Background-The mechanisms involved in the dysfunction of both endothelium-dependent vasodilatation (EDV) and NO biosynthesis related to smoking are unclear. In this study, EDV was assessed in healthy smokers and nonsmokers in vivo and, using serum from the same individuals, was related to the NO biosynthetic pathway in vitro. Methods and Results-Flow-mediated EDV of the brachial artery was measured in 23 male patients (8 nonsmokers and 15 smokers). Serum was collected, added to confluent (Ϸ85%) monolayers of human umbilical vein endothelial cells (HUVECs), and incubated for 12 hours. Basal and substance P-stimulated NO production was measured. The HUVECs used for measuring basal NO production were lysed, and both endothelial NO synthase (eNOS) protein expression and eNOS activity were determined. EDV was lower in smokers compared with nonsmokers (PϽ0.001). HUVECs treated with serum from smokers compared with nonsmokers showed significantly lower basal (PϽ0.0001) and stimulated (PϽ0.02) NO production, higher eNOS expression (PϽ0.0001), but lower eNOS activity (PϽ0.004). There was a significant positive correlation between in vivo EDV and in vitro substance P-stimulated NO production (rhoϭ0.57, PϽ0.01) and between basal NO production and eNOS activity (rϭ0.54, PϽ0.008) and a negative correlation between basal NO production and eNOS protein expression (rϭϪ0.60, PϽ0.003). Conclusions-This is the first study to combine an in vivo model with a near-physiological in vitro model to demonstrate an association between decreased NO production and reduced EDV. Cigarette smoking was associated with reduced EDV, NO generation, and eNOS activity in the presence of increased eNOS protein expression.

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