Dynamics of metabolic compensation and hematological changes in chicken (Gallus gallus) embryos exposed to hypercapnia with varying oxygen

In day 15 chicken embryos, we determined the time course responses of acid–base balance and hematological respiratory variables during 24 h exposure to 15, 20, 40 or 90% O2, in the presence of 5% CO2. Hypercapnic respiratory acidosis was initially (2 h) only slightly (∼20%) compensated by metabolic alkalosis in normoxic/hyperoxic embryos. After 6 h, respiratory acidosis was partially (∼40–50%) compensated not only in normoxic/hyperoxic embryos, but also in hypoxic embryos. However, partial metabolic compensation in 15% O2 could not be preserved after 24 h. Preservation of metabolic compensation required oxygen concentration ([O2]) above 20%, but the magnitude of partial metabolic compensation was unrelated to [O2]. Hematocrit (Hct), together with mean corpuscular volume (MCV), markedly increased in hypercapnic hypoxia, and was maintained at 24 h due to a subsequent increase in red blood cell concentration ([RBC]). In contrast, Hct, together with MCV, decreased in hypercapnic normoxia/hyperoxia accompanied by a subsequent decrease in [RBC] at 24 h. Regulation of variables takes place similarly irrespective of environmental [O2] above 20%, matching acid–base regulation.

► We study acid–base regulation and hematology under gas challenges in chick embryos.
► Gas challenges include hypercapnia (5% CO2) hypoxia, normoxia and hyperoxia (15, 20, 40 and 90% O2).
► Time course responses to respiratory acidosis vary with oxygen concentration under hypercapnia.
► Metabolic compensation is not maintained 24 h after exposure to hypercapnic hypoxia.
► The mechanism behind hematocrit regulation changes with gas exposure time.