Pig reticulocytes: II. Characterization of density-fractionated maturing reticulocytes

A simple centrifugation technique initially developed for fractionation of human red cells in their own plasma has been found to be readily applicable to the separation of reticulocytes normally appearing in the pig soon after birth as well as to those induced in the adult pig by phenylhydrazine administration. The density of the naturally occurring reticulocytes, maximally amounting to 10-15% of total cells derived from a 7-day-old pig, varied from 1.073 to 1.101, in contrast to the mature cells, presumed to be the fetal cell type, whose density ranged in a narrower limit, from 1.101 to 1.106. In adult animals, the reticulocytosis amounting to more than 70% takes place in response to daily administration of phenylhydrazine for 7 days. The density of these reticulocytes varied widely from 1.068 to 1.094; in contrast, the density of the mature adult red cells ranged from 1.095 to 1.106. Among various physiological parameters examined, a marked decrease in cell size, cell water content, RNA, Na+ -K+ -ATPase, and Ca2+ -ATPase activities was observed in the course of reticulocyte maturation in vivo in the adult animal. All these physiological parameters were found to undergo a similar reduction from the top to the bottom fractions of the reticulocytes separated according to their density, suggesting that the separation technique employed here represents separation of reticulocytes according to their age.