EFFECTS OF CHRONIC HYPOBARIC HYPOXIA ON BLOOD-OXYGEN BINDING IN PIGEONS

Effects of chronic hypobaric hypoxia on blood O-2 transport were studi ed using two groups of domestic pigeons (Columba livia). High-altitude (HA) birds were acclimated for 6 wk at 7 km simulated altitude (308 T orr, 25 degrees C); sea-level (SL) pigeons were maintained for 5-6 wk at 758 Torr (25 degrees C). Whole blood O-2 equilibrium curves (O(2)EC s) were generated for HA and SL pigeons at 37 degrees C and 41 degrees C using thin film techniques. At pH 7.50 and 41 degrees C, half-satur ation PO(2)s (P-50) for HA and SL birds were 32.9 +/- 1.4 (6); (mean /- S.E.M. [N]) and 35.6 +/- 0.6 (6) Ton; respectively. At pH 7.56 and 37 degrees C, the corresponding P(50)s were 26.5 a 1.8 (4) and 29.0 +/ - 0.6 (5) Ton, respectively. HA and SL pigeons exhibited similar Hb-O- 2 temperature coefficients (Delta H = -9.8 to -10.6 kcal/mole O-2) and CO2 (Bohr slopes (Delta log P-50/dpH = -.43 to -.44 at 37 degrees C; -.41 at 41 degrees C). Hill's n increased with increasing saturation f or both animal groups at 37 degrees C and 41 degrees C. Hypoxic acclim ation elicited a significant increase in O-2 capacity; %Hct and [Hb] i ncreased by 38% and 43%, respectively. Chronic hypoxia had no effect o n isohemoglobin composition; both groups exhibited two isoHb fractions in a 9:1 molar ratio. At PaO2 = 30 Torr, calculated in vivo CaO2 for HA (39.2 degrees C, pH 7.53) and SL (41 degrees 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 Oz capacity a nd the effect of hypoxia-induced hypothermia on Hb-O-2 affinity. (C) 1 997 Wiley-Liss, Inc.