Glycogen Metabolism in the Aerobic Hypertrophied Rat Heart

Abstract

Background Rates of glycolysis from exogenous glucose are accelerated in hypertrophied hearts. In this study, we determined whether alterations in the metabolism of glycogen, an endogenous storage form of glucose, also occur in hypertrophied hearts. Methods and Results Rates of glycolysis ([ 3 H]H 2 O production) and oxidation ([ 14 C]CO 2 production) from exogenous glucose and glycogen were measured in isolated working hearts from control and aortic-banded rats. Hearts in which glycogen was prelabeled with [5- 3 H]- or [U- 14 C]glucose were perfused with buffer containing 11 mmol/L [5- 3 H]- or [U- 14 C]glucose (different from the isotope used to prelabel glycogen), 0.4 mmol/L palmitate, 0.5 mmol/L lactate, and 100 μU/mL insulin. Rates of glycolysis from exogenous glucose 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 glucose 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 control hearts. Rates of glycolysis and oxidation from glycogen were not different between hypertrophied and control hearts. A greater proportion of glycogen was oxidized (80% to 100%) than the proportion of exogenous glucose oxidized (13% to 24%) in both groups. Additionally, 10.5±1.4 and 12.3±1.0 μmol/g dry wt of glycogen was synthesized in hypertrophied and control hearts, respectively, indicating that simultaneous synthesis and degradation (ie, glycogen turnover) occurred in both groups. Conclusions Thus, aerobic myocardial glycogen metabolism in the hypertrophied heart is similar to that observed in the normal heart even though exogenous glucose metabolism is altered in the hypertrophied heart.