Induction of biotransformation in the liver of eel ( Anguilla anguilla L.) by sublethal exposure to dinitro- o-cresol: An ultrastructural and biochemical study

Structural and functional alterations in hepatocytes of the European eel, Anguilla anguilla, following a 4-week-exposure to 5, 50, and 250 μg/liter dinitro- o-cresol (DNOC) were investigated by means of electron microscopy and biochemistry and compared to liver pathology in eels exposed to the chemical spill into the Rhine river at Basle in November 1986. Whereas phenological parameters (growth, condition factor) are unaffected, ultrastructural and biochemical alterations are detectable at ⩾50 and 5 μg/liter DNOC, respectively. Structural modifications include: rounding-up of the nuclei; fractionation and reduction of the rough endoplasmic reticulum; proliferation of the smooth endoplasmic reticulum (SER), mitochondria, peroxisomes, and lysosomes; bundles of rod-shaped SER profiles; annulate lamellae; membrane whorls within mitochondria; crystallization of the peroxisomal matrix and glycogen bodies; glycogen depletion and lipid augmentation. Structural changes can be correlated to an increase in hepatic lipid and protein contents as well as stimulation of mitochondrial (cytochrome c oxidase), peroxisomal (catalase, allantoinase, uricase), lysosomal (arylsulfatase), and microsomal (esterase) enzymes. An increase in NADPH-cytochrome c reductase and cytochrome P450 as well as UDP-glucuronyltransferase and arylsulfotransferase activities in the microsomal fraction document an induction of hepatic biotransformation as a functional correlate to SER proliferation. Maximum inducibility of biotransformation enzymes at 50 μg/liter indicates a biphasic, concentration-dependent reaction of eel liver. Comparison of DNOC-induced effects with liver pathology in eel exposed to the chemical spill in 1986 reveals striking similarities so that DNOC may not be excluded as a possible factor in the fish kill in the Rhine river.