Effects of enalapril on the vascular wall in an experimental model of syndrome X.

Evidence links the insulin resistance syndrome with endothelial dysfunction. Previously, we have described a decreased endothelial nitric oxide synthase (eNOS) activity in both aortic endothelium and cardiac tissue, and an increased proliferation of aortic primary cultured vascular smooth muscle cells (pC-VSMCs), obtained from fructose-fed rats (FFR), an experimental model of syndrome X. Because the participation of the renin-angiotensin system (RAS) in this model is still unclear, the present study examined the effect of chronic administration of an angiotensin converting enzyme (ACE) inhibitor enalapril (E) on pC-VSMCs proliferation and eNOS activity in a conduit artery (aorta) and in resistance vessels (mesenteric vascular bed) from fructose-fed rats. Male Wistar rats were used: Control, FFR, Control + E, and FFR + E (n = 8 in each group). After 8 weeks, tissue samples were obtained and 10% fetal calf serum (FCS) proliferative effect was examined in pC-SMCs of aortic and mesenteric arteries by [(3)H]thymidine incorporation. The eNOS activity was estimated in endothelial lining from both origins by conversion of [(3)H]arginine into [(3)H]citrulline. The FFR aortic and mesenteric pC-VSMCs showed a significantly increased 10% FCS-induced [(3)H]thymidine incorporation compared to controls. The FFR aortic and mesenteric endothelium eNOS activity was significantly decreased. Chronic treatment with E abolished the increased proliferation and restored eNOS activity. These data confirm that changes in VSMCs proliferation and endothelial dysfunction at different levels of the vascular system are involved in syndrome X, and that the inhibition of angiotensin II production can revert those changes, suggesting an important role for RAS and possibly kinins, in the physiopathologic mechanism of this model of syndrome X.