Long-term coronary stenosis in rats: cardiac performance, myocardial morphology, and contractile protein enzyme activity

Abstract

To determine the effects of chronic nonocclusive coronary constriction on cardiac hemodynamics, myocardial structure, and contractile protein enzyme activity, the left coronary artery was narrowed in rats, and measurements of ventricular pump function, extent and localization of tissue damage, and myofibrillar Mg2+ and Ca2+ myosin adenosinetriphosphatase (ATPase) activities were measured 3 mo later. In the presence of coronary artery stenosis averaging 56%, two different degrees of depression in global cardiac performance were identified, and the animals were divided in two groups. In the first group, left ventricular end-diastolic pressure (LVEDP) was increased and LV+ and/or--the first derivative of LV pressure (dP/dt) were decreased, whereas in the second group end-diastolic and peak systolic LV pressures, LV+ and -dP/dt and right ventricular dynamics were all impaired. Thus left ventricular dysfunction and failure occurred with coronary narrowing. Structurally, multiple foci of replacement fibrosis were found across the left ventricular wall, but the number of these lesion profiles was 2.6-fold larger in failing animals than in rats with cardiac dysfunction. Biochemically, Mg(2+)-ATPase activity in myofibrils and Ca2+ myosin ATPase were not altered biventricularly. On the other hand, a shift from V1 to V3 myosin isoenzymic content occurred in the failing left ventricle. In conclusion, the late impairment in ventricular pump function associated with prolonged coronary artery stenosis appears to be sustained more by the magnitude of myocardial damage than by defects in contractile protein enzyme activity.