Effect of polychlorinated biphenyls (PCBs) administration on phospholipid biosynthesis in rat liver

The effect of PCBs or phenobarbital on the biosynthesis of phospholipids in hepatic endoplasmic reticulum of rats was studied by the intraperitoneal injection of [³²P]orthophosphate, [Me?¹⁴ C]choline or [2?³H]glycerol. Significant increases in liver microsomal phospholipid content after the administration of either PCBs or phenobarbital indicated the actual proliferation of endoplasmic reticulum membranes. The rate of both [³²P] and [¹⁴C] incorporations into microsomal choline-containing phospholipids, such as phosphatidylcholine, sphingomyelin and lysophosphatidylcholine, was reduced to one fifth by PCBs administration compared with control animals. The incorporation of [³²P]orthophosphate into phosphatidylethanolamine or other phospholipid classes was less or not affected, respectively, by PCBs administration. The specific inhibitory effect of PCBs on the incorporation into cholinecontaining phospholipids was not observed when [2?³-H]glycerol was used as a precursor. Phenobarbital administration, however, increased significantly the rate of [³²P] incorporation into liver phospholipids, especially phosphatidylcholine. It is suggested that the increase in microsomal phospholipid content by PCBs administration is not due to the stimulation of synthesis but to the inhibition of the catabolism of membrane phospholipids and that the increase in content caused by phenobarbital is due at least in part, to the stimulation of synthesis. The possible site(s) of PCBs-induced inhibition of phospholipid biosynthesis in rat liver is discussed.     

Hepatic microsomal phospholipids in rats exposed intratracheally to coal fly ash

The effects of intratracheal administration of fly ash (50 mg/kg body weight, daily for 7 days) on hepatic microsomal phospholipid metabolism has been studied in rats using various phospholipid precursors, viz NaH₂ ³²PO₄, (methyl-¹⁴C)-choline, and (methyl-¹⁴C)-methionine. Fly ash administration significantly increased microsomal phosphatidylcholine (PC), and lysophosphatidylcholine (LPC). The incorporation of NaH₂ ³²PO₄ into total liver phospholipids, PC and Phosphatidyl ethanolamine (PE) was significantly increased in fly ash-treated rats as compared to the control. Fly ash administration also increased the incorporation of (methyl-¹⁴C)-choline into microsomal PC. Incorporation of (methyl-¹⁴C)-methionine into microsomal PC was not affected. Fly ash administration decreased the per cent distribution of arachidonic acid in PC and PE and increased that of oleic acid in PC and of linoleic acid in PE.     

Effect of phenobarbital on methyl transfer between methylated drugs and hepatic microsomal phospholipids.

The effect of phenobarbital on the incorporation of the label from N-[¹⁴C-Me]nicotine and [¹⁴C]formaldehyde into hepatic phospholipids of the rat has been studied. ¹⁴C was utilized for the formation of methylated phospholipids from both precursors. Phenobarbital elicited no significant action either on the synthesis of total hepatic phospholipids or on the incorporation of radioactivity into the total or individual liver phospholipid fractions. However, this treatment increased phospholipid content and the uptake of the label from nicotine into microsomal phospholipids. Phenobarbital raised microsomal phosphatidylethanolamine, -choline (PC), -serine (PS), and lysophosphatidylcholine contents and the incorporation of ¹⁴C-labeled methyl groups from nicotine into PC and PS fractions. Radioactivity from [¹⁴C]formaldehyde was also incorporated into hepatic phospholipids. Phenobarbital however, had no significant effect on the incorporation either into total or microsomal phospholipids. Comparing the utilization of ¹⁴C for synthesis of liver microsomal phospholipids from N-[¹⁴C-Me]nicotine or [¹⁴C]formaldehyde with the natural methyl donor, l-[¹⁴C]-Me]methionine, greater amounts were taken up from methionine than nicotine or formaldehyde. The methyl group of nicotine was probably incorporated into phospholipids via the metabolic pool; the enhancing effect of phenobarbital on this process was associated with increased metabolism and with increased methyl transfer into methyl group containing microsomal phospholipids.     

Covalent binding in vitro of polychlorinated biphenyls to microsomal macromolecules. Involvement of metabolic activation by a cytochrome P-450-linked mono-oxygenase system.

