Quantitative image analysis of angiogenesis in rats implanted with a fibrin gel chamber.

Angiogenesis, a fundamental process in various physiological and pathological events, is generally studied using in vivo models, such as the chick chorioallantoic membrane or the rabbit cornea, which are difficult to quantitate. We developed the quantitation of angiogenesis in an in vivo model previously described by Dvorak et al [6]. Perforated plexiglass chambers filled with human or rat fibrin were implanted into the dorsal subcutaneous space of a Wistar rat. After four days of implantation, a sequentially organized invasion of the fibrin gel by various blood cell types occurred through the holes and neovascularized granulation tissue buds appeared. These buds presented mature neovessels and a new collagen matrix. Three dimensional computer image analysis of the chambers was performed using macroscopic and microscopic parameters: total vascularized area, bud height and equivalent diameter, number of vessels per bud and percentage of central vessels. The time course of the angiogenic response to rat or human fibrin gel was studied and 14 days was found to be the optimum period of implantation. The bud height and number of neovessels were not found to be significantly different when rat or human fibrin gels were used. This quantitative study was a prerequisite for further investigations of the effects of biological and pharmacological agents on angiogenesis.