Diminution of the temperature effects on the oxygen affinity of hemoglobin after prolonged hypothermia.

The influence of temperature on the oxygen affinity of hemoglobin, expressed as half saturation tension P50, was investigated in male Sprague Dawley rats, which had been exposed to a cold environment for about 12 h. P50-values were determined by equilibrating blood samples to a known PO2 at different temperatures. The well known increase in oxygen affinity at low temperatures was observed, but after a longer hypothermic period this effect was diminished. This reduction of the temperature effect is manifested in a change of the ratio delta log P50/delta T from 0.022 in control experiments to 0.0115 in hypothermia. In cold adapted rats such an effect means a better oxygen supply to tissue at low body temperatures than in control animals. These changes in oxygen delivery after cold acclimatisation may partially be interpreted as the result of the decreased intraerythrocytic pH and elevated concentration of ATP found in the present study.