BLOOD CHEMISTRY 185 



constituents of the blood are present in the same concentra- 

 tion as they are in the plasma. From this protein-free ultra- 

 filtrate, the renal tubules reabsorb water and the so-called 

 threshold bodies including sodium and chloride, and return 

 these constituents to the blood stream. On the other hand, 

 the non-threshold substances, such as urea, are not reabsorbed 

 but appear in the urine in relatively concentrated solution due 

 to the reabsorption of water and other threshold substances. 

 Injury to the tubules might therefore be expected to result in 

 an increased excretion of water, sodium, and chloride due to 

 the inability of the kidney to reabsorb these substances. The 

 injury to the tubules may also result in the back diffusion of 

 non-threshold substances, such as urea, from the tubular 

 lumina to the blood and thus result in a faulty excretion of the 

 non-protein-nitrogen catabolites and their accumulation in the 

 body. As we have seen, these changes in the sodium, chloride, 

 and non-protein-nitrogen constituents of the blood are pre- 

 cisely those which occur in adrenal insufficiency. 



POTASSIUM AND OTHER CATIONS 



Simultaneously with the decrease in the sodium and chloride 

 contents of the blood plasma, one observes in adrenal insuffi- 

 ciency an increase in the concentration of potassium and mag- 

 nesium. Baumann and Kurland 44 found an increase of 42 and 

 23 per cent of these ions, respectively, above their normal 

 values in adrenalectomized cats. Hastings and Compere 285 

 observed potassium values as high as 20 millimoles per liter, 

 compared to 3 for normal animals. Changes in the blood 

 calcium are not noteworthy and rather irregular in their 

 occurrence. 625 



The large amounts of potassium which appear in the blood 

 in adrenal insufficiency may originate either from the ingested 

 food or from the tissues. Normally the potassium ingested in 

 the food is excreted in the urine. In adrenal insufficiency 

 where the loss of sodium and chloride through the kidney 



