DIETARY FAT-INDUCED AND PHENOBARBITAL-INDUCED ALTERATIONS IN HEPATIC ANTIOXIDANT FUNCTIONS OF MICE

Inbred strains of mice with differential response to known tumor promo ters were compared with respect to their susceptibility to modulation of hepatic antioxidant enzymes by long-term treatment with high fat di et (HF) and phenobarbital (PB). Mice of the C57BL/6J (C57), C3H/HeOuJ (C3H) and DBA/2J (DBA) strains were fed diets containing low (5%) or h igh (15%) amounts of fat (sunflower oil) for 26 weeks from the age of 6 weeks onwards. Groups of mice on the 5% fat diet received 0.05% PB i n their drinking water from 12 to 22 weeks of age. Mice of the C57 str ain are known to be refractory to promotion of hepatocarcinogenesis, t he C3H strain has a high incidence of spontaneous tumors and is sensit ive to promotion by HF and PB, and the DBA strain is especially sensit ive to promotion by PB. Within all strains of mice, and in both dietar y groups, the degree of oxidative stress in the liver was found to inc rease with age, as was indicated by the increased amounts of TBA react ive material (lipid peroxidation) and decreased glutathione (GSH) and phospholipid contents of the tissue. HF elevated the amount of TBA rea ctive material in the liver of C57 and C3H mice, induced GSH-peroxidas e and Mn-superoxide dismutase activities in the C3H strain, and depres sed the hexose monophosphate shunt activity within all mouse strains. PB drastically decreased the amount of TBA reactive material in the li ver in all mouse strains, increased catalase activity in all strains a nd the activity of GSH-peroxidase in the C3H and DBA strains. The abov e strain differences in responses of hepatic antioxidant functions to HF and PB parallel the differential responsiveness of these mouse stra ins to promotion of hepatocarcinogenesis by these agents, and the incr eased antioxidant capacity was proportional to susceptibility to tumor promotion.