Role of Chymase-Dependent Angiotensin II Formation in Regulating Blood Pressure in Spontaneously Hypertensive Rats

Abstract

Vascular smooth muscle cells in spontaneously hypertensive rats (SHR) express angiotensin II-forming chymase (rat vascular chymase [RVCH]), which may contribute to blood pressure regulation. In this study, we studied whether chymase-dependent angiotensin II formation contributes to the regulation of blood pressure in SHR. The systolic blood pressure in 16-week-old Wistar-Kyoto (WKY) rats was 113 ± 9 mmHg, compared to 172 ± 3 mmHg in SHR. Using synthetic substrates for measuring angiotensin-converting enzyme (ACE) and chymase activities, it was found that both ACE and chymase activities in extracts from SHR aortas were significantly higher than in those from WKY rat aortas. Using angiotensin I as a substrate, angiotensin II formation in SHR was found to be significantly higher than that in WKY rats, and its formation was completely suppressed by an ACE inhibitor, but not by a chymase inhibitor. RVCH mRNA expression could not be detected in aorta extracts from either WKY rats or SHR. In carotid arteries isolated from WKY rats and SHR, angiotensin I-induced vasoconstriction was completely suppressed by an ACE inhibitor, but not by a chymase inhibitor. Angiotensin I-induced pressor responses in both WKY rats and SHR were also completely inhibited by an ACE inhibitor, but they were not affected by a chymase inhibitor. In SHR, an ACE inhibitor and an angiotensin II receptor blocker showed equipotent hypotensive effects, but a chymase inhibitor did not have a hypotensive effect. These results indicated that chymase-dependent angiotensin II did not regulate blood pressure in SHR in the present study. (Hypertens Res 2005; 28: 457-464)

Role of Chymase-Dependent Angiotensin II Formation in Monocrotaline-Induced Pulmonary Hypertensive Rats

“…Chymase activity was measured by incubating the tissue extracts for 30 min at 37°C with 5 mM Suc-Ala-Ala-Pro-Phe-4-methylcoumaryl-7-amide (Peptide Institute) as a substrate for the measurement of chymase activity in 100 mM Tris-HCl buffer, pH 8.5, containing 200 mM NaCl (15). The enzyme reaction was terminated by the addition of 3% metaphosphoric acid (wt/vol).…”

Involvement of Vascular Angiotensin II-Forming Enzymes in the Progression of Aortic Abdominal Aneurysms in Angiotensin II- Infused ApoE-Deficient Mice

“…Chymase activity was measured by incubating the tissue extracts for 1 h at 37 with 5 mM Suc-Ala-AlaPro-Phe-4-methylcoumaryl-7-amide (Peptide Institute Inc., Osaka, Japan) as the substrate 18) . One unit of chymase activity was defined as the amount of enzyme required to cleave 1 mol of 7-amino-4-methylcoumarin/min.…”

“…ACE activity was measured by incubating tissue extracts for 1 h at 37 with 5 mM of hippuryl-HisLeu (Peptide Inst. Inc.) as the substrate in 100 mM phosphate buffer (pH 8.3) containing 300 mM NaCl 18) . One unit of ACE activity was defined as the amount of enzyme required to cleave 1 mol hippuric acid/min.…”

“…One unit of ACE activity was defined as the amount of enzyme required to cleave 1 mol hippuric acid/min. Ang -forming activity was measured by incubating tissue extracts for 2 h at 37 with 5 mM Ang in 10 nM phosphate buffer (pH 7.4) containing 150 mM NaCl 18) . One unit of Ang -forming activity was defined as the amount of enzyme required to form 1 mol Ang /min.…”

Tissue Angiotensin II Generating System by Angiotensin-Converting Enzyme and Chymase

“…When compared to ACE-related pathology, chymase-dependent pathology is even more localized, as described later. In addition, chymase inhibitors do not have a hypotensive effect (9). Indeed, ACE promotes both Ang II production and bradykinin degradation.…”