In vitro metabolism of vitamin D3 by isolated liver cells.

Liver cells were prepared from rats fed a rachitogenic diet to investigate the hepatic metabolism of [alpha-1,2-3H2] vitamin D3. Rat hepatocytes suspended in Hanks medium rapidly took up labeled vitamin D3 from the incubation medium and converted this sterol to various metabolites, including 25-hydroxy vitamin D3 (25-OH-D3). There was steady increment in the cellular production of 25-OH-D3 and of the more polar metabolites of vitamin D3 over 3 hr of incubation as determined by thin layer chromatography. Neither the addition of cyclic nucleotides or dexamethasone to, nor the removal of calcium or phosphate from the medium resulted in changes in the rate of conversion of vitamin D3 to its products. Rats pretreated with sodium diphenylhydantoin converted labeled vitamin D3 to its metabolites at the same rate as control rats. These data indicate that isolated liver cells retain the capacity for vitamin D3 hydroxylation, but suggest that the rate of this process does not undergo rapid changes in response to metabolic stimulation.