Bradykinin B2 receptor knockout mice are protected from thrombosis by increased nitric oxide and prostacyclin

Bradykinin (BK) liberates nitric oxide, prostacyclin, and tissue plasminogen activator from endothelial cells. We hypothesized that BK B2 receptor knockout (KO) mice (BKB2R(-/-)) have increased thrombosis risk. Paradoxically, the BKB2R(-/-) mice have long bleeding times and delayed carotid artery thrombosis, 78 +/- 6.7 minutes, versus 31 +/- 2.7 minutes in controls. The mechanism(s) for thrombosis protection was sought. In BKB2R(-/-) plasma coagulation, fibrinolysis and anticoagulant proteins are normal except for an increased prekallikrein and decreased factor XI. BKB2R(-/-) mice have elevated BK 1-5 (160 +/- 75 fmol/mL, vs 44 +/- 29 fmol/mL in controls) and angiotensin 11 (182 +/- 41 pg/mL, vs 49 +/- 7 pg/mL in controls). Ramipril treatment shortens vessel occlusion time. BKB2R(-/-) mice have elevated plasma 6-keto-PGF(1 alpha) (666 +/- 232 ng/mL, vs 23 +/- 5.3 ng/mL in controls) and serum nitrate (61 +/- 5.3 mu M, vs 24 +/- 1.8 mu M in controls). Treatment with L-NAME (W-monomethyl-L-arginine ester) or nimesulide shortens the thrombosis time. BKB2R-/- mice have increased angiotensin receptor 2 (AT(2)R) mRNA and protein expression. Treatment with an AT(2)R antagonist, PD123 319, normalizes the thrombosis time and nitrate and 6-keto-PGF1 alpha. The long bleeding times in BKB2R(-/-) mice also correct with L-NAME and nimesulide therapy. In BKB2R(-/-) mice, angiotensin 11 binding to an overexpressed AT(2)R promotes thromboprotection by elevating nitric oxide and prostacyclin. These investigations indicate a pathway for thrombosis risk reduction via the plasma kallikrein/ kinin and renin angiotensin systems.