Effect of dopamine on ventilatory response to incremental exercise in man.

We investigated whether dopamine, an inhibitory neuromodulator in the carotid body, would alter the ventilatory response typically associated with metabolic (lactic) acidosis during exercise. Six subjects performed incremental cycle ergometer exercise to exhaustion during infusions of dopamine (3 micrograms.kg-1.min-1) or saline. Ventilation and pulmonary gas exchange were computed breath-by-breath; arterialized venous blood was collected every 90 sec for measurement of lactate, potassium and blood gases. The resting ventilatory response to an isocapnic step decrease in end-tidal PO2 to 50 Torr was used as an index of carotid body drive. Dopamine diminished the hypoxic ventilatory response but had no effect on the ventilatory response during exercise. Peak lactate, potassium, and ventilation were unaffected by dopamine, and the degree of respiratory compensation for the metabolic acidosis was the same as in control experiments. Therefore, either the carotid bodies respond differently to hypoxia than to acute metabolic acidosis and/or hyperkalemia during heavy exercise, or the carotid bodies are not the sole mediators of hyperventilation above the lactate threshold.