Effect of ABT-263 on platelet receptor expression, PS exposure, and platelet function is dose-dependent. C57BL6 mice were administered ABT-263 (5 or 10 mg/kg) or an equal volume of vehicle by oral gavage, and whole blood sampled at the indicated times as described in “In vivo administration of ABT compounds.” Whole blood was analyzed for (A) platelet count as well as (B) PS surface expression (ANV+ve), (C) GPIbα, and (D) GPVI surface expression. (E) Template tail bleeding time was quantified as described in “Tail bleeding studies.” Histograms represent the data collected from 5 independent experiments (mean ± SEM). Data obtained from mice treated with 25 mg/kg ABT-263 have been included here for comparison purposes. These data have been taken from Figures 5 and 6 and are therefore represented here as broken lines/gray bars. (F-G) Bleeding time (F) and blood loss (hemoglobin levels) (G) were quantified following 3-mm tail transection as described in supplemental Methods. Histograms represent the data collected from 5 independent experiments (mean ± SEM), where closed bars represent the initial cessation of bleeding (1° bleeding time), and open bars represent rebleeding (2° bleeding time). Identical experiments performed on mice administered 1 mg/kg hirudin (Hir) have been provided for comparison. ns indicates not significant. *P < .05. **P < .01. ***P < .001.