Reduced norepinephrine response to dynamic exercise in human subjects during O2 breathing.

The purpose of this investigation was to study the influence of hyperoxia on catecholamine response to dynamic exercise. While breathing either 21 or 100% O2 seven subjects performed submaximal bicycle exercise. Arterial blood pressure was similar in both exercise experiments. The CO2 output was not influenced by 100% O2 breathing, but increments in plasma lactate concentration were reduced. The increases in plasma norepinephrine and epinephrine concentrations and heart rate were significantly lower during 100% O2 than during 21% O2 breathing. The results suggest that O2 plays an important role in the regulation of sympathetic nervous activity during dynamic exercise in humans.