SIMULTANEOUS EXPOSURE OF FISH TO ENDOSULFAN AND DISULFOTON IN-VIVO - ULTRASTRUCTURAL, STEREOLOGICAL AND BIOCHEMICAL REACTIONS IN HEPATOCYTES OF MALE RAINBOW-TROUT (ONCORHYNCHUS-MYKISS)

The response of male rainbow trout (Oncorhynchus mykiss) liver to comb ined prolonged exposure to 50 ng/l endosulfan (ES) and 0, 1, 5, or 10 mu g/l disulfoton (DS) was studied using electron microscopical, stere ological and biochemical techniques. Both acute and sublethal toxiciti es of DS increased exponentially by simultaneous exposure to ES. LC,, was determined at 50 ng/l ES plus 20 mu g/l DS. Major sublethal morpho logical alterations included a 50% increase in cytoplasmic volume due to a 100% increase, dilation and vesiculation of the RER, and a 50% de crease in glycogen deposits. Further reactions were proliferations of mitochondria, myelinated bodies and glycogenosomes, and, at 50 ng/l ES plus 1 mu g/l DS only, a transient increase in the absolute volume of peroxisomes and lysosomes. In terms of liver enzyme activities (mU/g liver), biochemical effects comprised induction of ethoxycoumarin- and ethoxyresorufin-O-deethylases, and of glutathione S-transferase, but depression of esterase, acetylcholine esterase, acid phosphatase, aryl sulfatase, glucose 6-phosphate dehydrogenase, malic enzyme and lactat e dehydrogenase, as well as increased lipid peroxidation. In terms of specific enzyme activities (mU/mg protein), there was an increase in u ricase, aryl sulfatase, glutathione S-transferase, whereas acetylcholi ne esterase, malic enzyme and esterase were reduced. No consistent cha nges were seen in succinate dehydrogenase, catalase, glucose 6-phospha te dehydrogenase, lactate dehydrogenase, and NADPH cytochrome P-45D re ductase specific activities. Findings indicate a biphasic reaction to combined ES and DS, with a shift from adaptive to degenerative reactio ns at 5 mu g/l DS, Acute toxicity of 50 ng/l ES plus 20 mu g/l DS is m ost likely due to reduced biotransformation capacities by lipid peroxi dation-induced membrane damage. Cytochrome P-45D induction and suppres sion of acetylcholine esterase as typical consequences of ES or DS exp osure, respectively, were found as further mechanisms of combined toxi city.