Endothelium-dependent vasodilation in the brachial artery is impaired in smokers: effect of vitamin C.

Cigarette smoking has been shown to cause endothelial dysfunction. To examine the effects of vitamin C and cigarette smoking on endothelium-dependent vasodilation, we measured the lumen diameter and flow velocity of the brachial arteries at rest, during reactive hyperemia following transient arterial occlusion, and after sublingual nitroglycerin (0.3 mg) in smokers (n = 20) and nonsmokers (n = 20) with high-resolution ultrasound after infusion of saline or saline plus vitamin C (10 mg/min for 20 min). We also performed the same study in smokers (n = 15) before and 10 min after cigarette smoking.

 In addition, we measured the serum levels of vitamin C and the plasma levels of thiobarbituric acid-reactive substances (TBARS) as an index of lipid peroxidation. The smokers had lower vitamin C levels, higher TBARS levels, and showed impairment of flow-dependent vasodilation (5.3 ± 1.9 vs. 9.2 ± 1.5%, P < 0.0001) compared with nonsmokers. Vitamin C administration improved the impairment of flow-dependent vasodilation (5.3 ± 1.9 to 9.0 ± 3.2%, P < 0.001) and decreased TBARS in smokers but not in nonsmokers.

Furthermore, cigarette smoking acutely worsened the impairment of flow-dependent vasodilation (5.4 ± 1.8 to 1.5 ± 1.3%, P < 0.01) and increased TBARS. We conclude that 1) endothelium-dependent vasodilation in the brachial arteries is impaired in smokers and this impairment is improved by vitamin C administration in association with a decrease in TBARS and 2) cigarette smoking produces acute impairment of endothelium-dependent vasodilation in smokers in association with an increase in TBARS