Abstract 622: Angiotensin-(1-12) Is A Better Substrate Compared To Angiotensin I To Generate Angiotensin Ii By Rat Chymase.
Angiotensin-(1-12) [Ang-(1-12)] is metabolized by chymase to generate angiotensin II (Ang II). We investigated the affinity of rat chymase to generate Ang II from Ang-(1-12) or angiotensin I (Ang I). Plasma membranes isolated from the heart of spontaneously hypertensive rats (SHR) were incubated with radiolabeled 125I-Ang-(1-12) or 125I-Ang I substrate in the absence or in the presence of a chymase inhibitor (chymostatin, 50 μM). 125I-Ang II formation was quantified by HPLC. The rate of 125I-Ang II formation from 125I-Ang-(1-12) by chymase in cardiac plasma membranes was significantly higher (5.7±0.2 fmol/min/mg protein, P<0.001) when compared to 125I-Ang I (0.82±0.13 fmol/min/mg protein). Substrate affinity of 125I-Ang-(1-12) for rat chymase was also confirmed by using an excess amount of unlabeled Ang-(1-12) or Ang I (0-250 μM). 125I-Ang II formation was significantly decreased by unlabeled Ang-(1-12) as compared to Ang I. We also investigated angiotensin-converting enzyme (ACE) mediated hydrolysis of 125I-Ang-(1-12) and 125I-Ang I in generating Ang II in SHR cardiac plasma membranes. No significant difference in 125I-Ang II formation was detected with either substrate. Moreover, the rate of 125I-Ang II production by ACE was lower (1.8±0.4 fmol/min/mg protein for Ang-(1-12) and 2.1±1.2 fmol/min/mg protein for Ang I) as compared to chymase. These data suggest that in the rat heart, Ang II formation from Ang-(1-12) is primarily mediated by chymase rather than ACE. Overall our findings suggest in the heart of SHR that compared to Ang I, Ang-(1-12) is the better substrate for Ang II formation. In addition, we confirm our previous observation that chymase is the main hydrolyzing enzyme responsible for Ang II generation from Ang-(1-12) in the rat heart.
Author Disclosures: S. Ahmad: None. J. Varagic: None. J.L. VonCannon: None. L.J. Dell'Italia: None. L. Groban: None. C.M. Ferrario: None.
- © 2014 by American Heart Association, Inc.