Angiotensin converting enzyme-independent angiotensin II production by chymase is up-regulated in the ischemic kidney in renovascular hypertension

Background. Tissue angiotensin II (ANG II) levels are elevated in both kidneys in renovascular hypertension (RVH). It has been demonstrated previously that intrarenal ANG 11 is augmented by an angiotensin converting enzyme (ACE) dependent mechanism in the non-ischemic kidney, but the role of ACE-independent production of ANG 11 in the kidney by the enzyme chymase is unknown. This study tested the hypothesis that intrarenal chymase activity is upregulated in RVH. Methods. A two-kidney, one-clip (2K1C) rat model was used to induce RVH (n = 6 rats/group). Regulation of intrarenal chymase activity by plasma ANG II was investigated using an ANG II-infusion model. At sacrifice 14 days post-operatively, steady-state ANG II levels in plasma and kidney were quantified by radioimmunoassay. ANG II production was quantified in kidney homogenates by incubating at 37 degrees C for 60 min with enzyme substrate (200 mu M ANG 1) alone or substrate containing the chymase inhibitor chymostatin. ANG 11 was separated and quantitated by HPLC. Chymase activity was defined as the fraction of ANG 11 production inhibited by Chymostatin. Results. 2K1C and ANG II-infused rats developed significant hypertension, compared to control rats (P = 0.0001 and P = 0.001, respectively). Chymase-dependent ANG 11 production was increased in the ischemic kidney, but not the non-ischemic kidney, of 2K1C rats compared to control animals (*P < 0.05). Intrarenal chymase activity was unchanged by ANG II infusion (P = NS). Conclusions. Chymase activity is up-regulated in the ischemic kidney of 2K1C rats. Plasma ANG II does not appear to regulate intrarenal chymase activity, suggesting that ischemia per se up-regulates chymase activity in the kidney. ACE-independent ANG II production by chymase may provide a mechanism for augmenting intrarenal ANG II in the ischemic kidney in RVH. (c) 2005 Elsevier Inc. All rights reserved.