218 METABOLIC HORMONES 



Aldosterone is secreted in response to adrenocorticotrophin, 

 ACTH, in rats, but not in the human (§4.231). 



5.312 Decrease o/Na+ in the blood 



There is no evidence for any hormones stimulating Na+ and 

 Cl~ excretion in invertebrates, and so far it is rather tentative in 

 vertebrates, especially in the cold-blooded classes. 



Amphibia. It has been shown that injection of a neurohypophy- 

 sial extract containing oxytocin increases Cl~ excretion in the 

 axolotl (Sawyer, 1956). 



Teleostei. Most marine teleosts maintain their body fluids at a 

 lower level of salt concentration than that of the sea, by means of 

 specialized salt excreting cells on the gills. If any of the endocrine 

 organs are concerned in stimulating this process, their action has 

 not yet been proved. Extracts of mammalian adrenal cortex, 

 ACH, have been injected into trout in sea water, and have been 

 found not to increase their survival time in the excessively saline 

 medium. Despite the fact that in other vertebrates ACH causes an 

 increase in salt reabsorption rather than its excretion, the author 

 suggests trying even larger doses (D. C. W. Smith, 1956). A single 

 test of mammalian neurohypophysial extract likewise failed to 

 increase the survival time of these trout, although it increases salt 

 excretion in mammals. It is known that other teleostean hormones 

 are very specific; also that the neurosecretory store in the neuro- 

 hypophysis of Callionymiis is depleted when this teleost is exposed 

 to a hypertonic medium (Arvy, 1957). It might, therefore, be 

 expected that extracts of fish neurohypophysis might be more 

 successful than mammalian hormones in increasing salt excretion. 

 On the other hand, salt excretion by the gills may be under quite 

 other control than that by the kidneys. 



Aves. The nasal glands of the cormorant, Phalacrocorax, and 

 probably of other oceanic birds* secrete salts, enabling them to 

 eliminate excess Na+ and Cl~ taken up from any hypertonic media 

 in which the birds may feed (Schmidt-Nielsen et al., 1958). It is 

 not yet known if this active transport is under hormonal control, 

 as might be expected. 



* The need for some such mechanism for flamingoes feeding in highly 

 alkaline water had already been indicated (Jenkin, 1957). 



