CHAN, Tammy P.; BURGGREN, Warren W.; University of North Texas, Denton; University of North Texas, Denton: Hypoxic Exposure Creates Highly Differential Morphological Effects in the Developing Chicken Embryo

Oxygen deprivation retards development in vertebrate embryos, but only poorly understood is whether all major organ systems are equally affected, or whether organ-specific effects occur. Chick embryos were exposed to chronic hypoxia (15% O2) during Day 1-6, Day 6-12, or Day 12-18 of development. Morphometric measurements of major organ systems were then made prior to hatching. Hypoxic exposure early in development significantly reduced pre-hatching embryo mass to a greater extent than exposure later in development. Also significantly reduced was mass of the eyes and beak in late development. However, the liver, brain, heart, kidneys, stomach, intestines and long bones of the skeleton were not significantly affected by hypoxia at any developmental stage. The mass of the chorioallantoic membrane (CAM), which is the gas exchange organ for the embryo, was unchanged by hypoxic exposure in early or mid-development, but increased in mass in response to hypoxic exposure during Day 12-18. Collectively, these data reveal that hypoxic exposure at different points in development results in highly differential effects on organ development, as well as various degrees of hypoxic susceptibility. We suggest that the increase in mass (and presumably vascularization) of the CAM maximizes oxygen delivery to the organ systems, thereby minimizing the detrimental effects of hypoxia on development and growth.