COMPARISON OF HEPATOCYTE PHENOTYPES AT THE GLUTATHIONE TRANSFERASE AND ALBUMIN LOCI IN SPRAGUE-DAWLEY AND NAGASE ANALBUMINEMIC RATS AND F1 PROGENY AFTER INITIATION AND PROMOTION

Hepatocarcinogenesis was examined in an initiation-promotion protocol with a single initiating dose of 7,12-dimethylbenz[a]anthracene (DMBA) followed by promotion with phenobarbital (PB) in the Nagase analbumin emic rat (NA), the Sprague-Dawley rat (SD) and their Fl crosses. All r ats received a 70% partial hepatectomy, followed at 24 h by 30 mg DMBA /kg body wt or the solvent. After a 2 week recovery following surgery, half of the solvent control and initiated groups received either basa l diet or promotion with 0.05% PB mixed into the basal NIH-07 diet. Af ter 12 weeks of promotion, the rats were killed and the livers perfuse d and fixed in situ with paraformaldehyde. Liver slices were paraffin embedded and stained for the placental isozyme of glutathione S-transf erase (PGST). The number of altered hepatic foci (AHF) expressing PGST per liver was determined by quantitative stereology and used as an en dpoint for comparison of initiation in the rat strains. The NA rat had a lower response to this initiation - promotion protocol than did the SD rat. The F1 progeny of the male NA and female SD rats were more si milar to the NA parent in their responsiveness to initiation, whereas the F1 progeny of the female NA and male SD were similar to the SD par ent in this respect. Putative mutagenesis and carcinogenesis were exam ined in the Fl progeny of the female NA and male SD rat. In these rats , serial liver sections were stained either for albumin to detect puta tive mutations at that locus, or PGST to identify putatively initiated hepatocytes. In the NA/SD Fl, the number of single hepatocytes with a putative mutation at the albumin locus was the same (3.7 X 10(5)/live r) as those expressing a common marker of preneoplasia (PGST). The num ber of AHF expressing PGST was -5% that of the single cells exhibiting an altered expression of albumin or PGST, indicating a possible quant itative correlation between initiation and mutation in vivo when indiv idual hepatocytes with altered gene expression were counted. These stu dies also suggest that only a subpopulation of the putatively initiate d hepatocytes expands clonally in the presence of the promoting agent, PB. The progeny of the female NA rat crossed with the SD male rat app ears to provide a useful model in which to compare mutation and carcin ogenesis simultaneously in vivo.