Catalytic and immunocytochemical detection of xenobiotic metabolizing enzymes in the olfactory organ of rainbow trout (Oncorhynchus mykiss)

The fish olfactory organ, which is covered with a sensory epithelium, is in direct contact with aquatic pollutants. In mammals, presence of xenobiotic metabolizing enzymes has been reported in the olfactory epithelium, but few studies have been carried out on this topic in fish. In the present study, xenobiotic metabolizing enzymes were investigated in the rainbow trout olfactory organ. Data show that cytochrome P450 reductase, p-nitrophenol hydroxylase and glutathione S-transferase specific activities were in the same range as that in the liver, whereas 7-ethoxyresorufin O-deethylase and 7-ethoxycoumarin O-deethylase specific activities were 80 and 30 times lower, respectively, in the olfactory organ compared to the liver. Immunocytochemical investigation shows that cytochrome P4501A1 was located in both the epithelial non-sensory cells and the basal cells of the sensory epithelium, as well as in goblet and microvilli cells of the non-sensory epithelium. The presence of such enzyme activities in the olfactory organ of rainbow trout addresses the question of their involvement in the detoxication/toxication of pollutants as well as in the olfactory function.