Platelet ADP pathway supports thrombin formation in vivo. (A) Collagen injection elicits intravascular fibrin formation. Transmission electron micrographs of lung from a wild-type (wt) mouse following injection of collagen plus epinephrine. (Left) Thrombus occluding a pulmonary vessel with some rare fibrin fibrils (arrowhead) (E indicates endothelium; C, collagen fibers; and P, platelet). Original magnification, × 14000. (Right) Higher magnification (× 148000) of the fibrin fibrils showing the periodicity of around 20 nm (arrows). (B) Collagen fails to activate thrombin generation in P2Y1 (–/–) mice. Plasma TAT levels following collagen-induced thromboembolism in wt and P2Y1 (–/–) mice, without or with clopidogrel. Empty columns indicate saline injection; filled columns, collagen plus epinephrine. Means ± SDs; n = 7 to 8. *P < .05 compared with same condition without collagen.
