656 ADVENTURES IN RADIOISOTOPE RESEARCH 



varied to a restricted degree only with a varying maternal plasma iron 

 level. From these observations he inferred that much of the maternal 

 plasma iron reaches the embryo after being previously incorporated 

 into ferritin of the placenta. 



We wished to study iron metabolism at an early stage of pregnancy 

 in which the liver of the embryo is to a large extent involved in hemo- 

 poiesis and furthermore, the effect of exposure to radiation on iron tur- 

 nover in the pregnant rabbit. 



Plasma samples of control and irradiated rabbits obtained 21 days after mating, 

 were incubated at 37° C for 20 minutes with 0.5 microgram of iron as citrate 

 labelled with ^^Fe of 5 microcurie of activity per one ml plasma, and then reinjected . 

 The animals were killed 11.5 to 17 hours after injection. The activity and iron 

 content of the plasma of the mother, total iron and activity of the livers of the 

 mother, and the foetus and the specific activity of their liver-ferritin was then 

 determined. We measured also the specific activity of the circulating hemoglobin 

 and of the hemoglobin present in the nuclear fraction of the liver of mother and 

 foetus. The amount of radioiron found in the embryos after removal of the liver 

 was determined as well. The weight of the rabbits varied between 3.2 and 4.1 kgm 

 the number of embryos between 4 and 11, their aggregate weight between 11 

 and 58 gm, and the aggregate Uver weight of the embryos between 1.4 and 5 gm. 



After wet ashing of the samples to be investigated, a knoA\Ti aliquot of the 

 sample was used for colorimetric determination of its iron content. The iron deter- 

 minations were made essentially according to the sulfosalicyhc acid method by 

 LoBBEB (1927). Another known ahquot of the ashed sample, after bringing its 

 iron content up to 500 microgram by adding FeSO^, was precipitated as sulphide 

 and filtrated through perforated aluminium dishes covered with filter-paper, as 

 described previously by Agner et al. (1954), prior to placing the dish under the 

 Geiger counter. 



The livers of the animals were homogenized in 9 vol. 0.25 molar sucrose contain- 

 ing 0.0018 m CaClg, centrifuged for 10 min at 2000 r. p. m. (Internat. refrigerated 

 centrifuge horizontal head No. 269), and the ferritin was precipitated from the 

 supernatant by addition of half a volume of ammoniumsulphate. The precipitate 

 was taken up in water and repeatedly fractionated with anunoniumsulphate. 

 The precipitate was then dissolved in water, heated to 70° C for a few minutes 

 and the cold solution filtered. The filtrate, which contained the ferritin, was then 

 asnalysed. 



The hemin of the purified red corpuscles was extracted with a mixture 

 of acetone and HCl (10 ml 20 p. c. HCl in 1 liter of acetone). It was 

 twice recrystallized from acetic acid and the crystals were washed with 

 diluted HCl. The non-water soluble hemoglobin of the liver fraction was 

 obtained from thoroughly purified nuclei, prepared according to Hoge- 

 boom-Schneider as described hj Bonnichsen, Ehrenstein and 

 Hevesy (1956). 



