OPIATE AGONIST AND ANTAGONIST ACTION ON GUINEA-PIG ISOLATED ILEUM

1. It is well known that morphine reduces acetylcholine output from th e guinea-pig isolated ileum during transmural stimulation. However, th e 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 effec t 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 r ange of 1-20 Hz. 4. Therefore, it appears that morphine does not alter tetanic responses and endogenous opiates do not modulate neuroeffecto r transmission in this model.