Metabolism of ^C-Labelled Steroids 9 



The nature of the radioactive material present in urine and 

 faeces was especially investigated in the animals sacrificed 

 at 144 hours. Thus, in the urine only 15 per cent of the 

 activity was removable by ether and, after acid hydrolysis 

 in the autoclave, only another 10 per cent became ether- 

 soluble, the rest, or roughly 75 per cent, being water-soluble. 

 The situation in the faeces was very similar, with only a small 

 portion soluble in ether. 



In the long duration experiment with 5 mice the loss of 

 CO2 was 2-0 per cent in the first 12 hours following injection. 

 Another estimation at 97 hours after administration gave an 

 elimination of 1 • 1 per cent for a 12-hour period. 



(2) Distribution of Progesterone. A complete distribution of 

 radioactivity after administration of radioactive progesterone 

 was determined in one tumour-bearing C3H mouse. The 

 following points were observed: (a) the radioactivity in 

 the plasma was not high and was within the range of that of 

 the red blood cells. The blood level may have been maintained 

 for a very long period since it remained appreciable at 144 

 hours. (6) A major role of biliary excretion was indicated 

 by a high concentration in the bile and large amounts in the 

 intestine at 12 hours after injection, (c) However, urinary 

 excretion tended to be more pronounced than faecal excretion, 

 at least during the first 12 hours following injection, (d) As 

 in the case of oestrone, partition of urine and faeces revealed 

 that the greatest proportion of the excreted material was 

 water-soluble and remained so after hydrolysis, (e) Neither 

 secondary sex organs, nor endocrines showed a high concentra- 

 tion of radioactivity. (/) The loss of radioactivity as COg 

 was 2-5 per cent within 12 hours after injection in the long 

 duration experiment with 5 mice. Another estimation at 

 97 hours after administration gave an elimination of • 9 per 

 cent for a 12-hour period. 



In another experiment, two mice were castrated and three 

 weeks later one of them received 2 /xg of oestradiol a day for 

 3 days, after which they both received the standard dose of 

 radioactive progesterone. The cestradiol-treated animal was 



