6 C. P. Leblond 



radioactive steroids: (1) We examined the distribution of 

 radio-iodine-labelled oestradiol and the outstanding findings 

 (presented in May, 1947, before the American Association for 

 Cancer Research) were the major role played by the gastro- 

 intestinal system in promptly disposing of the material, and 

 the lack of any remarkable concentration in the secondary 

 sex organs with the exception of the mammary glands. 

 Unfortunately, when the di-iodo- and mono-iodo-a-oestradiol 

 used were assayed in spayed rats by the vaginal smear test, 

 which is sensitive to 0-1 fig. of oestradiol, neither of these 

 substances displayed oestrogenic activity in doses up to 

 100 fig. Thus, some doubt has been cast on the significance 

 of the results obtained with these substances (Albert, Heard, 

 Leblond and Saffran, 1949). (2) Twombly, McClintock and 

 Engelman (1948) obtained similar results with equilin bro- 

 minated with radio-bromine. (3) A recent paper by Riegel, 

 Hartop and Kittinger (1950) deals with the metabolism of 

 [21-^^C]-progesterone in mice and rats. Their main findings 

 are that a considerable proportion of the material is recover- 

 able as labelled COg in the expired air. Some is excreted in 

 the faeces but none in the urine. Finally, a significant con- 

 centration of material is present in the pituitary, adrenals and 

 ovaries. 



Like the above, the results to be reported here are of a 

 preliminary nature and refer to pilot experiments only. Three 

 steroids have been investigated so far: [16-^*C]-oestrone, 

 [21-^*C]-progesterone, and [21-^*C]-deoxycorticosterone ace- 

 tate (DCA). 



Methods and Techniques 



(1 ) Preparation of Radioactive Steroids. Radioactive oestrone 

 was prepared by Heard, Saffran and Thompson by opening 

 ring D, addition of ^*C-diazomethane to the resulting aliphatic 

 side chain through the Arndt and Eisert reaction and pyrolysis 

 of the corresponding homo-di-acid back to the original 

 ketone. Radio-progesterone and radio-deoxycorticosterone 

 were obtained by Heard and Yates. [21-^*C]-progesterone 



