Oxidative Pathways of Carbohydrate Metabolism 173 



the pentose P pathway in the hyperthyroid rat Hver, the 

 glycolytic pathway competes more effectively for the available 

 substrate. It is interesting to compare these results with 

 those obtained by Spiro and Ball (1958) who made a com- 

 parison of the total and radioactive COg expired by normal 

 and hyperthyroid rats after injection of [l-^*C]glucose and 

 [6-i*C]glucose. Except for the first 15-minute period after 

 injection of the labelled glucose, the C-l/C-6 quotient was 

 found to be the same in the hyperthyroid as in the normal 

 animals, the average value for this quotient being 1 • 4. These 

 authors interpret this to mean that the enhanced metabolic 

 rate observed in the hyperthyroid rat reflects an approxi- 

 mately equal increase in the amounts of glucose metabolized 

 by the glycolytic and pentose P routes. 



The increased G6Pase activity shown in Fig. 6 may perhaps 

 be correlated with the low glycogen content of liver from 

 hyperthyroid rats (Cramer and Krause, 1913). Olsen (1951) 

 has stated that in rat liver the step between F6P and FliGPg 

 is rate-limiting in the sequence of reactions between G6P and 

 lactate. It would be of considerable interest to know the 

 activity of this enzyme in relation to those of the hexose- 

 monophosphate oxidative route in these hormonal conditions. 



Oxidative pathw^ays in liver tumours 



Wenner and Weinhouse (1956a) have calculated, from data 

 obtained on the incorporation of ^*C from labelled glucose into 

 lactic acid in a series of tumours, that the non-glycolytic 

 pathway could account for only a small part (from 0-16 per 

 cent) of the total glucose catabolized. That the pentose P 

 pathway does, however, operate in tumours is indicated from 

 experiments employing [l-i*C]glucose and [6-i*C]glucose. A 

 preferential conversion of C-1 of glucose to COg by various 

 types of liver tumours has been demonstrated by Abraham, 

 Hill and Chaikoff (1955), Emmelot (1955) and Wenner and 

 Weinhouse (1956a). The C-l/C-6 quotient of slices of liver 

 and liver tumours from rats fed DAB (Agranoff, Brady and 

 Colodzin, 1954) are shown in Table III. These results suggest 



