FREQUENCY AND DNA CONTENT OF MICRONUCLEI IN RAT PARENCHYMAL LIVER-CELLS DURING EXPERIMENTAL HEPATOCARCINOGENESIS

Liver carcinogenesis is considered to be a good experimental model to study the sequential changes leading to cancer and was applied here fo r the analysis of chromosome/genome mutations. Since the micronucleus test was shown to be an adequate method to detect and analyse chromoso me changes in dividing cells, the frequency of micronuclei (MN) togeth er with their relative DNA content (DNA content of the MN divided by t he DNA content of the corresponding nucleus) were analysed in hepatocy tes isolated from rats at different stages of experimentally induced h epatocarcinogenesis. The protocol used for the induction of liver canc er was based on the triphasic 'Gerlans protocol', a Solt-Farber proced ure supplemented with a phenobarbital (PB) promotion step. Male Wistar rats were initiated by a single i.p. dose of diethylnitrosamine (DENA ), followed by selection of the resistant hepatocytes by 2-acetylamino fluorene (2-AAF). Subsequent promotion was accomplished by chronic exp osure to phenobarbital. For each group of rats a mitotic stimulator (C Cl4) is necessary at the end of their treatment period to express the clastogenic and/or aneugenic lesions which may lead to micronuclei. Th e results of these experiments do confirm that genetic alterations are occurring at the chromosome level (MN expression) during the differen t steps of experimental rat liver carcinogenesis. DNA measurements see m to be a good genetic parameter to detect eventual differences betwee n the chromosomal content (whole chromosome or chromosome fragments) o f MN populations appearing in different stages of the carcinogenic pro cess. Moreover, a comparison between the mono- and bi-nucleated cell p opulation showed that the frequency of micronuclei is higher in mononu clear parenchymal liver cells.