Serotonergic regulation of canine enteric motility (measured as electrical activity) and absorption: physiologic and morphologic evidence.

To explore the effect of serotonin (5-HT) on enteric electrical activity, transit and absorption, four dogs were prepared with 50 cm jejunal and ileal Vella loops. Electrodes for recording enteric electrical activity were attached to the loops and to the main small bowel. After recovery, both loops were perfused with a [14C-]PEG-glucose-electrolyte solution via the proximal stomas, while effluent was collected from the distal stomas and enteric electrical activity was monitored. Control periods were compared with periods when 5-HT was infused intravenously at a rate of 10 micrograms kg-1 min-1 for 60 min. Serotonin increased the mean +/- SEM % of jejunal and ileal pacesetter potentials with spike potentials from 33 +/- 7% and 35 +/- 9%, before infusion to 63 +/- 4% and 61 +/- 5% after infusion (P less than 0.05). Serotonin also induced distally-migrating bursts of spikes in the incontinuity small bowel. The changes were blocked by atropine, but not by ketanserin. Absorption of water, sodium and glucose from the jejunal and ileal loop and transit through the loops was not changed by 5-HT. At autopsy, all layers of the jejunum and ileum contained varicose nerve fibres with a positive immunoreaction to 5-HT, while positive nerve cell bodies were largely confined to the submucosa.