Abstract
We have studied the changes in cell population kinetics and DNA-content of cycling parenchymal cells during the very early steps of rat hepatocarcinogenesis in Faber's protocol. Adult rats were initiated by a single dose of diethylnitrosamine (DENA, 200 mg kg-1), followed 2 weeks later by a 2-week diet of 0.03% 2-acetylaminofluorene (2-AAF) as selection phase. In the middle of selection time, a single necrogenic dose of carbon tetrachloride (CCl4, 2 ml kg-1) was administered by gavage. Twenty four hours thereafter, radiolabelled thymidine (3H-TdR, 1.5 microCi g-1) was given by repeated injections during 24 h. An emergence of small, pyroninophilic ('tigroid') foci was observed at the second, fifth and eighth days after the proliferative stimulus. The focal putative precancerous cells presented a significant higher labelling index (L1) than the non-affected parenchymal cells for all exposure times. However, the labelling intensity decreased from the second to the eighth day after CCl4, suggesting a dilution of the radiolabelled DNA by repeated divisions within the foci. The nuclei of the same foci were analysed for DNA-content by feulgen microdensitometry on neighbouring sections. A gradual reduction of nuclear DNA-content was observed in 66% of the foci at the fifth day and in 100% of foci at the eight day, as compared to surrounding tissue and untreated animals, where labelling and DNA-content remain in the same ratio.
Highlights
In previous works (Deleener et al, 1987; Kirsch-Volders et al, 1986) it was shown that nodular cells, induced by a triphasic protocol were predominantely diploid, in contrast to the mainly tetraploid cell population of a non-treated adult rat liver
After labelling with 3H-TdR, these necrotic cells were heavily labelled at 2 days after IS-CC14
This labelling disappeared after 8 days in these areas
Summary
In previous works (Deleener et al, 1987; Kirsch-Volders et al, 1986) it was shown that nodular cells, induced by a triphasic protocol (initiation, selection, promotion) were predominantely diploid, in contrast to the mainly tetraploid cell population of a non-treated adult rat liver. These findings were reported with several other carcinogenic regimens (Bassleer et al, 1985; Godoy et al, 1976; Inui et al, 1971; Pugh & Goldfarb, 1978; Schwarze et al, 1984; Styles et al, 1985, 1987; Sargent et al, 1989) and even in primary liver cancer of man (Saetar et al, 1987) These downward shifts in ploidy level were observed by classical cytodensitometry (Inui et al, 1971; Neal & Bulter, 1978), flow-cytometry of interphase cells (Schwarze et al, 1984; Styles et al, 1985) or by chromosome counting of dividing hepatocytes (Becker et al, 1971)
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