Histological change in cryopreserved rat aortic allograft.

In this study, we established an experimental cryopreserved aortic allograft model in rats and examined the long-term histological changes in the allograft. The thoracic aorta of Brown Norway rats (RT1n) was cryopreserved with 10% dimethylsulfoxide using a programmable freezer, and was allo-transplanted to the infrarenal abdominal aorta of Lewis rats (RT1l). Neither immunosuppressants nor anticoagulants were administered postoperatively. As a control, isografting was also performed between Lewis donor and recipient rats. In the allograft groups, cellular infiltration in the adventitia was massive at the acute phase after the operation and decreased gradually. Intimal thickening was predominantly observed from the early stage, followed by advancing thickening. In the media, decrease in cell number was detected after 1 month, and chondrocyte-like-cells were observed around which calcification was noted. Endothelial cells were observed in only one-third of the recipient investigated at 10 days and in over 80% of those at 12 months. In the isograft groups, a low grade of intimal thickening was detected over the experimental period. No decrease in cell number in the media was detected, and the degree of cellular infiltration in the adventitia was mild. After allotransplantation of the cryopreserved rat aorta, intimal thickening, medial necrosis and cellular infiltration in the adventitia, all the manifestations of rejection, occurred. Thus, as the cryopreserved tissue induces an immunological response, it is important to match the blood type and/or histocompatibility in clinical use.