The influence of the receptor Mas on thrombosis risk in Bdkrb2^−/− mice. (A) Proposed mechanism by which elevation of AngII leads to thromboprotection in Bdkrb2^−/− mice. In the absence of the bradykinin B2 receptor, bradykinin is elevated (unpublished data). Increased bradykinin stimulates ACE to degrade it to bradykinin 1-5, which has been demonstrated to be increased in Bdkrb2^−/− mice.³  ACE also converts angiotensin I to elevate AngII, which also has been demonstrated in Bdkrb2^−/−mice (Figure 1B).³  AngII stimulates an overexpressed AT2R (Figure 1F-G) to produce increased NO and prostacyclin providing thromboprotection.³  The AT2R is blocked by its antagonist PD123319.³  In the present report, we also demonstrate that some AngII is metabolized to Ang-(1-7) (Figure 1D). Plasma Ang-(1-7) levels remain at a higher baseline level in Bdkrb2^−/− mice even when losartan lowers AngII levels (Figure 1B-D). Ang-(1-7) binding to its receptor Mas, a G protein–coupled receptor, also stimulates NO and/or prostacyclin production.^11,12  In the present report, we propose that blockade of Mas alone with its antagonist A-779 is sufficient to correct the thrombosis protection in Bdkrb2^−/− mice and long bleeding time in these animals by reducing NO and prostacyclin elevation. This effect is similar to our previous report in which interruption of only the AT2R by PD123319 corrected their thrombosis protection.³  (B) The influence of the Mas antagonist A-779 on time to thrombosis. Wild-type mice (n = 5) were untreated or treated with A-779 or A-779 and PD123319; Bdkrb2^−/−mice were untreated (n = 4) or treated with A-779 or A-779 and PD123319 (n = 6) and the time to carotid artery thrombosis was determined on the Rose Bengal assay. (C) The tail bleeding time was determined in wild-type and Bdkrb2^−/− mice untreated or treated with A-779 (n = 6 in each group). (D) Determination of plasma nitrate. Plasma was collected from wild-type (n = 6), Bdkrb2^−/− (n = 6), and Bdkrb2^−/− treated with A-779 (n = 5). (E) Determination of plasma 6-keto-PGF_1α. Plasma was collected from wild-type (n = 6), Bdkrb2^−/− (n = 6), and Bdkrb2^−/− treated with A-779 (n = 5). (B–E) Analyzed by 1-way analysis of variance show differences among groups. The values shown are mean ± SEM. P values shown represent an analysis of difference between 2 groups.