Agonist-induced platelet aggregation is inhibited by Shh antagonists. Aggregation of platelets in PRP induced by collagen (0.5 μg/mL) (A), TRAP (2.5 μM) (C), or ADP (2.5 μM) (E) in the presence of vehicle (control), cyclopamine (10 μM), or vismodegib (25 μM), as indicated. Aggregation of washed human (G) and murine platelets (I) induced by 0.1 U/mL thrombin in the presence of vehicle (control), cyclopamine (10 μM), or vismodegib (25 μM) as indicated. (B,D,F,H,J) Represent corresponding bar diagrams showing percent aggregation (mean ± standard error of the mean) averaging ≥5 individual experiments. *P < .05 as compared with control.