Can the biochemical responses to a beta 2-adrenoceptor stimulant be used to assess the selectivity of beta-adrenoceptor blockers?

The extent to which beta-adrenoceptor blocking drugs counteract the biochemical responses to an infusion of terbutaline, a beta 2-adrenoceptor agonist, has been investigated. In this study the beta 1-selectivity of metoprolol was compared with the non-selective beta-adrenoceptor blocker propranolol. The hypokalaemia produced by an infusion of terbutaline was reduced by low dose (50 mg) and high dose (200 mg) metoprolol and by low dose (40 mg) and high dose (160 mg) propranolol. The effects of propranolol on terbutaline induced hypokalaemia were more marked than those of metoprolol at both low dose (P = 0.01) and high dose (P = 0.05). Furthermore low dose metoprolol had less effect than high dose metoprolol (P = 0.05). The serum potassium appeared to rise slightly after propranolol. Low and high doses of both beta-adrenoceptor blockers markedly reduced the terbutaline-induced hyperglycaemia, but the differences between the two drugs were not statistically significant.