230 METABOLIC HORMONES 



invertebrates, though it might perhaps be expected in land 

 Crustacea. That claimed for the cockroach, Blabera^ is an extract 

 which has only been shown to act on rats (Stutinsky, 1953); that 

 claimed for extracts of the post salivary glands of some Cephalopoda 

 has likewise only been tested on unrelated animals (Ersparner and 

 Boretti, 1950). 



Vertebrata. Increase in the water content of the tissues of 

 vertebrates can be obtained either from the food in the gut, where 

 no hormone action has been found, or from the environment, as 

 when Amphibia move from dry to damp conditions, or back to 

 water. An antidiuretic hormone from the neurohypophysis not 

 only increases skin permeability, to facilitate this water uptake, 

 but also favours water conservation by increasing its reabsorption 

 from the urine in the kidneys and bladder. Its action at all three 

 sites is to increase cell permeability and facilitate water endosmosis. 



Such antidiuretic hormones occur in most vertebrates and are 

 closely akin to the so-called "vasopressin" of mammals. Since the 

 main function, even of the latter, is not to control the tonus of 

 blood vessels as its name implies, but to increase reabsorption of 

 water from the urine in the kidneys and thereby reduce the urine 

 flow, "antidiuretin"* would seem to be a more descriptive name 

 for this type of hormone, so often referred to as ADH. 



ADH is secreted from the hypothalamus and stored in the 

 neurohypophysis (§ 2.1 1 1), whence it is released into the circulation 

 (Table 25, p. 208). 



Increase in permeability of the skin 



Amphibia. Since the skin of amphibians is moist and its per- 

 meability to water can be varied, it plays as important a part in the 

 control of the water balance in these animals as do the kidneys and 

 the bladder. There is no longer thought to be a ''water balance 

 principle", distinct from the antidiuretic hormone and acting 

 only on the skin of amphibians ; but the amphibian antidiuretic 

 HORMONE is chemically more akin to oxytocin than to mammalian 

 ADH ( = vasopressin). As a rule, frogs do not drink an appreciable 

 amount of water, unless they are immersed in a relatively saline 



* It should not be confused with "Antidiuretin", a commercial 

 product with a similar action. 



