ACUTE AND CHRONIC EFFECTS OF CIGARETTE-SMOKING ON EXHALED NITRIC-OXIDE

Cigarette smoking is associated with an increased risk of respiratory tract infections, chronic airway disease, and cardiovascular diseases, all of which may be modulated by endogenous nitric oxide (NO). We hav e investigated whether cigarette smoking reduces the production of end ogenous NO. We compared exhalations of 41 current cigarette smokers wi th normal lung function and 73 age-matched nonsmoking controls. Peak e xhaled NO levels were measured by a modified chemiluminescence analyze r. The effects of inhaling a single cigarette in smokers were also mea sured. In control subjects we also measured the effects of inhalation of NO itself and carbon monoxide, both constituents of tobacco smoke. Peak exhaled NO concentrations were significantly reduced in smokers ( 42 +/- 3.9 compared with 88 +/- 2.7 parts per billion in nonsmokers, p < 0.01), with a significant relation between the exhaled NO and cigar ette consumption (r = -0.77, p < 0.001). Smoking a single cigarette al so significantly (p < 0.02), but transiently, reduced exhaled NO. Inha lation of carbon monoxide and NO had no effect on exhaled NO in normal subjects. Cigarette smoking decreased exhaled NO, suggesting that it may inhibit the enzyme NO synthase. Since endogenous NO is important i n defending the respiratory tract against infection, in counteracting bronchoconstriction and vasoconstriction, and in inhibiting platelet a ggregation, this effect may contribute to the increased risks of chron ic respiratory and cardiovascular disease in cigarette smokers.