Stimulation of mucus output from rat colon in vivo

Sodium chloride (155 mM) and N-acetyl cysteine (6 mM) were recirculated through the colons of anaesthetized rats. Mucus accumulated in the perfusion fluid which was changed at intervals to allow mucus output to be estimated by measurement of hexose. The output of mucus could be stimulated by intravenous administration of the cholinergic drugs carbachol and bethanechol; this effect was inhibited by atropine. Mucus output could also be stimulated by intravenous 5-hydroxytryptamine. This was not a muscarinic cholinergic effect because atropine did not prevent it. Neither did methysergide inhibit it; but chlorpromazine did. Precursors of 5-hydroxytryptamine, 5-hydroxytryptophan and L-tryptophan, also stimulated mucus output if given in high dosage. The results suggest that in this preparation mucus output can be stimulated by two distinct mechanisms, one cholinergic, the other involving 5-hydroxytryptamine and perhaps 5-hydroxytryptophan.