The ontogeny of white leghorn chicken (Gallus domesticus) blood chemistry changes in response to acute exposure to 10 % O2

The embryonic chicken is a valuable model for studying the maturation of cardiovascular physiology and the responses of this organ system to environmental manipulations such as acute hypoxia. Hypoxia determines not only the general cardiovascular response but also is a tool to determine the system's maturation of reflexive control. Several studies suggest embryonic chicken's regulation of the cardiovascular response to hypoxia, but no studies have measured the blood chemistry changes that accompany these responses. To clarify the changes in blood parameters accompanying cardiovascular function changes during acute hypoxia, we designed a study to investigate the blood chemistry (pO₂, pCO₂, pH, lactate, glucose, and blood ions) in developing embryos during acute hypoxia (O₂ = 10 %). Embryos ranging from day 13 to 21 of incubation were sampled during a control period and at the end of a 5-min of hypoxia. Hypoxia caused bradycardia on all days of incubation. The maximal blood hypoxic response occurred on day 15, with lactate increasing 7-fold (2.5 to 16.6 mmol/l) while glucose levels decreased by 50 % (136 to 63 mg/dl). Furthermore, hypoxia reduced pH (7.40 to 7.26), which peaked on day 15. These data indicate that a 5-min exposure to 10 % O₂ is sufficient to induce dramatic changes in blood chemistry however chorioallantoic arterial blood pO₂ was unchanged on most days of the study. Therefore, given the cardiovascular response to hypoxia and the increase in blood lactate prior to airbreathing in the chicken embryo, the embryonic tissues experienced an acute stress that may be the basis for the change in cardiovascular function during the exposure.