The Interrelationship between Bradykinin and Cyclo-Oxygenase Products in the Rat Small Intestine

Abstract

The effect of bradykinin on the release of prostaglandins from the rat isolated terminal ileum has been investigated. The release of prostaglandins from the ileum, into the surrounding bathing fluid, was measured by radioimmunoassay and by bioassay. Under basal conditions more PGE-like than PGF-like material was released from the ileum. When the ileum was incubated with bradykinin, an increase in the release of PGF-like, but not PGE-like material was observed. The release of prostaglandin-like material from the rat isolated perfused terminal ileum was assayed on the rat fundus strip. Bradykinin perfused over either surface of the ileum contracted the rat fundus strip more than when the ileum was absent. No increase was observed in the presence of indomethacin. However, it was found difficult to quantify the release of prostaglandin-like material after exposure to bradykinin, since contractions of the assay tissue to bradykinin appeared to be potentiated by the release of prostaglandin-like material from the ileum. The effect of the cyclo-oxygenase inhibitor indomethacin, was investigated upon contractions of the rat isolated perfused ileum to bradykinin. Contractions of the ileal longitudinal muscle to bradykinin during mucosal, but not serosal perfusion of the ileum, were reduced in the presence of indomethacin. Furthermore, in the ileum from rats pretreated with indomethacin, contractions to bradykinin were also only reduced during mucosal perfusion. A similar interrelationship on the mucosal surface, between bradykinin and cyclo-oxygenase products, was demonstrated in the relaxation of the rat isolated perfused duodenum to bradykinin. The additional involvement of cyclic nucleotides and a neuronal mechanism in the response of the mucosal perfused rat small intestine to bradykinin is suggested. It is concluded that cyclo-oxygenase products are involved in the response of the mucosal, but not the serosal perfused rat small intestine to bradykinin, although the exact nature of this involvement is unclear.