§ 5.223 PROTEIN METABOLISM 2U5 



showing inhibition of protein synthesis (L'lIcHas, 1953). This 

 hormone, Hke that of the brain and corpora cardiaca, would there- 

 fore presumably favour protein synthesis. 



It seems that secretion of these hormones in arthropods is 

 stimulated mainly by the nervous system, with little trace of 

 endocrinokinetic control (§ 4.21), unless the neurosecretion 

 from the brain stimulates the secretion as well as the growth 

 of the corpora allata ; but on this the evidence is inconclusive 

 (Thomsen, 1952). The neurosecretion does not pass into the 

 blood. 



5.223 Decrease in protein synthesis or increase in protein 

 cataholisjn 



Crustacea. Evidence that in Carcinus the tips of the eyestalks 

 stimulate catabolism, which is decreased by their removal, suggests 

 the possible seat of a hormone that is antagonistic to those of the 

 rest of the eyestalk (§ 5.221) ; but it is as yet unidentified (Needham, 

 1955). 



Vertebrata. The hormone chiefly connected with increasing 

 protein catabolism and possibly restraining synthesis in the 

 vertebrates is one of those from the adrenal cortex (Chester 

 Jones, 1957fl); but results as yet seem to be rather contradictory, 

 and it is not clear whether this is really due to specific differences, 

 or to the restriction of different reactions to different organs in the 

 body. 



Mammalia. The state of nutrition of the animals is important : 

 in starvation, the administration of adrenocortical hormones of 

 the hydrocortisone type causes a much greater increase in 

 protein catabolism than it does in well-fed animals. Both stress 

 and ACTH (§ 4.231) injection into nephrectomized rats cause an 

 increase in urea formation, which is restrained by glucose injec- 

 tions. In part, this may be due to the concurrent action of the 

 hormones concerned with carbohydrate metabolism (Noble, 

 1955). 



It is clear that the endocrinokinetic control exercised by ACTH, 

 from the adenohypophysis, plays an important part in these 

 animals, in contrast to the situation in the Arthropoda. 



