664 X. VITAMINS D 



In later tests by Nicolayserij^^^'^^s it was observed that the loss of body 

 calcium and phosphate in the feces on a calcium-free and phosphorus-free 

 diet, in vitamin D deficiency, was greater than in parallel experiments in 

 which liberal amounts of vitamin D were present. This is interpreted as 

 evidence that vitamin D increases the absorption of endogenous calcium. 

 Moreover, it was found that, on phosphorus-free diets, the fecal excretion 

 of calcium was greater when the intake of calcium was progressively in- 

 creased. In all cases rats recei"\ang vitamin D absorbed more calcium 

 than did those on the \atamin D-free diets. Finally, it was observed that 

 the absorption of phosphate was complete on calcium-free diets in vitamin 

 D-deficient rats, irrespective of the source of the phosphate. 



Further e\adence that vitamin D acts by improving the absorption of 

 calcium from the gut was obtained from studies of isolated loops of in- 

 testine by Nicolaysen,-^'' who noted that calcium disappeared more slowly 

 from these isolated loops of intestine of vitamin D-deficient rats than from 

 corresponding loops when \'itamin D was present. On the other hand, 

 glycerophosphate was absorbed as rapidly in isolated loops from vitamin 

 D-deficient rats as in those from normal animals. ^^^ Patwardhan and 

 Chitre^^^ were unable to demonstrate any difference in the absorption of 

 calcium in the entire isolated small intestine of rats, over a three-hour 

 period, irrespective of whether the animals had pre\'iously been on a vita- 

 min D-free regimen or had received vitamin D in the ration. Nicolaysen^^° 

 obtained opposite results when the isolated loop experiments were extended 

 to twenty-four hours. 



Experiments using the Ca^^ isotope have given additional support to 

 the absorption theory as the mechanism for the action of \'itamin D. 

 Greenberg-^* observed no increased excretion as related to vitamin D con- 

 tent of rats, but he did note a marked acceleration in the absorption rate of 

 this isotope when \dtamin D was administered. Harrison and Harrison^^^ 

 noted only a sHght effect exerted by vitamin D on the absorption of Ca,^^ 

 and the effect occurred chiefly in the large intestine and not in the small 

 intestine. On the other hand, Lindquist"^ demonstrated a marked aug- 

 mentation of absorption which was evident within twelve hours after the 



^^ R. Nicolaysen, Biochem. J., 31, 107-121 (1937). 



2«6 R. Nicolaysen, Biochem. J., 31, 122-129 (1937). 



2«' R. Nicolaysen, Biochem. J., 31, 323-328 (1937). 



268 R. Nicolaysen, Biochem. J., 31, 1086-1088 (1937). 



2«3 V. Patwardhan and Chitre, Indian J. Med. Research., SO, 81-89 (1942). 



"OR. Nicolaysen, Acta Physiol. Scand., 22, 260-266 (1951). 



"1 D. M. Greenberg, J. Biol. Chem,., 157, 99-104 (1945). 



"2 H. E. Harrison and H. C. Harrison, J. Biol. Chem., 188, 83-90 (1951). 



"3 B. Lindquist, Kgl. Fysiograf. Sdllskap. Lund Forh., 20, 243-249 (1950). 



