ANZ J. Surg. 2004; 74: 486–490 SURGICAL RESEARCH Review Article ARTERIAL FLOW INDUCES CHANGES IN VENOUS ENDOTHELIUM WHICH ARE MODIFIED BY CALCIUM CHANNEL BLOCKERS JONATHAN GOLLEDGE Vascular Biology Unit, Department of Surgery, School of Medicine, James Cook University, Townsville, Queensland, Australia Introduction: Adaptation of saphenous vein to arterial flow may be critical to the results of bypass. The present paper summarizes work recently presented as a Hunterian Lecture. Work includes in vitro investigation of the response of saphenous vein endothelium to arterial flow and assessment of its clinical importance using a cohort of patients undergoing vein bypass surgery. Methods: Freshly excised human saphenous vein segments were placed in an in vitro flow circuit to simulate arterial and venous flow conditions. Changes in the endothelial expression of proteins were assessed using a combination of immunohistochemistry and Western blotting. The role of ion channels in the changes seen induced by arterial flow in the saphenous vein endothelium was assessed by addition of ion channel blocking medication to the medium perfusing vein segments. A cohort of patients undergoing vein bypass surgery were followed to assess graft patency and the influence of prescribed medication on its outcome. Results: After arterial flow conditions, the staining area for the endothelial adhesin ICAM-1 and nitric oxide synthase were increased, while that of the anticoagulant protein thrombomodulin was decreased. The concentration of the important stimulant of the clotting cascade tissue factor was unaffected by arterial flow. These changes were modulated by the addition of ion channel blocking drugs to the vein perfusate. In particular, nifedipine abolished the reduction in thrombomodulin, but increased the amount of tissue factor. In a series of 236 patients undergoing primary infra-inguinal vein grafts, prescription of calcium channel blocker was associ- ated with improved primary patency. Conclusions: Important changes in the venous endothelium are induced by arterial flow. Ion channel blocking drugs have the potential to modulate these responses. Key words: calcium channel blocker, endothelium, vein graft. Abbreviations: eNOS, endothelial nitric oxide synthase; ICAM-1, intercellular adhesion molecule 1; TM, thrombomodulin. INTRODUCTION Around a century ago John Hunter described the technique of superficial femoral artery ligation to treat popliteal aneurysm. 1 Today, elective surgery involves bypass, in addition to ligation of the popliteal aneurysm. Randomized trials have demonstrated vein to give superior results to prosthetic conduits for infra-geniculate bypass. 2 Direct surgical connection of vein segments to the arterial circulation provides an important means of revascularization in coronary and lower limb ischaemia, and is the principal method of long-term access for haemodialysis. However, approximately 30% of vein grafts fail within 1 year of surgery as a result of thrombotic occlusion or development of focal stenoses. 3 While the mechanism of graft failure over the first 12 months appears to be multifactorial, infiltration of leucocytes and altera- tion in the local control of thrombosis may be critical. 4,5 Leuko- cyte recruitment is controlled by expression of endothelial molecules, such as intercellular adhesion molecule 1 (1CAM-1), and soluble factors, such as nitric oxide produced by nitric oxide synthase (eNOS). 6 Thrombosis is determined by the balance between stimulating and inhibiting factors. For example, tissue factor is the most important stimulant of the clotting cascade, while thrombomodulin is an important endothelial anticoagulant. 7 Studies in cultured endothelial cells demonstrate important effects of shear stress and stretch on saphenous vein. One of the most rapid responses is the opening of ion channels, which can be transduced into alterations in protein expression. 8 Similar changes in vivo may lead to important changes in the luminal properties of saphenous vein after bypass. The aims of the present work were to investigate the effect of arterial flow on the expression of proteins controlling leucocyte recruitment and thrombosis and to assess the role of ion channel blocking drugs in modulating these responses. METHODS Development of an in vitro flow circuit Human vein samples were placed in a flow circuit and perfused with oxygenated physiological fluid at 36.5°C. Arterial and venous flow conditions were simulated. After exposure to 90 min of flow assessment of smooth muscle and endothelial function and measurement of tissue ATP concentrations confirmed vein viability. Endothelial preservation was confirmed by staining for the endothelial marker CD31. 9,10 Immunohistochemistry Vein specimens were immersed in Zamboni’s fixative overnight at 4°C, then washed thoroughly in PBS-sucrose over 3–7 days. This article is based on a Hunterian Lecture, October 2002, London. J. Golledge MA, Mchir, FRCS (General Surg.), FRACS (Vasc. Surg). Correspondence: J. Golledge, Associate Professor, Vascular Biology Unit, Department of Surgery, School of Medicine, James Cook University, Towns- ville, Qld 4811, Australia. Email: jonathan.golledge@jcu.edu.au Accepted for publication 28 October 2003.