Effect of dopamine on local segment work and O2 consumption in collateral-dependent myocardium

To test the hypothesis that dopamine-stimulated work and myocardial O2 consumption (MVO2) in collateral-dependent myocardium would be reduced, Ameroid constrictors were implanted around the circumflex coronary artery (CFX) in nine dogs. Four weeks later, in an anesthetized open-chest preparation, segment length (ultrasonic dimension gauge) and force (miniature force transducer) were measured in myocardium supplied by the CFX and left anterior descending (LAD) coronary arteries. Work in each region was calculated as the systolic area under the force-length curve. Corresponding regional MVO2 was calculated from local O2 extraction (microspectrophotometry) and flow (radiolabeled microspheres). Dopamine infusion (15 micrograms.kg-1.min-1) increased regional work from 262 +/- 56 to 733 +/- 171 mm.g.min-1 in the control (LAD) region, but to a much smaller extent in the collateral-dependent (CFX) region (from 249 +/- 82 to 414 +/- 81 mm.g.min-1). However, regional MVO2 increased to about the same extent in the CFX (from 6.0 +/- 0.7 to 12.4 +/- 0.9 ml O2.min-1 times 100 g-1) and the LAD region (from 7.0 +/- 0.6 to 14.5 +/- 1.3 ml O2.min-1 times 100 g-1). O2 extraction was not elevated in the CFX region. Therefore, the functional impairment was not secondary to O2 supply or consumption limitations.