Nicotine-induced morphological changes in rat aorta: the protective role of melatonin.

We analyzed the morphological changes in rat aortas during nicotine administration in order to investigate the involvement of vascular smooth muscle cells (VSMCs) in the regulation of vascular wall homeostasis. We also considered the possibility of restoring VSMC changes using melatonin as an antioxidant. We studied 4 groups of animals over 56 days. Three groups of rats were used as controls (the first without treatment, the second with melatonin alone and the third with nicotine alone). The last group of rats was orally treated with nicotine for the first 28 days and with melatonin for the last 28 days. Morphological changes in vessels were evaluated by histological procedures and immunohistochemical analysis using thrombospondin-1 (TSP-1), transforming growth factor-β1 (TGF-β1), plasminogen activator inhibitor-1 (PAI-1) and CD31 antibodies. We demonstrated that TSP-1, TGF-β1 and PAI-1 increased after nicotine administration. We believe that TSP-1 is responsible for neointima formation and that it is able to influence TGF-β1 and PAI-1 expression. Histological and immunohistochemical analysis by CD31 antibody showed that only a few endothelial cells were present in the aorta after nicotine administration compared to controls and rats treated with melatonin after nicotine administration. Moreover, histological analysis showed that neointima formation was present after nicotine treatment. Furthermore, melatonin inhibited neointima formation increasing TSP-1 expression. The ability of melatonin to inhibit neointima formation suggests that it could be a useful treatment for homeostasis of vascular walls.