Effects of pentazocine on the guinea-pig ileum

The pA2 values for pentazocine-Ach, pentazocine-5HT and pentazocine-histamine antagonism on the guinea-pig ileum were found to be 8.0, 7.92 and 7.08, respectively. When the effects of a constant dose of pentazocine on equipotent doses of Ach, histamine, 5HT, and nicotine were studied, its anti-5HT and anti-Ach activities were found to be equal and about 6.3 times higher than its antihistamine activity but 0.68 times lower than its anti-nicotine activity. The antihistamine activity of pheniramine was found to be 794 times that of pentazocine while the anti-Ach activity of atropine, the anti-5HT activity of cyproheptadine and the anti-nicotine activity of hexamethonium were 20, 10 and 2.2 times, respectively, higher than that of pentazocine.