In vivo-in vitro replicative DNA synthesis (RDS) test using perfused rat livers as an early prediction assay for nongenotoxic hepatocarcinogens: I. Establishment of a standard protocol.

To establish a standard protocol for an in vivo-in vitro hepatocyte replicative DNA synthesis (RDS) test using male F344 rats for screening nongenotoxic (the Ames-negative) hepatocarcinogens, experimental conditions were examined. After treatment with three model hepatocarcinogens, isolated hepatocytes showed highest RDS incidences when plated at a density of 5 x 10(4) cells/ml. Spontaneous RDS incidences in hepatocytes from rats aged 9 weeks or older showed a constant value. The use of hepatocytes from 9-week-old rats at the 5 x 10(4) cells/ml plating density was therefore determined as the standard. Based on the distribution of mean spontaneous RDS incidences over 105 additional experiments (0.4 +/- 0.18%, with SEM), an RDS incidence of over 1% was adopted as the criterion for a positive response in our rat liver RDS test.