EFFECT OX VARIOUS PHYSIOLOGIC PROCESSES 663 



c. On the Mechanism of Action of the Vitamins D on Calcium and 

 Phosphate Balances. The data which have been reviewed in the previous 

 sections can be mterpreted as evidence not only that vitamin D increases 

 the absorption of calcium and phosphate but also that it may decrease 

 the reexcretion of these minerals into the intestine. Much work has 

 been carried out to determine whether the action of vitamin D can best 

 be explained by the absorption or by the reexcretion theory. 



The reexcretion theory was a development of the current teaching during 

 the latter part of the nineteenth century that the calcium and phosphate in 

 the body was regulated by reexcretion into the intestine, presumably 

 chiefly into the large intestine. Thus, the intestine would act as a sort of 

 auxiliary kidney in the regulation of body minerals. Bergeim-^' believed 

 that his ferric oxide method supported the reexcretion theory. Gyorgy^ 

 accepted the reexcretion theory, as did Harris. ^^^ 



However, a number of observations have been recorded which appear 

 to gi\'e strong support to the absorption theory in explaining the action of 

 \'itamin D. These render the reexcretion theory quite untenable. In 

 1923, Orr and co-workers-^^ interpreted their data as e\'idence that vita- 

 min D increased the absorption of calcium and phosphate. Howe^•er, 

 there was no proof that the reduction of the amount of fecal calcium and 

 phosphate resulted from increased absorption of the minerals following 

 vitamin D therapy. Nicolaj'sen-^^ was the first to attempt to obtain 

 definite evidence as to which of these theories was the more probable. 

 His data seem to indicate fairly conclusively that vitamin D acts by in- 

 creasing the absorption of calcium. Thus, when the base level of fecal 

 calcium in dogs on a calcium-free diet was determined, it was found that the 

 fecal calcium was not increased by overloading the bJood stream \\ath in- 

 jected calcium, although an increased excretion of calcium via the urine 

 occurred. ^Moreover, no augmentation of the amount of calcium in the 

 feces was noted when the bone salts were mobilized by means of the para- 

 thjToid hormone. Finally, it was found that no change in fecal calcium 

 was produced when the entire colon w^as separated as a Thiery-^'ella fistula 

 and the feces were formed only in the distal part of the ileum, which was 

 anastomosed to the rectum. The basal calcium excreted in the feces un- 

 doubtedly arises from the digestive juices, which contribute approximately 

 1 g. of calcium to the intestinal contents per day. 



26' O. Borgeim, J. Biol. Chem., 70, 47-50, 51-58 (1926). 

 2«2 L. J. Harris, Ann. Rev. Biochem., 3, 247-2!)4 (1934). 



"^^ W. J. Orr, L. E. Holt, Jr., L. Wilkins, and F. H. Boone, .4/?!. J. Diseases Children, 

 26,362-372(1923). 



2" R. Xicolaysen, Skand. Arch. Physiol., 69, suppl., 1-66 (1934). 



