Effect of pregnancy and temperature on red cell oxygen-affinity in the viviparous snake Thamnophis elegans

The oxygen affinity of red cell suspensions from fetal garter snakes was higher than that of cell suspensions from their mothers. This difference appeared to be due to different concentrations of nucleoside triphosphate (NTP, primarily adenosine triphosphate). NTP concentrations were significantly higher, and oxygen affinities were significantly lower, in red cell suspensions from pregnant females compared with those from nonpregnant females or males; there is no precedent for such a pronounced effect of pregnancy on the oxygen affinity of maternal blood. These data indicate that pregnancy may result in an enhanced ability of adult blood to deliver oxygen to the fetus. Since the binding of organic phosphates and oxygen to hemoglobin is sensitive to temperature, and since these animals experience diurnal changes in temperature, we examined the influence of relatively low (20 degrees C) and high (34 degrees C) temperatures on red cell oxygen-affinity. The temperature increase of 14 degrees C resulted in a lowered oxygen-affinity of all red cell suspensions examined. However, this increase in temperature lowered the affinity of maternal red cells to a greater extent than it did the affinity of fetal red cells. This suggests that daytime temperatures may further enhance the ability of maternal blood to deliver oxygen to the fetus at times when fetal oxygen demand is probably greatest.