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

Abstract

Vascular endothelial growth factor (VEGF) is important for the proliferation, differentiation, and survival of microvascular endothelial cells. It is a potent angiogenic factor and a specific endothelial cell mitogen that increases fenestration and extravasation of plasma macromolecules. Recently, large quantities of VEGF were detected in human megakaryocytes. Incubation of human platelets with thrombin in vitro resulted in the release of large amounts of VEGF. To investigate whether VEGF is released from platelets during coagulation activation in vivo, we measured in human subjects VEGF at the site of plug formation, ie, in blood emerging from a standardized injury made to determine bleeding time (shed blood), VEGF was also determined in the same volunteers after treatment with the specific thrombin inhibitor recombinant hirudin (r-hirudin). In a double-blind, randomized, crossover study, 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 f1.2 (f1.2) and β-thromboglobulin (β-TG) were determined as indicators of coagulation and platelet activation, respectively. Concentrations of VEGF, f1.2, and β-TG in shed blood 4 minutes after injury were significantly 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; β-TG, 2290±170 versus 53.2±14.0 ng/mL, P<0.001). Administration of r-hirudin caused a >50% inhibition of the β-TG and f1.2 levels in shed blood. In a similar manner, much lower amounts of VEGF were detectable at the site of plug formation after r-hirudin treatment (69.0±9.5 versus 37.8±2.6 pg/mL per minute; P=0.0015). Our data indicate that substantial quantities of VEGF are released from platelets during the interaction with the injured vessel wall in vivo. This finding may be relevant with respect to wound healing and tissue repair, tumor vascularization, or arterial thrombus formation.