Quantitative analysis of multiple phenotype enzyme-altered foci in rat hepatocarcinogenesis experiments: the multipath/multistage model.

The promotional effect of phenobarbital and 1-hydroxymethyl-pyren on enzyme altered lesions in the rat liver were quantified within the framework of two separate multipath/multistage models. The experiment analyzed followed an initiation-promotion protocol in which female Wistar rats were initiated with a single dose of diethylnitrosamine at 0.15 mumol/g body wt followed by a 3 week treatment-free period. A promotor, 1-hydroxymethyl-pyren or phenobarbital was then administered continuously in the diet for 120 days. All animals were sacrificed 3 weeks after treatment and their livers were examined for enzyme histological changes. Focal lesions were classified into three phenotype categories: adenosine triphosphatase altered (ATPase), sulfotransferase altered (ST) and jointly altered lesions (ATPase and ST). Quantitative methods were used to analyze the data, which consisted of the number and sizes of these enzyme-altered lesions. Both multipath/multistage models fitted to the data clearly demonstrate that phenobarbital promotion produced more observable and larger foci than promotion via 1-hydroxymethyl-pyren and that the growth kinetics of the jointly altered lesions were elevated relative to the lesions expressing a single marker. It was not possible with these data to determine if there was a predominant sequence in the formation of jointly altered lesions.