LOCAL ISOTROPIC STIMULATION BY METHYLENE-BLUE DOES NOT IMPROVE MECHANICAL DYSFUNCTION DUE TO MYOCARDIAL STUNNING

We tested the hypothesis that reduction of intramyocardial cyclic guan osine monophosphate (GMP) by methylene blue (MB) would improve mechani cal dysfunction in stunned myocardium. Regional stunning was produced in nine open-chest anesthetized dogs by a 12-min left anterior descend ing coronary artery (LAD) occlusion. MB was infused into the LAD durin g reperfusion (1 mg/kg per min). Stunning reduced LAD force developmen t, introduced a significant time delay between the onset of force and shortening (delay) and caused significant systolic bulging to occur. S tunning reduced systolic regional work (the integrated product of forc e and segment shortening during systole), but did not significantly al ter regional oxygen consumption or cyclic GMP levels, MB decreased cyc lic GMP (1.8+/-0.2 to 0.9+/-0.1 pmol/g) and increased peak force (36+/ -5 to 55+/-10 g). However, MB increased delay (93.9+/-18.4 to 233+/-19 ms) and systolic bulging (5.9+/-2.1% to 9.3+/-2.8%) and further reduc ed systolic regional work (control: 4204+/-933 g x mm/min; stunned: 21 91+/-542 g x mm/min; MB: 1153+/-516 g x mm/min). MB increased regional myocardial oxygen consumption (7.4+/-1.0 to 15.6+/-2.7 ml O-2/min per 100 g). These results suggest that depressed contractility, while pre sent in myocardial stunning, is not the primary cause of mechanical dy sfunction.