Vasoactive and atherogenic effects of cigarette smoking: a study of monozygotic twins discordant for smoking.

The mechanism by which atherosclerotic disease is induced by cigarette smoking has not yet been identified unequivocally. Chronic cigarette smoking and the generation of vasoactive prostanoids and the size of carotid atherosclerotic plaques were studied in nine pairs of identical male twins discordant for smoking for over 20 years. The urinary excretion of 2,3-dinor-thromboxane B2 (thromboxane B2 metabolite) of the smoking twin was significantly higher (on average 1.8 times higher) in every pair and that of 2,3-dinor-6-keto-prostaglandin F1 alpha (prostacyclin metabolite) was significantly higher (on average 1.3 times higher) in eight of the nine pairs. The ratio of excretion of these metabolites was significantly higher, being 4.0 (95% confidence interval 2.7 to 5.4) among the smokers compared with 2.9 (2.1 to 3.8) among the non-smokers, thus favouring a mechanism of vasoconstriction. Excretion of the thromboxane B2 metabolite was related to the urinary concentrations of nicotine metabolites. Atherosclerotic plaques detected by ultrasonography in the carotid arteries were significantly larger among smokers but did not correlate with the urinary excretion of prostacyclin and thromboxane B2 metabolites or intensity of smoking. Smoking was concluded to induce activation of platelets by an effect mediated by nicotine. The increased prostacyclin production, on the other hand, suggested a compensatory mechanism for the general vasoconstrictive properties of cigarette smoking.