Effects of acute beta-adrenergic blockade on blood and muscle lactate concentration during submaximal exercise.

Heart rate and blood and muscle lactate concentrations were studied in 15 physically active males during submaximal exercise before and after oral administration of 80 mg propranolol (Inderal). First, a cycle exercise protocol, with a stepwise increased exercise intensity (30 W every 4 min until voluntary exhaustion) was performed before and after beta-blockade. Blood samples for lactate determination were obtained before each exercise intensity increase. In a second set of experiments, the procedure was repeated before and after beta-blockade, but exercise was terminated at the exercise corresponding to a blood lactate concentration of 4 mmol X l-1 l-1, as determined beforehand without beta-blockade (i.e., the same absolute work load was compared with and without beta-blockade), and a muscle biopsy was taken from m. vastus lateralis for subsequent lactate analyses. Following beta-blockade at low and high work loads, the heart rate decreased similarly by 22%-26%. Blood lactate concentration was unchanged at exercise intensities up to 150 W. At higher exercise intensities (180-240 W), a significant increase (P less than 0.05 - P less than 0.01) in blood lactate concentration occurred after beta-blockade. Muscle lactate concentration was unaffected by beta-blockade at a work load (130-230 W) where blood lactate was higher with than without blockade. Assuming a reduced blood flow to the exercising muscle, there are reasons to speculate that lactate production was diminished following beta-blockade even though blood lactate increased probably as a result of reduced lactate uptake by other organs.