Ionic composition of red cells in fetal, newborn, and adult sheep

¹ Department of Physiology, Yale University School of Medicine, New Haven, Connecticut

The concentrations of Na and K in the erythrocytes of the blood of adult, purebred Dorset ewes and their fetuses were determined by flame photometry. With respect to these cations, adult ewes can be divided into two groups; in one, Na is in higher concentration and, in the other, K concentration is higher. In every fetus studied, however, the K concentration exceeded the Na, and there was a higher K and a lower Na concentration than in the maternal erythrocytes. In lambs of mothers with a high Na concentration in their erythrocytes, the transition from the fetal to the adult electrolyte pattern was completed 7 or 8 weeks post partum. The relationship between the ionic composition of the red cells and the O₂ dissociation curves in mothers and their fetuses, and in both groups of adult sheep, is discussed. Differences in the concentrations of Na and K in the erythrocytes do not appear to explain the differences in O₂ dissociation curves observed among adult sheep.