DZIALOWSKI, E.M.; DECKER, S.; BLACK, J; BURGGREN, W.W.; TONHARDT, H.: Respiratory development of domestic chicken embyros in response to chronic hypoxia during the middle portion of incubation
Previous experiments in our laboratory have revealed that developing chicken embryos are most sensitive to chronic mild hypoxia (15% O2; PO2 ~ 110 mmHg) during the middle third of incubation from day 6 through 12. Long-term changes in metabolic rate of hatchlings from eggs incubated under chronic hypoxic conditions during the middle third of incubation were observed. Here we investigated the effect of chronic hypoxia during the middle third of incubation on the development of the chorioallantoic membrane (CAM) and levels of the allosteric regulator of hemoglobin oxygen binding 2,3-diphosphoglycerate (2,3-DPG) and its regulator cAMP in chicken embryos. Embryos were incubated in normoxia for the first six days of incubation (21% O2; PO2 ~ 150 mmHg). Half the eggs were then incubated under chronic hypoxic conditions from day 6 to 12. On day 12, all eggs were placed back into normoxia. Beginning on day 8 we measured levels of 2,3-DPG and cAMP every other day. Levels of hemoglobin modulators rose with age of development in both treatments. The gas exchange organ, the CAM, grew continuously from day 6 to 12 in control eggs, covering nearly 100% of egg surface by day 12. In hypoxic incubated eggs, the growth of the CAM was significantly slowed, with only 84% of the surface area of the egg covered by the CAM on day 12, a difference that persisted on day 16. We hypothesize that these differences in the CAM surface area may have resulted in the lower metabolic rate of hypoxic incubated embryos on day 18 of incubation.
