Granulation tissue in the chick embryo yolk sac blood vessel system.

The development of granulation tissue following acute vascular injury was studied in the yolk sac blood vessel system of chick embryos. Administration of irritant substances was carried out directly on the yolk sac at day 4 of incubation and changes were observed up to 72 h post-application. Reaction nodules developed at the impaired area within 48 h p.a. The nodules were studied by light and electron microscopy and enzyme histochemistry. A proliferation of phagocytosing and mesenchymal cells as well as capillary sprouting took place. Collagenous fibres could be detected within 72 h after administration. The model is suitable for the study of connective tissue proliferation, angiogenesis and possibly drug effects influencing these mechanisms. In accordance with the current legislation for animal protection it is a pain-free test system and can be applied before the onset of reflexes and sensitivity of the chick embryo.