Regional hypoxia elicits regional changes in chorioallantoic membrane vascular density in alligator but not chicken embryos

Hypoxic incubation increases vascularization in the chick chorioallantoic m embrane (CAM). The effect of regional hypoxia on the vascular density of Am erican alligator (Alligator mississippiensis) and chicken (Gallus gallus) C AMs was studied to determine if hypoxic proliferation of blood vessels is l ocalized or global across the CAM. Eggs were incubated under normoxic condi tions with a portion of the eggshell covered with non-toxic beeswax to indu ce external regional hypoxia. CAMs were examined under a microscope with a 'bulls eye' coverslip and a vascular density index (VDI) was determined. Th e hypoxic portions of the alligator CAMs were more vascular than the normox ic portions (VDI = 200.9 versus 157.8, respectively). Presumably this respo nse is maladaptive by causing increased blood flow to the poorly oxygenated portions, i.e. increased 'shunt'. Thus, we hypothesize increased vasculari ty due to hypoxic incubation is due to local release and subsequent rapid l ocal breakdown or uptake of angiogenic factors. In contrast, the hypoxic an d normoxic portions of the chick CAMs exhibited virtually no difference in VDI (VDI = 211.5 versus 217.9, respectively). We suggest the air cell and a ir space of the chicken eggs allows for circulation of gas in ovo, eliminat ing the possibility of regional internal hypoxia. (C) 2000 Elsevier Science Inc. All rights reserved.