Influence of environmental oxygen concentration on growth and vascular density of the area vasculosa in chick embryos.

The influence of different environmental oxygen concentrations on vascularization was studied in the yolk sac blood vessel system of chick embryos. The eggs were incubated at normoxic (20.9% oxygen, n = 29), hypoxic (10% oxygen, n = 36) or hyperoxic (100% oxygen, n = 26) conditions and evaluated on day 4 of incubation. In vivo photographs were taken of the vascularized part of the yolk sac membrane (area vasculosa). Prints of a given enlargement were evaluated by histometrical methods to measure the extension of the area vasculosa, the density and the total area of blood vessels. Hypoxia induced an increase in vascular density, in area occupied by blood vessels (44.4%, normoxia = 40.6%) and an enlargement of the area vasculosa (441 +/- 78.6 mm2, normoxia = 380 +/- 68.7 mm2). Hyperoxia also induced an increase in vascular density and in the area occupied by blood vessels (45.9%), but a decline in the extension of the vascularized area (287 +/- 48.8 mm2). Thus the total number of blood vesels as well as the total exchange surface decrease in hyperoxia. Our results indicate that in the area vasculosa of the early chick embryo hypoxia possibly causes an upregulation of vascular growth factors. From the present results it cannot be decided whether vasculogenesis or angiogenesis is stimulated.