Incubation of ¹⁴C-labeled polychlorinated biphenyls (PCBs) with rat, mouse or rabbit liver microsomes in the presence of an NADPH-generating system and molecular oxygen caused covalent binding of radioactive metabolites of PCBs to microsomal macromolecules. The binding was more pronounced with liver microsomes from animals pretreated with inducers of the microsomal mono-oxygenase system. The order of induction effect of the inducers used was KC-500 (a PCB preparation containing 55% chlorine) ≥ phenobarbital (PB) ? 3-methylcholanthrene (3-MC) in rats, PB > KC-500 > 3-MC in mice, and PB > KC-500 in rabbits. [¹⁴C]KC-300 (a PCB preparation containing 42% chlorine) was more effective than [¹⁴C]KC-500 as substrate for all the microsomal preparations. The binding reaction was dependent on both NADPH and oxygen, sensitive to carbon monoxide, glutathione, cysteine, hexobarbital, and aniline, and enhanced by EDTA, which inhibits lipid peroxidation. The addition of NADH, which was by itself a very poor electron donor, caused a synergistic increase of the NADPH-dependent binding of PCBs. It is concluded that the conversion of PCBs to active metabolites by the cytochrome P-450-linked mono-oxygenase system is prerequisite to the binding reaction. A survey of the effects of various inducers suggested that a cytochrome P-450 having a high aminopyrine N-demethylation activity is mainly responsible for the metabolic activation of PCBs in liver microsomes. Kidney and lung microsomes from untreated rats were virtually devoid of the PCB-binding capacity, but in kidney microsomes this capacity could be induced by pretreatment with 3-MC or KC-500, though not with PB.     

The effect of cytochromes P4501A induction and inhibition on the disposition of the cognition activator tacrine in rat hepatic preparations

1. The disposition of tacrine 1,2,3,4-tetrahydro-9-acridinamine monohydrochloride monohydrate (THA, Cognex®), was studied using livers obtained from control, phenobarbital (PB), isosafrole (ISO), and 3-methylcholanthrene (3-MC) treated rats.

2. Pretreatment of rats with PB, ISO, and 3-MC reduced AUC_{(10–120 min)} of THA in liver perfusates by 28, 32, and 86% respectively.

3. Elimination of [¹⁴C]-THA-derived radioactivity into bile was 7.6 ± 1.2%, 11.7±2.9%, 14.8 ± 2.0%, and 46.3±9.7% (mean ± SD) of the infusion dose for control, PB, ISO, and 3-MC pretreated isolated perfused rat livers, respectively.

4. In perfusion experiments using 3-MC pretreated livers, a marked increase in irreversible protein binding of 3-, 7-, and 8-fold was observed to microsomal, cytosolic and total liver proteins, respectively, compared to control. Only a slight effect was observed on protein binding in perfusion experiments using PB and ISO pretreated animals.

5. Co-incubations of [¹⁴C]-THA with the metabolic inhibitors enoxacin, ethimizol, and furafylline in hepatocyte preparations obtained from 3-MC pretreated rats markedly inhibited THA-derived irreversible protein binding. Furafylline, a specific inhibitor of cytochrome P4501A2, had the greatest inhibitory effect (approximately 70%).

6. These results are consistent with a major role of cytochrome P4501A in the metabolism and irreversible protein binding of THA in rat liver and demonstrate the utility of isolated liver perfusion and hepatocyte models for examining the effect of metabolic modulators.     

Effects of dl-propranolol on the synthesis of glycerolipids by rabbit iris muscle

