GLUCOSE AND OXYGEN UTILIZATION IN SYMPATHETIC GANGLIA 101 



E 



',2,3 



UPTAKE PERIOD 



Fig. 10. Effect of pentobarbital (0.5 mM) on resting rates of glucose consumption 

 and lactate production by rat ganglia. Glucose data are averages from five ganglia. 

 Lactate production was measured on two other ganglia, each represented by a different 

 symbol. Pentobarbital was added at the start of the fourth uptake period. The broken 

 line indicates the effect of removing pentobarbital from one ganglion at the start of 

 the sixth period. Each uptake period was about 50 minutes long. Rates in this figure 

 are based on wet weight of tissue. (Edwards and Larrabee, 1955). 



by acceleration of lactate production was caused by the application of pento- 

 barbital in two exploratory experiments (Fig. 10). In each case, the output 

 of lactate rose along a time course that closely paralleled that of the average 

 glucose uptake of several other ganglia exposed to the same concentration 

 (Edwards and Larrabee, 1955). 



We thus conclude that there is some limitation in rate of conversion of glu- 

 cose into materials other than lactate. It should be emphasized that under the 

 conditions of our experiments this limitation was not due to limitation of oxy- 

 gen diffusion, since the resting metabolic exchanges were not significantly 

 affected by moderate reduction in external oxygen tension, as mentioned earlier. 



Significance of Acceleration of Glucose Metabolism During Activity 



These observations raise a question as to the significance of the observed 

 acceleration in rate of glucose uptake during activity. The extra glucose does 

 not seem to supply additional substrate to the oxidative mill, since no more 

 glucose appears to be made available for this use than during rest. Moreover, 

 we can attach no special importance to the increase in the small amounts of 

 energy yielded from reactions which convert glucose into pyruvate. This is 

 because repetitive activity can still be elicited when lactate, which skips these 

 steps, is substituted for glucose. 



We are left with the possibility that the acceleration of glucose uptake may 

 serve no useful purpose at all. Can it be just an irrelevant by-product of ac- 



