Effect of aerobic conditioning on the peripheral circulation during chronic beta-adrenergic blockade

The relation of peripheral circulatory adjustments to exercise training during long-term beta-adrenergic blockade has not been investigated. In 12 healthy men aged 22 to 34 years, blood flow in the calf was evaluated with submaximal exercise before and after a 6 week aerobic conditioning program. During conditioning, six subjects received no drug and six received propranolol, 80 to 120 mg/day in divided doses. Treated and control subjects were studied on entry and at the conclusion of a conditioning program, 72 hours after drug withdrawal in subjects given propranolol. The training was intensive and equivalent in both groups. Control subjects increased maximal oxygen uptake from 47.5 ± 1.1 to 51.4 ± 0.4 ml/kg per min (p < 0.05), whereas those on propranolol did not improve. Immediately after exercise, blood flow in the calf was measured with strain gauge plethysmography after 3 minutes of supine exertion on a cycle ergometer. In control subjects, flow decreased from 15.7 ± 1.6 to 14.0 ± 1.4 ml/100 ml per min at 300 kg-m/min of exertion (p < 0.05) and from 26.5 ± 3.8 to 21.8 ± 2.3 ml/100 ml per min at 700 kg-m/min (p < 0.05). Vascular resistance was unchanged in these subjects at 300 kg-m/min (6.1 ± 0.8 to 6.7 ± 1.0 pru) (p = NS), but increased at 700 kg-m/min (4.2 ± 0.8 to 4.8 ± 0.7 pru) (p < 0.05). In subjects given propranolol, no change in flow or resistance occurred after training at either work load. It is concluded that the decrease in blood flow and increase in vascular resistance during submaximal exercise after conditioning in control subjects indicates an improved metabolic environment in trained skeletal muscle. Propranolol prevented this response, suggesting that the peripheral circulatory and metabolic adaptations to conditioning may not have occurred.