Antinociceptive Effect of the Combination of Pentazocine With Morphine in the Tail-Immersion and Scald-Pain Tests in Rats

抄録

We investigated the antinociceptive effect of pentazocine hydrochloride(pentazocine)in combination with morphine hydrochloride(morphine)using two antinociceptive tests;i.e., the tail−immersion and scald−pain tests, in rats.In the tail−immersion test, the rat’s tail was immersed in warm water at 47°C, and the latency to a nociceptive response was measured.In the scald−pain test, the right hind foot was scalded by immersion into hot water at 57°C.Two hours later, additional thermal stimulus was applied to the same foot, and the latency to a nociceptive response was measured.Subcutaneous treatment with either pentazocine(6, 12, 24 mg/kg)or morphine(1.5, 3, 6 mg/kg)alone dose−dependently showed antinociceptive effects in both tests.The ED₅₀ values(95% confidence limit)of pentazocine and morphine were 13.0(5.4−31.5)and 2.4(1.6−3.7)mg/kg in the tail−immersion test and 11.0(4.5−26.6)and 3.8(1.8−7.2)mg/kg in the scald−pain test, respectively.Simultaneous treatment with pentazocine at the similar dose augmented the morphine(1.5 mg/kg)−induced antinociception, but did not diminish the morphine(6 mg/kg)−induced antinociception in both tests.These results suggest that the simultaneous administration of pentazocine at the antinociceptive dose and morphine exerts additional antinociceptive activity against thermal and scald−induced inflammatory pain.