Oxygen consumption of the chicken embryo: interaction between temperature and oxygenation

We measured the effects of hypoxia and changes in ambient temperature (T) on the oxygen consumption (V˙O2) of chicken embryos at embryonic days 11, 16 and 20 (E11, E16 and E20, respectively), and post-hatching day 1 (H1). Between 30 and 39 °C, at E11 and E16, V˙O2 changed linearly with T, as in ectothermic animals, with a Q10 of about 2.1. At E20, V˙O2 did not significantly change with T, indicating the onset of endothermy. At H1, a drop in T increased V˙O2, a clear thermogenic response. Hypoxia (11% O2 for 30 min) decreased V˙O2, by an amount that varied with T and age. At H1, hypoxia lowered V˙O2 especially at low T. At E20, hypoxic hypometabolism was similar at all T. At E11 and E16, hypoxia lowered V˙O2 only at the higher T. In fact, at E11, with T = 39 °C even a modest hypoxia (15-18% O2) decreased V˙O2. Upon return to normoxia after 40 min of 11% O2, V˙O2 did not rise above the pre-hypoxic level, indicating that the hypometabolism during hypoxia did not generate an O2 debt. At E11, during modest hypoxia (16% O2) at 36 °C, the drop in V˙O2 was lifted by raising the T to 39 °C, suggesting that the hypoxic hypometabolism at 36 °C was not due to O2-supply limitation. In conclusion, the hypometabolic effects of hypoxia on the chicken embryo's V˙O2 depend on the development of the thermogenic ability, occurring predominantly at high T during the early (ectothermic phase) and at low T during the late (endothermic) phase. At E11, both low T and low oxygen force V˙O2 to drop. However, at a near-normal T, modest hypoxia promotes a hypometabolic response with the characteristics of regulated O2 conformism.