Effect of VEGF in combination with OPG on endothelial cell tube formation. HuDMECs were cultured on growth factor reduced matrigel for 8 hours and branch point number counted as described in materials and methods. (a) Untreated control, (b) OPG 10 ng/ml, (c) VEGF 1 ng/ml, (d) OPG 10 ng/ml and VEGF 1 ng/ml. (e) Quantification of tube formation through measurement of branch point number. Data represented as mean ± S.E.M. from three independent experiments performed in triplicate. ***, p < 0.001 compared to VEGF (1 ng/ml), OPG (10 ng/ml) or untreated control; +++, p < 0.001 compared to untreated control only.