Abbasali Abbasnezhad - Department of Basic Sciences, Faculty of Medicine, Gonabad University of Medical Sciences, Gonabad, Iran
Mohammad Reza Khazdair - Pharmaceutical Research Center and Department of Physiology, School of Medicine, Mashhad, Iran
Majid Kianmehr - Department of Physiology, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran

Objective(s): Analgesic effects of oxytocin and it's the other physiological effects were well-known. The aim of present study was determination of nitric oxide role on analgesic effects of oxytocin in mice. Materials and Methods: ۲۱۶ male Albino mice were divided randomly into two experimental groups, tail flick and formalin test. Each experimental group consists of three main groups including: saline, L-arginine (۵۰ mg/kg) and L-NAME (۱۰ mg/kg) intraperitoneal (IP) injection. ۱۵ min after injection in each of the following groups, the animals in each groups divided to the three subgroups including:  saline (n=۱۲), oxytocin (۱ mg/kg) (n=۱۲) and oxytocin (۱ mg/kg) + atosiban (۱ mg/kg) (n=۱۲) was injected IP and then after ۳۰ min of use the formalin test and tail flick were to evaluate the response to pain. Results: Area under the curve (AUC) in the late phase of the formalin test, in sub-groups oxytocin + saline and L-NAME were significantly decreased compared with saline + saline group (P<۰.۰۵ to P<۰.۰۰۱), and AUC in L-arginine + saline and atosiban + saline + oxytocin were significantly increased compared with oxytocin + saline group (P<۰.۰۵). Tail flick tests as well as a significant reduction in the AUC in oxytocin + L-arginine and atosiban + saline + oxytocin groups were compared with Oxytocin + Saline group (P<۰.۰۰۱). Conclusion: Oxytocin has analgesic effects in the acute and late phase of pain in the formalin test. Moreover, exogenous increasing of nitric oxide reduced the analgesic effect of oxytocin.

Analgesia, Mice, Nitric oxide, Oxytocin