Revascularization of skeletal muscle transplanted into the hamster cheek pouch: electron microscopy

Revascularization of bundles of skeletal muscle fibers transplanted into the cheek pouch of hamsters was examined previously by intravital and light microscopy. Some blood vessels survived the ischemia of transplantation and revascularization resulted from the growth of surviving vessels. We have now examined the cellular events of graft revascularization by electron microscopy (EM). Approximately 20 skeletal muscle fibers were autografted into the hamster cheek pouch. Segments of the graft were prepared for EM from 0.5 to 5 days after transplantation. At 0.5 day, the endothelial cells of surviving blood vessels had short processes extending from them. By 1.0 day, some endothelial cells had separated. At 1.5 days, many endothelial cells were undergoing mitosis. Blood vessels at 2 to 2.5 days were of narrow diameter and most were densely packed with erythrocytes. Circulation was reestablished between 2.5 and 3 days. The fine structure of the blood vessels changed little after 3 days except for a decrease in the number of vesicles in the endothelial cell cytoplasm and the formation of normal endothelial cell injections. After 5 days, blood vessels were larger in diameter, but otherwise similar to control capillaries. We conclude that, despite the initial absence of circulation, surviving blood vessels underwent a rapid, orderly sequence of growth.