Development of an in vitro model to study the response of saphenous vein endothelium to pulsatile arterial flow and circumferential deformation

Objectives: To develop an in vitro model of human saphenous vein bypass to facilitate study of the early adaptive responses of venous endothelium to arterial flow conditions. Design, material and methods: Segments of human saphenous vein (with or without external polytetrafluoroethylene (PTFE) stents to limit circumferential and radial deformation) were mounted in a bypass circuit and subjected to pulsatile flow with oxygenated Krebs solution to simulate arterial or venous flow conditions for a period of 90 min. The viability of the vein was assessed by the issue ATP concentration and vasomotor responses to phenylephrine, sodium nitroprusside and bradykinin (endothelium-dependent). Immunohistochemistry was used to assess both endothelial preservation (CD31) and the expression of proteins involved in leukocyte adhesion: E-selectin, P-selectin and ICAM-1. Freshly excised veins were used as controls. Results: The concentration of ATP was 320 +/- 11 nmol/g in freshly excised vein (n = 8) and following exposure to the arterial flow circuit increased to 566 +/- 60 nmol/g (n = 8, paired t-test, p = 0.003) in unstented veins and to 421 +/- 49 nitroprusside-induced vasodilatation responses were preserved after veins were exposed to the arterial flow circuit, but the sensitivity to phenylephrine was increased: EC50 decreasing from 9 mu M to 1 mu M, p = 0.008. There was a 5-10% decrease in staining area for CD31 after veins, stented or unstented, were exposed to the arterial flow circuit. However, after exposure to the arterial flow circuit, the staining area ratio for ICAM-1/CD31, which remained unchanged in externally stented veins, increased two-fold in unstented veins, p > 0.01: there were no changes in the staining area ratio P-selectin/CD31 and no staining for E-selectin was observed. Conclusion: Vasomotor responses and tissue ATP concentrations indicate that the viability of saphenous vein can be maintained for up to 90 min in an ex vivo flow circuit and the CD31 staining indicated endothelial preservation. This opens up the possibility of investigating the early changes in saphenous vein endothelium following exposure to arterial pressure, as at bypass surgery. First results suggest that there is rapid upregulation of the leukocyte adhesion molecule ICAM-1, which can be prevented by limiting the circumferential deformation of the vein with an external PTFE stent.