Effect of beta-adrenergic receptor blockade on development of training-induced bradycardia in rats.
Metoprolol-treated and untreated rats were subjected to the same treadmill running program for 12 weeks. After training and withdrawal of metoprolol, the treated rats had a more pronounced bradycardia during submaximal exercise than non-treated rats, although they had a lower heart weight/body weight ratio. The intrinsic heart rate (IHR) was slightly but not significantly lower in trained than in untrained untreated animals. The IHR was not altered by a period of metoprolol treatment neither alone nor in combination with training. It is concluded that chronic cardioselective beta-blockade during training augments the training-induced bradycardia but may impair the development of cardiac hypertrophy. The training-induced bradycardia is thus not related to the degree of heart rate increase during exercise for its development.
D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000818:Animals; D006332:Cardiomegaly / Q000209:etiology; D005260:Female; D006339:Heart Rate / Q000187:drug effects*; D008790:Metoprolol / Q000494:pharmacology*; D009929:Organ Size / Q000187:drug effects; D010806:Physical Education and Training; D011412:Propanolamines / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains
D000319:Adrenergic beta-Antagonists; D011412:Propanolamines; D008790:Metoprolol