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. Therefore, mice were divided into four groups: 1) Zinc-deficient, 2) Pair-fed, 3) Control-morphine, and 4) Control-saline groups. Mice were fed during 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 and 20 min later the antinociceptive effect of morphine was evaluated by tail immersion test. In spite of morphine injection, the tail withdrawal latency of zinc-deficient mice was not different from control-saline (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 control-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 antinociceptive effects of morphine. Zinc may be necessary in physiologic range for morphine to exert antinociception activity.