Effects of acute and chronic metoprolol administration during submaximal and maximal exercise

The effects of different dosages of the beta 1-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. Heart rate, ventilation, oxygen consumption, and plasma concentrations of free fatty acids, glucose, and lactate were determined at rest and during exercise. After the low (0.15 mg/kg) i.v. dose, the heart rate during maximal exercise was reduced from 189 +/- 2 to 155 +/- 2 bts/min (P less than 0.001). This reduction was significantly smaller than that after the high (0.30 mg/kg) i.v. dose (177 +/- 3 to 137 +/- 4 bts/min, P less than 0.001) and during chronic treatment (176 +/- 3 to 132 +/- 2 bts/min, P less than 0.001). The difference between the high i.v. dose and chronic treatment was not significant. 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.(ABSTRACT TRUNCATED AT 250 WORDS)