The effect of dopamine on pulmonary diffusing capacity and capillary blood volume responses to exercise in young...

What is the Central question? Does dopamine, a pulmonary vascular vasodilator, contribute to the regulation of pulmonary diffusing capacity and capillary blood volume responses to exercise and exercise tolerance? What are the main findings and their importance? Dopamine appears not to be important for regulating pulmonary diffusing capacity or pulmonary capillary blood volume during exercise in healthy participants. Dopamine blockade trials demonstrated that endogenous dopamine is important for maintaining exercise tolerance; however, exogenous dopamine does not improve exercise tolerance.

Pulmonary capillary blood volume (V_c ) and diffusing membrane capacity (D_m ) expansion are important contributors to the increased pulmonary diffusing capacity (DL_CO ) observed during upright exercise. Dopamine is a pulmonary vascular vasodilator, and recent studies suggest that it may play a role in V_c regulation through changes in pulmonary vascular tone. The purpose of this study was to examine the effect of exogenous dopamine and dopamine receptor-2 (D₂ -receptor) blockade on DL_CO , V_c and D_m at baseline and during cycle exercise, as well as time-to-exhaustion at 85% of $$ . We hypothesized that dopamine would increase DL_CO , V_c , D_m and time-to-exhaustion, while D₂ -receptor blockade would have the opposite effect. We recruited 14 young, healthy, recreationally active subjects ( $$ 45.8 ± 6.6 ml kg^-1  min^-1 ). DL_CO , V_c and D_m were determined at baseline and during exercise at 60% and 85% of $$ under the following randomly assigned and double blinded conditions: (1) intravenous saline and placebo pill, (2) intravenous dopamine (2 µg kg^-1  min^-1 ) and placebo pill, and (3) intravenous saline and D₂ -receptor antagonist (20 mg oral metoclopramide). Exogenous dopamine and dopamine blockade had no effect on DL_CO , V_c and D_m responses at baseline or during exercise. Dopamine blockade reduced time-to-exhaustion by 47% (P = 0.04), but intravenous dopamine did not improve time-to-exhaustion. While dopamine modulation did not affect DL_CO , V_c or D_m , the reduction in time-to-exhaustion with D₂ -receptor blockade suggests that endogenous dopamine is important for exercise tolerance.