Dose‐dependent biphasic effects of phenobarbital on growth and differentiation of primary culture rat hepatocytes

The actions of phenobarbital, a liver tumour promoter, on growth and differentiation of primary culture normal rat hepatocytes change biphasically as a function of its concentration. At low concentrations of 0.5-2 mmol/L, phenobarbital enhances DNA synthesis of normal adult rat hepatocytes in the presence of epidermal growth factor (EGF) and/or dexamethasone. This is also true for normal suckling (1-2-week-old) rat hepatocytes, without added growth factor(s), in serum-free primary culture. Contrarily, phenobarbital at high concentrations (3-4 mmol/L) suppresses DNA synthesis of suckling rat hepatocytes. Furthermore, phenobarbital inhibits DNA synthesis of transforming growth factor-a-stimulated primary hepatocytes from normal adult rats in a dose-dependent manner within a concentration range of 3-6 mmol/L. When normal adult rat hepatocytes are led to undergo multiple proliferative cycles upon stimulation with hepatocyte growth factor (HGF) and EGF in the chemically defined hepatocyte growth medium (HGM), 3 mmol/L phenobarbital also remarkably suppresses DNA synthesis. Phenobarbital at 3 mmol/L effectively keeps these hepatocytes morphologically differentiated and accelerates restoration of the expression of markers characteristic of differentiated cells after the initial cellular growth phase. In addition, phenobarbital efficiently supports prolonged survival of the hepatocytes.