Comparative effects of hypertension and nicotine on injury-induced myointimal thickening

Although hypertension has been shown to increase myointimal thickening after arterial injury, a similar effect of nicotine has not been demonstrated. To compare the influence of nicotine with the known effect of hypertension, a standard balloon catheter injury was created in the aortas of four groups of experimental animals. A preliminary group (P) (n = 11) consisted of adult Wistar Kyoto rats used to determine the degree of denudation and the time course of arterial healing; group I (n = 10) consisted of adult Wistar Kyoto rats; group II (n = 13) consisted of spontaneously hypertensive rats; and group III (n = 16) consisted of Wistar Kyoto rats fed nicotine. Endothelial denudation was achieved after an identical injury with an aortic balloon catheter; completeness of denudation was confirmed in group P with Evans blue stain. Injured vessels were fixed by perfusion at 2- and 9-week intervals. Intima to media (I/M) ratios were measured at 82 points per animal by use of light microscopy. Computer-assisted statistical analysis was performed with the t test and Wilcoxon nonpaired rank sum test. Serum nicotine levels were maintained in group III at 73.3 +/- 36.7 ng/ml, which is comparable to levels in human smokers. There were no significant differences in I/M ratios between any of the groups at 2 weeks. At 9 weeks both groups II and III had significantly higher I/M ratios than did control subjects (p = 0.039). The nicotine-treated group had greater myointimal thickening than did the hypertensive animals (p = 0.02). Since there was no hypertension or tachycardia in nicotine-treated rats, we postulate that our data reflects the desquamating effect of nicotine.