Dietary antioxidant effects on the hepatic mixed-function oxidase system of rainbow trout ( Salmo gairdneri)

Abstract

Rainbow trout ( Salmo gairdneri) were fed a control diet with or without an antioxidant—3,5-di- tert-butyl-4-hydroxytoluene (BHT), 2(3)- tert-butyl-4-hydroxyanisole (BHA), mono- tert-butylhydroquinone (TBHQ) or ethoxyquin (EQ)—at a level of 5.56 mmol in 100 g oil/kg diet for 6 wk. The treated trout had reduced liver weight/body weight ratios. In comparison with trout fed control diet, microsomal protein content was lowered by 13% in TBQH-fed trout and elevated by 28% in EQ-fed trout, cytochrome P-450 content was 21% lower in BHA- and TBHQ-fed and 18% lower in EQ-fed trout and cytochrome b 5 content was 46% lower in EQ-fed trout. Activities of benzo[ a]pyrene hydroxylase, epoxide hydratase and ethoxycoumarin- O-deethylase were, respectively, 3.2–4.8, 1.2–1.7 and 1.3–5.5 times higher in antioxidant-fed trout. NADPH-cytochrome c reductase was elevated 1.2–1.3 times over the control value with dietary BHA, TBHQ and BHT, but was lowered with EQ. p-Nitroanisole- O-demethylase activity was completely suppressed in antioxidant-fed trout. The content of post-mitochondrial acid-soluble sulphydryl groups was 42% lower in BHA- and BHT-fed trout. Alterations in the enzyme activities of the mixed-function oxidase system, changes in the ethyl isocyanide binding ratio and decreases in cytochrome P-450 content suggest that dietary antioxidants could alter carcinogen activation and/or detoxification mechanisms in the hepatic microsomes of rainbow trout.