Abstract
The uptake and release of exogenous 3H-5-hydroxytryptamine (5-HT) by the electrically stimulated longitudinal muscle-myenteric plexus preparation of the guinea-pig ileum was measured. No significant difference in uptake was seen between normal and morphine-tolerant strips. The preparation releases 5-HT spontaneously and electrical stimulation increases the efflux. The electrically induced release of radioactive neurotransmitter was blocked by tetrodotoxin but not by atropine. Morphine did not affect the release. Further studies support recent findings that the morphine-tolerant guinea-pig ileum is supersensitive to 5-HT. Morphine inhibited 5-HT-induced twitches less effectiyelv in tolerant preparations, and submaximal electrical stimulation applied to tolerant strips caused greater twitch tensions compared with normal strips. These studies suggest that the action of morphine does not affect the presynaptic release of serotonin. The narcotic opiate could act postsynaptically.
Footnotes
- Received November 15, 1973.
- Accepted May 10, 1974.
- © 1974 by The Williams & Wilkins Co.
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