EARLY ISCHEMIC ULTRASTRUCTURAL AND HISTOCHEMICAL ALTERATIONS IN THE MYOCARDIUM OF THE RAT FOLLOWING CORONARY-ARTERY OCCLUSION

The early ultrastructural and histochemical changes in the myocardium following coronary artery occlusion in the rat were studied. Hearts from rats in which the left main coronary artery had been occluded for 5, 10, 20, 30, 40, 60, and 180 min were examined. Evidence of damage to myocardial cells and the microvasculature was present at 5 min of ischemia and became progressively more severe with time. Both by electron microscopic and histochemical techniques glycogen depletion was observed within 10 min of the onset of ischemia; neutral fat accumulated at 60 to 180 min of ischemia, predominately in apparently viable cells surrounding the cells with more severe ischemic injury. Loss of oxidative enzyme activity, as determined histochemically, lagged behind ultrastructural evidence of mitochondrial damage. Thus morphologic evidence of ischemic myocardial damage occurs earlier in the rat than in dogs. Wavy fibers were identified in the ischemic zone, but showed less ultrastructural damage than other cells in the same microscopic fields. By histochemical techniques, wavy fibers in the ischemic zone showed glycogen loss but still had oxidative enzyme activity 3 hr after the occlusion. © 1979.