212 METABOLIC HORMONES 



Concentration of the blood by reabsorption of salts through the kidney 



i\MPHiBiA. In most circumstances, and especially in fresh 

 water, the function of the kidney is to reabsorb sodium (Na+), 

 and possibly chloride ions (Cl~) actively, and to excrete a certain 

 amount of potassium (K+). Figure 5-13 shows that, over a wide 

 range of sodium ion concentrations in the glomerular filtrate, at 

 least 95 per cent is reabsorbed in the tubules. Active transport of 

 sodium here is comparable with that through the skin. In adrenal- 

 ectomized fiogs sodium is excreted more rapidly (presumably 

 because less is reabsorbed) than in normal controls (Fig." 5-14). 

 There is a slight concurrent increase in muscle potassium (Fowler, 

 1956). Moreover, saline treatment can maintain life in the adrenal- 

 ectomized frog, as it can in mammals. This seems to support the 

 case for supposing that an adrenocortical hormone (ACH) is 

 concerned in stimulating salt reabsorption in the kidney tubules 

 of frogs, as in mammals. 



It may well be that ACH secretion in Amphibia is under the 

 endocrinokinetic control of ACTH (§ 4.231), since hypophysect- 

 omy is followed by symptoms closely similar to those resulting 

 from adrenalectomy ; other evidence is, however, defective (Chester 

 Jones, \9Sla). 



Teleostei. The established function of the adenohypophysis in 

 protecting some teleosts, such as Fundulus (Burden, 1956), against 

 the osmotic stress of transfer from sea water to fresh is probably 

 endocrinokinetic ; it seems to favour the retention of sodium and, 

 more particularly, of chloride ions ; but it is not yet clear if this is 

 due to the release of adrenocorticotrophin, ACTH (§ 4.231), or of 

 thyrotrophin, TSH (§ 4.221). Neither of these are replaceable by 

 the corresponding mammalian hormone, and it has even been 

 postulated that some other "unknown factor" may be present in 

 the hypophysis of euryhaline teleosts. ACTH might be expected 

 to stimulate secretion by the anterior interrenal bodies, which 

 are the homologues in fish of the tetrapod adrenal cortex ; but they 

 do not seem to have been investigated in this connection (Rasquin 

 and Rosenbloom, 1954). The effect of injecting extracts of adrenal 

 cortex into trout has only been examined in the converse situation 

 of their being exposed to excess salinity in sea water (see below). 



