The role of cholinergic receptors in the analgesic effect of uridine

Pain is a health problem that negatively affects daily life and reports that there is a situation in the body that is not going well. The variation of pain threshold from person to person, constantly changing and developing technology and the side effects of existing analgesics are an obstacle to determination of a standard pain treatment. Therefore, our study aimed to investigate the possible analgesic effect of uridine on acute thermal and mechanical nociception and the role of the cholinergic system in this effect. Study was conducted in two stages as dose and experimental study; by using male Sprague Dawley rats. In dose study; following the intraperitoneally (i.p.) injection of saline or 0.1; 0.5; 1 and 2 mmol/kg doses of uridine, the thermal pain threshold was assessed with Tail Flick, Hot Plate and Plantar Tests at 1st, 2nd, 3rd and 4th hours and the mechanical threshold was assessed with the von Frey Test. After determining the effective dose and time in the the experimental phase; atropine (5 mg/kg; i.p.) or mecamylamine (1 mg/kg; i.p.) was injected 2 hours later following saline or uridine administration, and thermal and mechanical tests were performed 30 minutes after the injections. The results are presented as the percentage of maximum potential effect (%MPE) that takes into account differences between rats. The rats administered uridine at the dose of 1 mmol/kg had the highest %MPE values; this dose provided a significant antinociceptive effect, especially at the 2nd hour. When the role of cholinergic system in analgesia was evaluated, it was determined that the inhibition of both nicotinic (nAChRs) and muscarinic (mAChRs) acetylcholine receptors significantly decreased the %MPE values, hence played a role in the analgesic activity. However, mAChRs were found to be more effective in this analgesia compared to nAChRs. Intraperitoneally administered uridine has been shown to cause a dose dependent analgesic effect in acute pain. Uridine is thought to have minimum side effects due to being an endogenous substance therefore it is expected to be an alternative approach for the treatment of acute pain.