Morphological changes in the coronary circulation following experimental myocardial ischemia in swine

The diagonal branches of the left anterior descending coronary artery in ten pigs were ligated for 5, 15, 30, 60 and 120 minutes. Pieces of occluded vessels were fixed with 2.5% buffered glutaraldehyde and processed for scanning and transmission electron microscopy. After 5 to 30 minutes of occlusion, endoplasmic reticulum and mitochondria begin to swell, vacuoles appear, and the number of pinocytic vesicles in endothelial cells decrease. After 60 minutes, endothelial cells contained numerous vacuoles, endoplasmic reticulum and mitochondria were markedly swollen, leukocytes and fragments detached from smooth muscle cells had infiltrated the subendothelial space, and endothelial cells were partially disrupted. Following 120 minutes of occlusion, internal elastic lamina had split, leukocytes had migrated into tunica media and smooth muscle cells had obviously penetrated into the subendothelial space, but no endothelial denudation or associated platelet accumulation was seen. These observations indicate that leukocyte infiltration and intrusion of partially disrupted endothelial cells precede, and may promote proliferation of medial smooth muscle cells into the tunica intima during myocardial ischemia. The events are reported for large conduit arterial branches of a main coronary artery.