The effects of
2-acetylaminofluorene (2-AAF),
sodium phenobarbital (PB) and
4,4'-diaminodiphenylmethane (
DDPM) on the developmental sequence of
N-nitrosomorpholine (NNM) induced changes in the rat liver was investigated using a histological, histochemical and morphometric approach. Male Sprague-Dawley rats were treated with NNM for 3 weeks, maintained on basal diet for 1 week and then fed on diets containing either 0.005%
2-AAF, 0.05% PB, 0.08%
DDPM or, as
carcinogen controls, no addition (basal diet, BD) for a further 48 weeks. Control and experimental groups were sacrificed at weeks 4, 16, 28, 40 and 52 of the investigation. The incidence of the
hepatocellular carcinomas observed at weeks 40 and 52 was markedly enhanced by
2-AAF treatment and slightly increased after PB administration.
2-AAF also exerted a positive influence on the development of
angiosarcomas, benign
hemangioendotheliomas and cystic
cholangiomas.
DDPM did not show clear effects on the development of
liver cell carcinoma but enhanced the induction of cholangiofibromas, cholangiofibrosis and, very markedly, spongiosis hepatis. No neoplastic lesions were observed in animals treated with
2-AAF, PB or
DDPM without prior application of NNM. Morphometric analysis of
enzyme-altered foci revealed contrasting effects of
2-AAF, PB and
DDPM, not only on number and size of lesion but also on their histochemical phenotype. Thus whilst
2-AAF administration was primarily linked with increase in number of lesions, PB appeared to stabilise their phenotypic cellular changes and increased the activity of G6PDH.
DDPM did not significantly influence the number of focal lesions but seemed to effect a decrease in phenotypic alteration within foci. The results suggest that changes in the nature of
enzyme-altered foci may be correlated with enhancement or inhibition of
tumorigenesis.