Effects of chronic hypobaric hypoxia on blood O2 transport were studied using two groups of domestic pigeons (Columba livia). High-altitude (HA) birds were acclimated for 6 wk at 7 km simulated altitude (308 Torr, 25°C); sea-level (SL) pigeons were maintained for 5-6 wk at 758 Torr (25°C). Whole blood O2 equilibrium curves (O2ECs) were generated for HA and SL pigeons at 37°C and 41°C using thin film techniques. At pH 7.50 and 41°C, half-saturation PO2s (P50) for HA and SL birds were 32.9 ± 1.4 (6); (mean ± S.E.M. [N]) and 35.6 ± 0.6 (6) Tort, respectively. At pH 7.56 and 37°C, the corresponding P50s were 26.5 ± 1.8 (4) and 29.0 ± 0.6 (5) Torr, respectively. HA and SL pigeons exhibited similar Hb-O2 temperature coefficients (ΔH = -9.8 to -10.6 kcal/mole O2) and CO2 (Bohr slopes (Δlog P50/ΔpH = -.43 to -.44 at 37°C; -.41 at 41°C). Hill's n increased with increasing saturation for both animal groups at 37°C and 41°C. Hypoxic acclimation elicited a significant increase in O2 capacity; %Hct and [Hb] increased by 38% and 43%, respectively. Chronic hypoxia had no effect on isohemoglobin composition; both groups exhibited two isoHb fractions in a 9:1 molar ratio. At P(a)O2 = 30 Torr, calculated in vivo C(a)O2 for HA (39.2°C, pH 7.53) and SL (41°C, pH 7.50) birds were 14.2 vol % and 7.6 vol %, respectively. Results suggest that altitude tolerance of pigeons is enhanced by the increased blood O2 capacity and the effect of hypoxia-induced hypothermia on Hb-O2 affinity.
|Number of pages||8|
|Journal||Journal of Experimental Zoology|
|State||Published - 1 Mar 1997|