§ 4.231 MESODERMAL ENDOCRINE GLANDS OF VERTEBRATA 143 



glycaemia, or diabetes mellitus, results and may even become 

 permanent (of. § 5.211). 



4.23 MESODERMAL ENDOCRINE GLANDS OF VERTEBRATA 



4.231 Adrenal cortex stimulated by ACTH 



In most vertebrates there is some evidence that the secretion of 

 CORTICAL HORMONES is Stimulated by adrenocorticotrophin, 

 ACTH, from the adenohypophysis. Since the actions of the corti- 

 cal hormones are mainly metabolic, there is no doubt here, as there 

 can be vv^ith the thyroid, that the endocrinokinetic hormone is in 

 fact stimulating the secretion of metabolic hormones, and not only 

 of morphogenetic hormones. 



The stimulation of the adrenal cortex by ACTH presents an 

 interesting problem. Although the actions of cortical hormones 

 connected with electrolyte and v^^ater balance all lead to concentra- 

 tion of salts in the blood, it is clear that two distinct types of 

 hormone are involved : the aldosterone-like hormones which 

 increase salt reabsorption (§ 5.311), and the hydrocortisone-like 

 hormones which mainly cause water diuresis (§ 5.321). Neverthe- 

 less, the tentative suggestion that there may be more than one 

 hormone in ACTH only indicates a separate control for increasing 

 the weight of the adrenal cortex from that inducing its secretion. 

 There appears to be no indication of separate hormones for 

 stimulating the secretion of the different hormones from the 

 cortex (Munson and Briggs, 1955). Most authors, however, still 

 support the view that adrenocorticotrophin, ACTH, is a single 

 substance (Astwood, 1955). 



Secretion of aldosterone-like hormones from the adrenal cortex 



Aldosterone is chemically quite distinct from the other cortical 

 hormones in having an 18-aldehyde group in the molecule. It is 

 biologically very active in stimulating salt retention or reabsorp- 

 tion by the kidneys, although it is secreted in relatively minute 

 quantities. Little is known of the means by which its secretion is 

 controlled ; but there is some evidence that it is secreted in response 

 to stimulation by ACTH in the rat, though not in man (Simpson 

 and Tait, 1955). Elsewhere it appears to be directly stimulated by 

 a lowering of salt concentration in the blood. 



