The effects of morphine and nicotine co-administration on body weight, food intake and appetite-regulating peptides in rats

Previous studies in humans and animals have reported that nicotine administration decreases body weight
and caloric intake. Opiate and cigarette have been used concomitantly as drug abuse. The aim of the present study was, therefore, to analyze the effect of chronic co-administration of nicotine and morphine on food intake, body weight and on some feeding-associated peptides. All experiments were carried out on male Wistar rats. Animals were randomly assigned to the free-fed and pair-fed control groups, nicotine- and
morphine-treated and nicotine plus morphine groups. Morphine sulfate (20 mg/kg for 14 days s.c.) and
nicotine (4 mg/kg for 14 days i.p.) were injected to the rats. The serum levels of leptin and neuropeptide Y
(NPY) were measured by enzyme immunosorbant assay and radioimmunoassay, respectively. The results
showed that nicotine had a greater suppressing effect on total food intake than morphine alone or nicotine
plus morphine. Furthermore, chronic injection of nicotine significantly decreased body weight as compared
with before injection, while body weight changes were not observed in morphine-treated rats. The mean body
weight in the morphine-treated rats was lower than that in the free-fed control animals. The serum level of
NPY was decreased just in the nicotine-injected group. A significant decrease in leptin levels was observed
in the drug treated and pair-fed groups. In conclusion, morphine modulates the decreasing effect of nicotine
on food intake, and it seems that the mechanism underlying the attenuating effects of morphine on the
nicotine effects involves mediation, at least in part, by preventing the effect of nicotine on NPY levels.