Endothelial heterogeneity in the chick wing bud: a morphometric study.

The microvascular endothelium of the chick wing bud at stages 22, 27, and 32 was evaluated by ultrastructural morphometry. The rationale for this study is based on the hypothesis that endothelial cells exhibit variation in structure and function during cytodifferentiation. The microvessels had a luminal diameter range such that they were classified as capillaries. The thin continuous endothelium was devoid of a basal lamina. The endothelium had a very small number of plasmalemmal vesicles; vacuoles were however present for all stages and in some cases were abundant. The temporal findings were that endothelial cell thickness increases, plasmalemmal vesicle densities decrease, and the densities of cytoplasmic vacuoles increase. The spatial results were that endothelial cells in proximal regions of the limb have a greater thickness, contain fewer vesicles and have more vacuoles than those in distal regions. In general, these results indicate that endothelial ultrastructural heterogeneity occurs within a 3 1/2 day time-span of wing bud development. The discussion considers the results with regard to recent reports on endothelial cell heterogeneity.