Chapter XIII 



THE ADRENALS AND THE RESPIRATORY 

 METABOLISM 



The basal metabolic rate of an organism, measured usually 

 by the rate of oxygen consumption in the fasting, resting con- 

 dition, is constant and predictable from a knowledge of the 

 animal's size. This metabolism representing as it does the 

 intensity of the metabolic processes is easily altered by any 

 factor which modifies the activity of one or more organs. 

 The thyroid gland is preeminently important in regulating the 

 metabolic rate, but other organs, including the adrenals, may 

 also alter the metabolism either through their effects on the 

 thyroid or on the anterior lobe of the hypophysis (which in 

 turn affects the thyroid) or by their direct effects on the metab- 

 olic processes of the tissues. The exclusion from the animal 

 economy of a hormone necessary for the normal activities of a 

 tissue or organ will result in a change in the respiratory metab- 

 olism. The observation of such a change does not imply, 

 however, that the hormone in question controls the metab- 

 olism in the same sense as one is justified in speaking of the 

 control of the metabolism by the thyroid. 



Epinephrine, as we have already seen (Chapter VII), in- 

 creases the metabolic rate by direct action on the tissues. It is 

 very doubtful, however, if the medullary secretion normally 

 controls or affects to any great extent the metabolic rate, al- 

 though, to be sure, some effect will secondarily result from 

 any stimulus which affects the secretion of epinephrine. Ad- 

 renalectomized animals maintained on adequate doses of 

 cortical hormone, or rats, in which the medullary tissue has 

 been removed leaving only cortical tissue, have a normal 

 metabolic rate. These experiments indicate the dispensability 



205 



