Comparative effects of intraduodenal psyllium and senna on canine small bowel motility

To define the possible contribution of altered small intestinal motor activity to side-effects of bulking fibres, we sought to compare the relative effects of intraduodenal and intracolonic administration of the bulking fibre psyllium and the anthraquinone laxative senna on canine small intestinal motor activity.

Motor activity was recorded by serosal strain gauges implanted along the small intestine in 6 dogs. In random order, the motor responses to the instillation of psyllium (in doses of 5 or 10 g), senna (10 mg/kg) or appropriate vehicle (200 ml water infusion or saline 5 ml bolus) into either the proximal duodenum or proximal colon were assessed.

The intra-duodenal administration of psyllium in either dose consistently induced a prolonged burst of 'clustered' contractions; in contrast, clusters were infrequent and of short duration following instillation of either vehicle or senna (P < 0.05). Intraduodenal instillation of psyllium inhibited migrating motor complex (MMC) migration and consistently delayed the onset of the next MMC cycle; a similar inhibition occurred with vehicle, however. Neither senna nor its vehicle inhibited MMC migration. None of these agents had any effect on small intestinal motor activity when instilled directly into the colon.

Psyllium administered directly into the duodenum inhibits MMC activity and consistently induces 'clustered' contractions. Whilst the MMC-inhibitory effect appears to be a non-specific volume-related phenomenon, the induction of clusters is independent of volume or laxation. These motor effects of psyllium may contribute to the gastrointestinal symptomatology related to such agents and could be avoided by the preferential release of psyllium in the colon.