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EFFECTS OF ANESTHESIA (MS222) ON LIVER BIOTRANSFORMATION IN RAINBOW TROUT (ONCORHYNCHUS MYKISS)
Kolanczyk, R C., P N. Fitzsimmons, J M. McKim, AND P. K. Schmieder. EFFECTS OF ANESTHESIA (MS222) ON LIVER BIOTRANSFORMATION IN RAINBOW TROUT (ONCORHYNCHUS MYKISS). Presented at Society of Toxicology Meeting, San Francisco, CA, March 25-29, 2001.
Tricaine methanesulfonate (3-aminobenzoic acid ethyl ester methanesulfonate; MS222) is a widely used fish anaesthetic. While there have been several studies addressing the impact of its use on subsequently measured biotransformation rates, the measured influence on normal functioning of Phase I and Phase II enzyme systems appears sensitive to experimental design. The current study measures rates of Phase I (ring-hydroxylation) and Phase II (glucuronidation) metabolism of phenol in microsomes prepared from adult rainbow trout with and without exposure to MS222. Microsomes were prepared from livers of control (unexposed) trout, fish exposed for 2 h to 100 mg/L MS222, and fish exposed to 2 h then allowed to recover in fresh water for 24 h. Fish were artificially ventilated during the 2 h exposure to the anesthetizing dose of MS222. There were no observed differences in total cytochrome P-450 protein or EROD activity between treatments and control groups. After 2 h continuous exposure to MS222 the rates of phenol microsomal ring hydroxylation, measured as formation of to hydroquinone (HQ) or catechol (CAT), decreased by 15-30%, while the formation of phenylglucuronide (PG) decreased 10-25% compared with production measured in microsomes prepared from unexposed fish. Following a 2 h MS222 exposure and 24 h recovery, ther was only a slight decrease noted in HQ (5%) and CAT (15-20% less) production. Depuration had little effect on the rate of PG formation. Overall, a 5-25% reaction dependent decrease in metabolic rate following anesthesia may need to be considered when comparing biotransformation rate information in rainbow trout.