The effect of diphenylhydantoin and cortisol on the cell cycle.

Normal human lymphocytes cultured in the presence of phytohemagglutinin were blocked in G0G1 when diphenylhydantoin (DPH) or cortisol 3.6 X 10(-4) M was added at the beginning of culture. The suppression of culture growth was analyzed by flow cytometry and confirmed by [3H]thymidine incorporation and mitotic rate analysis. The correlation of these measurements with flow cytometry was good for DNA synthesis and excellent for mitosis. There was an additive effect on the G0G1 retention of cells when both drugs were present in the culture. These data may partially explain the suppression of cell-mediated immunity which occurs in DPH-treated patients.