Naloxone and the ventilatory response to exercise in mana

Summary

Endogenous opiate peptides are known to exert a depressant action on ventilation ($\dot V_E$), and their plasma levels have been shown to be elevated during a variety of exercise protocols. We investigated whether they might modulate the control of the hyperpnea of short-term constant-load (CLE) and incremental (IE) cycle-ergometer exercise. Four healthy subjects performed CLE tests at ca. 80% of the anaerobic threshold (θ_an) for 5 min following a period of unloaded pedaling, and IE tests (10 or 20 W min⁻¹) to the limit of tolerance. Normal saline (3 ml) or the opiate antagonist naloxone (1.2 mg in 3 ml) were administered intravenously prior to each test. Naloxone elicited no discernible effect on $\dot V_E$, alveolar gas tensions, or heart rate throughout the entire range of work rates; neither were θ_an nor the maximum work rate affected. It is concluded that, for short-term exercise ranging in intensity from moderate to severe, the role played by endogenous opiate peptides in the control of the exercise hyperpnea appears to be neglible in man.