Recovery after cardioplegia in the hypertrophic rat heart

Background. Enhanced recovery after cardioplegic arrest has been observed i n rat hearts with hypertrophy induced by hemodynamic overload. We hypothesi ze that this is related to altered characteristics of hypertrophied myocard ium-reflected by increased V-3 isomyosin and glycolytic potential-other tha n increased left ventricular mass. Materials and methods. Isolated hearts from age-matched nonoperated and sha m-operated control rats and from aortic-banded, hyperthyroid, and hypothyro id rats-groups in which hypertrophy and V-3 as a percentage of left ventric ular myosin vary independently-underwent 2 h of multidose cardioplegic arre st at 8 degrees C followed by reperfusion at 37 degrees C, Left ventricular V-3 isomyosin was evaluated after separation by gel electrophoresis. Results. Moderate left ventricular hypertrophy was produced by aortic bandi ng or hyperthyroidism and atrophy by hypothyroidism. V-3 isomyosin was incr eased in banded (28%) and hypothyroid (75%) rats compared to control (12%) and hyperthyroid rats (7%). Myocardial glycogen content closely paralleled %V-3. At 30 min of working reperfusion, functional recovery (assessed as pe rcentage prearrest cardiac output) was 66 +/- 4 and 68 +/- 5% in control an d hyperthyroid hearts and 81 +/- 2 and 80 +/- 5% in hearts from banded and hypothyroid rats (each P < 0.05 vs controls), respectively. At 30 min, hear ts from banded and hypothyroid rats were also more efficient (as indexed by cardiac output at constant mean aortic pressure/myocardial oxygen consumpt ion) than control and hyperthyroid hearts. Conclusions. The data suggest that recovery is related not to increased mas s but to other changes in overload hypertrophy, Increased percentage V-3 is omyosin and glycogen reflect these changes and may themselves contribute to improved functional recovery after cardioplegic arrest, as may increased p ostischemic efficiency. (C) 2000 Academic Press.