Reactivity of chicken chorioallantoic arteries, avian homologue of human fetoplacental arteries

The reactivity of human fetoplacental arteries is regulated by humoral and local factors of maternal and fetal origin. The chorioallantoic (CA) arteries of bird embryos are homologous to fetoplacental arteries and fulfill the same gas-exchange purpose without maternal influences, but their reactivity has not been studied in detail. In the present study we hypothesized that CA arteries would respond to vasoactive factors similarly to fetoplacental arteries and the response would change during development between maximal vascular CA expansion (15 of the 21 days incubation period) and prior to hatching. Therefore, we analyzed the reactivity of third order arteries (≈200 μm) from the CA membrane of 15 and 19 day chicken embryos. CA arteries contracted in response to K(+), the thromboxane A(2) mimetic U46619, endothelin-1, acetylcholine and acute hypoxia, but showed no reaction to α-adrenergic stimulation (phenylephrine). The nitric oxide donor sodium nitroprusside, the adenylyl cyclase agonist forskolin, and the β-adrenergic agonist isoproterenol relaxed CA arteries pre-contracted with K(+) or U46619. The contraction evoked by acetylcholine and the relaxations evoked by sodium nitroprusside and isoproterenol decreased with incubation age. In conclusion, CA arteries share many characteristics with human fetoplacental arteries, such as pronounced relaxation to β-adrenergic stimuli and hypoxic vasoconstriction. Our study will be the foundation for future studies to explain disparate and common responses of the CA and fetoplacental vasculature.