Postnatal changes in oxygen affinity of rat blood

1. 1. The respiratory properties and 2,3-DPG concentration were studied in blood of rats from birth to 83 days of age and compared with adult values. 2. 2. Newborn rat blood had a Hb concentration of 9.3 ± 1.1 g% significantly lower (P < 0.01) than 14.2 ± 1.4 g% for adults. 3. 3. The lowest value for Hb concentration occurred at day 5, then it rose to reach adult levels by 83 days of age. 4. 4. The Bohr factor for rat blood was −0.603 ± 0.066 Δ log pO2/ΔpH (N = 18). 5. 5. The P50 of newborn rats was significantly lower (P < 0.01) than adult values (24.6 ± 1.0 vs 38.7 ± 1.8mm Hg), but rose to the adult level by day 23 of life. 6. 6. The concentration of 2,3-DPG in newborn rat blood was 2.53 ± 1.78 μmol/g Hb, significantly lower (P < 0.01) than 13.93 ± 1.66 μmol/g Hb for adults. 7. 7. The concentration of 2,3-DPG rose steadily in the postnatal period and reached adult levels by day 18, close to the time when P50 values also reached the adult range. 8. 8. The pH difference across the red cell membrane decreased with age and therefore does not explain the rise in P50. Neither P50 nor 2,3-DPG concentration values in the neonate overshot adult values. 9. 9. The data collected in this study and information available for other species suggest that the time of disappearance of postnatal anemia depends upon the growth rate of the species.