§5.211 CARBOHYDRATE METABOLISM 193 



cold-blooded vertebrates and birds has shown that they resemble 

 those in mammals. There are two different diabetogenic systems 

 that can increase the blood-sugars in different species: either 

 glucagon from the pancreas or a hormone from the adrenal cortex 

 (Table 21). 



Teleostei. The tunny, Thunnus germo, and other fish secrete a 

 substance like glucagon from the a cells of the pancreas, but the 

 action of an extract has only been tested on rats (Mialhe, 1952). 



Amphibia. In frogs, Rana^ the adrenal cortex probably plays 

 a part in the control of the sugar balance by secreting a diabeto- 

 genic hormone ; for adrenalectomy and the consequent lack of this 

 hormone results in hypoglycaemia, or a low level of blood-sugar. 

 Adrenalectomy is also said to reduce the frog's capacity to absorb 

 glucose and galactose from the gut, and to cause loss of glycogen 

 reserves from the liver (Chester Jones, 1957a). The first effect is 

 due to the unopposed action of insulin, the presence of which has 

 now been recorded in frogs. The last effect is probably indirect; 

 for the hypoglycaemia induced by the insulin would in due course 

 inhibit further insulin secretion and so prevent the building up of 

 glycogen reserves, even if it would not cause their depletion 

 (§5.212). 



In Urodela the diabetogenic hormone is also cortical, but comes 

 from the interrenal tissue. 



Reptilia. There is recent evidence for glucagon being the 

 diabetogenic hormone in some lizards (Miller and Wurster, 

 1959). 



AvES. The total blood-sugars are normally about twice as high 

 in birds as in mammals, and show a cyclical change, increasing by 

 14 per cent near the time of egg-laying. It is possible that, like 

 mammals, different birds have different diabetogenic hormones. 

 In the intact pigeon, Columba, injections of adrenocorticotrophin, 

 ACTH, cause a great increase in blood-sugar, lasting about 10 hr. 

 Pancreatectomy does not influence this reaction, but adrenalectomy 

 eliminates it (Riddle et al, 1947). This is the same as in the rat, 

 where the adrenal cortex is the source of the main diabetogenic 

 hormone. In the chick, on the other hand, blood-sugar can be 

 raised by STH, the so-called growth hormone of the anterior 

 pituitary (Hsieh, Wang and Blumenthal, 1952). This seems to be 



