Regional Distribution of Glycogen and Phosphorylase in the Ventricles of the Heart

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Abstract
In rat, rabbit, dog, and ox hearts, the glycogen concentration varied throughout the walls. The concentration gradient decreased from endocardium to epicardium in the right and left ventricles. In the septum, the interior part of the wall had a lower concentration of glycogen than tissue sections closer to the endocardial surfaces. The maximum values for glycogen concentration in endocardial sections were from two to six times higher than the minimum values. This gradient was much greater than the 30% differences observed between apex and base of the ventricles. Since our studies have demonstrated a very large variation for glycogen content in layers of myocardium parallel to sides of the ventricular wall, there is an obvious need for caution in sampling hearts for glycogen analysis. In the ox heart, the right bundle branch and A-V node were dissected out, and the glycogen values were compared with those for the rest of the myocardium. Glycogen values of the conduction system, especially of the bundle of His, were considerably higher than for any part of the myocardium studied, indicating that the myocardial gradients observed may be related to distribution of the Purkinje fibers. Phosphorylase values decreased from endocardium to epicardium in a pattern similar to that observed for glycogen, indicating a possible function in association with glycogen concentration. In the hearts perfused with a glucose-free medium by the Langendorff technique, glycogen diminished throughout the heart, but the general pattern of gradients was preserved. This suggested that glycogen is utilized as an energy source for contraction.