JANSKY 

 DISCUSSION 



HANNON: I was particularly interested in your cytochrome 

 oxidase measurements since we have assayed the activity of this 

 enzyme in the liver and muscle of warm and cold acclimatized 

 rats. As you are no doubt aware the manometric technique for 

 measuring cytochrome oxidase leaves a lot to be desired. Des- 

 pite this, however, we have used the same procedure as you have 

 and have found that cold acclimatization leads to a marked increase 

 in the activity of this enzyme in both liver and muscle tissue. 

 Besides this acclimatization effect, we were also most interested 

 in the fact that our studies showed the liver has about six times 

 more cytochrome oxidase than muscle. Thus, if this enzyme is 

 an index of maximum metabolic capability, as you suggest, the 

 liver would have six times greater metabolic capacity per gram 

 of tissue than muscle. And, to speculate a bit further, if we assume 

 that the level of cytochrome oxidase reflects the capacity of a 

 tissue to produce heat and if we take into account the fractions of 

 the total body mass represented by liver and muscle, then the 

 theoretical ratio of total muscle heat production to total liver heat 

 production would be about 2:1. It will be most interesting to see 

 whether or not this theoretical ratio will be verified by future exper- 

 iments where organ heat production is directly measured. 



JANSKY: In our own recent experiments concerning the cyto- 

 chrome oxidase activity in various organs of cold acclimated rats we 

 have found a liver :muscle ratio of 2.5:1 for cytochrome oxidase acti- 

 vity. These values of organ cytochrome oxidase correspond to the 

 values of maximal metabolism, which can be measured in working 

 animals or animals exposed to extreme cold. At present it is prac- 

 tically impossible to measure organ heat production in moving ani- 

 mals or on animals in extreme cold. The body temperature of small 

 laboratory animals falls very rapidly under these same conditions. 



HANNON: In your data on mice and rats I noticed a convergence 

 of the curves for work metabolism with the curves for metabolism 

 in the cold. In the golden hamster, on the other hand, such a conver- 

 gence was not apparent. If you had carried the temperature lower, do 

 you feel the same convergence might have occurred in the hamster? 



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