Enzymes in Irradiated Tissues 45 



complete the synthesis of their haemoglobin after a dose of 

 radiation which will ultimately stop new haemoglobin forma- 

 tion entirely. 



However interesting may be these results which show 

 immediate stimulation of fatty acid synthesis and of haemin 

 and globin formation, there is always the doubt that they are 

 direct or indirect effects of radiation since they have been 

 obtained with tissue preparations from animals which had 

 received whole body radiation. Therefore the effects might be 

 secondary and due to environmental change, i.e. change in 

 available substrates in the tissues. In vitro work with such 

 enzyme systems might give the answer. 



To turn now to experiments where rather simpler conditions 

 have been used than irradiation of the whole body : 



Formation of adrenal steroids 



Ungar and co-workers (1955) have found that irradiation 

 of the perfused adrenal gland of the calf reduces the formation 

 of adrenal steroids. These glands, obtained from the slaughter- 

 house, are perfused and irradiated simultaneously for 2-3 

 hours, the dose being around 2,000 r of gamma-radiation from 

 ^^Co. The blood, to which ACTH was added to stimulate 

 steroid formation, is passed through the gland only once and 

 therefore received only a small dose of radiation. At the end 

 of the perfusion the adrenal steroids in the blood were 

 isolated and estimated chromatographically. Production of 

 hydrocortisone, corticosterone and unidentified steroids was 

 markedly diminished. 



Rosenfeld and co-workers (1955) further showed that if 

 various steroid precursors were added to the perfusing blood, 

 irradiation inhibited their conversion. 



Table III shows that lip-, 17a- and 21-hydroxylations are 

 inhibited as well as oxidation of the A^-Sp-hydroxyl group to 

 to A^-3-ketone group. The percentage decrease in the conver- 

 sion products paralleled both in range and variability the 

 percentage decrease in corticoid output which was found in 