Propranolol (0.03?0.3 mM), an amphiphilic cationic drug which is used therapeutically as a β-blocker, was found to alter significantly the incorporation of [¹⁴C]glucose, [¹⁴C]glycerol, [¹⁴C]acetate, ³²Pi, [³H]cytidine, [³H]inositol, [¹⁴C]choline, [¹⁴C]ethanolamine and [¹⁴C]serine into phospholipids of the iris muscle. Furthermore, it was found to exert a stimulatory effect on the [¹⁴C]serine incorporation into phosphatidylserine of the muscle and microsomes. In contrast, sotalol, another β-blocker-but lacking the hydrophobicity of propranolol-exerted no effect on lipid metabolism. Whereas norepinephrine stimulated only the turnover of the phosphate moiety of phosphatidic acid and phosphatidylinositol, in general propranolol caused the following changes: (a) it stimulated by 2- to 6-fold the labelling of phosphatidic acid and phosphatidylinositol from [¹⁴C]glucose, [¹⁴C]glycerol, [¹⁴C]acetate, ³²Pi and [³H]inositol, (b) it increased by 5- and 38-fold the incorporation of ³²Pi and [³H]cytidine, respectively into CDP-diglyceride, (c) it inhibited appreciably the incorporation of [¹⁴C]glucose, [¹⁴C]glycerol, [¹⁴C]acetate and ³²Pi into phosphatidylcholine and phosphatidylethanoalmine. However, while it inhibited significantly the [¹⁴C]choline incorporation into the former, it stimulated by 60 per cent the ethanolamine incorporation into the latter phospholipid. These results indicate that propranolol probably redirects phospholipid synthesis de novo, by inhibiting phosphatidate phosphohydrolase, such that the increase obtained in the biosynthesis of phosphatidylinositol is accompanied by a corresponding decrease in the synthesis of phosphatidylcholine and phosphatidylethanolamine.Propranolol also caused a 250 per cent increase in the [¹⁴C]serine incorporation into phosphatidylserine of the iris muscle and 28 per cent increase in that of microsomes. The drug appears to stimulate the Ca²⁺ -uptake by muscle and microsomes, which in turn could act to stimulate the Ca²⁺-catalyzed base-exchange reaction.In addition the metabolic pathways involved in the biosynthesis of the major phospholipids of the iris, a smooth muscle, are reported for the first time. These pathways were found to be essentially similar to those reported for other tissues.     

Mechanism of induction of hepatic drug-metabolizing enzymes by ethanol—I: Limited role of microsomal phospholipids

Two groups of female Sprague-Dawley rats were pair-fed nutritionally adequate liquid diets containing 36 per cent of total calories as ethanol or additional carbohydrate (controls). One group was fed a high fat diet (35 per cent of total calories as fat); the other group was fed a low fat diet (2 per cent of total calories as linoleate as the only source of fat). When given with the high fat diet, ethanol increased cytochrome P-450 and microsomal phospholipid content per g of liver. When given with a low fat diet, it increased cytochrome P-450 to a lesser extent and did not alter the microsomal phospholipid content when expressed per g of liver or per 100 g of body weight. Phosphatidylcholine accounted for the greater porportion of phospholipids and was increased by ethanol only with the high fat diet. L-Methionine-methyl[³H] and [¹⁴C]choline incorporation into phosphatidylcholine was unaltered by ethanol in either model. The fatty acid composition of phosphatidylcholine was altered by ethanol more significantly with the high fat diet. Since ethanol similarly enhances the activity of benzphetamine demethylation in both dietary models, quantitative and qualitative differences in microsomal phospholipids produced by ethanol are probably not responsible for the induction by ethanol of this drug-metabolizing enzyme activity. Further evidence to that effect was obtained from the measurement of benzphetamine demethylation in vitro by partially purified cytochrome P-450, reductase and lipid fractions of ethanol-fed and control rats fed a high fat diet. The stimulation of benzphetamine demethylation by the lipid fraction was identical whether using lipids from microsomes of ethanol-fed animals or control animals. Dietary fat plays a role in the induction by ethanol of cytochrome P-450 and NADPH-cytochrome P-450 reductase and on microsomal phospholipid content and composition. The effects of ethanol on microsomal phospholipids are probably not related to the induction of benzphetamine demethylation activity.     

Effect of chlorpromazine on protein, phospholipid and RNA synthesis or degradation in rat liver

Chlorpromazine (CPZ) administration to rats (25 mg/kg ip) significantly stimulated (14C)-leucine incorporation to liver microsomal proteins, (14C)-orotic acid incorporation to liver RNA and (32P) incorporation to liver microsomal lipids. CPZ administration did not modify the decay of radioactivity of liver microsomal lipids prelabeled with (32P) or that of microsomal proteins prelabeled with [(14C)-guanidino]-arginine. Results suggest that CPZ administration stimulates protein, phospholipids and RNA synthesis but does not affect their degradation. The relation of these findings with CPZ preventive effects on CCl4-induced liver injury is discussed.     

