Evaluation of in vivo partial beta 1/beta 2-agonist activity: a dose-ranging study with carteolol

1. The aims of this study were to investigate the partial agonist profile of carteolol and evaluate methodology for differentiating relative beta 1 and beta 2 partial agonist activity (PAA) in vivo. 2. Eight normal subjects received single oral doses of carteolol 10 mg, 30 mg and 60 mg; nadolol 40 mg; pindolol 30 mg and placebo, given in a single-blind, randomised crossover design. 3. beta 1-PAA was demonstrated with carteolol by dose-related increases in resting heart rate and systolic blood pressure, and a plateau in the dose-response curve for attenuation of exercise tachycardia. beta 2-PAA with carteolol was evidenced by a dose-related increase in resting finger tremor and progressive attenuation of exercise-induced hyperkalaemia. beta 2-adrenoceptor antagonism was shown by attenuation of terbutaline induced hypokalaemic, chronotropic and finger tremor responses. 4. Carteolol behaved as a non-selective beta-adrenoceptor antagonist with both beta 1 and beta 2-PAA components. In the standard clinical dose range of 10-30 mg, its in vivo PAA effects were relatively beta 1-selective. Thus at low doses, there appeared to be a dissociation between selectivity of antagonist and partial agonist activity. 5. Attenuation of exercise hyperkalaemia appears to be a novel and sensitive method for the evaluation of beta 2-PAA in vivo.