Angiotensin and thrombin‐induced endothelial dyfunction involves RhoA activation and elevated arginase activity

Abstract

Elevated arginase (ARG) activity can decrease L‐arginine availability to NO synthase (NOS) and NO production, and thus contributes to endothelial dysfunction (ED). We previously observed that increased ARG activity is involved in diabetic coronary ED in rats and mice and in impaired NO production by endothelial cells (EC) exposed to high glucose or peroxynitrite. Elevated angiotensin II (AII) and thrombin (TH) levels in diabetes are major factors contributing to its vascular complications. We tested whether activation of arginase is involved in AII or TH‐induced ED. We determined levels of ARG activity and expression and NO production (response to ionomycin) in bovine coronary EC exposed to AII or TH for 24 hrs. Both AII (10−6M) and TH (0.5 U/ml) decreased NO production by 55 and 45%, respectively, and increased ARG activity by 48% and 43%, respectively. ARG I protein expression increased by 52–58% after exposure to AII or TH. AII and TH also elevated active RhoA levels by 60 and 45%, respectively. Pretreatment with the RhoA kinase inhibitor Y‐27632 (10−5M), simvastatin (10−7M, a blocker of RhoA activation), prevented the AII‐ or TH‐ induced increases in ARG and RhoA activity and maintained normal NO production. Our results suggest AII and TH decrease NO production and cause vascular ED by mechanism(s) involving reduced L‐arginine availability for NOS via RhoA‐mediated elevations in ARG activity.