The effect of chronic nicotine and its withdrawal on ED50 inspired halothane requirement in rats.
BACKGROUND
Based on previously observed antinociceptive effect of chronic nicotine treatment in rats, the authors measured the ED50 inspired halothane, concentrations in rats having withdrawn from chronically infused nicotine, and in control rats.


METHODS
Rats in nicotine group (n = 19) were chronically exposed to nicotine (6 mg/kg/day for 28 days) infusion via Alzet osmotic pumps. Those in the control group (n = 16) were subjected to a sham operation. In each group, half of the rats was used one month later to explore the effect of nicotine withdrawal. Halothane in oxygen was delivered at a rate of 2 L/min to a box measured 2,912 cm3. The ED50 halothane concentration, measured by mass spectrophotometry, was a midway gas tension at which 50% of rats responded to the tail pinching applied to the distal third of the tail for 30 s.


RESULTS
In nicotine group, the results showed a lower concentration of ED50 inspired halothane on days 1 and 3 in the first week (p < 0.05). In the control group, repeated exposures to halothane gradually decreased the ED50, reaching lowest value on day 7 (p < 0.05 compared to day 1). Nicotine withdrawal did not alter the ED50 concentration of halothane in test rats compared with control rats.


CONCLUSIONS
We conclude that chronic nicotine infusion could temporarily decrease the ED50 concentration of inspired halothane, and withdrawal of nicotine did not modify the ED50 concentration of halothane. In addition, the ED50 halothane concentration might be influenced by stress.
Yang
C Y
CY
Department of Anesthesiology, Chang Gung Memorial Hospital, Kweishan, Taoyuan, Taiwan, R.O.C.
Wu
W H
WH
Zbuzek
V K
VK
D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D001835:Body Weight / Q000187:drug effects; D004347:Drug Interactions; D006221:Halothane / Q000494:pharmacology*; D008297:Male; D009538:Nicotine / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley
D018685:Anesthetics, Inhalation; D009538:Nicotine; D006221:Halothane