CAPILLARY SPROUTS RESTRICT MACROMOLECULAR EXTRAVASATION DURING NORMALANGIOGENESIS IN THE CHICK CHORIOALLANTOIC MEMBRANE

During angiogenesis in the chorioallantoic membrane (CAM) of the chick , capillary proliferation occurs primarily by intussusceptive growth. Previously, we reported that such growth in the CAM proceeded without substantial macromolecular extravasation. Neovascularization involving capillary sprout formation, on the other hand, has been associated wi th a concomitant loss of endothelial selectivity. Thus, the present st udy tested the hypothesis that endothelial selectivity during angiogen esis is dependent on the mode of microvascular growth. Capillary sprou t formation occurs in peripheral regions of the CAM, in addition to th e more centrally located areas of intussusceptive growth. In this stud y, angiogenic endothelial permselectivities were evaluated in these re spective areas of CAM microvascular growth by intravital fluorescent m icroscopy of a graded series of FITC-dextrans. In both cases, the angi ogenic endothelia restricted extravasation of macromolecules greater t han or equal to 20 kDa. Furthermore, capillary sprout endothelia, like the intussusceptive CAM endothelia, remained tightly sealed at the ju nctional clefts. Thus, angiogenic endothelial permselectivity in the C AM is not dependent on the mode of microvascular growth. Whether disti nct cellular mechanisms are operable in capillary endothelial sprouts of the CAM, relative to those of other proliferating sprout endothelia , remains to be tested. (C) 1996 Academic Press, Inc.