B2-kininergic action of linear and cyclic tryptophan6- and tyrosine6-kallidin.

This study was undertaken to determine the importance of the central aromatic moiety in the kallidin and cyclokallidin molecules, using the relaxation of the isolated duodenum of the rat. Replacement in kallidin of the central phenylalanine by tryptophan increased the potency from an EC50 of 3 x 10(-10)M to 2 x 10(-12)M. Replacement by tyrosine decreased the potency to an EC50 of 8 x 10(-8)M. In cyclo-kallidin (EC50: 10(-8)M) the potencies were decreased: cyclo-Trp6-kallidin showed an EC50 of 10(-6)M and cyclo-Tyr6-kallidin of 3 x 10(-7)M. The relaxation of the rat duodenum by linear and cyclic kinins was potentiated by the bradykinin potentiating peptide BPP5a and antagonized by the B2 antagonist HOE-140. At a concentration of 10(-9)M, HOE-140 significantly decreased the potencies of bradykinin and cyclo-kallidin, but not of the B1 agonist desArg9-bradykinin.