Histological changes were examined in the left ventricular free wall of the heart in 40 rats after ligation of the distal anterior descending coronary artery for 15, 30 minutes and 1, 2, 3, 4, 5, 6 hours. Auto-injection of tracers for light microscopy was used to examine the development of collateral circulation. Morphological changes of the ischemic myocardium were observed by PAS staining and transmission electron microscopy. Fifteen minutes after coronary occlusion, the dye was observed in the vein of the ischemic zone; however, 30 minutes after coronary occlusion, the dye appeared in the capillaries of the outer-third layer. These findings suggested that the collateral circulation becomes functional between 15 and 30 minutes after coronary occlusion. Collateral circulation increased gradually in the capillaries of the ischemic zone. Thirty minutes after coronary occlusion the dye was seen only in the outer-third layer of the ventricular ischemic zone. One hour after occlusion, the dye appeared in the superficial space and the middle-third layer. Three hours after occlusion, the dye was seen in all layers of the ischemic zone. The dye appeared in the ischemic zone, where myocardium damage was not homogeneous. The positive reaction obtained by PAS staining corresponded with the capillaries, veins and superficial spaces in which the dye was evident. These results suggest that collateral circulation, verural back flow and superficial space flow are able to prevent myocardial infarction in early ischemia.
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