Ultrastructure of rat aortic grafts

This study compares the ultrastructure of three syngeneic and three allogen eic grafts of rat abdominal aorta (Lewis to Lewis and BN to Lewis, respecti vely); the tissue was sampled three months after transplantation (TPL). The endothelial plate was preserved and mononuclear cell adherence was absent. In syngeneic grafts the intima and media remained close to normal with wel l-preserved smooth muscle cells (SMC). The thickened ailograft neointima co nsisted of elongated spindle cells and rich intercellular matrix. The cells were typical SMC without apparent signs of dystrophy or degeneration. On t he other hand, most SMC of the media showed complete disruption and disorga nization of membrane and organelles suggestive of accomplished necrosis. Ho wever, the framework of elastic lamellae was preserved, without apparent ru ptures or lytic changes. Intraintimal migration of medial SMC was not recor ded while some cytoplasmic strips were seen to extend across the outer elas tic lamella (possible rudimentary outgrowth of SMC?). Lymphocytes and histi omonocytic cells (macrophages) were found in the adventitia but not in the destroyed media. Thus electron microscopy elucidated the histological pictu re of "anuclear allograft media" and confirmed the predominance of SMC in t he thickened neointima. However, signs of the mediointimal SMC invasion wer e not apparent three months post TPL.