Dopamine receptor blockade improves pulmonary gas exchange but decreases exercise performance in healthy humans

Abstract

Pulmonary gas exchange, as evaluated by the alveolar-arterial oxygen difference (A-aDO2), is impaired during intense exercise, and has been correlated with recruitment of intrapulmonary arteriovenous anastomoses (IPAVA) as measured by agitated saline contrast echocardiography. Previous work has shown that dopamine (DA) recruits IPAVA and increases venous admixture (Q̇s/Q̇t) at rest. As circulating DA increases during exercise, we hypothesized that A-aDO2 and IPAVA recruitment would be decreased with DA receptor blockade. Twelve healthy males (age: 25 ± 6 years, V̇O2 max : 58.6 ± 6.5 ml kg(-1) min(-1) ) performed two incremental staged cycling exercise sessions after ingestion of either placebo or a DA receptor blocker (metoclopramide 20 mg). Arterial blood gas, cardiorespiratory and IPAVA recruitment (evaluated by agitated saline contrast echocardiography) data were obtained at rest and during exercise up to 85% of V̇O2 max . On different days, participants also completed incremental exercise tests and exercise tolerance (time-to-exhaustion (TTE) at 85% of V̇O2 max ) with or without dopamine blockade. Compared to placebo, DA blockade did not change O2 consumption, CO2 production, or respiratory exchange ratio at any intensity. At 85% V̇O2 max , DA blockade decreased A-aDO2, increased arterial O2 saturation and minute ventilation, but did not reduce IPAVA recruitment, suggesting that positive saline contrast is unrelated to A-aDO2. Compared to placebo, DA blockade decreased maximal cardiac output, V̇O2 max and TTE. Despite improving pulmonary gas exchange, blocking dopamine receptors appears to be detrimental to exercise performance. These findings suggest that endogenous dopamine is important to the normal cardiopulmonary response to exercise and is necessary for optimal high-intensity exercise performance.

© 2015 The Authors. The Journal of Physiology © 2015 The Physiological Society.

Figures

Figure 1

Mean ± SEM pulmonary gas exchange response to dopamine blockade during exercise A-a (middle) was significantly decreased with dopamine blockade at 85% of , *P < 0.05. was significantly increased with dopamine blockade at 70% and 85% of (n = 12, n = 10 at 85% of max).

Figure 2

Correlations between change in pulmonary gas exchange (A-a ), cardiac output and IPAVA score with dopamine blockadeA, relationship between individual changes in cardiac output and A-a with blockade at 85% of (R2 = 0.50, P = 0.02), n = 10. B, relationship between individual changes in IPAVA score and A-a with blockade at 85% of (R2 = 0.01, P = 0.58), n = 10. C, individual changes in cardiac output and IPAVA score with blockade at 85% of There was no statistically significant positive correlation (R2 = 0.04, P = 0.30), n = 10.

Figure 3

Mean (±SEM) ventilatory response to graded exercise with dopamine blockade was increased in blockade condition at 85% but decreased at 100% of , *P < 0.05. Blockade decreased , +P < 0.05 (n = 15).