A. FORSSBERG AND G. HEVESY 



slight differences could be noticed in the amount of ^ 'COg exhaled from 

 irradiated and controls. It would seem, therefore, that the effect has not 

 mainly been caused by a depressed transport rate of the injected NaH^^GOg 

 through the blood plasma. 



Some experiments were performed in order to elucidate the mechanism 

 of this X-ray effect. Resorption is presumably mediated through hormonal 

 action. This line of thought induced us to investigate the effect of the 

 administration of various hormones. Subcutaneous injection of ACTH in 

 amounts of •008-0-04 I. U. on the two days previous to the experiments 

 and 0-04-0 -2 I.U. one hour before injecting NaH^^COg affected the exhala- 

 tion of ^^COg in an opposite way to the irradiation, giving an increased 

 output of some 30 per cent in the first minutes. When irradiating the mice 

 after an ACTH administration it appeared that this combined treatment 



18r- 



Figure 1. Exhalation of ^*C02 from intraperi- 



toneallj injected "i^aH^^CO.^ in irradiated (•) and 



control (o) mice 



cancelled out the difference between treated and control mice. It may be 

 suggested that the diminished resorption rate observed in the exposed mouse 

 is due to a blocking effect by the irradiation of ACTH formation. The 

 biological half-life of the injected ACTH is about 5 min and the half-life 

 of the ACTH secreted into the circulation may have a similar value^. 

 Blocking of ACTH formation through irradiation would therefore soon mani- 

 fest itself. 



The combined effect of administration of hormones and irradiation is, 

 however, rather complicated as visualized by the following experiments with 

 adrenaline. Subcutaneous injection of 2 y adrenaline per mouse 5-15 min 

 before the injection of NaH^^COg caused a similar initial decrease in the 

 output of ^^COg as did the irradiation. Administration of adrenaline may 

 produce vasoconstriction which depresses the rate of resorption*. The 

 hypothesis that the irradiation effect on ^'^COg exhalation is caused by an 

 interaction of released adrenaline in the circulation could not be substanti- 

 ated as the concentration of adrenaline in the urine of irradiated animals 

 and controls was found to be similar in direct tests. This negative finding 

 does not necessarily disprove the hypothesis as a transient increase of 



149 



