Background: Tissue angiotensin II (ANG II) levels are elevated in both kidneys in renovascular hypertension (RVH). It has been demonstrated previously that intrarenal ANG II is augmented by an angiotensin converting enzyme (ACE) dependent mechanism in the non-ischemic kidney, but the role of ACE-independent production of ANG II in the kidney by the enzyme chymase is unknown. This study tested the hypothesis that intrarenal chymase activity is up-regulated 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 microm ANG I) alone or substrate containing the chymase inhibitor chymostatin. ANG II was separated and quantitated by HPLC. Chymase activity was defined as the fraction of ANG II 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 II 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.