Isolation of the liver from the circulation of rats eliminates almost completely their ability to convert [1,2]-3H vitamin D3 into its biologically active metabolite, 25-hydroxycholecalciferol, as well as certain other metabolites. It is concluded that the liver is the major if not the only physiologic site of hydroxylation of vitamin D3 (cholecalciferol) into 25-hydroxycholecalciferol.

The osteodystrophy and the higher requirements for vitamin D observed in hepatic insufficiencies may be due to an inability of the liver to transform vitamin D into its metabolically active form.

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“Activation” of vitamin D by the liver

The metabolism of vitamin D(3) has been studied after intravenous injection of 10 IU of [1,2-(3)H]-vitamin D(3) to vitamin D-deficient rats. The disappearance of the radioactivity from the plasma follows a very peculiar pattern characterized by an early rapid disappearance followed by a rebound of radioactivity before assuming still a third rather slow disappearance rate. The "rebound" phenomenon is concomitant with a rapid release of the radioactivity from the liver and is accounted for by the appearance of 25-hydroxycholecalciferol and other metabolites in the blood. It is postulated that the liver is the major site of transformation of vitamin D(3) into 25-hydroxycholecalciferol.

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The role of the liver in the metabolism of vitamin D

Studies on amphibian yolk. 8. The estrogen-induced hepatic synthesis of a serum lipophosphoprotein and its selective uptake by the ovary and trasformation into yolk platelet proteins in Xenopus laevis.

Studies on the Biosynthesis in Vitro of Parathyroid Hormone II. THE EFFECT OF CALCIUM AND MAGNESIUM ON SYNTHESIS OF PARATHYROID HORMONE ISOLATED FROM BOVINE PARATHYROID TISSUE AND INCUBATION MEDIUM

D.L. Hansen

Papers

Improved solubilization procedures for liquid scintillation counting of biological materials