CHAPTER 5 

 METABOLIC HORMONES 



The term metabolic hormone is in general use, unlike the term 

 kinetic introduced above; but some authors extend it to include 

 morphogenetic hormones (Knowles and Carlisle, 1956). It is here 

 applied to those hormones activating, inhibiting, or controlling the 

 rate of certain biochemical processes of metabolic importance, 

 occurring within the cells of the animal body, even w^hen these 

 processes can only be measured by their end-products, or by the 

 accompanying changes in oxygen consumption. It is not used for 

 those morphogenetic processes which, although they depend upon 

 and are often limited by cell metabolism, yet manifest themselves 

 in growth and differentiation. 



Metabolic hormones in this limited sense differ sharply from 

 kinetic hormones, because they do not act upon specific effectors 

 or replace a type of control that is otherwise exerted by nerves. 

 They control the rates of some cell activities which are often under 

 no other apparent control, but appear to be determined genetically 

 and to persist unaltered throughout the animal's life, at least until 

 senescence intervenes. For instance, the absorptive activity of the 

 gut cells of most animals seems to be as uncoordinated as the 

 flagellar beat of sponge collar cells! 



The hormones which introduce variability and control into some 

 of these biochemical systems are further differentiated from kinetic 

 hormones, at least among vertebrate examples, in that their 

 secretion is not directly induced by nerves. In many cases the 

 stimulus to secretion, apart from general nervous ''stress", comes 

 from an endocrinokinetic hormone (§ 4.2) intervening between the 

 metabohc hormone and any possible nerve control. It follows that 

 the action of these metabolic hormones is usually long-term in 

 character, the most rapid probably being those concerned with 



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