Fibroblast growth factor-2 selectively stimulates angiogenesis of small vessels in arterial tree

There is a critical need for quantifiable models of angiogenesis in vivo, a nd in general, differential effects of angiogenic regulators on vascular mo rphology have not been measured. Because the potent angiogenic stimulators fibroblast growth factor (FGF)-2 (basic FGF) and vascular endothelial growt h factor (VEGF) are reported to stimulate angiogenesis through distinct sig naling pathways, we hypothesized that FGF-2 stimulates vascular morphology differently than does VEGF and that stimulation of angiogenesis by FGF-2 is directly correlated to FGF receptor density. FGF-2 was applied at embryoni c day 7 (E7), E8, or E9 to the quail chorioallantoic membrane (CAM); subseq uent response of the arterial tree was measured by the fractal dimension (D -f), a mathematical descriptor of complex spatial patterns, and by several generational branching parameters that included vessel length density (L-v) . After application of FGF-2 at E7, arterial density increased according to D-f as a direct function of increasing FGF-2 concentration, and FGF-2 stim ulated the growth of small vessels, but not of large vessels, according to L-v and other branching parameters. For untreated control specimens at E7, L-v of small vessels and D-f were 11.1+/-1.6 cm(-1) and 1.38+/-0.01, respec tively; at E8, after treatment with 5 mu g FGF-2/CAM for 24 hours, L-v of s mall vessels and D-f increased respectively to 22.8+/-0.7 cm(-1) and 1.49+/ -0.02 compared with 16.3+/-0.9 cm(-1) and 1.43+/-0.02 for PBS-treated contr ol specimens. Application of FGF-2 at Es and E9 did not significantly incre ase arterial density. By immunohistochemistry, the expression of 4 high-aff inity tyrosine kinase FGF receptors was significantly expressed at E7, when CAM vasculature responded strongly to FGF-2 stimulation, but FGF receptor expression decreased throughout the CAM by E8, when vascular response to FG F-2 was negligible. In conclusion, the "fingerprint" vascular pattern elici ted by FGF-2 was distinct from vascular patterns induced by other angiogeni c regulators that included VEGF(165), transforming growth factor-beta 1, an d angiostatin.