1,25 dihydroxyvitamin d-induced inhibition of3H-25 hydroxyvitamin D production by the rachitic rat liverin vitro
- Cite this article as:
- Baran, D.T. & Milne, M.L. Calcif Tissue Int (1983) 35: 461. doi:10.1007/BF02405077
The effect of the vitamin D metabolites 1,25 dihydroxyvitamin D (100 pg/ml) and 25-hydroxyvitamin D (30 ng/ml) on hepatic production of3H-25 hydroxyvitamin D was investigated using rachitic liver perfusions and homogenates. 1,25 dihydroxyvitamin D inhibited hepatic3H-25 hydroxyvitamin D production in the liver perfusion (3.6 ± 0.4 vs 2.0 ± 0.5 pmol/liver,P<0.05) and in liver homogenates (11.9 ± 0.6 vs 10.1 ± 0.4 pmol/g liver protein/3 h,P<0.02). Inhibition was time and dose dependent. 25-hydroxyvitamin D inhibited production in liver homogenates (11.9 ± 0.6 vs 9.2 ± 0.1 pmol/g liver protein/3 h,P<0.05) but not in the intact liver (3.6 ± 0.4 vs 3.4 ± 0.5 pmol/liver). The data indicate that 1,25 dihydroxyvitamin D is able to feedback regulate the production of its precursor, 25-hydroxyvitamin D. Although 25-hydroxyvitamin D also inhibits its own production in liver homogenates, it failed to alter total production in the intact liver, suggesting that this metabolite may require immediate access to the vitamin D 25-hydroxylase, located on the microsomes and mitochondria, to induce inhibition.