252 METABOLIC HORMONES 



the secretion of which is stimulated by a high phosphate level in 

 the blood, actively decreases phosphate reabsorption in the kidney 

 tubules (Bartter, 1954). 



The initial effect of parathormone injection may, however, be an 

 increase in blood phosphates, because, in addition to its effect on 

 excretion, the hormone also facilitates the transfer of phosphates 

 with calcium from the skeleton to the blood stream. 



A balance is normally maintained in the blood by a feed-back 

 system, as in the case of insulin (§ 5.212), whereby any decrease in 

 concentration of P in the blood induces a decrease in the secretion 

 of parathormone, while a rise in P causes a rise in parathormone. 

 If the high level in the blood is maintained, the parathyroid gland 

 may even become hypertrophied (Engfeldt and Hjerquist, 1952). 

 There is no sound evidence for any endocrinokinetic control of the 

 secretion of the parathyroid (§ 5.521). 



5.5 General considerations 



5.51 characteristics of the metabolic hormones 



In one respect the metabolic hormones reviewed in this chapter 

 are like some kinetic hormones; wherever they have been most 

 thoroughly investigated, a pair of hormones has been found ; they 

 may be synergistic, like glucagon and insulin that between them 

 control the balance of sugar in the blood (§ 5.21), or antagonistic, 

 like the cortical and neurohypophysial hormones which between 

 them determine its salt concentration (§ 5.3). In a somewhat 

 similar way, the moult-promoting and moult-inhibiting hormones 

 of Crustacea may between them control the protein metabolism; 

 but this is not yet fully elucidated, nor is the function of the eye- 

 stalk tip established (§ 5.22). It seems possible that in some cases 

 where, as yet, only one hormone has been determined, an antago- 

 nist still awaits discovery. Such might be an antidiabetogenic or an 

 antidiuretic hormone for Crustacea, or a hormone facilitating 

 protein synthesis in vertebrates. Equally promising might be the 

 search in invertebrates for hormones akin to those now known to 

 control the active transport of Na+ and Cl~ ions in vertebrates 

 (§ 5.31). It is clear from the tables that much more information is 



