ONTOGENY OF MICROVASCULAR PERMEABILITY TO MACROMOLECULES IN THE CHICKCHORIOALLANTOIC 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-da y gestation. The chorioallantoic membrane (CAM) was prepared for intra vital fluorescence confocal microscopy. A graded series of FITC-dextra ns (20, 40, 70, and 150 kDa) was injected via vitelline vein. The chan ges in interstitial optical intensity due to FITC-dextran extravasatio n were-evaluated by computer-assisted image analysis. Apparent permeab ility coefficients (P-s) were calculated for first order postcapillary vessels from the changes in intensity as a function of time. On Day 4 .5, P-s 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 P-s values f ell 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, P-s values for all these FITC-dextrans we re equal to 0.7 +/- 0.3. The evaluation of FITC-Dextran 10 on Day 5.5 yielded a P-s value of 1.9 +/- 0.3. Our data demonstrate a rapid reduc tion in microvascular permeability to macromolecules during normal ang iogenesis in the, early stages of CAM development. Our data also sugge st that these changes in permeability may reflect functional adaptatio ns of the CAM. A comparison of our data to those available in the lite rature for adult and tumoral tissues demonstrates that microvascular p ermeability properties in these tissues are different from those of th e CAM. (C) 1995 Academic Press, Inc.