Effect of chronic administration of zinc supplements (ZnO and nano ZnO) with and without aerobic exercise on nociception in male rats

Introduction: The use of zinc supplements can decrease somatic and visceral pains. Exercise also increases the pain tolerance. In recent years, production and use of nano metal particles such as nano ZnO for pharmaceutical, hygienic and industrial purposes is rapidly increasing, while studies about its effects on human health are limited. The aim of the present study was to compare the effect of chronic administration of nano and conventional ZnO on nociception in the presence and absence of anti nociception mechanisms induced by aerobic exercise. Methods: In this investigation, adult male Wistar rats (185±10 gr) were used in the following groups: Control (receiving saline, without exercise), exercise, conventional ZnO and/or nano ZnO daily (1 mg/kg i.p., 5 days a week) for 6 weeks with and without aerobic exercise. Exercise groups did daily protocol of exercise for 30 minutes after drug injection. In the end, analgesia time was evaluated by hot plate test. Results: Exercise, ZnO and nano ZnO significantly reduced pain (P<0.01, P<0.05, P<0.01). Nano ZnO showed a better analgesic effect in comparison to conventional ZnO, but this difference was not significant. Similarly, no significant difference was found between the group that had only exercise and groups treated with ZnO and/or nano ZnO. Conclusion: Antinociception mechanism induced by exercise is not potentiated with nano and conventional ZnO.