Modifications of phospholipid metabolism induced by chlorpromazine, desmethylimipramine and propranolol in C6 glioma cells

The effects of chlorpromazine (CPZ), desmethylimipramine (DMI) and propranolol (PRO) on phospholipid metabolism in C6 glioma cells were studied by following the incorporation of 32Pi, [U-14C]glycerol, [2-3H]glycerol and [1-14C]oleate into lipids. The drugs produced a dose-dependent increase in the incorporation of 32Pi and [U-14C]glycerol, but not of [1-14C] oleate, into total phospholipids, that reached a plateau at 200 microM CPZ and 500 microM DMI and PRO. The three drugs shifted the incorporation of precursors from neutral [phosphatidylcholine (PC) and phosphatidylethanolamine (PE)] to acidic phospholipids [phosphatidic acid (PA), phosphatidylinositol (PI), phosphatidylglycerol, phosphatidylinositol-4-phosphate (PIP) and phosphatidylinositol-4,5-bisphosphate (PIP2)] in a dose-dependent, qualitatively similar manner. The incorporation of [2-3H]glycerol into diacylglycerol was also depressed markedly by CPZ. Addition of 1 mM 1,2-dioleoylglycerol, 1-oleoyl-2-acetylglycerol or oleate only partially reversed the decrease in PC labeling caused by CPZ. 12-O-Tetradecanoylphorbol-13-acetate counteracted this effect of CPZ completely but greatly increased PC labeling even in the absence of the drug. Polyphosphoinositides rapidly incorporated 32Pi at early times reaching a plateau in about 40 min. The labeling rate of PI was not parallel to that of PIP or PIP2 and continued to increase even after the polyphosphoinositides had reached a plateau. CPZ increased PI labeling much more than that of PIP and PIP2. These data suggest that cationic amphiphilic drugs may act by inhibiting CTP:phosphocholine cytidylyltransferase, thus decreasing incorporation of precursors into PC and PE; inhibiting PA phosphohydrolase with increased formation of phosphatidyl-CMP, the intermediate for the synthesis of acidic phospholipids; and stimulating the inositol exchange reaction, forming a pool of PI that is not available for PIP and PIP2 synthesis.     

An in vitro study of hemicholinium-3 on phospholipid metabolism of Krebs II ascites cells

With [Me-¹⁴C]choline as marker and after separation of choline and phosphocholine by ion-exchange column chromatography or thin layer chromatography on alumina, it is shown that 40 μM hemicholinium-3 (HC-3) inhibits the cytosolic choline-kinase of rat liver and Krebs cells. This inhibition is competitive (Km different, Vm similar) in the first case and mixed in the second (Km and Vm different). Despite this general inhibition of the phosphocholine formation, the synthesis of phosphatidylcholine (PC) by post-nuclear supernatants of rat liver and Krebs cells is different when tested with HC-3. It is unaffected in rat liver; however, HC-3 induces a PC deficiency in Krebs cells which is time-course dependent between 15 and 120min and proportional to the drug concentrations in the interval 5–40 μM. Incorporation of AT-[γ³²P] or [2-¹⁴C]ethanolamine into phospholipids shows that the sequential methylation pathway is not detectable in Krebs cells. These results are discussed in relation to those established concerning HC-3 action on phospholipid metabolism in other tissues.     

Effect of pentobarbital on regional brain phospholipid synthesis

Rats were given 45 mg/kg i.p. sodium pentobarbital 15 min prior to the intraventricular injection of 200 μCi [³²P]phosphoric acid and 50 μCi [³H]glycerol. The animals were sacrificed 1 hr later, subcellular fractions were prepared from four subcortical brain regions and phospholipids were extracted. Pentobarbital significantly increased the ratio of [³H]- and [³²P]-triphosphatidylinositol (TPI) to diphosphatidylinositol (DPI) in the microsomal but not synaptosomal fractions. The possible relationship of this change to nicotinic receptor activity is discussed. Pentobarbital specifically decreased ³²Pi but not [³H]glycerol incorporation into synaptosomal phosphatidylinositol (PI). Thus, pentobarbital induced the opposite of the “neurotransmitter effect” on PI turnover. Pentobarbital either decreased or had no effect on the incorporation of ³²Pi and [³H]glycerol into phosphatidylserine (PS), phosphatidylcholine (PC) and phosphatidylethanolamine (PE).     

