§ 4.231 MESODERMAL ENDOCRINE GLANDS OF VERTEBRATA 145 



secretion. The reaction varies with the exact type, duration and 

 severity of the stress. If, for instance, anaesthetized rats are given 

 some relatively mild noxious stimulus, such as haemorrhage or an 

 injection of histamine, or if normal rats have a bout of severe 



Sudano- 



philic 



substance 



S 



100 



75 



50 



25. 



24 



Fig. 4-9. Diagram to show the type of change that occurs in the 

 adrenal cortex, following brief secretion of ACTH from the adeno- 

 hypophysis, induced by non-fatal haemorrhage for 1 hr. The 

 sectors of gland, above, indicate the change in its size and in the 

 amount of its sudanophilic content. The ascorbic acid (O) and 

 cholesterol (•) in the gland are graphed in percentages over a 

 24 hr period. These and the sudanophilic substance show a sudden 

 drop in response to the ACTH stimulus at hour until the end of 

 stress at hour 1 ; this corresponds with the release of the whole 

 store of cortical hormone. During the rest of the 24 hr the store is 

 gradually built up again. Similar effects can be produced by a 

 sudden bout of exercise, or an injection of histamine or of ACTH 

 itself (from Sayers and Sayers, 1949). 



exercise, ACTH is released and causes a rapid increase in the 

 amount of circulating adrenocortical hormone, ACH, revealed by 

 a reduction in adrenal ascorbic acid (Fig. 4-9). In these cases 

 recovery occurs within 24 hr. In more severe stress, depletion 

 of ACH may be so complete that recovery may not be possible, 

 and death results. 



The release of ACTH is also related to the amount of ACH 

 already in circulation ; when the latter is high it inhibits further 



