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(Hypertension. 2005;45:120.)
© 2005 American Heart Association, Inc.
Scientific Contributions |
From the Department of Pharmacology (J.H.M.v.E., B.T., W.W.B., R.d.V., A.H.J.D.) and Internal Medicine (J.M.G.v.G., R.J.A.d.B.), Erasmus MC, Rotterdam, The Netherlands; CEA (V.D.), Départment dIngénierie et dEtudes des Protéines, CE-Saclay, France; and Department of Organic Chemistry (D.G., A.Y.), Laboratory of Organic Chemistry, University of Athens, Panepistimiopolis, Zografou, Greece.
Correspondence to Dr A.H.J. Danser, Professor, Department of Pharmacology, Room EE1418b, Erasmus MC, Dr Molewaterplein 50, 3015 GE Rotterdam, The Netherlands. E-mail a.danser{at}erasmusmc.nl
Somatic angiotensin-converting enzyme (ACE) contains 2 domains (C-domain and N-domain) capable of hydrolyzing angiotensin I (Ang I) and bradykinin. Here we investigated the effect of the selective C-domain and N-domain inhibitors RXPA380 and RXP407 on Ang Iinduced vasoconstriction of porcine femoral arteries (PFAs) and bradykinin-induced vasodilation of preconstricted porcine coronary microarteries (PCMAs). Ang I concentration-dependently constricted PFAs. RXPA380, at concentrations >1 µmol/L, shifted the Ang I concentration-response curve (CRC) 10-fold to the right. This was comparable to the maximal shift observed with the ACE inhibitors (ACEi) quinaprilat and captopril. RXP407 did not affect Ang I at concentrations
0.1 mmol/L. Bradykinin concentration-dependently relaxed PCMAs. RXPA380 (10 µmol/L) and RXP407 (0.1 mmol/L) potentiated bradykinin, both inducing a leftward shift of the bradykinin CRC that equaled
50% of the maximal shift observed with quinaprilat. Ang I added to blood plasma disappeared with a half life (t1/2) of 42±3 minutes. Quinaprilat increased the t1/2
4-fold, indicating that 71±6% of Ang I metabolism was attributable to ACE. RXPA380 (10 µmol/L) and RXP407 (0.1 mmol/L) increased the t1/2
2-fold, thereby suggesting that both domains contribute to conversion in plasma. In conclusion, tissue Ang III conversion depends exclusively on the ACE C-domain, whereas both domains contribute to conversion by soluble ACE and to bradykinin degradation at tissue sites. Because tissue ACE (and not plasma ACE) determines the hypertensive effects of Ang I, these data not only explain why N-domain inhibition does not affect Ang Iinduced vasoconstriction in vivo but also why ACEi exert blood pressureindependent effects at low (C-domainblocking) doses.
Key Words: angiotensin bradykinin angiotensin-converting enzyme
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