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Department of Medicinal Chemistry (M.O.J., Z.T.), University of
Florida-Gainesville;
The Whitney Laboratory (M.O.J., A.H.A., K.M.),
University of Florida-St. Augustine; and
Department of Veterinary
Physiology, Pharmacology, and Toxicology (K.M.K.), Louisiana State
University
These studies demonstrated that intestinal mucosa of the channel
catfish contained activities comparable with liver for several phase 2 xenobiotic-metabolizing enzymes, and showed that CYP1A-dependent monooxygenase activities were inducible in intestine but not liver by
dietary exposure to low concentrations of the Ah agonist,
-naphthoflavone (BNF). The diets administered were
laboratory-prepared, semisynthetic pellets of known composition,
commercial chow, or chow supplemented with BNF at 10 or 100 mg BNF/kg
chow. Very low intestinal benzo(a)pyrene hydroxylase [aryl
hydrocarbon hydroxylase (AHH)] and ethoxyresorufin O-deethylase (EROD) activities were found in catfish fed
the semisynthetic diet. Intestinal EROD and AHH activities were
elevated by the commercial chow diet and further induced by
supplementation with 10, but not 100, mg BNF/kg diet. In
vitro studies showed that catfish EROD and AHH activities were
sensitive to inhibition by BNF, with mean IC50 values of
0.078 and 2.2 µM, respectively. Thus, residues of BNF retained in
intestinal mucosa may have masked monooxygenase induction in catfish
fed the 100 mg BNF/kg diet. Microsomal UDP-glucuronosyltransferase and
cytosolic PAPS-sulfotransferase activities with
3-hydroxybenzo(a)pyrene as substrate were largely unaffected by the diets studied, and intestinal activities were similar
to hepatic activities. Glutathione S-transferase activity was slightly induced in intestinal, but not hepatic cytosol of catfish
treated with BNF at the 10 mg/kg diet level relative to chow controls.
Epoxide hydrolase activity with styrene oxide as substrate was not
affected by diet in intestinal microsomes.
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