CARBOHYDRATE METABOLISM 447 



cell or it increases the activity of the phosphorylating enzyme glucoki- 

 nase or perhaps both. Some investigators believe that a large part of 

 the glucokinase reverts to an inactive form in the absence of insulin 

 but that this process is reversed when insulin is administered. 



A lowered utilization of glucose due to a deficiency of insulin is 

 called diabetes. The disease is characterized by high levels of blood 

 glucose after ingestion of sugars and by urinary excretion of glucose 

 (called glucosmia). Weight loss, impaired muscular activity, poor 

 healing of wounds, and nervous disorders are other symptoms and 

 increase in severity with the degree of metabolic disturbance. The 

 rather mild forms common in older people can usually be controlled 

 with diets low in soluble sugars. More severe cases, especially those 

 in children, require the regular administration of insulin since the 

 hormonal deficiency is much greater in such people. Some progress 

 with other drugs has been reported in those individuals still synthesiz- 

 ing a little insulin. Apparently it is possible to stimulate formation 

 of the hormone if the specialized cells have not completely atrophied. 

 Formerly life expectancy was very low for diabetic children and other 

 individuals with severe cases. Now availability of insulin from cattle, 

 sheep, and swine, together with increased dietary knowledge has as- 

 ured diabetics of reasonably long and productive lives. 



Administration of an excess of insulin or hyperactivity of the secret- 

 ing cells dangerously reduces blood glucose and may lead to the 

 comatose condition called insulin shock, an ever-present hazard in the 

 treatment of severe diabetes. In normal animals the hypophyseal 

 hormone antagonizes the effect of insulin, tending to increase the level 

 of blood glucose. Epinephrine and the hyperglycemic-glycogenolytic 

 factor both operate with a similar result by promoting the conversion 

 of glycogen to glucose. 



Thyroxin, the special amino acid hormone of the thyroid gland, 

 catalyzes the general level of metabolism and indirectly the utilization 

 of glucose. Yet excessive activity of the thyroid can, in fact, somehow 

 simidate mild diabetes. Steroids from the adrenal cortex also indi- 

 rectly affect blood glucose and tend to elevate the levels. Thus the 

 level of glucose in the blood depends on the complex interplay of diet, 

 activity, and a number of hormones. 



METABOLISM OF OTHER CARBOHYDRATES 



Ingested polysaccharides may be either digested or excreted, depend- 

 ing on the animal species and the nature of the carbohydrate. Gly- 



