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1. In subjects with normal renal function there was a strong positive correlation between serum concentrations of 25-hydroxycholecalciferol and 24,25-dihydroxycholecalciferol, as measured by competitive protein-binding assay. 2. The 24,25-dihydroxycholecalciferol concentration was about 7% of the prevailing 25-hydroxycholecalciferol concentration. 3. In contrast, sera from anephric patients contained very low or undetectable amounts of 24,25-dihydroxycholecalciferol even after the serum 25-hydroxycholecalciferol concentrations in these patients had been elevated by oral administration of 25-hydroxycholecalciferol. 4. In a further group of anephric patients, all having normal serum 25-hydroxycholecalciferol concentrations, no radioactively labelled 24,25-dihydroxycholecalciferol was formed from an injected pulse dose of [3H,14C]cholecalciferol. 5. These results indicate that in man the kidney is the major site of 24-hydroxylation of 25-hydroxycholecalciferol.

Original publication




Journal article


Clin sci mol med suppl

Publication Date





541 - 547


Adult, Aged, Cholecalciferol, Dihydroxycholecalciferols, Female, Humans, Hydroxycholecalciferols, Hydroxylation, Kidney, Male, Middle Aged, Nephrectomy