VASCULAR ENDOTHELIAL GROWTH-FACTOR (VEGF) IS RELEASED FROM PLATELETS DURING BLOOD-CLOTTING - IMPLICATIONS FOR MEASUREMENT OF CIRCULATING VEGF LEVELS IN CLINICAL-DISEASE

1. Dysregulated vascular endothelial growth factor (VEGF) expression h as been reported in several pathological states based upon evidence of elevated serum VEGF levels. Using two immunoassays for VEGF, this stu dy determines normal plasma and serum VEGF ranges, determines which ar e more likely to reflect circulating VEGF levels and investigates a po tential contribution of VEGF from platelets to VEGF levels detected in serum. 2. The presence of soluble VEGF receptor. sflt-1, at a molar e xcess of 7:1 significantly reduced mea sured VEGF levels in both assay s. Serum VEGF levels were higher than plasma levels in children [(mean +/- S.E.M.) 306.1 +/- 39.4 versus 107.4 +/- 24.9 pg/ml, P < 0.0001] a nd adults (249.4 +/- 46.4 versus 76.1 +/- 10.7 pg/ml, P < 0.0001). Ser um VEGF increased with clotting time (P = 0.0005 t(0) compared with 2h samples); plasma VEGF le, els were not affected by time between sampl ing and centrifugation. 3. Calcium-induced clotting of platelet-rich b ut not platelet-poor plasma induced VEGF release with a proportional r esponse between platelet count and VEGF level and isolated platelets r eleased significant quantities of VEGF upon incubation with thrombin. Reverse transcriptase-PCR studies confirmed that platelets express VEG F(121) and VEGF(165) mRNA. 4. These data suggest that plasma is the pr eferred medium to measure VEGF levels; a significant and highly variab le platelet-mediated secretion of VEGF during the clotting process inv alidates the use of serum as an indicator of circulating VEGF levels i n disease states.