Effects of Allyl Isothiocyanate, Acetaminophen, and Dipyrone in the Guinea-Pig Ileum

Allyl isothiocyanate (AITC, mustard oil, 50-200 µmol/l), depending on specific dosages, inhibited the cholinergic twitch response in the longitudinal muscle-myenteric plexus (LMMP) strip of the guinea-pig ileum. AITC also induced short-lasting contractile responses, and decreases of the basal tone of the LMMP strip at low concentrations and increases at high concentrations. Hexamethonium, a blocker of nicotinic ganglionic transmission, was able to prevent the AITC-evoked inhibitory effect, an effect that was also observed with the opioid antagonist naloxone. The P2 purinoceptor antagonist pyridoxalphosphate-6-azophenyl-2'-4'-disulphonic acid and guanethidine had no significant influence on the inhibitory effect of AITC. Since AITC also reduced the electrical stimulation-induced myogenic smooth muscle contractions in the LMMP preparation, its contractile and relaxant actions can be regarded as neurogenic and myogenic in nature. The analgesics, acetaminophen (paracetamol, 100-500 µmol/l) and dipyrone (metamizole, 100-500 µmol/l), reduced both the cholinergic twitch and the myogenic contractions in the LMMP strip to the same extent; therefore, their action in the intestinal smooth muscle can be regarded as myogenic spasmolytic in nature.