Remodeling of the porcine pulmonary autograft wall in the aortic position

Objective: Dilatation and valve regurgitation are disturbing sequelae of th e pulmonary root functioning at systemic pressures. We tried to characteriz e the histologic mode of adaptation of the neoaortic wall. Methods: We compared routine histologic studies, immunohistochemical staini ng, and computer-assisted morphometric analysis of aortic, pulmonary autogr aft, and native pulmonary wall specimens from pigs in which, as a newborn, a valveless pulmonary autograft had been implanted in the aorta. Results: Histologic examination of the pulmonary autograft revealed a viabl e, normally revascularized wall without degenerative phenomena. Smooth musc le cells were enlarged and rearranged. The characteristic "pulmonary" media l elastin lamellar structure was retained, which was confirmed by morphomet ry. Immunohistochemistry of the autograft revealed relatively strong staini ng of type III collagen and alpha smooth muscle actin, exclusive staining o f basic fibroblast growth factor, and no staining of proliferation markers proliferating cell nuclear antigen and Ki67. Conclusion: The developing pulmonary autograft in the aortic position becom es normally revascularized, lacks major degenerative phenomena, and retains its own typical pulmonary morphologic features. Remodeling is accomplished by increased extracellular matrix deposition with collagen as an important constituent. The marked expression of growth factors in the autograft sugg ests the persistence of increased metabolic activity.