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) over dot>(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) over dot>(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) over dot>(E)) and in ventilatory equivalent (<(V) over dot>(E)/<(V) over dot>(O2)) during acute hypoxia (15 and 10% O-2, 20 min each) or hypercapnia (2 and 4% CO2, 20 min each). Both at the early and late hours (<(V) over dot>(E)) chemosensitivity was lower in 4% CO2 than in C. The <(V) over dot>(E)/<(V) over dot>(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. (c) 2008 Elsevier B.V. All rights reserved.