Postnatal changes in blood respiratory characteristics in an American opossum (Didelphis virginiana).

The oxygen affinity of opossum blood changes in the postnatal period. The youngest opossums studied were 53 days of age (dated from the day of transit from vagina to pouch) and still confined to the maternal pouch: they had a blood P50 of 32.6 +/- 2.9 mm Hg. The blood P50 value then increased significantly, in two steps. First, while the young were still in the pouch, blood P50 rose secondary to a rise in the concentration of 2,3-diphosphoglycerate (DPG). Blood P50 and DPG concentration then remained stable until the animals left the maternal pouch, when DPG rose again, causing a further increment in the blood P50 which peaked at 48.7 +/- 4.5 mm Hg in animals 148 days old. Blood P50 subsequently decreased significantly, reaching the adult value (42.0 +/- 1.9 mm Hg) at about 250 days.