Abstract

The effects of different dosages of the beta1-adrenoceptor blocker metoprolol and of acute and chronic administration of this beta-blocker during physical exercise were compared in healthy normotensive subjects. Placebo, 0.15 mg/kg, and 0.30 mg/kg metoprolol were administered intravenously 10 min before a progressive bicycle ergometer test up to exhaustion. Thereafter, subjects were treated for 4 weeks with placebo or slow-release metoprolol (1 x 200 mg/day). At the end of each 4th week of treatment, a maximal exercise test was performed. After the i.v. dose, the heart rate during maximal exercise was reduced from 189 +/- 2 to 155 +/- 2 bts/min. This reduction was significantly smaller than that after the high i.v. dose (177 +/- 3 to 137 +/- 4 bts/min) and during chronic treatment (176 +/- 3 to 132 +/- 2 bts/min. After the low i.v. dose, the heart rate was the only variable affected. After the high i.v. dose, the heart rate, exercise time, maximal oxygen uptake, and plasma glucose and free fatty acid concentration during maximal exercise were reduced, and maximal lactate concentration tended to be lower. During submaximal exercise, no significant differences between placebo or beta-blocker administration were found, except for heart rate, which was reduced after beta-blockade. No significant difference between the effects of i.v. administration of 0.30 mg/kg and of a 4-week chronic oral treatment with metoprolol was found. Verf.-Referat