Red cell oxygen affinity in fetal sheep: role of 2,3-DPG and adult hemoglobin

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Abstract
Studies were carried out during fetal life in sheep to determine the relationship of 2,3-diphosphoglycerate (DPG), the intracellular red cell and extracellular pH and the switchover to adult Hb synthesis in regulating the position of the fetal red cell oxygen-affinity curve in utero. Adult Hb first appeared near 120 days of gestation. The mean oxygen tension at which Hb is half saturated (P50) prior to 120 days of gestation remained constant at 13.9 .+-. 0.3 (SD) Torr and then increased gradually as gestation continued, reaching 19 Torr at term. During the interval of fetal life studied, the level of DPG was 4.43 .+-. 1.63 (SD) .mu.mol/g Hb and the .DELTA.pH between plasma and red blood cells was 0.227 .+-. 0.038 (SD); neither was affected by gestaional age. The decrease in the red cell oxygen affinity after 120 days of gestation correlated with the amount of adult Hb present in the fetus (r [correlation coefficient] 0.78; P < 0.001). This decrease can be attributed only to the amount of the adult-type Hb present, and not to DPG, or to changes in the .DELTA.pH between plasma and red blood cells, because both remained stable during the last trimester.

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