A Novel Bradykinin-Related Peptide, RVA-Thr(6)-BK, from the Skin Secretion of the Hejiang Frog; Ordorrana hejiangensis: Effects of Mammalian Isolated Smooth Muscle

A novel naturally-occurring bradykinin-related peptide (BRP) with an N-terminal extension, named RVA-Thr(6)-Bradykinin (RVA-Thr(6)-BK), was here isolated and identified from the cutaneous secretion of Odorrana hejiangensis (O. hejiangensis). Thereafter, in order to evaluate the difference in myotropic actions, a leucine site-substitution variant from Amolops wuyiensis skin secretion, RVA-Leu(1), Thr(6)-BK, was chemically synthesized. Myotropic studies indicated that single-site arginine (R) replacement by leucine (L) at position-4 from the N-terminus, altered the action of RVA-Thr(6)-BK from an agonist to an antagonist of BK actions on rat ileum smooth muscle. Additionally, both BK N-terminal extended derivatives (RVA-Thr(6)-BK and RVA-Leu(1), Thr(6)-BK) exerted identical myotropic actions to BK, such as increasing the frequency of contraction, contracting and relaxing the rat uterus, bladder and artery preparations, respectively.