EFFECT OF SCOPOLAMINE ON PAIN AND ANALGESIC ACTIVITY

Thirty minutes after the intraperitoneal administration of scopolamine to rabbits at a dose of 4 mg/kg, the pain threshold, measured by the potassium iontophoresis method, was increased by 49%. If the same dose of scopolamine was given intravenously, the pain threshold was increased by 37% when measured 20 minutes after administration. However, when 5 μg of scopolamine were given to each rabbit intraventricularly, the pain threshold was increased by 53%. These results indicate that scopolamine has certain analgesic action. When scopolamine (4mg/kg) was given in combination with dolantin (60 mg/kg) intraperitoneally, the pain threshold was increased by 147%. In contrast, if dolantin (60 mg/kg) was given alone, the pain threshold was increased by 93%. It appears that there is a synergistic action between scopolamine and dolantin.When scopolamine (1.25 mg/kg) or dolantin (10 mg/kg) was given to rats intraperitoneally the pain threshold, measured by the hot plate method 15 minutes after drug administration, was increased by 62% or 23%, respectively. When these two drugs were given in combination, the pain threshold was found to beincreased by 126%. this is consistant with the result obtained in the experiments for rabbits.Ten minutes after the intraventricular administration of 20 μg of noradrenaline to a rabbit, the pain threshold was decreased by 46%. When noradrenaline was given in combination with dolantin, the analgesic effect of the latter compound was also diminished. In addition, administration of scopolamine with noradrenaline, the pain threshold decreasing effect of the latter was antagonized. These results seem to suggest that the analgesic effect of scopolamine is related to. its antagonistic action to the effects of noradrenaline.