Training-induced bradycardia in rats on cardioselective and non-selective beta receptor blockade

After 12 weeks of treadmill training 10 Sprague-Dawley rats got a significant bradycardia at exercise of submaximal intensities compared to 10 sedentary controls. Twenty rats were subjected to the same training programme during oral treatment with the cardioselective beta receptor blocker metroprolol (10 rats) or propranolol (non-selective, 10 rats). Both treated groups developed a training-induced bradycardia at submaximal exercise of the same magnitude as the trained untreated group. It is concluded that the stimulation of cardiac beta receptors or the heart rate increase during exercise are not critical for the development of training bradycardia and that in this respect the effects of cardioselective and non-selective beta receptor blockade were not significantly different.