Vein adaptation to arterialization in an experimental model

Purpose: The events preceding myointimal thickening in vein grafts after va scular reconstructions are not well characterized. Indeed, the injury respo nse associated with vein graft arterialization may be different than that o bserved in the balloon angioplasty model. Therefore, we used a rat model to study the early cellular response after arterialization of vein grafts. Methods: Epigastric veins were placed as femoral artery interposition graft s in 37 male Lewis rats (weight range, 350-400 g). Vein grafts and contrala teral epigastric veins were harvested at different time points (6 hours, 1 day, 2 daps, 3 days, 7 days, 14 days, 21 days, 30 days, and 70 days). Tissu e specimens were processed for histology and immunohistochemistry with anti bodies for the proliferating cell nuclear antigen (PCNA) and for different cell types. Terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) assay was used as a means of determining the presence of apoptosis. Electron microscopy was used as means of assessing the integ rity of the endothelial cell surface (SEM) and confirming the presence of a poptosis (TEM). Specimens were also snap frozen in liquid nitrogen for RNA isolation and molecular analysis. Results: At 1 day, endothelial denudation with platelet deposition on the s urface was shown by means of SEM. Both apoptosis and necrosis of smooth mus cle cells (SMCs) were present in the media, along with monocyte infiltratio n. Cellular proliferation and apoptosis were most intense within the first week of implantation. PCNA staining was first seen in the adventitial fibro blasts and microvessels, then in the medial SMCs at 3 days. With reverse tr anscriptase polymerase chain reaction, upregulation of vascular endothelial growth factor (VEGF) messenger RNA (mRNA) was noted at 1 day. Myointimal t hickening progressively developed, with no apparent diminution of the lumin al area as long as 70 days after implantation. By means of the analysis of the transforming growth factor beta1, mRNA showed expression during intimal thickening and accumulation of extracellular matrix. Reendothelialization was complete at 30 days. Conclusions: These observations indicate that the cellular composition in o ur vein graft model is similar to human stenotic explants. Endothelial denu dation is observed in rat vein grafts with complete regeneration by 30 daps . VEGF mRNA is upregulated at 1 day, followed by proliferation of microvess el endothelial cells in the adventitia. Cellular proliferation and apoptosi s are minimal after 21 days, with progressive intimal thickening likely to be the result of matrix accumulation.