Difference between endocardial and epicardial utilization of glycogen in the ischemic heart

In the nonischemic canine left ventricle, levels of glycogen, glucose-6-phosphate (G6P), and lactate, and phosphorylase activity in the endocardial layers were higher than those in the epicardial layers, but the phosphocreatine (PCr) level in the endocardial layers was lower than that in the epicardial layers, and there were no differences in the adenosine triphosphate (ATP) level between the endo- and epicardial layers. Upon ligation of a small branch of the left descending coronary artery, levels of glycogen and PCr decreased, while those of G6P and lactate increased, and the activity of phosphorylase increased. The level of ATP was not affected by the coronary ligation. Thus the coronary ligation accelerated the glycogenolysis and glycolysis in the myocardium without affecting ATP level, and the acceleration in metabolism in the endocardial layers was more rapid and marked than that in the epicardial layers.