Effect of oestrogen and 1,25-dihydroxycholecalciferol on 25-hydroxycholecalciferol metabolism in primary chick kidney-cell cultures

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Abstract
Primary cultures of chick kidney cells convert 25-hydroxycholecalciferol into more-polar metabolites. Cells from vitamin D-deficient chicks have high 25-hydroxycholecalciferol 1 .alpha.-hydroxylase (1 .alpha.-hydroxylase) activity, but no 25-hydroxycholecalciferol 24-hydroxylase (24-hydroxylase) activity. Physiological concentrations of 1,25-dihydroxycholeclaciferol suppress 1 .alpha.-hydroxylase and induce 24-hydroxylase activity. Inhibition of 1 .alpha.-hydroxylase preceded the induction of 24-hydroxylase. Estradiol-17 .beta. had no effect on the activity of either hydroxylase under a variety of experimental conditions. Apparently 1,25-dihydroxycholecalciferol, but not estrogen, acts directly on kidney cells to regulate 25-hydroxycholecalciferol metabolism.