A bradykinin-like substance in rat stomach.

A bradykinin (BK)-like substance (P1) in the rat stomach was extracted with acetic acid, n-butanol, distilled water and methanol. The gradient and equilibrium chromatography were carried out on SP-Sephadex C-25 columns with the extract containing P1. P1 had a different retention time from BK, kallidin and methionyl-lysyl-bradykinin (MLBK), on the equilibrium chromatography. The apparent molecular weight of P1 estimated by gel chromatography was over 1,300. P1 was classified as a biologically BK-like peptide of mammalian origin which is distinct from BK, kallidin and MLBK. Another kind of biologically active substance (P2) which contracts the isolated rat uterus and duodenum was detected during the course of the extraction and purification of P1. The contractile activity of P2 was abolished by the presence of dibenamine or methysergide, but was not influenced by chymotrypsin, trypsin or papain digestion. The hypotensive effect of P2 on rabbit blood pressure was similar to that of serotonin (5-HT). The retention times of P2 on the equilibrium chromatography on the SP-Sephadex C-25 column, and on the gel chromatography were the same as those of 5-HT. P2 proved to be 5-HT.