison of the beta 1-selectivity of single doses of bisoprolol and atenolol.

The beta 1-adrenoceptor selectivity of bisoprolol (BPL) was investigated using the forearm circulation of eight healthy subjects. Each subject was studied twice, with at least 10 days in between each investigation. A brachial artery was cannulated for intra-arterial (i.a.) monitoring of blood pressure and for i.a. infusion of isoproterenol (ISO) and epinephrine (EPI). ISO was given in doses of 0.02-0.10-0.40 and 1.20 ng/kg/min, for 3 min per dose. After 20 min rest, EPI was infused in doses of 0.08 and 2.0 ng/kg/min for 6 min per dose. Subsequently, the subjects received an oral dose of either 20 mg BPL or 100 mg atenolol (ATL), and 2 h later, the ISO and EPI infusions were repeated. Forearm blood flow was measured by venous occlusion strain-gauge plethysmography. ISO produced a dose-dependent vasodilatation, whereas the response to EPI varied between individuals. After administration of BPL and ATL, the ISO dose-response curves were shifted to the right by 2.8 and 2.6 times, respectively (both p less than 0.01). Both beta-blockers influenced the vascular effect of EPI in the direction of vasoconstriction. However, this was only significant for ATL (p less than 0.05). From the latter observation it is concluded that BPL is slightly more beta 1-adrenoceptor-selective than ATL, using the forearm vascular bed.