A dopamine receptor antagonist modulates or enhances the analgesia of morphine and analysis of their synergetic analgesic mechanism / 中国病理生理杂志

ABSTRACT

AIM: To observe the synergetic analgesic effects of low dose of haloperidol, a dopamine antagonist and under-threshold dose of morphine on mice induced by thermal and acetic acid, and to analyze the major mechanism of their synergetic actions. METHODS: To examine the analgesic synergetic effect of haloperidol (0.315 mg/kg, 0.625 mg/kg, 1.25 mg/kg, ip respectively), morphine (3.125 mg/kg, 6.25 mg/kg, 12.5 mg/kg ip, respectively) or combining effect of haloperidol (0.3125 mg/kg) with morphine (3.125 mg/kg) on mice, we compared the change of pain threshold stimulated by thermal, latent period of twisting, the number of times of twisting by acetic acid, and we also estimated the antagonistic effect of d -amphetamine (10 mg/kg) and naloxone (5 mg/kg) on haloperidol and morphine group. RESULTS: Combination of haloperidol with morphine significantly enhanced pain threshold of mice induced by thermal, prolonged latent period of twisting and decreased the number of times of twisting. Naloxone markedly antagonized the combination of analgesic action of haloperidol and morphine and not d -amphetamine. CONCLUSION: Combination of haloperidol with morphine have synergetic analgesic effect and morphine is the dominant factor.