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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

Environmental Health Science Laboratory, Sumitomo Chemical Co., Ltd., 1-98-3 Kasugade-naka, Konohana-ku, Osaka, 554, Japan

Chise Tateno

Environmental Health Science Laboratory, Sumitomo Chemical Co., Ltd., 1-98-3 Kasugade-naka, Konohana-ku, Osaka, 554, Japan

Mina Tuda

Environmental Health Science Laboratory, Sumitomo Chemical Co., Ltd., 1-98-3 Kasugade-naka, Konohana-ku, Osaka, 554, Japan

Akira Yoshitake

Environmental Health Science Laboratory, Sumitomo Chemical Co., Ltd., 1-98-3 Kasugade-naka, Konohana-ku, Osaka, 554, Japan

The distributions of a gap junctional protein, connexin 32 (cx 32), and proliferating cell nuclear antigen (PCNA) were examined immunohistochemically 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. The treatment with clofibrate caused the appearance of GST-P-negative foci, 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 hepatocytes in GST-P-negative foci was significantly higher than in the surrounding parenchyma, indicating increased cell proliferation. The numbers of cx 32-positive spots per hepatocyte in GST-P-negative foci were clearly decreased, reaching 65.4% at week 20 and 51.8% at week 30 of values for surrounding normal hepatocytes. In GST-P-positive foci induced by DEN, only a slight decrease (80%) was observed at week 8. These findings show that a positive association between the sustained inhibition of gap junctional intercellular communication and increased cell proliferation of GST-P-negative foci in Fischer-344 male rats induced with DEN and promoted with clofibrate.

Key Words: Gap junction • peroxisome proliferator • cell proliferation • hepatocarcinogenesis

Toxicologic Pathology, Vol. 24, No. 6, 690-695 (1996)
DOI: 10.1177/019262339602400603


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