Sucrose-induced analgesia in mice: Role of nitric oxide and opioid receptor-mediated system

BACKGROUND: The mechanism of action of sweet substance-induced analgesia is thought to involve activation of the endogenous opioid system. The nitric oxide (NO) pathway has a pivotal role in pain modulation of analgesic compounds such as opioids. OBJECTIVES: We investigated the role of NO and the opioid receptor-mediated system in the analgesic effect of sucrose ingestion in mice. MATERIALS AND METHODS: We evaluated the effect of intraperitoneal administration of 10 mg/kg of NO synthase inhibitor, N-nitro-L-arginine methyl ester (L-NAME) and 20 mg/kg of opioid receptor antagonist, naltrexone on the tail flick response in sucrose ingesting mice. RESULTS: Sucrose ingestion for 12 days induced a statistically significant increase in the latency of tail flick response which was unmodified by L-NAME, but partially inhibited by naltrexone administration. CONCLUSIONS: Sucrose-induced nociception may be explained by facilitating the release of endogenous opioid peptides. Contrary to some previously studied pain models, the NO/cyclic guanosine monophosphate (cGMP) pathway had no role in thermal hyperalgesia in our study. We recommend further studies on the involvement of NO in other animals and pain models.