The changeover from the fetal type Hbf, to the adult, HbA, type of hemoglobin begins before birth and continues after birth (Figure 3.11). Because the oxygen affinity of HbA is lower than that of Hbf, mainly because the former binds DPG, the P50 value rises, i.e. hemoglobin-oxygen affinity declines as the ODC moves to the right.
The decrease in affinity of hemoglobin after birth is also accelerated by a substantial rise in blood diphosphoglycerate (DPG) concentration.
In the dog, P50 increases from 21 mmHg at birth to 35 mmHg after 60 days, then falling to the adult value of 32 mmHg. DPG concentration similarly peaks around 60 days of age, then falls back toward adult values.
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