208 CELLULAR METABOLISM 



In an investigation carried out by Forssberg and the writer (92), 

 administration of cyanide to mice led to a marked depression of the 

 amount of CO2 exhaled and, correspondingly, to an increase in the ac- 

 tivity level of exhaled CO2. The latter reflects an increased C^"* incor- 

 poration into glycogen, which after administration of labeled bicarbonate 

 and non-labeled glucose mainly takes place, according to Wood (HI), 

 in the 3,4 position of the molecule. The increased incorporation of 

 C^'* into liver-glycogen carbon in mice previously injected with cyanide 

 is not due to an increased glycogen formation, but to the increased 

 activity level of the expiratory CO2. Increased C^^ incorporation into 

 liver glycogen of irradiated rats has correspondingly to be interpreted 

 as due to a metabolic depression. 



The writer, in the investigation of the effects of irradiation on the 

 incorporation of C^*-labeled acetate on the various tissue fractions (dry 

 tissue, total fat, and proteins) in 200 fed mice, studied in ten groups, 

 found that, though the mean value of C^^ incorporation into all but 

 the protein fraction of the intestinal mucosa was higher in the irradiated 

 rats than in the controls, these differences cannot, in many instances, 

 be considered significant. An increase, apparently significant, in the 

 incorporation of C^^ into dried brain tissue (34 per cent; P less than 

 0.03 per cent), into brain proteins (16 per cent; P less than 0.05 per cent), 

 brain fats (31 per cent; P less than 0.015 per cent), dried plasma (12 

 per cent; P less than 0.01 per cent), liver proteins (12 per cent; P less 

 than 0.04 per cent) in the irradiated mice was, however, observed. 



Forssberg and the writer found (92), when investigating the effect of 

 irradiation with 900 r on 340 fasting mice, no significant change in the 

 incorporation of acetate C^* into liver and other investigated protein 

 fractions. A significantly reduced incorporation (12 per cent; P equal 

 to 0.001 per cent) into the fatty acids was, however, observed. 



Under the effect of an x-ray dose of 300 r or more, the rate of absorp- 

 tion of the alpha-carbon-labeled glycine from the intestinal tract of the 

 rat was found to be markedly reduced (85). Other constituents of the 

 diet, as glucose (132), may be reabsorbed from the intestinal tract of 

 the irradiated animal at a slower rate as well. A depressing effect of 

 irradiation on the metabolic rate was furthermore observed by Barron 

 (89a). 



That, after administration of labeled glycine, more C^* was taken up 

 by acutely starved rats (90) than by the controls is possibly also due 

 to a decrease in the sensitivity of the radioactive indicator in starv- 

 ing rats. Salomon (93) found irradiation with 600 r to increase the C^'^ 

 ratio of hemin to globulin. In these experiments, glycine labeled in the 

 methylene group was administered to rats. A greatly increased incor- 



