Detection and quantification of ploidy, nuclearity, and DNA synthesis in rat hepatocytes after administration of a peroxisome proliferator.

The peroxisome proliferator methylclofenapate (MCP) induces species-specific liver growth and cancer in rats and mice. The acute hyperplastic effects of MCP were studied in rats given MCP (25 mg/kg by daily gavage) and injected IP (0.5 mL, 50 mM) with bromodeoxyuridine (BrdU) 6 hr before each sampling time. The animals were killed at 6-hr intervals and hepatocyte suspensions prepared from their livers by collagenase perfusion. The cells were stained with propidium iodide (PI) and BrdU antibody combined with fluorescein isothiocyanate (FITC). DNA content (PI-red fluorescence) and S phase (BrdU/FITC-green fluorescence) were analyzed simultaneously by two-parameter flow cytometry and the frequency of S phase in different ploidy classes determined. At the same time, S-phase cells from different ploidy groups were sorted onto slides by fluorescence-activated cell sorting and examined microscopically to determine the frequency of binucleated cells undergoing DNA synthesis. The results show that MCP-induced acute hyperplasia occurs mainly in a sensitive subpopulation of binucleated hepatocytes.