Effets du blocage des récepteurs bêta-adrénergiques sur l'hyperlactacidémie induite par des exercices d'intensités différentes

Abstract

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; ±O₂max: 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% ±O₂max). In group 2 (n = 10), they were running during 9 minutes at 8 km.h⁻¹ (79.4 + 1.5% ±O₂max). The subjects of the third group (n= 10) were submitted to a 4 minutes run at 9,5 km.h⁻¹ 92 ± 1.6% ±O₂max). 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 < 0.001) by propranolol in each group. Lap was significantly reduced by 15% by propranolol (P < 0.005) at the lowest exercise intensity (55.6% O₂max), remained unchanged at 79.4% O₂max and was significantly enhanced by 16% during the recovery period following the run at 92% O₂max.

These results clearly showed that the effects of acute beta-adrenergic blockade on Lap depend on exersise intensity.