High susceptibility to ADP-induced thrombus formation in mast cell-deficient W/Wv mice.

We used mast cell-deficient W/Wv mice to clarify whether mast cell-derived heparin may play a role in inhibiting thrombus formation in the living organism. Small veins in the mesentery of W/Wv or congenic +/+ mice were stretched over an inverted microscope; a micropipette filled with varying concentrations of ADP was set close to the outside of a vein by using a micromanipulator. Thrombus formation was directly examined under the microscope. The concentration of ADP necessary for thrombus formation was significantly lower in the W/Wv mice than in the congenic +/+ mice. Furthermore, the concentration of ADP necessary for aggregation of platelets in platelet-rich plasma (PRP) was significantly lower in W/Wv mice than in +/+ mice. The higher sensitivity of PRP of W/Wv mice is not attributed to the platelets, but to the plasma, since platelets of +/+ mice suspended in platelet-poor plasma (PPP) of W/Wv mice were more sensitive to ADP than platelets of W/Wv mice suspended in PPP of +/+ mice. The present results suggest that plasma of W/Wv mice may lack any inhibitory factor(s) or contain promoting factor(s) for platelet aggregation.