EFFECT OF DOPAMINE ON LOCAL SEGMENT WORK AND O-2 CONSUMPTION IN COLLATERAL-DEPENDENT MYOCARDIUM

To test the hypothesis that dopamine-stimulated work and myocardial O-2 consumption (MVo(2)) 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 MVo(2) was calculated from local O-2 extraction (microspectrophotometry) and flow (radiolabeled microspheres). Dopamine infusion (15 mu g . 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 MVo(2) increased to about the same extent in the CFX (from 6.0 +/- 0.7 to 12.4 +/- 0.9 ml O-2 . min(-1) . 100 g(-1)) and the LAD region (from 7.0 +/- 0.6 to 14.5 +/- 1.3 ml O-2 . min(-1) 100 g(-1)). O-2 extraction was not elevated in the CFX region. Therefore, the functional impairment was not secondary to O-2 supply or consumption limitations.