Myocardial reaction to experimental ischemic injury in the rat.

The purpose of the experiments reported was to study the reaction of non-necrotic myocardium to a right ventricular infarct produced by right coronary ligation in the rat. Samples were taken from the right ventricle to investigate the reaction in the marginal zone of the infarct, and from the left ventricle to observe the changes in the cardiac muscle remote from the necrosis. Sham operations were performed in order to investigate the effect of the operative trauma. The evolution of findings in the left ventricular myocardium was correlated in time with the known post-operative increase of myocardial resistance, in an effort to find the possible myocardial factors responsible for this increase. Cardiac muscle cells in the marginal zone and some of the subepicardial muscle cells displayed a variety of histochemical and electron microscopic changes suggestive of an impairment of the cellular function and an increased importance of alternative metabolic pathways, in order to preserve the structural integrity of the cells and to meet their energy requirements. The findings in this area were apparently related to the progressive anoxia which resulted from the fibrotic transformation of granulation tissue surrounding the infarct. Biochemical, histochemical and electron microscopic studies of the left ventricular myocardium remote from necrosis suggested that the preparatory procedure resulted in a temporary stimulation of the proteosynthetic activity in the cardiac muscle cells and that this may form the basis for their increased resistance and adaptability. The findings support the hypothesis of a myocardial factor being important in the resistance against various noxious stimuli