Angiogenic stimulation compared with angiogenic reaction to injury: distinction by focal and general application of trypsin to the chick chorioallantoic membrane.

We have addressed the problem of distinguishing angiogenesis induced in the chick chorioallantoic membrane by injury and inflammation from angiogenesis induced by primary stimulation. Focal, slow-release application of trypsin stimulated a localized spoke-wheel pattern of vascularity. In comparison, a range of doses up to a sublethal amount of trypsin applied generally, in liquid form, resulted in no change in DNA synthesis or vessel content, despite a transient influx of inflammatory cells. This contrasts with previous work with fibrin degradation products, histamine and heparin which each produce characteristic patterns of increased DNA synthesis leading to angiogenesis in the entire 'dropped' area of the chorioallantoic membrane. Such general application, therefore, avoids the danger of misinterpretation of focal, toxic effects.