Indirect effects of bradykinin on ion transport in rat colon descendens: mediated by prostaglandins and enteric neurons.

The effect of bradykinin on two preparations of rat colon descendens was examined. In a mucosa-submucosa preparation consisting of the submucosal plexus, the mucosal plexus and the epithelium bradykinin (10(-10)-5 X 10(-9) mol.l-1) caused an increase in Isc, Gt and Pd which was to more than 70% diminished by TTX. However, in a mucosa preparation consisting of only the mucosal plexus and the epithelium bradykinin caused an increase in Isc, Gt and Pd, which was not affected by TTX. Ten times higher concentrations of bradykinin were needed in the mucosa preparation to reach the same effects as in the mucosa-submucosa preparation. All effects of bradykinin were markedly reduced in the presence of indomethacin indicating that they were mediated by prostaglandins in both preparations. The bradykinin effect in the mucosa-submucosa preparation but not in the mucosa preparation was reduced about 50% by atropine. The results suggest that bradykinin activates prostaglandin synthesis. Prostaglandins subsequently stimulate neurons in the submucosal plexus which induce a secretory response on the epithelium partially mediated by a muscarinic receptor. In a high concentration bradykinin due to the induction of prostaglandin synthesis can also activate directly the mucosal epithelium.