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 bypas s to facilitate study of the early adaptive responses of venous endoth elium to arterial flow conditions. Design, material and methods: Segme nts of human saphenous vein (with or without external polytetrafluoroe thylene (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 conditi ons 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). Immunohis tochemistry was used to assess both endothelial preservation (CD31) an d the expression of proteins involved in leukocyte adhesion: E-selecti n, P-selectin and ICAM-1. Freshly excised veins were used as controls. Results: The concentration of ATP was 320 +/- 11 nmol/g in freshly ex cised 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 u nstented 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 dec reasing from 9 mu M to 1 mu M, p = 0.008. There was a 5-10% decrease i n staining area for CD31 after veins, stented or unstented, were expos ed to the arterial flow circuit. However, after exposure to the arteri al flow circuit, the staining area ratio for ICAM-1/CD31, which remain ed unchanged in externally stented veins, increased two-fold in unsten ted veins, p > 0.01: there were no changes in the staining area ratio P-selectin/CD31 and no staining for E-selectin was observed. Conclusio n: 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 prese rvation. This opens up the possibility of investigating the early chan ges in saphenous vein endothelium following exposure to arterial press ure, as at bypass surgery. First results suggest that there is rapid u pregulation of the leukocyte adhesion molecule ICAM-1, which can be pr evented by limiting the circumferential deformation of the vein with a n external PTFE stent.