Ontogeny of microvascular permeability to macromolecules in the chick chorioallantoic membrane during normal angiogenesis.

Chick embryos were incubated using standard shell-less techniques for microscopic observations at Days 4.5, 5.0, and 5.5 of the normal 21-day gestation. The chorioallantoic membrane (CAM) was prepared for intravital fluorescence confocal microscopy. A graded series of FITC-dextrans (20, 40, 70, and 150 kDa) was injected via vitelline vein. The changes in interstitial optical intensity due to FITC-dextran extravasation were evaluated by computer-assisted image analysis. Apparent permeability coefficients (Ps) were calculated for first order postcapillary vessels from the changes in intensity as a function of time. On Day 4.5, Ps values (means +/- SE x 10(-7) cm/sec) in the CAM microvessels for FITC-Dextran 20, 40, 70, and 150 were 11.8 +/- 1.0, 6.4 +/- 0.4, 3.1 +/- 0.5, and 1.5 +/- 0.5, respectively. The respective Ps values fell dramatically on Day 5.0 to 2.2 +/- 0.5, 0.7 +/- 0.2, 0.6 +/- 0.2, and 0.6 +/- 0.2. On Day 5.5, Ps values for all these FITC-dextrans were equal to 0.7 +/- 0.3. The evaluation of FITC-Dextran 10 on Day 5.5 yielded a Ps value of 1.9 +/- 0.3. Our data demonstrate a rapid reduction in microvascular permeability to macromolecules during normal angiogenesis in the early stages of CAM development. Our data also suggest that these changes in permeability may reflect functional adaptations of the CAM. A comparison of our data to those available in the literature for adult and tumoral tissues demonstrates that microvascular permeability properties in these tissues are different from those of the CAM.