OPIATE AGONIST AND ANTAGONIST ACTION ON GUINEA-PIG ISOLATED ILEUM

1. It is well known that morphine reduces acetylcholine output from the guinea-pig isolated ileum during transmural stimulation. However, the effect of morphine on tetanic responses of this preparation has not been examined. 2. The present study shows that responses elicited over the frequency range of 1-20 Hz were unaffected by a concentration of morphine which markedly reduced twitch responses. Similarly, the effect of naloxone on responses elicited in this preparation to transmural stimulation is not known. 3. We report here that naloxone (1 mu M) had no effect on either twitches or tetanic responses elicited over the range of 1-20 Hz. 4. Therefore, it appears that morphine does not alter tetanic responses and endogenous opiates do not modulate neuroeffector transmission in this model.