Multivariate Characterization of Blood Vessel Morphogenesis in the Avian Chorioallantoic Membrane (CAM): Cell Proliferation, Length Density and Fractal Dimension

Abstract

The development of blood vessels in the CAM of chicks between 6 and 19 days of development was characterized as a time series of their fractal dimension D. The growth rate of endothelial and other cells that constitute the vessel walls, was estimated in terms of numerical density N _A , and the arterial vessel length density L _A was also assessed. Image analysis and stereology were used for this quantitative study. D changed between day 10 and 14 from the initial 1.3 to 1.5, whereas N _A dropped from 2500 mm⁻² to 250 mm⁻². L _A showed only an increase from 4 mm⁻¹ to 6 mm⁻¹, and the total vessel length was estimated to expand from 2.5 m to 50 m. The effect of Vascular Endothelial Growth Factor on the bifurcation frequency was documented by an increased D of 1.8. Multiple scatter plots were used for visualization of the data, which suggest mainly “intussusceptive” (i.e. by mesh formation without sprouting) capillary growth. This explains the increased density of hemodynamic sources and sinks in the capillary layer, which is the anatomical correlate of a postulated functional shunt. The very rich vascularization of the older CAM rather is a side-effect of angiogenic factors acting in the embryo than optimal metabolic adaptation.