Quantitative assays for the chick chorioallantoic membrane

Focal application of angiogenic substances to the chick chorioallantoic membrane is quick and easy as a rapid screening test, bur is susceptible to artefactual stimulation induced by carriers, hyperosmolarity, proteolytic activity, and indeed any cause of damage to the CAM. This can be deceptive and unanticipated. Focal application methods can be used for subsequent measurement by morphometry of the increased vascularity forming the typical spokewheel pattern of supply vessels. If test and control substances are applied in liquid form to the whole dropped CAM surface, then a much wider variety of quantitative morphometric, histological and biochemical techniques can be applied. Assessment of arterial vascularity, terminal arterial branching, supply vessels in cross-sections, and CAM haemoglobin content are direct measures of angiogenic effects, but are time-consuming. Biochemical assays of collagen, protein and DNA synthesis parallel the other assays, and these parameters can be estimated more quickly within the working week. There is inherent variability in the outbred strains of hen eggs currently commercially available. This means that all assays require substantial group numbers to achieve statistical validity, generally not less than 10 eggs per group. The biochemical assays yield interesting time-course patterns that distinguish between different types of angiogenic stimulants.