Effects of brief hypoxia and hyperoxia on tissue trace element levels in the developing chick embryo

Brief hypoxia or hyperoxia has been shown to affect growth and metabolism of chick embryos during the late stages of development. The objective of this study was to alter the availability of oxygen to chick embryos developing in ovo and to determine the effects on tissue zinc, copper, iron and manganese levels. On day 15 of incubation fertile chicken eggs were divided into three groups: 15% O2 (hypoxic), 60% O2 (hyperoxic) and 21% O2 (normoxic) and incubated under these conditions for 72 h to day 18. Hypoxia reduced embryo, heart, brain and liver wet weights, whereas hyperoxia increased embryo, heart, lung and liver wet weights compared to normoxic controls. Chorioallantoic membrane (CAM) wet weight was increased by hypoxia and reduced by hyperoxia. Livers from hyperoxic embryos contained more zinc, iron and manganese and less copper than livers from hypoxic or normoxic embryos. Tissue concentrations of zinc, copper, iron and manganese were reduced in brains from hyperoxic compared to hypoxic or normoxic embryos. Hyperoxia increased the zinc and copper concentrations in CAM, whereas hypoxia reduced zinc and iron levels. The contents of zinc and copper were increased in hyperoxic compared to normoxic or hypoxic lungs. Hearts from hyperoxic embryos had more zinc, copper and manganese than hypoxic or normoxic hearts. Hypoxic yolk sac contained more zinc and manganese than hyperoxic or normoxic yolk sac. Except for yolk sac, the trace element content of tissues from normoxic embryos increased from day 15 to day 18 of incubation in concert with tissue growth. We conclude that the availability of oxygen to the developing chick embryo affects tissue trace element levels through its effects on tissue growth, as a result of adaptation by specific tissues to different oxygen tensions, or via effects on the regulation of trace element uptake and assimilation by the tissues.