Studies of Myocardial Actomyosin and Myosin After Shock, Acute Hemorrhage, Acute Hypoxia, and Cardiopulmonary Bypass

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Abstract
Decreases in cardiac efficiency have been observed in experimental endotoxic shock, acute hemorrhage, and cardiopulmonary bypass. Diminished coronary blood flow, tissue anoxia, or metabolic alteration may affect the contractile protein which, in turn, causes cardiac inefficiency. To test this hypothesis, cardiac actomyosin and myosin were extracted with Guba-Straub solution, and intrinsic viscosity, ATP (adenosinetriphosphate) activity, ATP sensitivity, the rate of ATP hydrolysis, and myosin-ATPase activity were determined. Under these experimental conditions, both myosin and actin were altered. In order to exclude the possible effect of hypoxia of the arterial blood upon the cardiac contractile system, acute hypoxia was produced in dogs and the physicochemical properties of actomyosin and myosin were studied. During acute hypoxia, the myosin-ATPase was affected, but actin appeared to remain unaltered. These changes of actomyosin and myosin may cause insufficient energy utilization by the contractile system and thereby affect the cardiac efficiency.

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