Potentiating Effects of Bradykinin-related Substances on Bradykinin-induced Contraction of Guinea Pig Ileum and Hypotension in Rats

Bradykinin-related substances were studied in vitro and in vivo for bradykinin-potentiating activity. Of the ten peptides which augmented the contractile response of isolated guinea pig ileum to bradykinin, des-Pro2-bradykinin was the most potent. Its potency was 1.9 times that of potentiator B, a bradykinin potentiating peptide obtained from the venom of Agkistrodon halys blomhoffii. This peptide also potentiated the vasode-pressing activity of bradykinin in rats and inhibited angiotensin converting enzyme. These findings indicate that des-Pro2-bradykinin, like venom peptides, potentiates the activity of bradykinin, possibly by inhibiting angiotensin converting enzyme (kininase II).