Originally published in Acta Physiol. Scand. 38, 184 (1956). 



66. EMBRYONAL IRON TURNOVER. 



G. Ehrenstein and G. Hevesy 

 From the Institute of Organic Chemistry and Biochemistry, University of Stockholm 



VoSBURGH and Flexner (1950) were the first to inject labelled iron 

 as FeClg into the circulation of the guinea-pig and to study the passage 

 of radioiron through the placenta. The amount of iron passed into the 

 foetus of the guinea-pig varied between 16 and 119, with an average 

 of 56 microgram of iron per gram of placenta per day. They found 

 no correlation with gestation age. This finding induced them to suggest 

 that the passage of iron across the placenta appears to involve a different 

 mechanism than that which is concerned with other substances which 

 they studied. The rate at which water, sodium and inorganic phosphate 

 cross a unit weight of the guinea-pig's placenta increases about 10 

 times during the last half of pregnancy. This increase of rate is corre- 

 lated with thinning of the barrier between maternal and foetal circu- 

 lation and increased area of exchange, and is in the predicted direction 

 if the process is essentially diffusion. Iron, however, crosses the placenta 

 at a rate which shows no correlation with the duration of pregnancy, 

 i. e. there is no evident difference between the rates in early and late 

 stages. In addition, there may be a considerable difference in the amount 

 of iron transferred to members of the same litter during the course of 

 the experiment. They emphasize that these characteristics of iron trans- 

 port across the placenta suggest the existence of a rather complex 

 regulatory mechanism which may be analogous to that concerned with 

 the absorption of iron from the gastrointestinal tract, since ferritin has 

 Ijecn demonstrated in the placenta of the guinea-pig by Latham and 

 VosBURGH (1950) and in the human placenta by Mazur et al. (1955). 

 The above view recently received much support by the work of Wohler 

 (1955), discussed by him and lay Heilmeyer (1956). Wohler injected 

 1.25mgmof labelled ferrosulfite into the circulation of pregnant rabbits, 

 and found the ferritin extracted from the placenta to show a marked 

 radioactivity already 40 minutes after injection. He demonstrated, 

 furthermore, the marked dependency of the total iron content of the 

 placenta and the foetal plasma iron on the plasma iron content of the 

 mother, in contrast to the ferritin content of the placenta. The latter 



