Plasma catecholamine and ventilatory responses to cycling after propranolol treatment

The purpose of the present study was to examine the relationship between minute ventilation (VE) 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 O2 uptake, CO2 output, blood lactate, pH, or VE 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 VE 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 VE-EPI and the VE-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 VE. These findings suggest that catecholamines may not be important substances in regulating breathing during exercise.