Patients who have undergone successful repair of coarctation of the aorta(COA) at any age have been shown to have persistent abnormalities of the pre-coarctation vascular bed, including increased stiffness and diminished vasodilation. These changes contribute to increased morbidity and mortality from cardiovascular causes. We sought to investigate whether these changes in aortic compliance resulted from intrinsic abnormalities in the phenotype or the types of collagen produced by the smooth muscle cells of the aortic media in these patients. A higher collagen I/III ratio reflects a greater degree of stiffness of the vessel, where type I collagen lends rigidity and type III contributes to elasticity. Smooth muscle cells from the media of the pre-COA, coarctation and post-COA tissue resected from eight patients were isolated by dissection and grown in culture. The pattern of expression of alpha smooth muscle actin (SMA) was determined by immunostaining of cells in monolayer and immunoblotting of cell lysates. Secretion of collagen types I and III was determined by isolation of radiolabeled collagen from the media of confluent plates, pepsin digestion, and separation of collagen types I and III by polyacrylamide gel electrophoresis. The ratio of collagen I/III was determined by densitometry.

Neonatal aortic smooth muscle cells from all areas co-expressed SMA prominently with F-actin stress fibers. Quantitation of this isoactin by Western blotting demonstrated similar amounts of SMA in pre-COA, post-COA and coarctation cells. The ratio of collagen I/III was similar in pre-COA and post-COA cell lines but was higher in coarctation cell lines. Total procollagen secretion was similar in pre- and post-COA cells, but again was higher in the coarcted cell lines. CONCLUSION: Smooth muscle cells from the media of pre-COA, coarcted, and post-COA human neonatal aorta have similar phenotypes in vitro as evidenced by their similar expression of alpha smooth muscle actin. The amount of collagen secreted and the ratios of collagen I/III in pre- and post-COA cells were similar, suggesting that increased pre-COA vascular stiffness does not result from an increase in the amount or difference in the types of collagen secreted by smooth muscle cells of the pre-COA vascular bed.