THE EFFECT OF BUTYLATED HYDROXYTOLUENE ON THE GROWTH OF ENZYME-ALTERED FOCI IN MALE FISCHER-344 RAT-LIVER TISSUE

Butylated hydroxytoluene (BHT) is a synthetic, food-use, phenolic anti oxidant. It has previously been demonstrated to be operationally non-g enotoxic and, in addition, failed to induce biologically significant i ncreases in cellular proliferation in the liver, urinary bladder and t hyroid gland on feeding to young adult Wistar rats, Nevertheless, it h as been reported to enhance the yield of liver tumors when fed to rats or mice that developed an appreciable background incidence of these t umors without treatment, In order to resolve this situation, cell prol iferation in response to BHT treatment was studied in enzyme-altered f oci (EAF) induced in male Fischer 344 rats using the Solt-Farber proce dure, It was demonstrated that feeding 0.5% dietary BHT for 30 days af ter the induction of EAF led to a 20- to 30-fold increase in the gamma -glutamyltranspeptidase-positive areas in both DEN- and saline-initiat ed rat livers, but to no major effects in glutathione S-transferase pl acental form (GSTP)-positive foci, Cell proliferation rates within EAF and surrounding normal liver were measured using different histologic al techniques, Nuclear labeling with [H-3]thymidine and proliferating cell nuclear antigen (PCNA) over the total hepatocyte population indic ated that BHT approximately doubled nuclear labeling in rats initiated with DEN, PCNA labeling in GSTP-positive foci was not affected by BHT . In GSTP-positive foci, evaluation of nucleolar organizer regions (Ag NOR), which reflect cell proliferative in addition to transcriptional activity of ribosomal RNA, was achieved using a novel double staining technique, BHT diet did not affect the number of AgNOR per nucleus or the percentage AgNOR area/nucleus, Nevertheless, both PCNA labeling an d the AgNOR area per nucleus were significantly greater in GSTP-positi ve foci compared with non-focal regions in rats fed either BHT or cont rol diets, These results are discussed in the light of further experim ental work required to determine the relevance of these data to possib le human risk assessment for BHT.