204 M. J. Karvonen 



level. A similar conclusion applies to an eventual "potassium 

 pump". The erythrocytes of a foetus are larger than those of 

 an adult. With constant activity of the electrolyte pumps an 

 increase in the cell sodium and a decrease in potassium would 

 be expected from foetal to adult life. This is the direction of 

 development in the ruminants, but not in the other species 

 examined. It is rather questionable whether the decrease in 

 cell size even in the ruminants is an important cause of the 

 changes of the red cell electrolytes. 



With the aid of in vitro studies much progress has been 

 made in elucidating the mechanism of cation transfer across 

 the red cell membrane. The application of these methods to 

 the erythrocytes of the foetus suffers from a serious limitation : 

 the cells of foetuses (at least human and sheep) haemolyse 

 spontaneously and rather fast in vitro. To some extent the 

 rate of haemolysis is dependent on oxygen tension, high 

 oxygen tension increasing the rate of haemolysis, but haemo- 

 lysis also occurs at an appreciable rate in blood exposed to 

 nitrogen. Haemolysis in human cord blood may also be 

 retarded by administering ascorbic acid to the mothers before 

 delivery, but even so the rate of spontaneous haemolysis 

 remains considerably higher than in adult blood. An addition 

 of ascorbic acid in vitro is without effect (Raiha, 1956, and 

 personal communication). 



Summary 



Information on changes in the electrolyte metabolism of 

 individual erythrocytes during their life cycle is meagre. 

 However, the claims that young and old cells may be separ- 

 ated with the aid of centrifugation or serial haemolysis suggest 

 that changes in the electrolyte metabolism may be involved 

 in the ageing of the red cells. Differences in the actual sodium 

 and potassium concentrations have not, however, been 

 demonstrated. 



In sheep and cattle the erythrocytes of a foetus contain 

 more potassium and less sodium than those of an adult. In 

 man, pig and guinea pig, a difference in the opposite direction 



