CHAPTER 26 

 ELEMENTS CONSTITUTING MAJOR MINERAL METABOLITES 



Ellsworth C. Dougherty 



26.1. Introduction. For purposes of this volume the major elements 

 constituting mineral metabolites have been selected on the basis of their role 

 in the metabolism of higher animals and accordingly are the following five: 

 sodium, magnesium, chlorine, potassium, and calcium. Hydrogen, carbon, 

 oxygen, and phosphorus are also of major importance in mineral metabolism, 

 but have already been considered in the preceding section. The five listed 

 are the elements that form, along with hydrogen, carbon (as carbonates), 

 oxygen (in all complex ions), and phosphorus (as phosphates), the main 

 essential electrolytes of the protoplasm and extracellular and vascular fluids 

 of higher animals. In addition, magnesium and calcium, along with carbon, 

 oxygen, and phosphorus, are the main mineral constituents of bone — the 

 principal skeletal material of the higher vertebrates. Useful tracer isotopes 

 have been applied in animals for all except magnesium, for which tracer 

 study has been limited to one experiment in plants on photosynthesis. 



The study of normal mineral metabolism with isotopic tracers began in 

 1935 with the work of Chievitz and Hevesy on phosphorus uptake and dis- 

 tribution in the rat [P77]. Since that time a considerable body of literature 

 has grown up, particularly in connection with the dynamics of electrolytes in 

 the mammal and with the metabolism of bone. It has recently been thor- 

 oughly reviewed by Hevesy [Gen76]. 



26.2. Sodium. Sodium, like phosphorus, has but one stable isotope, and 

 consequently its tracers are radioactive. Two useful species exist: Na 24 , the 

 short-lived form (14.8-hr half-life) produced in the cyclotron by the reaction 

 Na 23 (d, p)Na 24 and in the nuclear pile by the reaction Na 23 (n, 7)Na 24 , and 

 Na 22 , the long-lived form (3-year half -life), produced in the cyclotron by the 

 reaction Mg 24 (d, a)Na 22 . Both Na 24 and Na 22 can be used for in vivo studies 

 since penetrating nuclear gamma rays attend the decay of both. Inasmuch 

 as sodium forms the most important extracellular cation in vertebrates, 

 study of its electrolyte dynamics is of great significance. It is also of minor 

 importance in bone. 



Studies with Na 24 have been directed toward the determination of the 

 time and mode of normal uptake [Nal0,15,31,36,37, etc.], distribution 

 [Nal7,33,51, etc.], and excretion [Na31,39,62,67, etc.] of sodium in the mam- 



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