Reconstituted collagen is not capable of activating factor XII but causes intrinsic coagulation by activating platelets.

Using a rheological technique to measure the coagulation of plasma in collagen-coated tubes, we studied the intrinsic coagulant activities of different types (I, III, IV and V) and structures of reconstituted collagen. Recalcified, platelet-free plasma (PFP) in contact with the collagen surface did not clot, irrespective of the type and structure of collagen. Coagulation of platelet-rich plasma (PRP) did occur, although the time of onset of coagulation was highly dependent on the type and structure of the collagen used. Coagulation of PRP occurred rapidly on a collagen surface consisting of highly ordered fibrils (banded structure) to which large numbers of aggregated platelets adhered with shape change. In contrast, initiation of coagulation was delayed in PRP after incubation with 5 mM dibutyrylcyclic AMP (DB-cAMP) for 50 min. Coagulation of PRP was completely suppressed after 30 min incubation with colchicine (5.0 mg/ml). This suggested that disruption of platelet microtubules completely suppressed the stimulation of platelets associated with the initiation of intrinsic coagulation on the collagen surface. We conclude that reconstituted collagen is not capable of activating factor XII. Initiation of coagulation of recalcified PRP in contact with the reconstituted collagen surface is caused by the activation of platelets.