Endothelin-1 limits increases in blood flow to native and collateral-dependent myocardium

We hypothesized that blood flow to collateralized and noncollateralized myocardium is improved by antagonism of endothelin (ET) A receptors. Coronary collateral development was stimulated by placing an ameroid constrictor around the left circumflex coronary artery (LCx; collateralized region) in 11 swine. After 35 +/- 2 days, the left anterior descending coronary artery (LAD; noncollateralized region) was autoperfused at constant pressure using blood from a femoral artery. In group 1 (n = 6) transmural blood flow was measured using radioactive microspheres in the LAD, LCx, and border regions (i.e., area between LAD and LCx) during pacing stress while vehicle (phosphate-buffered saline) was infused into the LAD coronary artery (pace 1). Approximately 55 min later, a second period of pacing (pace 2) was performed in the presence of ETA receptor antagonism (BQ-123; 5 mg.ml-1.min-1 ic). In the time control group (group 2, n = 5) vehicle was infused during both pacing periods. Indexes of myocardial oxygen demand were similar between paces 1 and 2 in each group. Compared with the first pacing period, transmural blood flow (ml.100 g-1.min-1) was higher (P < 0.05) during ETA receptor antagonism (i.e., pace 2) in the LAD (105 +/- 8 vs. 139 +/- 9), border (51 +/- 5 vs. 83 +/- 7), and LCx regions (22 +/- 3 vs. 41 +/- 4, respectively) in group 1. In group 2, while perfusion in the border (98 +/- 17 vs. 103 +/- 16) and LCx regions (19 +/- 4 vs. 27 +/- 6) was similar in paces 1 and 2, LAD transmural flow was greater (134 +/- 9 vs. 160 +/- 13; P < 0.05) during the second pacing period. However, the percent increase in LAD flow comparing pace 1 with 2 was greater (P < 0.05) in group 1 (39 +/- 6%) compared with group 2 (20 +/- 7%). These data suggest that during the stress of pacing blood flow to collateralized and noncollateralized myocardium is improved in the presence of ETA receptor blockade.