AMIODARONE-INDUCED PHOSPHOLIPIDOSIS: AN IN VIVO [14C]-ACETATE UPTAKE STUDY IN RAT

ABSTRACT

Amiodarone (AD), a potent antiarrhythmic drug, is often associated with several adverse effects. It is shown to accumulate phospholipids in various tissues, and the impaired catabolism of phospholipids has been implicated in AD-induced phospholipidosis. The synthesis of phospholipids in tissues has not been dealt with. Hence, the incorporation of [¹⁴C]-acetate into phospholipids has been studied to understand the AD-induced phospholipidosis in lung and liver. A significant increase in lung and liver phospholipids was observed after 21 and 28 days of AD (175 mg/kg body weight/day) treatment. In the lung and liver, the incorporation of [¹⁴C]-acetate into all phospholipid fractions was elevated, while in the lung mitochondria phosphatidylcholine, phosphatidyl ethanolamine and the cardiolipin levels were significantly increased. The results indicate that, in addition to the impaired catabolism of phospholipid, AD treatment resulted in increased phospholipid synthesis.     

Studies on the mechanism of alteration by propranolol and mepacrine of the metabolism of phosphoinositides and other glycerolipids in the rabbit iris muscle

We have investigated the effects and mechanism of action of propranolol and mepacrine, two drugs with local anesthetic-like properties, on phospholipid metabolism in rabbit iris and iris microsomal and soluble fractions. In the iris, propranolol, like mepacrine [A. A. Abdel-Latif and J. P. Smith, Biochim, biophys. Acta 711, 478 (1982)], stimulated the incorporation of [14C]arachidonic acid ( [14C]AA) into phosphatidic acid (PA), CDP-diacylglycerol (CDP-DG), phosphatidylinositol (PI), the polyphosphoinositides (poly PI) and DG, and it inhibited that of phosphatidylcholine (PC), phosphatidylethanolamine (PE), triacylglycerol (TG) and the prostaglandins. Similarly, mepacrine, like propranolol [A. A. Abdel-Latif and J. P. Smith, Biochem. Pharmac. 25, 1697 (1976)], altered the incorporation of [14C]oleic acid, [3H]glycerol, 32Pi and [14C]choline into glycerolipids of the iris. Time-course studies in iris muscle prelabeled with [14C]AA showed an initial decrease in the production of DG and a corresponding increase in that of PA by the drugs, followed by an increase in accumulation of DG at longer time intervals (60-90 min). The above findings are in accord with the hypothesis that these drugs redirect glycerolipid synthesis by inhibiting PA phosphohydrolase. Propranolol and mepacrine stimulated the activities of DG kinase and phosphoinositide kinases and inhibited that of DG cholinephosphotransferase. The drugs had little effect on the activity of DG acyltransferase. It is concluded that propranolol and mepacrine redirect glycerolipid metabolism in the iris by exerting multiple effects on the enzymes involved in phospholipid biosynthesis. We suggest that these drugs could exert their local anesthetic-like effects by effecting an increase in the synthesis of the acidic phospholipids (PA, PI and the poly PI) and subsequently the binding of Ca2+- to the cell plasma membrane.     

Alterations in metabolism of cytidine components in rat liver after oral administration of butylated hydroxytoluene (in vivo study)

The administration of the antioxidant, butylated hydroxytoluene (BHT) to rats decreased the utilization of [2-14C]orotic acid for the synthesis of cytidine nucleotides in the acid-soluble extract and RNA of the liver. The specific activity of the uridine components was slightly decreased. The depression of the specific activity of the cytidine components depended on the dose of the drug. Simultaneously preformed [U-14C]cytidine in experimental rats was to a higher degree transported to the liver and incorporated into RNA cytosine; its deamination was markedly suppressed. Both phenomena depend on the BHT dose. The concentration of both the uridine and the cytidine components of the acid-soluble extract remained unaffected by the administration of BHT. The utilization of [2-14C]orotic acid for the synthesis of DNA cytosine was depressed after the administration of BHT; by contrast, the specific activity of DNA thymine was higher. The incorporation of [1-14C]palmitic acid into microsomal phospholipids was not substantially influenced over the dose range 25--500 mg BHT/kg. The specific activity of neutral lipids in microsomes increased.     

