A NEW MEDIUM‐TERM BIOASSAY SYSTEM FOR DETECTION OF ENVIRONMENTAL CARCINOGENS USING DIETHYLNITROSAMINE‐INITIATED RAT LIVER FOLLOWED BY D‐GALACTOSAMINE TREATMENT AND PARTIAL HEPATECTOMY

The effects of D‐galactosamine on induction of preneoplastic glutathione S‐transferase placental form positive liver foci were investigated in F344 rats pretreated with diethylnitrosamine (DEN) in an attempt to improve the predictive value of the medium‐term bioassay system developed in our laboratory. Two weeks after the initial single ip dose (200 mg/kg) of DEN, administration of test compounds was commenced simultaneously with an ip injection of D‐galactosamine at a dose of 300 mg/kg body wt. All rats were then subjected to two‐thirds partial hepatectomy (PH) at week 5 and sacrificed for assessment of lesion yield at week 8. Measurement and comparison of the numbers and areas of glutathione S‐transferase placental form positive (GST‐P(+)) foci per cm(2) revealed a positive response to more carcinogens, including non‐hepatocarcinogens, than did the same bioassay system without injection of D‐galactosamine. Thus the results suggest that inclusion of this extra proliferative stimulus may improve the medium‐term detection of carcinogens and modifiers.