The effects of growth factors on the day 13 chorioallantoic membrane (CAM): a study of VEGF165 and PDGF-BB.

The in vivo effects of two growth factors, VEGF165 and PDGF-BB, were studied in the chick chorioallantoic membrane (CAM). The factors were air-dried on Thermanox discs and the inverted discs were placed on the day-13 CAM for a period of 3 days. The specimens were then fixed, examined under a stereomicroscope and processed for semi- and ultrathin sectioning. VEGF165 induces marked vascular growth. Many new blood vessels emerge from the precapillary arterioles, and a brush-like formation of vessels can be seen in this region. In the venous part of the vascular system, the formation of sinusoidal or lacunar vessels can be seen. Edema does not develop. PDGF-BB induces thickening of the CAM due to extracellular-matrix production and the proliferation or immigration of fibrocytes. These lie just beneath the ectodermal epithelium and are oriented parallel to it. Out of the four factors we have already studied (PDGF-BB, VEGF165, Angiogenin, bFGF), only VEGF165 specifically induces the growth of blood vessels.