Originally published in Nature, 164, 1007 (1949). 



82. EFFECT OF MUSCULAR EXERCISE AND OF 

 URETHANE ADMINISTRATION ON THE INCORPORATION 

 OF CARBON-14 INTO ANIMAL TISSUE 



G. Hevesy 



From the Institute for Research in Organic Chemistry and the Pharmacological 

 Laboratory, Karohnska Institute, Stockholm 



As a result of the observations described in a previous note^^\ according 

 to which irradiation with X-rays influences the pattern of incorporation 

 of carbon-14 into animal tissue, it became particularly important to 

 investigate the effect of muscular exercise on the incorporation of this 

 isotope. 



Five minutes after intraperitoneal administration of 4 ^curies of 

 carboxyl labelled acetate to each individual of twenty mice, half the 

 animals were made to swim for twenty minutes. At the end of this 

 period these mice and an equal number of controls Mere decapitated. 

 The activities were then determined of the dry tissue, of the ether-alcohol 

 extract (fatty fraction) and the protein residue obtained by extraction 

 with trichloracetic acid of the organs listed in the accompanying table. 

 Incorporation of carbon-14 is seen to be significantly decreased in almost 

 all cases. 



Similar results were obtained in 3 hr experiments where swimming 

 was replaced by more moderate exercise, the mice being encouraged to 

 move each time they stopped. The percentage reduction in incorporation 

 was, however, smaller, amounting in most fractions investigated to about 

 5 per cent only. 



In another series of experiments, 20 mgm of urethane was injected 

 into each of thirty mice, followed by the administration of labelled 

 acetate. The animals obtaining urethane were found after a period of 

 4 • 5 hr to have incorporated markedly more carbon-14 than did the 

 controls. The results listed in the table, demonstrate the great sensitivity 

 of this method, in which the incorporation of carbon-14 in tissue fractions 

 serves as an index of particular metabolic processes. The usual methods, 

 such as the comparison of the Q^o o^ ^^^^ ^o values of surviving tissue 

 slices of urethane-treated mice (20 mgm per animal) and of controls 

 do not show any significant difference^^^ On the other hand, its 

 depressing effect on tissue metabolism is clearly brought out by the 

 above figures. 



