Ventilatory chemosensitivity and thermogenesis of the chicken hatchling after embryonic hypercapnia

Hypoxia during incubation results in hatchlings with a reduced thermogenic capacity and a blunted ventilatory (V˙E) chemosensitivity (Szdzuy, K., Mortola, J.P., 2007b. Ventilatory chemosensitivity of the 1-day-old chicken hatchling after embryonic hypoxia. Am. J. Physiol. (Regul. Integr. Comp. Physiol.) 293, R1640–R1649). We asked if similar effects occurred with embryonic hypercapnia, that is, with a non-hypoxic sustained stimulation of the chemoreceptors. White Leghorn chicken eggs were incubated at 38 °C either in air (controls, C) or in 4% CO2 from embryonic day 5 (4% CO2), hatching included. The 4% CO2 embryos hatched about 12 h later than C, with similar body weight. On the day of hatching the thermogenic capacity, assessed from the changes in oxygen consumption (V˙O2) during 1 h at 30 °C, increased from the early (about 3 h old) to the late hours (about 20 h old), and was similar between 4% CO2 and C. Ventilatory chemosensitivity was evaluated from the changes in (V˙E) and in ventilatory equivalent (V˙E/V˙O2) during acute hypoxia (15 and 10% O2, 20 min each) or hypercapnia (2 and 4% CO2, 20 min each). Both at the early and late hours (V˙E) chemosensitivity was lower in 4% CO2 than in C. The V˙E/V˙O2 responses of 4% CO2 in hypoxia and hypercapnia averaged, respectively, about 45 and 60% of C. A separate set of eggs incubated in 2% CO2 gave results qualitatively intermediate between C and 4% CO2. We conclude that prenatal hypercapnia does not compromise the newborn's thermogenesis, but, like hypoxia, affects the development of respiratory control, resulting in a blunted chemosensitivity.