The Effects of Route of Exposure and Combined Exposure of Mixed-Function Oxidase Inducers and Supressors on Hepatic Parameters in Rainbow Trout (Salmo gairdneri)
Hepatic microsomes obtained from rainbow trout (Salmo gairdneri) administered β-naphthoflavone (βNF) either by a single intraperitoneally (IP) injected dose of 100 mg/kg body wt. or by feeding 500 ppm for 1 wk showed increased cytochrome(s) P-450 content and increased aryl hydrocarbon hydroxylase (AHH) and ethoxycoumarin-O-deethylase (ECOD) activities compared to controls. The microsomal maximum absorbance wavelength of carboxyferrocytochrome P-450 was 450 nm for the control trout, 448 nm for the trout administered βNF by diet, and 449 nm for the trout administered βNF by IP. Hepatic microsomes from trout fed 500 ppm phenobarbital (PB) for 3 wk showed no induction as demonstrated by cytochrome(s) P-450 content, NADPH-cytochrome c reductase, ethoxyresorufin-O-deethylase (EROD), ECOD, and benzphetamine-N-demethylase (BND) activities. The S20 liver fractions from trout fed βNF were less efficient in converting aflatoxin B1 to a mutagen to Salmonella typhimurium TA 98 than were the S20 liver fractions from control trout. This suggests that dietary βNF may suppress the microsomal conversion of aflatoxin B1 to the active 2,3-oxide in trout. Trout fed 500 ppm βNF for 3 wk followed by 3 more wk of βNF plus 0, 50, 150, 300, 450, or 600 ppm cyclopropenoid fatty acids (CPFA's) exhibited a significant decrease in the following parameters with an increase in dietary CPFA's: liver wt./body wt. percent, microsomal protein and cytochrome(s) P-450 content, and NADPH-cytochrome c reductase, ECOD, AHH, and glutathione transferase activities. Feeding 300 ppm CPFA's with 500 ppm βNF caused a shift in the maximum absorbance wavelength from 448 nm to 449 nm and decreased cytochrome(s) P-450 content by 71% whereas 450 ppm CPFA's caused a further shift to 450 nm and a corresponding 77% decrease in cytochrome(s) P-450 content. βNF induced and CPFA's suppressed the trout hepatic mixed function oxidase system.
Eisele, T.A., R.A. Coulombe, N.E. Pawlowski and J.E. Nixon (1984). The effects of route of exposure and combined exposure of mixed-function oxidase inducers and supressors on hepatic parameters in rainbow trout (Salmo gairdneri). Aquatic Toxicol. 5:211-216.