Effects of bradykinin and some of its fragments on smooth muscles and chemotaxis.

Bradykinin (BK) and two of its C-terminal fragments, namely H-Phe-Ser-Pro-Phe-Arg-OH and H-Ser-Pro-Phe-Arg-OH were found to be potent inhibitors of the chemotaxis of rat polymorphonuclear neutrophils (PMN). The activity of the three peptides was significantly enhanced by SQ 14225, a rather specific inhibitor of kininase II. A shorter C-terminal sequence of BK (Phe-Arg-OH) was inactive. The whole peptide (BK) exerted potent actions on blood pressure and on isolated organs, e.g. the rabbit mesenteric vein or the guinea pig ileum, but none of its fragments showed similar effects. The present findings suggest that rat PMN possess membrane receptors which cannot be considered identical to B1- and B2-receptors, previously characterized on isolated smooth muscles.