The Effect of Dopamine on Pulmonary Diffusing Capacity and Capillary Blood Volume Responses to Exercise

  • Author / Creator
    Michaelchuk, Wade W
  • Pulmonary diffusing capacity increases during exercise to meet the increasing oxygen (O2) demand of the body. Expansion of pulmonary capillary blood volume (Vc) and diffusing membrane capacity (Dm) are important contributors to the increased diffusing capacity observed during upright cycle exercise. Recent studies have shown that circulating dopamine, a pulmonary vascular vasodilator, may play an active role in Vc regulation through changes in pulmonary vascular tone. Subsequently, these changes may be responsible for the reduction in exercise tolerance seen during heavy exercise with dopamine receptor blockade. Thus, the purpose of this study was to examine the effect of exogenous dopamine as well as dopamine receptor-2 (D2-receptor) blockade on pulmonary diffusing capacity (DLCO), Vc, and Dm at baseline and during upright cycle exercise. Additionally, the effect of dopamine and D2-reeceptor blockade on time-to-exhaustion during heavy cycle exercise at 85% of VO2peak was assessed. Based on previous work, it was hypothesized that dopamine would increase DLCO, Vc, Dm, and exercise tolerance, while D2-receptor blockade would decrease DLCO, Vc, Dm, and exercise tolerance. Hemoglobin adjusted DLCO, Vc, and Dm were determined at rest and during exercise in 14 young, healthy, recreationally active, non-smoking subjects (VO2peak 45.8 ± 6.6 mL ∙ kg-1 ∙ min-1) using the Roughton and Forster (1957) multiple FIO2-DLCO method. Dependent variables were evaluated at baseline, as well as cycling at 60 and 85% of VO2peak under the following randomly assigned conditions: 1) intravenous saline and a placebo pill, 2) intravenous dopamine (2 µg ∙ kg-1 ∙ min-1) and a placebo pill, 3) intravenous saline and an oral D2-receptor antagonist (20 mg metoclopramide). The effect of dopamine on cycle time-to-exhaustion at 85% of VO2peak was also examined in the three conditions. Exogenous dopamine and dopamine blockade had no effect on DLCO, Vc, and Dm at baseline or at any intensity of exercise. Blockade reduced time-to-exhaustion (blockade, 259 ± 120 seconds; placebo, 367 ± 198 seconds; P<0.05), but intravenous dopamine did not improve time-to-exhaustion. Overall, dopamine does not appear to be important in the regulation of DLCO, Vc, and Dm at rest or during exercise. While endogenous dopamine appears to be important for the maintenance of time-to-exhaustion, providing exogenous dopamine does not appear to enhance exercise tolerance.

  • Subjects / Keywords
  • Graduation date
    Fall 2017
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.