Tolerance to and dependence on opioids in isolated longitudinal muscle of guinea pig ileum. Validity of the muscle preparation as a receptor model for opioids
Kaneto, H.; Watanabe, J.
Nihon Yakurigaku Zasshi. Folia Pharmacologica Japonica 76(5): 347-354
1980
ISSN/ISBN: 0015-5691 PMID: 6259029 Document Number: 159521
Contractions evoked by electrical stimulation of isolated longitudinal muscle preparations of guinea pig ileum were inhibited by the addition of opioids in the order of morphine = methionine enkephalin greater than pentazocine pethidine. Incubation of the preparation in the medium containing opioids at 4 degrees C for 22 hr resulted in a tolerance to the inhibitory effect in morphine and pethidine but in the case of pentazocine and met-enkephalin tolerance did not develop under the conditions employed. The same treatment with morphine, pethidine and pentazocine resulted in the development of dependence as demonstrated by naloxone provoked contracture or increase in the height of contraction. Opiate and enkephalin receptors are known to be unevenly distributed in the ileum and a significant difference was also observed in the distribution patterns of both receptors. Distribution of the receptors did not parallel the effect of opioids, thereby indicating a multiplicity in receptors. However, under the conditions employed in the present experiments, our results reflect the in vivo effects of opioids, such as analgesic effect or tolerance and dependence liability, and the validity of this preparation for the evaluation of opioids was confirmed.