Zinc accumulation and metabolism in primary cultures of adult rat liver cells. Regulation by glucocorticoids.

Adult rat liver parenchymal cells were isolated by the collagenase perfusion technique and cultured as a monolayer for up to 20 h. The quantity of zinc accumulated from the extracellular environment was significantly increased by adding physiological concentrations of certain glucocorticosteroids to the medium. The degree of stimulation was directly related to glucocorticoid potency. Sex steroids, certain peptide hormones and prostaglandins E2 and F2alpha did not influence zinc accumulation. Control cells exhibited a decline of zinc accumulation after 4 h in culture although uptake processes were still operative. When dexamethasone, the most potent glucocorticoid used, was present in the medium the cells accumulated zinc at a linear rate greater than that seen in control cells, for at least 20 h. The dexamethasone-induced stimulation of zinc accumulation was relatively specific since 45Ca, 14C-labelled amino acids and [35S]cystine accumulation was not influenced by the hormone. A lag of 4 h was observed before an effect of dexamethasone on zinc accumulation could be detected. Moreover, the hormone-stimulated phase of accumulation was blocked when the cells were simultaneously incubated with either actinomycin D or cycloheximide. The additional complement of zinc accumulated by the dexamethasone-treated cells was localized in the cytosol fraction. Gel filtration and ion-exchange chromatography confirmed that this additional cytosol zinc was bound to metallothionein. [35S]Cystine was incorporated into metallothionein in hormone-treated cells indicating that the protein was synthesized de novo during periods of enhanced zinc accumulation.