VEGF and bFGF stimulate myocardial vascularization in embryonic chick.

We tested the hypothesis that early vascularization of the embryonic heart is enhanced after bolus injections of vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) into the vitelline vein before the onset of myocardial vasculogenesis (3.5 days, stage 21). Electron and light microscopy were utilized to obtain morphometric data. At stages 29 and 31, myocardial vessel volume or numerical density were higher in embryos injected with 50 ng bFGF than in the saline-injected controls. A VEGF injection increased vascular volume density at stage 29 and both volume and numerical density at stage 31. bFGF, but not VEGF, was associated with an enhancement of the sinusoidal system (spongy layer of the ventricle) at stage 29. This effect disappeared by stage 31. In conclusion, 1) enhancement of bFGF or VEGF before myocardial vascularization increases vascular growth, but the initial effect of bFGF is greater; 2) the effects of these growth factors on vascular volume and numerical density are temporally dependent; and 3) bFGF, in addition to its effects on the coronary vasculature, influences ventricular modeling by apparently acting on myocytes as well as endothelial cells.