AJP - Gastrointestinal and Liver Physiology, Vol 263, Issue 3 306-G311, Copyright © 1992 by American Physiological Society
Ascending contraction mediated by 5-hydroxytryptamine3 receptors in canine small intestine
M. Mizutani, T. Neya and S. Nakayama
Department of Physiology, Okayama University Medical School, Japan.
We investigated the mechanism of ascending contraction induced by
activation of 5-hydroxytryptamine3 (5-HT3) receptors in anesthetized dogs.
Pressure-measuring balloons were inserted into a loop of extrinsically
denervated jejunum. Drugs were administered via the arterial tree to the
oral or the anal segment and the ensuing mechanical responses were
monitored. Administration of 2-methyl-5-HT (440 pmol-44 nmol) to the anal
segment caused contractions in the oral segment in a dose-dependent manner.
This response was inhibited by treating the anal segment with ICS 205-930,
cocaine, hexamethonium, or tetrodotoxin and by treating the oral segment
with atropine or hexamethonium. The response persisted even after abolition
of contraction in the anal segment by nifedipine. These results imply that
activation of 5-HT3 receptors can induce an ascending contraction through
an enteric excitatory pathway formed by a series of cholinergic
interneurons and final cholinergic motor neurons, apart from the anal
contraction.
