Use of Online Microdialysis Sampling to Determine the in Vivo Rate of Phenol Glucuronidation in Rainbow Trout

Abstract

ABSTRACT:A quantitative microdialysis (MD) sampling method was used to study phenol (PH) glucuronidation in vivo in rainbow trout. The method employs internal calibrators to account for changes in MD probe performance (in vitro-to-in vivo and sample-to-sample) and yields data of high temporal resolution that are well suited for developing kinetic models. Initially, trout were dosed with phenyl glucuronide (PG) by intravascular infusion for 24 h and then depurated for 48 h. Measured concentrations of PG in blood were well described by a one-compartment clearance-volume model. Massbalance calculations showed that 93% of infused PG was eliminated in urine during the depuration period. Peak concentrations of PG in urine averaged 3.4 times higher than those in blood, and the fitted PG clearance constant (15.7 ml/kg/h) was about 2.6 times higher than the reported glomerular filtration rate for trout. These findings confirm earlier work suggesting that PG is actively secreted by the trout kidney. In a second set of experiments, trout were exposed continuously to PH in water. In vivo rate constants for PH glucuronidation were estimated using a pair of linked (PH and PG) one-compartment clearance-volume models. Expressed on a whole-fish basis, the glucuronidation rate averaged 0.049/h, which was about 7% of the total rate of PH elimination. This study demonstrates the utility of quantitative MD sampling for kinetic studies of xenobiotic metabolism in fish.Microdialysis (MD) is a well established in vivo technique that is used to sample or deliver chemicals in blood or interstitial water of selected tissues. The MD method employs a semipermeable membrane that is perfused on its inner surface with physiological saline. Chemicals diffuse across the membrane and are collected for analysis by HPLC or other techniques, often without the need for additional processing steps. "On-line" MD is characterized by direct transfer of dialysate samples to the analytical instrument, resulting in near realtime analysis of samples. MD sampling methods were initially developed to measure endogenous compounds in the CNS (Benveniste and Hüttemeier, 1990) but have since been used in a wide range of scientific disciplines, including studies of chemical kinetics and biotransformation. The use of MD in pharmacokinetic studies with mammals has been extensively reviewed (Ståhle, 1992;Elmquist and Sawchuk, 1997;Davies, 1999;Hansen et al., 1999;Verbeeck, 2000).In a pioneering effort, McKim et al. (1993) used MD probes implanted in the dorsal aorta of rainbow trout to measure blood borne concentrations of phenol (PH) and its phase II metabolic product, phenyl glucuronide (PG), during continuous PH exposures. This method was then combined with periodic urine sampling to characterize the renal elimination of PH, PG, and two additional PH metabolites, phenyl sulfate and hydroquinone (McKim et al., 1999). These studies showed that phenyl sulfate and PG are the principal products of PH metabolism in trout and that the trout kidney actively secretes these c...

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