An in vivo microdialysis method for the qualitative analysis of hepatic phase I metabolites of phenol in rainbow trout (Oncorhynchus mykiss).

Development of reliable and accurate methodologies for determination of xenobiotic hepatic biotransformation rate and capacity parameters is important to the derivation of precise physiologically-based toxicokinetic (PB-TK) models. Biotransformation data incorporated into PB-TK models has, for the most part, depended on in vitro techniques designed to mimic the in vivo environment; however, data from direct in vitro/in vivo comparisons is limited. In this investigation we describe for the first time a method using in vivo microdialysis (MD) to qualitatively assess hepatic xenobiotic biotransformation of phenol in an unanesthetized fish. MD probes were surgically implanted into the livers of adult rainbow trout which were subsequently confined to respirometer-metabolism chambers. Phenol (1-300 mM) was delivered directly to the liver via the MD probe at a perfusion rate of 1 microl min(-1) which consistently resulted in a relative delivery of 77-85% of the phenol in the perfusate to the tissue over a 3 day experimental time frame. Location of the probe within the liver was also shown to have no effect on the delivery of phenol or on the type or quantity of phase I metabolites formed. Production of hydroquinone (HQ) and catechol (CAT), the primary phase I metabolites of phenol, was monitored through direct sampling of the hepatic extracellular fluid space via the MD probe. HQ and CAT production increased with increasing time of perfusion and with increasing concentration of phenol delivered to the liver. In the future, data obtained through in vivo MD will be useful in resolving uncertainties in biotransformation rate and capacity parameters, which are central to fish PB-TK modeling of chemical disposition.