Bradykinin Competitive Antagonists for Classical Kinin Systems

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Abstract
The substitution of D-phenylalanine for proline at position 7 of bradykinin (BK) converts BK into a specific antagonist. Additional modifications of the nonapeptide structure, especially the inclusion of β-2-thienylalanine residues (Thi) for phenylalanine at positions 5 and 8, increase antagonist potency in the classic smooth muscle (isolated rat uterus and guinea pig ileum) and rat blood pressure kinin assays. [ Thi5,8,DPhe7]-BK had a pA2 value of 6.5 for inhibition of the BK response on rat uterus, and 6.3 on guinea pig ileum. Addition of Lys-Lys- or a D-Arg- residue to the N-terminal of D-Phe7-substituted antagonists decreases uterine agonist activity, but does not affect inhibitory potency on the ileum. Addition of a D-proline residue in place of proline in position 3 of D-Arg- extended antagonists produces specific uterine inhibitors which show no antagonism on the ileum. The D-Phe7-analogs did not inhibit smooth muscle responses to substance-P or angiotensin-II, and the antagonism of kinin responses was competitive.

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