The effect of hyperoxia on embryonic and organ mass in the developing chick embryo.

It is known that hyperoxia stimulates growth late in incubation when the chick embryo outgrows the O2 diffusion capacity. We wondered whether hyperoxia could have an effect in the early period prior to the stage where metabolism exceeds the oxygen diffusion capacity of the eggshell. For this we studied four groups of chicken eggs: control group (CG; n = 100) and three test groups (TGs) exposed during 48 h to 60% O2 on days 10, 14, and 18. In the CG, embryonic and organ mass (brain, heart, lungs, liver and intestine) were measured from day 10 until day 21 of incubation. In the TGs embryonic and organ mass were obtained from 24 h after the start of hyperoxia exposure until the end of incubation. In all TGs the most striking growth rate acceleration was observed in the liver and intestine, maximum growth rate accelerations were respectively, 19 and 42% in TG1, 43 and 173% in TG2 and 39% and 84 in TG3. In contrast, the brain was little affected by the hyperoxia exposure, the maximum growth rate acceleration was 14% in TG2. The results suggest that also in the middle of the incubation period O2 availability can be a limiting factor for growth, before metabolism exceeds the oxygen diffusion capacity of the eggshell.