Ventilatory response to hypoxia of the 1-day old chicken hatchling after prenatal cold-induced hypometabolism

• Sustained prenatal hypoxia decreases embryonic metabolic rate and blunts the postnatal hypoxic ventilatory response (HVR).
• We tested the possibility that the prolonged hypometabolism may be a contributing factor.
• Chicken embryos were incubated at 35 °C to lower their prenatal oxygen consumption without changes in oxygenation.
• One-day old hatchlings had pulmonary ventilation, oxygen consumption and HVR as in controls.
• Hence, sustained prenatal decrease in metabolic rate by itself does not carry obvious consequences on the newborn's HVR.

Sustained prenatal hypoxia decreases the growth and metabolic rate of the embryo and causes a blunted hypoxic ventilatory response (HVR) in the newborn. The most likely interpretation is that the sustained hypoxic stimulation may interfere with the normal prenatal development of the chemoreceptors. However, we wanted to consider the possibility that the prolonged hypoxic hypometabolism may be a contributing factor. Chicken embryos were incubated at 35 °C (Cold group, N = 14), which is known to lower the embryonic oxygen consumption (V˙O2) by ∼30% throughout incubation, or at 37.5 °C (Controls, N = 16). Cold incubation delayed hatching by ∼2 days. The 1-day old hatchlings had normal pulmonary ventilation (V˙E), measured by the barometric technique, and oxygen consumption (V˙O2), simultaneously measured by an open flow methodology. During acute hypoxia (∼15% or ∼11% O2) the hyperventilation (increase in V˙E/V˙O2), the hyperpnea and the hypometabolism were almost identical between the two groups of hatchlings. We conclude that a sustained decrease in metabolic rate during the embryonic period by itself does not carry obvious consequences on the newborn's resting V˙E and HVR.