Urinary metabolites of vitamin D 3

Abstract

Relatively little is known regarding the identity of the terminal metabolites of vitamin D 3, yet measurement of these compounds would give additional useful data on the normal and pathophysioogy of vitamin D in man. We have therefore investigated the metabolism of [26.27- 3H]-25-hydroxy vitamin D 3 administered orally to a human subject. A relatively minor proportion of radioactivity was excreted in urine during the first 7 days of collection and faecal excretion was not determined. The state of conjugation of the urinary metabolites was determined by fractionation of Amberlite XAD-2 organic extracts by Sephadex DEAR LH-20 chromatography before and after hydrolysis. Of the [ 3H]-radioactivity recovered, 15% was excreted as neutral compounds, 60% as glucuronides of neutral steroids. 8%, as acids released by glucuronidase hydrolysis and 5% as monosulphates. In an additional experiment, an attempt has been made to identify (by GC/MS) metabolites in urine of a patient with hypophosphalemic vitamin D resistant rickets (VDRR) following administration of an oral dose of 5 mg vitamin D 3. The primary metabolites of vitamin D 3 (e.g. 25-hydroxy vitamin D 3; 24,25-dihydroxy vitamin D 3) were not detected, but five components gave mass spectra indicative of vitamin D 3 structure. All five components had 25-hydroxyl groups; one almost certainly had, in addition, a 24-hydroxyl and one a 26-hydroxyl. The possibility that they were hydroxylated sterols can be tentatively excluded by the fact that these compounds were not found in the urine of the same patient during a period when he was off vitamin D therapy.