PLASMA-CATECHOLAMINE AND VENTILATORY RESPONSES TO CYCLING AFTER PROPRANOLOL TREATMENT

The purpose of the present study was to examine the relationship between minute ventilation (V-E) and plasma concentrations of epinephrine (EPI) and norepinephrine (NE) during incremental cycling (20 W . 2 min(-1)) performed under conditions of beta-adrenergic blockade (80 mg of propranolol) and placebo in six untrained male subjects. No significant differences existed between treatments in O-2 uptake, CO2 output, blood lactate, pH, or V-E during the submaximal work stages of incremental exercise common to both treatments (20-220 W). During exercise with beta-blockade, EPI, and NE concentrations were both significantly elevated compared with control levels at every submaximal work stage. Significant positive correlations between V-E and plasma levels of EPI and NE were found during both beta-blockade (r = 0.98 and 1.00) and control conditions (r = 0.98 and 0.96). Although the high correlations were unchanged during exercise with beta-blockade, the slopes of the regression lines for the V-E-EPI and the V-E-NE relationships were both significantly reduced compared with control conditions. beta-blockade resulted in elevated plasma levels of both EPI and NE compared with control conditions without causing a change in exercise V-E. These findings suggest that catecholamines may not be important substances in regulating breathing during exercise.