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Inhibition of the contractile action of bradykinin on isolated smooth muscle preparations by derivatives of low molecular weight peptides.

The carbonyl terminal tripeptide sequence of bradykinin (Pro-Phe-Arg) is molecularly manipulated to obtain agents with potent antagonistic activity towards the smooth muscle contractile activity of bradykinin. Screening of various peptide derivatives revealed that heptyl amides or esters of H-D-Pro-Phe-Arg, and H-D-Phe-Phe-Arg possessed relatively stronger antibradykinin activity on the isolated smooth muscle preparation. The parent tripeptides, H-D-Pro-Phe-Arg-OH, and H-D-Phe-Phe-Arg-OH, and their amino acid components, i.e. D-Proline, D-Phenylalanine, L-Phenylalanine and Arginine, did not possess any antibradykinin activity in concentrations of up to 10(-4) M. When the heptyl derivatives of these peptides were incubated with either heparinized or citrated whole blood or plasma, the antibradykinin activity was not lost. Incubation of these peptide derivatives with either carboxypeptidase A or B did not result in any loss of the pharmacological effect. However, pancreatic protease extract produced a significant loss of the anti-oxytocic action on the isolated rat uterus preparation. H-D-Pro-Phe-Arg-NH-lauryl derivative also blocked the action of bradykinin and this effect sustained for a longer period of time comparative to the blockade with H-D-Pro-Phe-Arg-NH-heptyl derivative. In concentrations of 10(-7) M and 10(-8) M and 1 min incubation, which blocked the contractile action of bradykinin (1 nmole) on the isolated guinea pig ileum, these peptide derivatives did not block the action of acetylcholine, histamine, and serotonin. However, in concentrations of about 10(-6) M and higher with 5 min. incubation histamin is also blocked. On the isolated rat uterus preparation the contractile action of acetylcholine, angiotensin, oxytocin and vasopressin was blocked at concentrations of 10(-6) M. These findings warrant a differential pharmacological evaluation and in vivo testing of these peptide derivatives to investigate their therapeutic potential.