144 KINETIC HORMONES — II 



Secretion of hydrocortisone-like hormones from the adrenal cortex 



Cold-blooded Vertebrata. There is apparently not much 

 direct evidence of ACTH stimulating secretion by the adrenal 

 CORTEX in vertebrates other than mammals, although growth of 

 the adrenal tissue, or of the anterior interrenal tissue which is its 

 main homologue in fish, has been established in relation, not only 

 to mammalian ACTH, but also to extracts of a similar fraction 

 from the hypophysis of fish (Pickford and Atz, 1957). There is 

 some evidence (§ 5.411) that in Astyanax the secretion of cortical 

 hormones can continue in the absence of ACTH (Rasquin and 

 Rosenbloom, 1954); but the rate of secretion does not seem to 

 have been measured. ACTH derived from the pituitary of the 

 salmon, Salmo salar, causes reduction of ascorbic acid in the rat, 

 but has not been tested on fish (Rinfret and Hane, 1955). 



Mammalia. The hydrocortisone-like hormones, ACH (some- 

 times referred to as the glucocorticoid hormones, from their 

 diabetogenic action on carbohydrate metabolism), are the most 

 abundant secretions from the adrenal cortex. In normal circum- 

 stances the release of ACH from the cortex into the blood is 

 continuous, but it has a slight diurnal rhythm of change in rate. In 

 the human, for instance, this is lowest at night and highest in early 

 morning. In response to any stress, or tissue damage, there is an 

 immediate increase in the rate of secretion. Since small injections 

 of ADRENOCORTicoTROPHiN, ACTH, from the adenohypophysis, 

 can influence the rate of secretion, it is thought that there is also a 

 basic rate of secretion of this endocrinokinetic hormone, but that 

 it can very quickly be increased in response to damage or stress, 

 and that this induces the cortical reaction (Munson and Briggs, 

 1955). 



Secretion of ACH from the cortex is accompanied by a marked 

 loss of ascorbic acid (as well as of cholesterol and a sudanophilic 

 substance, Fig. 4-9), which is not replaced until more hormone is 

 synthesized. The amount of the acid present at any time can be 

 assayed in the frozen glands of rapidly killed specimens. Its 

 disappearance under stress provides a measure of the hormone 

 secretion, which follows it closely (Slusher and Roberts, 1957). It 

 can, therefore, be used as an indication of the rate of ACTH 