Liver lipid metabolism in T-2 toxicosis

The acute effects of oral administration of a single dose of T-2 toxin (2.0 mg/kg body wt) to rats on whole liver lipid metabolism were studied at 8, 16 and 24 h post-treatment. Administration of T-2 toxin significantly increased liver and microsomal total lipids, free cholesterol, esterified cholesterol and triglycerides initially at 8 h, which subsequently returned to control values at 24 h. However, no significant alterations were observed in the contents of whole liver and liver microsomal total phospholipids and phosphatidyl choline, except that phosphatidyl ethanolamine and sphingomyelin + lysophosphatidyl ethanolamine contents in liver at 16 and 24 h and sphingomyelin + lysophosphatidyl ethanolamine content in liver microsomes at all three periods were significantly lower. The incorporation of 1-¹⁴C-acetate into whole liver and liver microsomal total lipids was reduced at 16 and 24 h post feeding. However, the incorporation of 1-¹⁴C-acetate into liver and microsomal free cholesterol, esterified cholesterol and triglycerides was significantly higher at 8 h, subsequently returning to the control value at 24 h; incorporation was significantly lower even into microsomal triglycerides. The incorporation of 1-¹⁴C-acetate into liver and its microsomal total phospholipids, phosphatidyl choline, phosphatidyl ehtanolamine and sphingomyelin + lysophosphatidyl ethanolamine, was significantly decreased at all three periods post toxin treatment. The results suggested that T-2 toxin inhibited the incorporation of ¹⁴C-acetate mainly into liver and its microsomal phospholipids and their subfractions in rats.     

Factors influencing the microsome- and mitochondria-catalyzed in vitro binding of diethylnitrosamine and N-nitrosopiperidine to deoxyribonucleic acid.

[¹⁴C]Diethylnitrosamine ([¹⁴C]DEN) and [¹⁴C]N-nitrosopiperidine ([¹⁴]NPiP) bind covalently to calf thymus DNA in an in vitro incubation system containing rat liver microsomes. The reaction is NADPH-dependent. Pretreatment of the animals with phenobarbital (PB) enchances the binding of both DEN and NPiP to DNA, whereas the binding of DEN to DNA decreases after 3-methylcholanthrene pretreatment. The PB effect, as observed from the binding of DEN to DNA. is more pronounced in young rats than in the older animals. Addition of cytosol to the incubation system enhances the binding of DEN 3- to 4-fold and the binding of NPiP 2- to 3-fold. Addition of mitochondria to the incubation system increases the binding of [¹⁴C]DEN only slighty. but increases the binding of NPiP more than 5-fold. Addition of mitochondria has no effect on the binding of [¹⁴C]dimethylnitrosamine ([¹⁴C]DMN). Mitochondria alone markedly catalyze the binding of NPiP to DNA. Addition of benzylamine. which is a substrate of mitochondrial monoamine oxidase as well as an inhibitor of DMN-demethylase, inhibits the binding of NPiP catalyzed by microsomes and microsomes plus mitochondria.     

Phosphatidylcholine metabolism in lung microsomes and lung surfactant of rats exposed intratracheally to coal fly ash

The effect of intratracheal administration of fly ash has been studied on lung microsomal and lung surfactant phosphatidylcholine (PC) metabolism in rats using [methyl-14C]choline and [methyl-14C]methionine. Fly-ash administration significantly increased total phospholipids, PC, phosphatidylethanolamine (PE), and phosphatidylglycerol (PG) of lung surfactant. Fly-ash administration stimulated the formation of lung microsomal PC (as measured by the incorporation of labeled precursors) both by the cytidine 5'-diphosphate (CDP)-choline pathway and by the N-methylation pathway, but this stimulation was fourfold higher in the latter case and only twofold higher in the former as compared to the control. Likewise, the secretion of PC formed by the N-methylation pathway was sixfold higher as compared to the control whereas secretion of PC formed by the CDP-choline pathway was only threefold higher as compared to the control. Fly-ash administration further increased total saturation and decreased unsaturation in PC, PE, and lysophosphatidylcholine (LPC) of lung and in PC, PE, LPC, and PG of lung surfactant as compared to the controls.     

