Effects of chronic beta-adrenergic blockade on hemodynamic and metabolic responses to endurance training

To study the influence of chronic propranolol therapy on hemodynamic and metabolic adaptations associated with endurance training, five dogs given 250 mg X d-1 propranolol therapy (P) and five control dogs (NP) were endurance trained for 7 wk using a continuously increasing treadmill workload. The P group was also evaluated pre- and post-training off the drug (P-OD) to separate drug and training effects. Training lowered mean heart rate score (HR) to a standardized multistage dog treadmill test in the NP and P-OD (P less than 0.05) and had no effect on the HR of the P group while on propranolol. At a fixed submaximal workload there were also slight reductions in cardiac output in the P group which were more pronounced (P less than 0.10) following training, and a corresponding increase in a-vDO2. Pre- and post-training metabolic studies were performed at rest, during a fixed submaximal workload, and following 30 min of recovery. During exercise, blood glucose levels were significantly lower in the P group both before and after training. While NP showed no significant change in high-density lipoprotein bound cholesterol after training, the P-OD group demonstrated a significant fall in high-density lipoprotein bound cholesterol after training (P less than 0.05). These data indicate that endurance exercise training done in the presence of chronic beta-adrenergic blockade produces training-induced hemodynamic adaptations to exercise, but beta-blockade inhibits the changes in serum lipids and lipoprotein fractions normally seen in response to an exercise conditioning program.