Background—Plasma concentrations of hepatocyte growth factor (HGF), a powerful angiogenic growth factor inducible by heparin, increase in thrombus-associated disorders such as myocardial infarction and unstable angina. The mechanism of this thrombus-associated HGF release, however, is unknown.

Methods and Results—Wistar rats received through the tail vein (1) normal saline (NS), (2) 50 µg of the mast cell-degranulating agent CP48/80, or (3) 1000 U/kg heparin. Blood samples were collected at 10 minutes or 30 minutes after the injections, or from untreated rats, for measurements of HGF. The same experiments were performed in mast cell-deficient white spotting (Ws) rats. Ws rats have a small deletion of the c-kit gene and are deficient in mast cells. Intravenous heparin immediately increased plasma HGF in both Wistar (38.02±2.08 ng/mL versus 1.11±0.70 ng/mL in untreated rats, P<0.0001) and Ws rats (36.39±4.15 ng/mL versus 0.66±0.18 ng/mL in NS-treated rats, P<0.0001). Injection of CP48/80 also increased plasma HGF in Wistar rats (9.12±1.11 ng/mL versus 0.65±0.24 ng/mL in NS group, P=0.004) but not in Ws rats (0.67±0.27 ng/mL versus 0.66±0.18 ng/mL in NS group, P=0.997). In a rat carotid artery microthrombus model, intra-arterial thrombus formation increased circulating HGF in Wistar rats (2.12±0.70 ng/mL versus sham 0.61±0.15 ng/mL in sham-operated Wistar rats, P=0.0064) but not in Ws rats (0.76±0.33 ng/mL versus 0.21±0.04 ng/mL in sham-operated Ws rats, P=0.29). In addition, in vitro stimulation of rat peritoneal mast cells with thrombin rapidly induced degranulation in a dose-dependent manner.

Conclusions—These observations indicate that mast cell degranulation stimulated by thrombin is necessary for the rapid induction of plasma HGF in intravascular thrombus-associated disorders.