GLUCOSE AND OXYGEN UTILIZATION IN SYMPATHETIC GANGLIA 



99 



since in ganglia the extra glucose was apparently not oxidized, but was simply 

 converted to lactate. In Fig. 7, for example, the increase in lactate produc- 

 tion during activity was almost exactly equal to the increase in glucose uptake. 



Certain control experiments may be briefly mentioned. The increments were 

 shown not to be artifacts of the stimulating current, since their magnitudes 

 were much smaller when the ganglion was cut off from the preganglionic nerve 

 and the nerve was placed on the electrodes by itself. Therefore, the metabolic 

 changes must have been associated with conduction and discharge of impulses. 

 We have also shown that the acceleration of glycolysis is not due to a functional 

 anoxia brought on by the increased rate of oxygen utilization. This was con- 

 cluded from the fact that lowering the oxygen concentration in the equilibrat- 

 ing gas from 95% to 80% caused little or no alteration in the rates of glucose, 

 lactate, or oxygen exchanges when the neurons were at rest. Even in the pres- 

 ence of 60% oxygen there were no consistent changes. It is possible that limita- 

 tions of oxygen diffusion came into play at the highest rates of activity, and 

 may then have influenced the metabolic responses. However, the phenomena 

 with which we are concerned developed progressively, starting with the lowest 

 frequencies of stimulation, where the oxygen supply was evidently adequate. 



Glucose and lactate exchanges as a function of frequency of activity are 

 shown in Fig. 8. Both rates increased with frequency. However, the differ- 

 ence between them remained approximately constant. This difference is a 

 measure of the amount of glucose available for oxidation. Assuming complete 

 oxidation of this amount, we can calculate the amount of oxygen required, 

 with results shown as a function of frequency by the lower line in Fig. 9. 

 The approximate constancy of the glucose available for oxidation is emphasized 

 by the absence of upward or downward trend in this line. By contrast, the 

 upper line in this figure shows the rate at which oxygen was actually consumed. 

 This increased considerably with the frequency of activity. The difference be- 



IACTATE PROOUCED 



FREQUENCY OF STIMULATION 



Fig. 8. Rates of glucose consumption and lactate production by rat ganglia as 

 functions of frequency of supramaximal stimulation of the preganglionic nerve. Each 

 point is the average of results on 2 to 5 ganglia. 



