Studies upon the mode of action of vitamin D

Abstract

The absorption of Ca from a diet nearly free from P and the absorption of P from a diet nearly free from Ca was studied in normal and vitamin D deficient rats. In P starvation the absorption of 15, 45 and 90 mg. Ca in vitamin D deficient rats was 50, 36 and 28% as compared with 100, 57 and 47% in rats receiving 50 I.U. vitamin D daily. In Ca starvation the absorption of the combined P of acid-extracted meat powder was equally impaired (about 15%) in both normal and vitamin D deficient rats, whilst the absorption of P from inorganic phosphate, glycerophosphate and caseinogen was complete both in normal and vitamin D deficient rats. This was the case also in rats completely deprived of their previous stores of vitamin D. The action of vitamin D in the gut of the rat is thus confined to the absorption of Ca. The well known reduced absorption of P in vitamin D deficiency is due to a precipitation by the increased amount of Ca in the bowel.