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 24h exposure to 15, 20, 40 or 90% O(2), in the presence of 5% CO(2). Hypercapnic respiratory acidosis was initially (2h) only slightly (∼20%) compensated by metabolic alkalosis in normoxic/hyperoxic embryos. After 6h, respiratory acidosis was partially (∼40-50%) compensated not only in normoxic/hyperoxic embryos, but also in hypoxic embryos. However, partial metabolic compensation in 15% O(2) could not be preserved after 24h. Preservation of metabolic compensation required oxygen concentration ([O(2)]) above 20%, but the magnitude of partial metabolic compensation was unrelated to [O(2)]. Hematocrit (Hct), together with mean corpuscular volume (MCV), markedly increased in hypercapnic hypoxia, and was maintained at 24h 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 24h. Regulation of variables takes place similarly irrespective of environmental [O(2)] above 20%, matching acid-base regulation.