Altered lipid metabolism in 2,5-hexanedione-induced testicular atrophy and peripheral neuropathy in the rat

2,5-Hexanedione (HD) induces testicular atrophy and peripheral neuropathy in rats. Since altered lipid metabolism is frequently associated with these disease states, lipid metabolism was investigated in vitro in testes and sciatic nerves of rats fed 1% HD in the drinking water for 6 weeks. Testes from HD-treated rats were 30–60% smaller and weighed threefold less than testes from pair-fed control (PFC) rats. Compared to testes from PFC rats, testes from HD rats exhibited increased incorporation of [¹⁴C]acetate into phospholipids (344%), triacylglycerols (281%), and cholesteryl esters + hydrocarbons (246%) but decreased incorporation into free fatty acids (25%) and sterols + diacylglycerols (65%). The increased incorporation of [¹⁴C]acetate into phospholipids induced by HD reflected an approximate 300% increase into phosphatidyl choline, lysophosphatidyl choline, phosphatidyl serine + phosphatidyl inositol, and phosphatidyl ethanolamine and a disproportionate 800% increase into sphingomyelin. HD rats exhibited clinical signs of peripheral neuropathy, including everted and flat foot placement and hindlimb weakness; similar changes were not observed in PFC rats. In sciatic nerves, the incorporation of [¹⁴C]leucine was decreased into sterols + diacylglycerols (47%), digitoninprecipitable sterols (45%), and cholesteryl esters + hydrocarbons (40%) in HD compared to PFC rats; incorporation of [¹⁴C]leucine into free fatty acids, triacylglycerols, and phospholipids was similar in HD and PFC rats. In contrast to the testis and nerve, lipid metabolism in the liver was similar in HD and PFC rats. The concentrations of 2,5-hexanedione and 2,5-dimethylfuran, respectively, were 0.6 ± 0.3 and 6.5 ± 0.9 μg/g wet weight in the testes and 3.1 ± 0.4 and 3.0 ± 0.4 μg/g wet weight in the livers of HD rats. The data indicate that altered metabolism is associated with HD-induced testicular atrophy and distal axonopathy.     

Effect of chronic intoxication with (+)-amphetamine on its concentration in liver and brain and on (14C) leucine incorporation into microsomal and cytoplasmic proteins of rat liver

Rats were treated with increasing concentrations of (+)-amphetamine sulphate in drinking water for 90 days. The ingested dose of amphetamine was found to increase from 16 mg kg^?1 on the first day up to 90 mg kg^?1 on the 32nd day of treatment. The rats were maintained on the highest dose regime for a further 58 days without any deaths, which showed that tolerance to the overall toxicity of the drug developed. The concentrations of [³H]amphetamine in liver and brain of chronically treated rats were significantly higher than those of controls. Chronic treatment with amphetamine significantly reduced body and liver weight of rats, but did not influence the relative liver to body weight. A marked inhibition of [¹⁴C]leucine incorporation into liver microsomal and cytoplasmic proteins was observed after 90 days of treatment with amphetamine. The relation between inhibition of microsomal protein synthesis and the increase of amphetamine concentrations in liver and brain is discussed.     

Metabolism of 2,5,2′-trichloro-, 2,5,2′,5′-tetrachloro-, and 2,4,5,2′,5′-pentachlorobiphenyl in rat hepatic microsomal systems

The polychlorinated biphenyls (PCBs) are important environmental contaminants. The relationship between degree of chlorination of these compounds and metabolism in rat liver microsomes was studied. [¹⁴C]2,5,2′-trichloro-, [¹⁴C]2,5,2′,5′-tetrachloro-, and [¹⁴C]2,4,5,2′,5′-pentachlorobiphenyl were incubated with a NADPH-generating system in microsomal systems prepared from phenobarbital-pretreated rats. Metabolites were isolated, purified by thin-layer chromatography and identified by mass spectroscopy. It was found that the number and quantitative significance of metabolites decreased with increasing degree of chlorination of PCBs. The approximate percentages of the applied doses recovered as metabolites after 4-hr incubation were 62% for trichlorobiphenyl, 36% for tetrachlorobiphenyl, and 7% for pentachlorobiphenyl. The major metabolite of each PCB was identified as a monohydroxylated product.