Effects of propranolol and exercise on cardiac dynamics and organ blood flow distribution in dogs

The additive effects of propranolol and exercise on peripheral blood flow distribution were studied in conscious dogs. During treadmill exercise (8-10 km/h and 0% grade for 15 min.) cardiac performance increased significantly in parallel with myocardial and muscular blood flow (greater than 100%). Blood perfusion to liver and spleen decreased significantly (30% and 34%) while blood flow to other organs was unaltered. Under resting conditions propranolol only modified blood flow to liver and spleen (-50% and -38%). During exercise after propranolol a limited augmentation in cardiac performance and in myocardial and muscular blood flow was observed; splanchnic blood flow which was most affected by propranolol at rest did not further decrease during exercise after propranolol. The present observations demonstrate that propranolol, despite minor haemodynamic modifications, induces significant alterations in blood flow to splanchnic organs. The influence of beta-adrenoreceptor blockade was even more evident under conditions of augmented sympathetic activity as reflected by a significant limitation of increase in cardiac performance, myocardial and muscular blood flow and by a sustained redistribution of splanchnic blood flow during exercise after propranolol.