Platelet counts following collagen plus epinephrine challenge. Mice were given injections of 600 ng/g collagen plus 60 ng/g epinephrine via tail vein and platelet counts were measured 15 minutes after injection. Symbols represent platelet counts of a single mouse. Bars represent the mean values of groups. Platelet counts after the challenge were significantly lower in Adamts13^–/– mice (n = 14) than Adamts13^+/+ mice (n = 11) at 7.7 ± 2.9 × 10⁴/μL and 16.4 ± 6.2 × 10⁴/μL, respectively (mean ± SD; P < .001), whereas platelet counts without challenge were not different between groups (Adamts13^–/–, 86.2 ± 13.2 × 10⁴/μL; Adamts13^+/+, 83.7 ± 3.3 × 10⁴/μL; mean ± SD of 4 mice).