Large amounts of vascular endothelial growth factor at the site of hemostatic plug formation in vivo

Vascular endothelial growth factor (VEGF) is important for the proliferatio n, differentiation, and survival of microvascular endothelial cells. It is a potent angiogenic factor and a specific endothelial cell mitogen that inc reases fenestration and extravasation of plasma macromolecules. Recently, l arge quantities of VEGF were detected in human megakaryocytes. Incubation o f human platelets with thrombin in vitro resulted in the release of large a mounts of VEGF. To investigate whether VEGF is released from platelets duri ng coagulation activation in vivo, we measured in human subjects VEGF at th e site of plug formation, ie, in blood emerging from a standardized injury made to determine bleeding time (shed blood). VEGF was also determined in t he same volunteers after treatment with the specific thrombin inhibitor rec ombinant hirudin (r-hirudin). In a double-blind, randomized, crossover stud y, 17 healthy male volunteers (aged 20 to 35 years) were investigated. VEGF concentrations were measured in venous blood and in shed blood by the use of an immunoassay 10 minutes after intravenous administration of r-hirudin (0.35 mg/kg of body weight) or physiological saline. Prothrombin fragment f 1.2 (f1.2) and beta-thromboglobulin (beta-TG) were determined as indicators of coagulation and platelet activation, respectively. Concentrations of VE GF, f1.2, and beta-TG in shed blood 4 minutes after injury were significant ly higher than in venous blood (VEGF, 55.8+/-9.2 versus <20 pg/mL, P<0.001; f1.2, 71.3+/-10.4 versus 0.78+/-0.03 nmol/L, P<0.001; beta-TG, 2290+/-170 versus 53.2+/-14.0 ng/mL, P<0.001). Administration of r-hirudin caused a >5 0% inhibition of the beta-TG and f1.2 levels in shed blood. In a similar ma nner, much lower amounts of VEGF were detectable at the site of plug format ion after r-hirudin treatment (69.0+/-9.5 versus 37.8+/-2.6 pg/mL per minut e; P=0.0015). Our data indicate that substantial quantities of VEGF are rel eased from platelets during the interaction with the injured vessel wall in vivo. This finding may be relevant with respect to wound healing and tissu e repair, tumor vascularization, or arterial thrombus formation.