Liver cytosol, trout

Because the metabolism of DEHP was catalyzed by so many fractions of the trout liver homogenate, these fractions were characterized by measurement of marker enzymes to determine which organelles actually were responsible for the observed DEHP metabolism. Succinic dehydrogenase activity was used as a marker for mitochondria, whereas glucose-6-phosphatase was used as a marker for microsomes. The distribution of DEHP oxidase activity (production of polar metabolites 1 and 2 with added NADPH) and of DEHP esterase activity (production of monoester without added NADPH) were also determined. It was found (Figure 2) that the distribution of DEHP oxidase activity parallels the distribution of microsomal activity and the distribution of DEHP esterase activity parallels the distribution of microsomal activity, but is also present in the cytosol fraction. 

In an effort to characterize further the metabolism of DEHP by trout, the effect of the mixed function oxidase inhibitor, piperonyl butoxide, upon the metabolism of DEHP by these trout liver fractions and serum was examined. Because of the use of piperonyl butoxide as an insecticide synergist, it is possible that fish might be exposed to this chemical in the environment. The data in Table VII show that piperonyl butoxide inhibited overall metabolism of DEHP by liver homogenates and microsomes whether NADPH was added or not. The hydrolysis of DEHP by serum was also blocked by piperonyl butoxide and although not shown, this was also the case with liver cytosol. These latter results were surprising because piperonyl butoxide has been known as a mixed function oxidase inhibitor only, and would not be expected... 

Fish liver microsomes are capable of both hydrolytic and oxidative metabolism of phthalate esters. In addition, trout liver cytosol and blood serum exhibited esterase activity against DEHP. 

Curtis, L.R., M.J. Hemmer and L.A. Courtney. Dieldrin induces cytosolic [3H]7,12-dimethylbenz[a]an-thracene binding but not multidrug resistance proteins in rainbow trout liver. J. Toxicol. Environ. Health A... 

Pottinger, T.G., F.R. Knudsen and J. Wilson. Stress-induced changes in the affinity and abundance of cytosolic cortisol-binding sites in the liver of rainbow trout, Oncorhynchus mykiss (Walbaum), are not accompanied by changes in measurable nuclear binding. Fish Physiol. Biochem 12 499-511, 1994. 

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