[Effects of beta-adrenergic receptor blockade on hyperlactacidemia induced by exercise of different intensity]

The effects of beta-adrenergic blockade on the exercise-induced hyperlactatemia (Lap) have been studied in 31 adult male subjects [age: 25 +/- 1 years; body weight: 69 +/- 1 kg; VO2max: 54 +/- 1 ml O2.kg-1.min-1 (mean values +/- SEM)] randomly divided in 3 groups. All exercises were performed on a 10% inclined treadmill. In group 1 (n = 11), the subjects were walking during 20 minutes at 5 km.h-1 (55.6 +/- 1.4% VO2max). In group 2 (n = 10), they were running during 9 minutes at 8 km.h-1 (79.4 + 1.5% VO2max). The subjects of the third group (n = 10) were submitted to a 4 minutes run at 9.5 km.h-1 92 +/- 1.6% VO2max). These exercises were performed 1 hour after ingestion of a placebo or a single dose of 40 mg propranolol, in a double-blind randomized order. Blood samples were drawn at regular time intervals from an antecubital vein. Exercise tachycardia was reduced by about 20% (P less than 0.001) by propranolol in each group. Lap was significantly reduced by 15% by propranolol (P less than 0.005) at the lowest exercise intensity (55.6% VO2max), remained unchanged at 79.4% VO2max and was significantly enhanced by 16% during the recovery period following the run at 92% VO2max. These results clearly showed that the effects of acute beta-adrenergic blockade on Lap depend on exercise intensity.