Dynamics of blood viscosity regulation during hypoxic challenges in the chicken embryo (Gallus gallus domesticus)

Hypoxia in chicken embryos increases hematocrit (Hct), blood O-2 content, and blood viscosity. The latter may limit O-2 transport capacity (OTC) via increased peripheral resistance. Hct increase may result from increased nucleated red blood cell concentration ([RBC]) and mean corpuscular volume (MCV) or reduced plasma volume. We hypothesized changes in Hct, hemoglobin concentration ([Hb]), [RBC] and MCV and their effects on viscosity would reduce OTC. Five experimental treatments that increase Hct were conducted on day 15 embryos: 60 min water submergence with 60 min recovery in air; exposure to 15% O-2 with or without 5% CO2 for 24 h with 6 h recovery; or exposure to 10% O-2 with or without 5% CO2 for 120 min with 120 min recovery. Control Hct, [Hb], [RBC], MCV, and viscosity were approximately 26%, 9 g%, 2.0 10(6) mu L-1, 130 mu m(3), and 1.6 mPa s, respectively. All manipulations increased Hct and blood viscosity without changing blood osmolality (276 mmol kg(-1)). Increased viscosity was attributed to increased [RBC] and MCV in submerged embryos, but solely MCV in embryos experiencing 10% O-2 regardless of CO2. Blood viscosity in embryos exposed to 15% O-2 increased via increased MCV alone, and viscosity was constant during recovery despite increased [RBC]. Consequently, blood viscosity was governed by MCV and [RBC] during submergence, while MCV was the strongest determinant of blood viscosity in extrinsic hypoxia with or without hypercapnia. Increased Hct and blood O-2 content did not compensate for the effect of increased viscosity on OTC during these challenges. (C) 2015 Elsevier Inc. All rights reserved.