GLYCOGEN-METABOLISM IN THE AEROBIC HYPERTROPHIED RAT-HEART

Background Rates of glycolysis from exogenous glucose are accelerated in hypertrophied hearts. In this study, we determined whether alterati ons in the metabolism of glycogen, an endogenous storage form of gluco se, also occur in hypertrophied hearts. Methods and Results Rates of g lycolysis ([H-3]H2O production) and oxidation ([C-14]CO2 production) f rom exogenous glucose and glycogen were measured in isolated working h earts from control and aortic-banded rats. Hearts in which glycogen wa s prelabeled with [5-H-3]- or [U-C-14]glucose were perfused with buffe r containing 11 mmol/L [5-H-3]- or [U-C-14]glucose (different from the isotope used to prelabel glycogen), 0.4 mmol/L palmitate, 0.5 mmol/L lactate, and 100 mu U/mL insulin. Rates of glycolysis from exogenous g lucose were greater (3471+/-114 versus 2665+/-194 nmol glucose.min(-1) .g dry wt(-1), P<.05, n=4 to 6, mean+/-SEM) and rates of exogenous glu cose oxidation (445+/-36 versus 619+/-16 nmol glucose.min(-1).g dry wt (-1), P<.05, n=4 to 6) were lower in hypertrophied hearts than in cont rol hearts. Rates of glycolysis and oxidation from glycogen were not d ifferent between hypertrophied and control hearts. A greater proportio n of glycogen was oxidized (80% to 100%) than the proportion of exogen ous glucose oxidized (13% to 24%) in both groups. Additionally, 10.5+/ -1.4 and 12.3+/-1.0 mu mol/g dry wt of glycogen was synthesized in hyp ertrophied and control hearts, respectively, indicating that simultane ous synthesis and degradation tie, glycogen turnover) occurred in both groups. Conclusions Thus, aerobic myocardial glycogen metabolism in t he hypertrophied heart is similar to that observed in the normal heart even though exogenous glucose metabolism is altered in the hypertroph ied heart.