Abstract
Summary
Transmural levels of citrate synthase and lactate dehydrogenase (LDH) were measured in left ventricles which had enlarged by approximately 35% due to pressure overload. Citrate synthase activity in whole homogenates and isolated mitochondria served to estimate potential oxidative capacity and mitochondrial mass. In control animals, the endocardium had a small (9%) but significantly lower citrate synthase activity when compared to the epicardium. This difference was accentuated (16%) in the enlarged ventricle due to reduced enzyme activity in the endocardium. Total citrate synthase activity was elevated approximately 25% in enlarged ventricles while enzyme activity in isolated mitochondria was not significantly altered. It appears that accumulated left ventricular mass outstrips mitochondrial mass particularly in the endocardial portion of the enlarged ventricle. LDH activity was utilized as a marker for potential anaerobic metabolic capacity. Pressure overload had no significant effect on either LDH enzyme activity measured at three different substrate concentrations or LDH isoenzyme composition. The present studies suggest that seemingly appropriate enzymatic adaptations do not accompany pressure-induced left ventricular enlargement.
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