INFLUENCE OF PROPRANOLOL AND ACEBUTOLOL ON ISOPRENALINE-INDUCED CHANGES IN HEART-RATE AND PERIPHERAL-BLOOD FLOW IN MAN

The variations were studied of the effects of isoprenaline hydrochloride on heart rate (.beta.1) and on peripheral blood flow of the upper extremity (.beta.2), determined by plethysmography, in a group of 5 men with a mean age of 31 .+-. 3 yr. The trial was conducted on a single-blind cross-over basis, each subject being infused over 30 min with propranolol (30 .mu.g/kg), acebutolol (150 .mu.g/kg) or a placebo (isotonic glucose solution) with at least an 8 day interval between each administration. At the end of the infusion they received isoprenaline (0.01-0.075 .mu.g/kg, in logarithmic progression) every 15 min, for 1 h. The doses of isoprenaline were injected randomly using a latin square design. The peripheral flow, assessed by the curve of the initial part of the plethysmogram for the first 10 s, increased with the dose of isoprenaline in the placebo series (Tg.alpha. [slope of the 1st part of the curve] = 219.9 log d + 583.4; P < 0.01), did not increase in the propranolol series and increased with the dose in the acebutolol series (Tg.alpha. = 221.5 log d + 567.7; P < 0.01); the variations in flow with isoprenaline after placebo and after acebutolol, did not differ significantly. The heart rate increased with the dose of isoprenaline in the placebo series (+ 55%) but tachycardia was inhibited by propranolol and acebutolol. Under the experimental conditions of this trial, propranolol inhibited .beta.1 and .beta.2 receptors at the same time; acebutolol inhibited only .beta.1 receptors.