2. Endocrines and Populations 213 



There is much to learn about the differences in hormonal response to 

 different stimuli. There are excellent reasons to believe that the various 

 adrenocortical hormones are not always secreted in any fixed proportion to 

 each other independently of the nature of the stimulus or its degree of 

 severity (cf. above). Therefore it seems advantageous to speak of the 

 responses evoked by the specific stimulus in each case rather than of a 

 generalized nonspecific response to "stress." 



(3) Regulation of secretion of the fascicular hormones. The regulation 

 of the secretion of the hormones of the cortical zona fasciculata has been 

 investigated intensively, and a great deal is known about the mechanisms 

 involved, although many questions still remain unanswered. It is well 

 established that adrenocorticotropin (ACTH), a protein hormone secreted 

 by the anterior pituitary, stimulates corticoid production and release from 

 the adrenal fasciculata and to a lesser extent stimulates the secretion of 

 aldosterone from the zona glomerulosa (Wexler et al., 1955; Allen, 1957; 

 Farrell ct al, 1955; Jones, 1957; Li et al, 1957; Farrell et al, 1958, and 

 other references cited earlier) . ACTH also stimulates cellular hyperplasia 

 and hypertrophy of the cortex, although pituitary growth hormone may 

 play an important role in stunulating cortical hypertrophy (Cater and 

 Stack-Dunne, 1953, 1955; Jones, 1957; Lostroh and Li, 1958), possibly 

 acting synergistically with ACTH (Lostroh and Woodward, 1958). How- 

 ever, growth hormone has no effect on the release of corticosteroids (Rosen- 

 feld and Bascom, 1956; Guillemin et al, 1958) . ACTH also has a number of 

 extra-adrenal actions; for example, it stimulates the preputial glands and 

 other sex accessories, but not to the same extent as does testosterone 

 (Davidson and Moon, 1936; Davidson, 1937; Jacot and Selye, 1951; 

 Lostroh and Li, 1957) . The regulation of the release of ACTH from the 

 pituitary is not clearly understood, although there no longer can be any 

 doubt that for the most part a neurohumor from the hypothalamus has a 

 major role in regulating the production and release of ACTH (IMcCann, 

 1953; McCann and Brobeck, 1954; Harris, 1955a, b; Fortier, 1957; Wood- 

 bury, 1958). The regulation of the release of ACTH has been reviewed by 

 Harris and Fortier (1954), Harris (1955b), and Fortier (1956), but advances 

 in this field are rapid, and much additional information is available which is 

 not included in these reviews. Some doubt has been cast on the role of the 

 hypothalamus in regulatmg ACTH secretion in response to surgical trauma 

 (Story efai., 1959). 



The adenohypophysis has a double arterial supply: a portal system 

 draming from the hypothalamus and a direct systemic arterial supply 

 (Green, 1951). Branches from the superior hypophyseal arteries form a 

 tufted plexus of capillaries in the median eminence of the hypothalamus in 



