IMMUNOHISTOCHEMICAL DEMONSTRATION OF THE GAP JUNCTIONAL PROTEIN CONNEXIN-32 AND PROLIFERATING CELL NUCLEAR ANTIGEN IN GLUTATHIONE-S-TRANSFERASE PLACENTAL FORM-NEGATIVE LESIONS OF RAT-LIVER INDUCED BY DIETHYLNITROSAMINE AND CLOFIBRATE

The distributions of a gap junctional protein, connexin 32 (cx 32), an d proliferating cell nuclear antigen (PCNA) were examined immunohistoc hemically in glutathione S-transferase placental form (GST-P)-negative foci, induced in rat liver by initiation with diethylnitrosamine (DEN , 200 mg/kg) followed by promotion with clofibrate (1% in diet) in an in vivo medium-term assay system for hepatocarcinogenesis. The results were compared to those in GST-P-positive foci induced by DEN alone, T he treatment with clofibrate caused the appearance of GST-P-negative f oci, increased in size as compared to GST-P-positive foci in the same liver or induced by the DEN alone. The proportion of PCNA-positive hep atocytes in GST-P-negative foci was significantly higher than in the s urrounding parenchyma, indicating increased cell proliferation. The nu mbers of ex 32-positive spots per hepatocyte in GST-P-negative foci we re clearly decreased, reaching 65.4% at week 20 and 51.8% at week 30 o f values for surrounding normal hepatocytes. In GST-P-positive foci in duced by DEN, only a slight decrease (80%) was observed at week 8. The se findings show that a positive association between the sustained inh ibition of gap junctional intercellular communication and increased ce ll proliferation of GST-P-negative foci in Fischer-344 male rats induc ed with DEN and promoted with clofibrate.