THE ROLE OF SUPERSENSITIVITY TO ACETYLCHOLINE IN THE PRODUCTION OF TOLERANCE TO MORPHINE IN STIMULATED GUINEA‐PIG ILEUM

Abstract

1 Morphine caused a dose-dependent reduction in both the height of contraction and acetylcholine release from coaxially stimulated strips of guinea-pig ileum. 2 Exposure of the tissue to morphine for 90 min produced acute tolerance to the effect of subsequent doses of morphine on contraction height. 3 There was no change in the ability of morphine to suppress acetylcholine release. 4 The responses of morphine-tolerant ileum to exogenous acetylcholine were enhanced 3 to 10-fold. 5 If the ileum did not show tolerance to morphine it did not become more sensitive to acetylcholine. 6 The results presented suggest that tolerance to morphine could result from a form of disuse supersensitivity.