Induction of tryptophan oxygenase by dexamethasone in isolated hepatocytes. Dependence on composition of medium and pH.

Hepatocytes were isolated from perfused rat livers. 4 x 10-6 cells/ml were incubated at at 37 degrees C in different media in the absence and presence of a steroid hormone, dexamethasone phosphate (2 x 10-5 M). 1. Hormonal enzyme induction occurred in cells suspended in a simple salt medium, devoid of amino acids and macromolecules. This induction was completely blocked by addition of either actinomycin D (2 mu-g/ml) or cycloheximide (50 mu-g/ml). 2. Incubation of cells in media containing defatted albumin did not enhance hormonal enzyme induction, although disintegration of cells during incubation was reduced. Addition of a crude albumin fraction reduced tryptophan oxygenase induction and dextran completely blocked enzyme induction by dexamethasone. 3. An increase of dexamethasone concentration in the presence of albumin to 9 x 10-5 M was unable to raise enzyme induction further, and a still higher concentration of hormone, 3 x 10-4 M, resulted in reduced enzyme induction. 4. The hormonal induction of tryptophan oxygenase was most pronounced when the pH of the medium was between 7.0 and 7.6, with an optium at 7.3. No induction was found when the pH of the medium was either 6.6 or 7.8. The basal tryptophan oxygenase activity was much less influenced by similar pH variations. It is concluded that hepatocytes in suspension are able to carry out hormone-stimulated enzyme synthesis and that factors influencing this process may be studied under controlled conditions in such systems.