Enhancement of lung tumor formation in mice by dietary butylated hydroxytoluene: dose-time relationships and cell kinetics.

Strain A/J mice given injections of 1,000 mg urethan/kg and fed for 12 weeks a diet containing 0.75% of butylated hydroxytoluene (BHT) had significantly more tumors per lung 4 or 9 months later than animals given urethan and fed a control diet. A 2-week exposure to dietary BHT (0.75%) was sufficient to significantly enhance tumor development, and the lowest effective BHT concentration was 0.1%, fed for 8 weeks. Tumor development was also enhanced in animals treated once with 3-methylcholanthrene, benzo[a]pyrene, or N-nitrosodimethylamine and, beginning 24 hours later, fed BHT for 8 weeks. Cell kinetic studies showed that BHT given in the diet produced increased proliferation of type II alveolar cells during the first 2 weeks and that initial cell proliferation was delayed in urethan-treated animals.