Ventilatory chemosensitivity of the 1-day-old chicken hatchling after embryonic hypoxia

We investigated the effects of sustained embryonic hypoxia on the neonatal ventilatory chemosensitivity. White Leghorn chicken eggs were incubated at 38'C either in 21% O-2 throughout incubation (normoxia, Nx) or in 15% O-2 from embryonic day 5 (hypoxia, Hx), hatching time included. Hx embryos hatched similar to 11 h later than Nx, with similar body weights. Measurements of gaseous metabolism (oxygen consumption, (V) over dotO(2)) and pulmonary ventilation ((V) over dotE) were conducted either within the first 8 h (early) or later hours (late) of the first posthatching day. In resting conditions, Hx had similar (V) over dot O-2 and body temperature (Tb) and slightly higher (V) over dotE and ventilatory equivalent ((V) over dotE/(V) over dotO(2)) than Nx. Ventilatory chemosensitivity was evaluated from the degree of hyperpnea (increase in (V) over dotE) and of hyperventilation (increase in (V) over dotE/(V) over dotO(2)) during acute hypoxia (15 and 10% O-2, 20 min each) and acute hypercapnia (2 and 4% CO2, 20 min each). The chemosensitivity differed between the early and late hours, and at either time the responses to hypoxia and hypercapnia were less in Hx than in Nx because of a lower increase in (V) over dot(E) and a lower hypoxic hypometabolism. In a second group of Nx and Hx hatchlings, the (V) over dotE response to 10% O-2 was tested in the same hatchlings at the early and late hours. The results confirmed the lower hypoxic chemosensitivity of Hx. We conclude that hypoxic incubation affected the development of respiratory control, resulting in a blunted ventilatory chemosensitivity.