758 Comparative Animal Physiology 



stored glycogen in the body and in blood sugar, and exhibit grfeatly decreased 

 nitrogen excretion, the latter indicating decreased protein catabolism. Con- 

 versely, after injection of cortical extracts normal specimens show an increase 

 in both stored glycogen and blood sugar, while exhibiting increased nitrogen 

 excretion. Since these changes occur even, in fasting specimens, it is reason; 

 able to consider that all the carbohydrate increase has occurred at the ex- 

 pense of body protein. In fact, the amount of nitrogen excreted under these 

 circumstances appears to be of the proper order of magnitude to render this 

 explanation highly probable. 



In partially depancreatized rats with glycosuria maintained by appropriate 

 feeding, adrenalectomy is followed by a marked reduction in glycosuria, 

 which may be restored to its original high level by cortical extracts. Hy- 

 pophysectomy of depancreatized or normal rats is also accompanied by carbo- 

 hydrate reduction in the body, an effect which may in part be reversed by 

 administration of cortical extracts. It would therefore appear that at least a 

 part of the influence of the pituitary on carbohydrate metabolism is exerted 

 through its adrenotropic factor. Of the cortical principles, corticosterone and 

 dehydrocorticosterone influence carbohydrate metabolism much more strongly 

 than do desoxycorticosterone and progesterone, although the latter are very 

 influential in maintaining the electrolyte balance and life of the organism. 



It would appear from the available evidence that the adrenal cortex influ- 

 ences carbohydrate metabolism largely through the stimulation of produc- 

 tion of carbohydrate at the expense of protein. 



The thyroid of the mammal through the action of its hormone, thyroxin, 

 exerts a powerful influence on the basal metabolism and hence on the oxida- 

 tion of such normal substrates' as hexosemonophosphate. Its mode of action 

 would therefore appear to be through the activation of those enzyme sys- 

 tems which limit the rate of the process— probably dehydrogenases. 



A number of principles from the anterior lobe of the pituitary influence 

 various aspects of intermediary metabolism.^^^- ^^ Through the action of a 

 pancreatropic principle the normal amount of islet tissue and hence of nor- 

 mal insulin production is maintained. An adrenotropic principle is essen- 

 tial to continued normal production of carbohydrate-influencing cortical prin- 

 ciples. A diabetogenic principle is believed to inhibit insulin secretion and 

 hence give rise to the characteristic symptoms of diabetes— namely hyper- 

 glycemia, glycosuria, and ketonuria. Through a thyrotropic principle the 

 thyroid is caused to continue its normal production and liberation of thyrox- 

 in. Other principles of anterior pituitary origin which more questionably 

 possess separate identities are believed by many to influence metabolism more 

 directly. A heat-stable glycotropic principle appears to act as an anti-insulin, 

 having no influence on metabolism apart from its action relative to insulin. A 

 glycostatic principle may retard or inhibit the oxidation of hexosemonophos- 

 phate. A ketogenic factor (possibly identical with the glycostatic, adreno- 

 tropic, or diabetogenic factor) is believed to influence fat metabolism in such 

 a manner as to result in the production of ketone bodies, organic acids 

 characteristically found in the blood of diabetics. 



The observation of Houssay and his associates that removal of the an- 

 terior lobe of the pituitary from depancreatized mammals diminishes the 

 intensity of the diabetic condition of these animals, thereby demonstrating 



