Angiogenesis in chicken chorioallantoic membrane under hypoxic incubations

Under hypoxic conditions, angiogenesis in the chorioallantoic membrane exhibits a sensitive response depending on the developmental timing and intensity and duration of the hypoxia. Furthermore, the effects of hypoxia on vascularization in the chorioallantoic membrane are controversial. In this study, we used microscopy to determine the vascular density index of chicken embryonic chorioallantoic membrane and quantitative PCR to examine the expression of the HIF-1α and VEGFA genes. Two levels of hypoxia (15% and 13% O2) and three durations (days 0–10, 11–18, and 0–18) were applied. The results showed that 13% O2 incubation restrained angiogenesis in the chorioallantoic membrane at an early stage of embryonic development as seen on day 6, but incubation under 13% or 15% O2 efficiently stimulated vascularization of the chorioallantoic membrane as seen on days 16 and 18. Notably, 13% O2 incubation caused visible curling of the blood vessels in the chorioallantoic membrane on day 18. The increased vascular density index under hypoxia was accompanied by an increase in the expression of VEGFA and HIF-1α. Curled blood vessels were observed on day 18 under 13% O2 incubation; however, the curling was not a result of VEGFA overexpression. Thus, the present study helps in elucidating vascularization of the chorioallantoic membrane under hypoxic conditions.