MAXIMAL STEADY STATE METABOLISM AND ORGAN 

 THERMOGENESIS IN MAMMALS 



L. Jansky 



The studies of basal metabolic rates in mammals and the rela- 

 tion of metabolic rates to body weight have been the subject of many 

 papers and reviewssince the middle of the nineteenth century. These 

 studies have not confirmed the validity of the "surface area theory" 

 and have proved that the basal metabolic rates were proportional to 

 W^*^^ where W is the body weight (Kleiber, 1947). 



On the other hand, very few data are available on the upper 

 limits of metabolic rate that can be sustained for long periods in 

 different species. It is known that very high rates of heat produc- 

 tion, up to 100 times the basal level, can be measured in man and 

 horse under extreme exercise (Brody, 1945). However, these rates 

 cannot be sustained for long periods and do not result from steady 

 state effort. Methods of estimating steady state effort and a com- 

 parison of results in different species varying in body weight will be 

 considered in this paper. In addition, the total cytochrome oxidase 

 activity, which can yield values for metabolism which are theoreti- 

 cally maximal in different species (Jansky, 1961), will also be con- 

 sidered. This method also provides a means for estimating the theo- 

 retical maximal values for different organs of the same species and 

 their relative contributions to the metabolic capacity of the whole 

 animal. 



Maximal Steady State Metabolism 



For the purposes of this paper, the upper limit of metabolism 

 will be called the "maximum steady state metabolism" and will be 

 defined as the highest oxygen consumption compatible with sustained 

 aerobic effort when there is no progressive accumulation of lactic 

 acid in muscles. It is known for man (Wells et al., 1957) rats (Sreter 

 and Friedman, 1958), and deer mice (Hart and Heroux, 1954) that a 

 certain level of exercise can be attained without accumulation of 



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