Ultrastructural and Autoradiographic Study of the Effects of Bleomycin on the Interphase Nucleus of Cultured Normal Cells

Primary cultures of hepatocytes and epithelial endometrial cells were treated with bleomycin (10 to 200 µg/ml) for 30 to 300 min. Structural changes were studied with a staining method which contrasts ribonucleoproteins. The earliest visible alteration was the accumulation of perichromatin granules in association with the nucleolus. This disturbance was frequently accompanied by modifications in the nucleolar architecture. After larger treatments, the most striking changes were nucleolar segregation and the appearance of spherical clear bodies in the nucleolus. In the extranucleolar area, a remarkable diminution of ribonucleoprotein fibrils and clustering of interchromatin granules were observed. Functional disturbances in the synthesis and transporting of RNA to the cytoplasm were studied by high-resolution quantitative autoradiography after labeling with tritiated uridine. Bleomycin produces a strong inhibition of RNA synthesis in nucleolar and extranucleolar areas. Important decreases of [3H]uridine incorporation were observed as early as 30 min after the administration of drug. Alterations of processing and/or transporting of RNA to the cytoplasm were found after treatments with bleomycin (100 µg/ml) for 30 to 300 min. It is suggested that the diminution of ribonucleoprotein fibrils is related to the inhibition of RNA synthesis while the accumulation of perichromatin granules is connected to alteration of the transporting and/or processing.