Effects of Nicotine on the Subcutaneous Microcirculation of the Bat 1,2

Abstract

Summary

The intraperitoneal toxicity of nicotine was studied in bats (Myotis lucifugus). The LD₅₀ was 39.7 mg/kg (33.1–47.7 mg/kg; 95% confidence limits). Thus, nicotine appears to be less toxic to the bat than to the mouse, rat, or rabbit.

Direct quantitative observations of vascular diameters in unanesthetized bats were made with a microscope combined with a closed circuit television system. The diameter of innervated minute arteries markedly increased with intraperitoneal nicotine administration. Minute vein diameter slightly increased while minute vein vasomotion slightly decreased. Sympathetic denervation abolished the increase in minute artery diameter when nicotine was administered. However, minute vein diameter decreased and was also accompanied by decreased minute vein vasomotion. Nicotine caused an increase in heart rate which was not found to be significant. These data suggest that nicotine may produce vasoconstriction by direct action on the peripheral vasculature, and that minute vein dilatation may have been mediated via the sympathetic system. However, we cannot presently exclude the possibility that a passive dilation of the minute vein occurs for the innervated series because minute artery dilatation may have increased minute vein pressure and flow. Since a decrease in vasomotion has usually been found to accompany an increase in minute vein diameter, our data suggests that minute vein diameter and vasomotion can be manipulated independently.