[Effect of selective and non-selective adrenoceptor blockade during physical work on energy metabolism and sympatho-adrenergic system (author's transl)].
The influence of an acute beta-adrenoceptor blockade on work capacity, oxygen intake, plasma catecholamines, and on energy metabolism was investigated in 9 healthy subjects during graduated ergometric exercise. The examinations were carried out after p.o. administration of 10 mg bunitrolol (BU), methypranol (ME) and placebo in random sequence. The exercise capacity shows a 15% decrease after both beta-blockers; heart rate shows a maximum 20% (BU) and 25% (ME) reduction, respectively. On account of the greater sympathetic intrinsic activity BU does not influence the resting heart rate, in contrast to ME (-8%; p greater than 0.05). BU leads to a decrease of the catecholamine levels (with low sympathetic tone), which is assumed to be caused by an effect on presynaptic receptors. At the same submaximum exercise levels plasma catecholamines are higher after BU and ME than after placebo; however, the maximum levels are not reached with placebo. In relation to the relative oxygen intake, which is inhibited by 4-6% by BU and ME (p greater than 0.05), the differences of the catecholamines decrease in performance caused by beta-blockade. BU does not show an influence on lactate, glucose, free fatty acids, and glycerin and thus represents a more selective blockade. ME inhibits lipolysis (measured by the glycerin level) by a maximum of approx. 50%. Lactate level increase is approx. 30% lower with ME. Glucose level decrease is approx. 20% higher with ME than with placebo.