Release of endogenous 5-hydroxytryptamine from the myenteric plexus of the guinea-pig isolated small intestine.
The presence of 5-hydroxytryptamine (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) in, and the release of these substances from, the myenteric plexus-longitudinal muscle (MPLM) layer of the guinea-pig isolated small intestine were investigated. 5-HT and 5-HIAA were measured by high performance liquid chromatography and electrochemical detection. Freshly prepared MPLM contained measurable amounts of 5-HT and 5-HIAA. For the release experiments, the MPLM was incubated in a medium containing the 5-HT uptake inhibitor fluoxetine and the monoamine oxidase inhibitor nialamide; this led to a decrease in the 5-HIAA content of the MPLM whereas the 5-HT content remained unchanged. There was a spontaneous release of 5-HT and 5-HIAA from the MPLM. The release of 5-HT was so small that it was just detectable; it seemed equivalent to about 0.8% of the tissue stores released per min. Depolarization of the tissue by increasing the [K+] or by exposing it to veratridine enhanced the release of 5-HT in a Ca2+-dependent manner whereas the release of 5-HIAA was not increased. Tetrodotoxin inhibited the veratridine-evoked release of 5-HT but did not affect the K+-evoked release of 5-HT. The presence of 5-HT in myenteric neurones and the characteristics of the release of 5-HT from these neurones strongly support the hypothesis that 5-HT is an enteric neurotransmitter.
D000818:Animals; D002851:Chromatography, High Pressure Liquid; D005260:Female; D006168:Guinea Pigs; D006897:Hydroxyindoleacetic Acid / Q000378:metabolism; D066298:In Vitro Techniques; D007421:Intestine, Small / Q000294:innervation / Q000378:metabolism*; D008297:Male; D009197:Myenteric Plexus / Q000378:metabolism*; D012701:Serotonin / Q000378:metabolism*
D012701:Serotonin; D006897:Hydroxyindoleacetic Acid