Pig reticulocytes. III. Glucose permeability in naturally occurring reticulocytes and red cells from newborn piglets.

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Abstract
The loss of facilitated glucose transport of red cells occurring in the newborn pig was monitored in 11 density-separated cells from birth to 4 wk of age. At birth there was a 3-fold increase in glucose permeability from the lightest cells to the most dense, suggesting that cells having progressively less glucose permeability are released into the circulation as gestation proceeds. Because of extraordinary stimulation of erythropoietic activity, the uppermost top fraction constituting 2-3% of the total cells is composed purely of reticulocytes in the growing animal. The glucose permeability of these reticulocytes which at birth has a slow but significant rate of 3.7 .mu.mol/ml cell .times. min at 25.degree. C is rapidly decreased within 3-4 days to the level of reticulocytes produced in the adult in response to phenylhydrazine assault. Reticulocytes themselves discard their membrane permeability to glucose in the course of maturation to red cells. Even though reticulocytes at birth are permeable to glucose, they will become red cells practically impervious to glucose within a few days. The transition from a glucose-permeable fetal stage to a glucose-impermeable postnatal state is apparently brought about by 2 mechanisms: dilution of fetal cells by glucose-impervious cells produced coincidentally with or shortly after birth; elimination of fetal cells, which have a shorter half-life, from the circulation.