QUANTITATIVE STUDY OF INTUSSUSCEPTIVE CAPILLARY GROWTH IN THE CHORIOALLANTOIC MEMBRANE (CAM) OF THE CHICKEN-EMBRYO

In an attempt to sort out the respective contributions of sprouting an d intussusceptive microvascular growth (IMG) during chicken chorioalla ntoic membrane (CAM) development, we analyzed the morphology and the q uantitative growth of the capillary bed of the CAM by light microscopy . By perfusing the CAM microvasculature with highly concentrated collo idal gold particles, the capillaries could be unambiguously distinguis hed from the surrounding unlabelled tissue. This allowed us to identif y, count and measure the intercapillary tissue pro files. By means of morphometric analysis we could show that CAM angiogenesis undergoes th ree phases of development. In an early phase, from Day 5 to Day 7, the major mechanism of capillary network growth is sprouting. In an inter mediate phase, from Day 8 to Day 12, IMG is prevailing, and at Days 13 and 14, CAM structure is undergoing expansion with only a small incre ase in complexity. These findings are important in view of experimenta l protocols using the CAM as a model for testing angiogenetic factors. Indeed, care has to be taken not to misinterpret normal age-dependent alterations of the CAM vascular architecture as specific responses to tested agents. (C) 1997 Academic Press.