ENDOTHELIAL-CELL REPLICATION IN AN IN-VIVO MODEL OF AORTIC ALLOGRAFTS

Previous studies of aortic valve allograft viability have used in vitr o assessments that may not reflect in vivo properties. This study eval uated in vivo endothelial cell replication in experimental valved aort ic grafts and examined the consequences of histoincompatibility and cr yopreservation. Valved aortic conduits were heterotopically transplant ed into syngeneic or allogeneic rats. Tritiated thymidine was administ ered to graft recipients and control rats. After 72 hours, monolayers from the native aortas and the aortic portion of the grafts were prepa red for autoradiography, with six or more silver grains per nucleus co nsidered evidence of replication. Percentages of replicating cells in native aortas ranged from 0.3% to 2.3% (p = not significant). Percenta ges of replicating cells in the fresh isografts (12.4%) and allografts (12.2%) were not significantly different from each other, although ea ch was significantly greater than the percentage in its native aorta ( p < 0.04). Cryopreserved allografts and isografts displayed few endoth elial cells, none of which was replicating. Immunologic differences do not affect endothelial cell replication in this early period after fr esh graft transplantation. Cryopreservation, however, results in the a bsence of replicating endothelium.