Morphological Changes in Silver-stained Nucleolar Organizer Regions (AgNORs) Related to Proliferative Activity in Glutathione S-transferase Placental Form (GST-P) Positive Foci of Rat Liver

Abstract

Silver (Ag)-staining nucleolar organizer region (NOR) proteins are closely related to the cell cycle and reflect proliferative activity. In this study, we examined morphological changes of AgNORs in both glutathione S-transferase placental form (GST-P) positive foci and background parenchyma of rat liver by double staining. To induce GST-P positive foci, eight male F344 rats were given a single injection of diethylnitrosamine (20 mg/kg b.w., i.p.), and fed a diet containing 0.01% 2-acetylaminofluorene in diet from weeks 2 to 4 and subjected to 2/3 partial hepatectomy at week 3. At the end of week 5, liver sections were processed for double staining of GST-P and AgNOR. No statistically significant difference was observed for the number of AgNORs between GST-P positive foci and background parenchyma. However, areas of AgNORs relative to nuclear area (dot-to-nuclei ratio) in GST-P positive foci were significantly increased and the roundness was decreased as compared to values for surrounding hepatocytes. Frequencies of cells with big and bizarre (low roundness) dots were elevated in GST-P positive foci. Hence, our data suggest that AgNOR area and shape rather than number may reflect cell proliferation more acurately, so that assessment of these parameters may be useful for evaluating the biological nature of preneoplastic lesions.