Respiratory characteristics of opossum (Didelphis virginiana) blood during chronic anemia

In five adult opossums (Didelphis virginiana), blood hemoglobin concentration was lowered from 12.3g% to 6.4g% by daily bleeding. Blood P50 rose significantly (P is less than 0.05) from 44.5 mm Hg to 47.4 mm Hg and the concentration of 2, 3-diphosphoglycerate (DPG) increased from 14.17 mumol/g Hb to 20.90 mumol/g Hb. The observed shift in blood oxygen affinity was of similar magnitude to that recorded in humans with a similar degree of anemia, but the concomitant rise in DPG concentration was greater in opossums than in humans. In the opossum the shift in P50 with anemia can be attributed entirely to the action of DPG as a non diffusible intraerythrocytic anion.