Potentiation of des-Arg9-kallidin-induced vasoconstrictor responses by metallopeptidase inhibition in isolated human umbilical artery.

Several metallopeptidases have been reported to be involved in bradykinin (BK) B(1) receptor agonist metabolism. Our goal was to evaluate in vitro roles of metallopeptidases [e.g., neutral endopeptidase (NEP), aminopeptidase M (APM), and angiotensin-converting enzyme (ACE)] as functional inactivators of the selective BKB(1) receptor agonist Lys-des-Arg(9)-BK (DAKD) in isolated human umbilical artery (HUA) rings. Concentration-response curves (CRCs) to DAKD were performed after a 5-h incubation period. Treatment with 10 microM phosphoramidon (NEP inhibitor) or 10 microM amastatin (APM inhibitor) potentiated DAKD-elicited responses, whereas 1 microM captopril (ACE inhibitor) had no significant effects. However, when the three enzymes were simultaneously inhibited, a significant potentiation over responses obtained under concurrent NEP and aminopeptidase M inhibition was observed. In contrast, responses induced by the peptidase resistant BKB(1) receptor agonist Sar-D-Phe(8)-des-Arg(9)-BK were not modified by triple peptidase inhibition. In addition, endothelial denudation failed to alter DAKD-induced responses in HUA. Finally, in the presence of NEP, ACE, and APM inhibition, Lys-des-Arg(9)-[Leu(8)]-BK, the potent BKB(1) receptor antagonist, produced a parallel, concentration-dependent, rightward shift of DAKD CRCs. The obtained pK(B) (8.57) and the Schild slope not different from unity are in agreement with an interaction at a single homogeneous BKB(1) receptor population. In summary, this work constitutes the first pharmacological evidence that metallopeptidases NEP, APM, and ACE represent a relevant inactivation mechanism of the endogenous BKB(1) receptor agonist DAKD in isolated HUA.