THE EFFECT OF ZINC-DEFICIENCY ON MORPHINE ANTINOCICEPTION

The present study is designed to examine the effect of zinc deficiency and possible role of zinc on morphine antinociception in mice. Theref ore, mice were divided into four groups: 1) Zinc-deficient, 2) Pair-fe d, 3) Control-morphine, and 4) Control-saline groups. Mice were fed du ring eight weeks of the study. At the end of this period 1.5 mg.Kg(-1) morphine was injected into mice except for the control-saline group a nd 20 min later the antinociceptive effect of morphine was evaluated b y tail immersion test. In spite of morphine injection, the tail withdr awal latency of zinc-deficient mice was not different from control-sal ine (p > 0.05). The same parameter in pair-fed group was significantly different from control-saline (p < 0.05) and control-morphine groups. On the other hand, there was no difference between pair-fed and contr ol-morphine groups (p > 0.05). In addition, plasma zinc levels of zinc -deficient mice were significantly lower than other groups (p < 0.05). Our results suggest that zinc deficiency may prevent the antinocicept ive effects of morphine. Zinc may be necessary in physiologic range fo r morphine to exert antinociception activity.