Graduate Thesis Or Dissertation
 

B-Naphthoflavone induction and its effect on hepatic phospholipid metabolism in rainbow trout (Salmo gairdneri)

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/rr172093p

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  • The induction of drug-metabolizing enzymes is a complex biochemical process manifested not only by increases in various cytochrome P-450 isozymes and related activities, but also by alterations in endoplasmic reticulum membranes. Little work has been done to examine how cytochrome P-450 inducing agents influence other cellular processes, such as phospholipid metabolism. Furthermore, characterization of the poikilotherm mixed-function oxidase (MFO) system has lagged considerably behind numerous sophisticated mammalian studies, although differences between the two species have been reported. With the proposal that fish be used as monitors of environmental pollution for man, the importance of characterizing fish MFO induction and related cellular events becomes apparent. The present study was undertaken with this in mind in an effort to further evaluate the consequences of induction by polyaromatic hydrocarbons (PAH) in fish. This may be one of the first reports of the effects of PAH induction on liver phospholipid metabolism in poikilotherms. B-Naphthoflavone (BNF) induction of microsomal cytochrome P-450 and its effects on various aspects of liver phospholipid (PL) metabolism were examined in rainbow trout 24 and 96 hours after intraperitoneal injection. Spectrophotometrically-measured microsomal cytochrome P-450 content from BNF-induced trout liver showed no significant elevation 24 hours after injection, but increased substantially at 96 hours to approximately double the P-450 content in control liver. This corresponds to results from computer-analyzed laser densitometry scans of LDS-polyacrylamide gels of 96-hour BNF-treated liver microsomal proteins, where a tentatively-identified cytochrome P-448 (P-450LM4) increased 90% relative to controls. BNF-induced alterations in microsomal phospholipid (PL) composition of trout liver occurred before and after the actual observed increase in cytochrome P-450 contents. A substantial elevation in liver microsomal PL/mg protein (34%) was noted at 24 hours after BNF injection, with a significant accumulation of choline, ethanolamine and inositol PLs. This was accompanied by a slight reduction in serine PLs when compared to 24-hour controls. At 96 hours much of the initial increase of individual PLs had subsided, although total PL content remained higher in BNF-treated microsomes. This was apparently due to a sustained elevation of ethanolamine PLs, which remained at the same level at 96 hours as at 24 hours. The most significant observation at 96 hours was the substantial depletion of serine PLs (33%) . The observed alterations in PL composition and possible metabolic pathways responsible are discussed in relation to previous findings. The fatty acid compositions of the two major microsomal lipid constituents, choline and ethanolamine PLs, were not significantly different from controls at either 24 or 96 hours after a single injection of BNF. In addition, the enzyme activities of de novo hepatic choline phospholipid synthesis were not significantly altered at 24 hours. Following 96 hours of exposure to BNF, some differences in enzyme activity were noted; choline kinase and cytidylyltransferase activities were reduced, while cholinephosphotransferase activity was substantially increased. In light of the current information available on how induction affects liver microsomal PL metabolism in mammals, these results suggest that trout hepatic enzymes may not be able to respond with the same degree of complexity as mammalian systems to inducers of monooxygenase activity.
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