Endothelial dysfunction and denudation in rat aortic allografts.

Clinical evidence suggests that early endothelial cell (EC) dysfunction may predict the development of graft vascular disease. We wished to assess the early functional and morphological changes in the graft endothelium in a commonly used animal model of graft vascular disease, the rat aortic interposition allograft model. To assess graft EC function, regulation of vascular tone by ECs was monitored in aortic rings from grafts harvested at various times after transplantation (Tx). EC morphology was assessed by silver staining, which was followed by en face inspection of the luminal side of the grafts. Acetylcholine-induced EC-dependent vasorelaxation was reduced in allografts at post-Tx days 7 and 14, whereas in syngeneic grafts EC-dependent relaxation was unaffected at any time after Tx. In separate grafts collected at the same time points, massive leukocyte adhesion at post-Tx day 7 and EC denudation at days 14 and 28 were evident in allografts but not in syngeneic grafts. At post-Tx day 56 (a time at which vessel wall remodeling is pronounced in this model), an intact EC layer covered the grafts. EC dysfunction and morphological changes were prevented by immunosuppression of recipient rats with cyclosporine. Our study shows that Tx-induced EC dysfunction in rat aortic allografts can be observed within 1 week of Tx in rat aortic allografts and that this is occurring concomitantly with enhanced leukocyte adhesion to the graft ECs. These changes occur before any other morphological or functional changes described thus far in this model and appear to be immune-driven. Taken together, these results show that Tx-induced early EC dysfunction, as described in patients, may be studied in the model of rat aortic Tx.

Complete loss of functional smooth muscle cells precedes vascular remodeling in rat aorta allografts.

BACKGROUND: The functional consequences of vascular remodeling in rat aorta allografts were studied at different times after transplantation (Tx). METHODS: At days 1, 3, 7, 14, 28, and 56 after Tx, rat aorta allografts (Dark Agouti [DA]-to-Lewis) were mounted as isolated organs, and their contractile properties tested with phenylephrine, KCl, or endothelin-1. Controls were native DA-aortae and DA-syngeneic grafts. Changes in alpha smooth muscle actin and morphology were assessed by immunoblotting and histology. RESULTS: PostTx syngeneic grafts presented similar functional and morphological properties to native aortae. In allografts, no morphological changes was detected at day 7 after Tx, but phenylephrine-induced vasoconstriction was reduced by 60%. Signs of medial smooth muscle cell (SMC) loss and adventitial inflammation were observed at day 14 after Tx, without neointima formation. A complete loss of contractile property was observed at day 28 after Tx in association with a 75% decrease in alpha-SMC actin, severe adventitial inflammation, and reduced medial cellularity. At this time, neointima was restricted to both edges of allografts. At day 56 after Tx, allografts were also not functional and exhibited neointima on their entire length. All these changes were prevented by treating recipients with cyclosporine (7.5 mg/kg/day). CONCLUSION: These results indicate that, after Tx, the contractile property of rat aorta allografts is altered before manifest vascular remodeling. Because this can be prevented by cyclosporine, it most likely reflects an acute rejection of SMC. These results also show that vascular graft dysfunction can be used to monitor the development of rejection in the rat aorta allograft model.