Sex differences in the metabolism of hexachlorobenzene by rats and the development of porphyria in females

Male and female F 344 rats were dosed every other day for 103 days with 50 μmole of hexachlorobenzene (HCB)/kg. Females developed a hepatic porphyria, the urine and liver levels of porphyrins being 40- and 310-fold high respectively than those of males. Urine was periodically hydrolysed and analysed for the three metabolites pentachlorophenol, 2,3,5,6-tetrachlorobenzene-1,4-diol and pentachlorothiophenol (derived from the mercapturate). The combined urinary excretion of these was greater in females than males, especially during the first 10 weeks. Pentachlorthiophenol was particularly high in female urine. After 103 days this metabolite was slightly less in female faeces than in male's but free hepatic pentachlorothiophenol was 3.6-fold greater. Although total 24 hr excretions of metabolites were higher by females than males and after 7 daily doses of HCB, a difference in this respect was not conclusively proven. However, total pentachlorothiophenol excretion was always significantly greater by females. The male/female ratios for pentachlorophenol and pentachlorothiophenol in bile were identical to those for faeces. Excretion of metabolites by both adult males and females was stimulated by pretreatment with diethylstilboestrol (DES). No sex differences in metabolism were observed with immature rats.     

Hepatic arachidonic acid metabolism is disrupted after hexachlorobenzene treatment

Hexaclorobenzene (HCB), one of the most persistent environmental pollutants, can cause a wide range of toxic effects including cancer in animals, and hepatotoxicity and porphyria both in humans and animals. In the present study, liver microsomal cytochrome P450 (CYP)-dependent arachidonic acid (AA) metabolism, hepatic PGE production, and cytosolic phospholipase A2 (cPLA2) activity were investigated in an experimental model of porphyria cutanea tarda induced by HCB. Female Wistar rats were treated with a single daily dose of HCB (100 mg kg(-1) body weight) for 5 days and were sacrificed 3, 10, 17, and 52 days after the last dose. HCB treatment induced the accumulation of hepatic porphyrins from day 17 and increased the activities of liver ethoxyresorufin O-deethylase (EROD), methoxyresorufin O-demethylase (MROD), and aminopyrine N-demethylase (APND) from day 3 after the last dose. Liver microsomes from control and HCB-treated rats generated, in the presence of NADPH, hydroxyeicosatetraenoic acids (HETEs), epoxyeicosatrienoic acids (EETs), 11,12-Di HETE, and omega-OH/omega-1-OH AA. HCB treatment caused an increase in total NADPH CYP-dependent AA metabolism, with a higher response at 3 days after the last HCB dose than at the other time points studied. In addition, HCB treatment markedly enhanced PGE production and release in liver slices. This HCB effect was time dependent and reached its highest level after 10 days. At this time cPLA2 activity was shown to be increased. Unexpectedly, HCB produced a significant decrease in cPLA2 activity on the 17th and 52nd day. Our results demonstrated for the first time that HCB induces both the cyclooxygenase and CYP-dependent AA metabolism. The effects of HCB on AA metabolism were previous to the onset of a marked porphyria and might contribute to different aspects of HCB-induced liver toxicity such as alterations of membrane fluidity and membrane-bound protein function. Observations also suggested that a possible role of cPLA2 in the early increase of AA metabolism cannot be excluded. However, the existence of other pathway(s) for metabolizable AA generation different from cPLA2 activation is also proposed.     

The delay in polyhalogenated aromatic hydrocarbon-induced porphyria: the effect of diet preparation

Porphyria development in female Wistar rats has been followed by dosing the animals with hexachlorobenzene (HCB) either dissolved in corn oil or as a solid mixed with the diet. It was found that the corn oil preparation resulted in much faster uptake of HCB into the liver, and much faster accumulation of liver porphyrins. Diet preparation is thus shown to be a major factor in determining whether the development of porphyria is associated with the delay phenomenon. Evidence is also presented suggesting that the neurological symptoms of porphyria are not caused by high porphyrin levels.     

Hexachlorobenzene-induced porphyria in Japanese quail. Effect of pretreatment with phenobarbital or beta-naphthoflavone

In an effort to determine the role that metabolism by the cytochrome P-450 system plays in the development of hexachlorobenzene (HCB)-induced porphyria, Japanese quail were pretreated with either beta-naphthoflavone (BNF) or phenobarbital (PB) and then treated with HCB. PB or BNF pretreatment appeared to have no effect on the response of quail hepatic enzymes to HCB. There were no differences between the two groups in either the content of cytochrome P-450 or the activities of NADPH-cytochrome c reductase, glutathione transferase (microsomal or cytosolic), ethoxycoumarin-O-deethylase or ethoxyresorufin-O-deethylase following HCB treatment. These pretreatments did, however, markedly influence the development of porphyria in quail. BNF-treated birds had higher delta-aminolevulinic acid-synthetase (ALA-S) activities and developed porphyria much more rapidly than birds treated with HCB alone. Birds pretreated with PB did not exhibit porphyria even following 10 days of HCB. Although the ALA-S activities in this group were elevated slightly following HCB, they were about one-half of those seen in the BNF-pretreated HCB-treated group. These results may reflect a difference between the PB and BNF groups in the production of a porphyrogenic metabolite of HCB.     

Metabolism of the "mixed" cytochrome P-450 inducer hexachlorobenzene by rat liver microsomes

Hexachlorobenzene (HCB) was metabolised by phenobarbital-induced liver microsomes from male rats to pentachlorobenzene, pentachlorophenol, tetrachloro-1,2-benzenediol and tetrachloro-1,4-benzenediol (1:88:2:9). Metabolites were identified and quantified by electron capture g.l.c. Structures were confirmed by selective ion monitoring g.l.c.-m.s. The formation of pentachlorophenol was dependent on the presence of NADPH and O2 and inhibited by CO, SKF 525A and metyrapone. Conversion of HCB to pentachlorophenol was stimulated by pretreatment of rats with phenobarbital (PB) but not by 3-methylcholanthrene (3-MC), or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). In contrast, the conversion of pentachlorophenol to tetrachloro-1,4-benzenediol was markedly induced by 3-MC but poorly by PB. HCB, Aroclor 1254 and isosafrole stimulated both hydroxylations. The cytochrome P-450c inhibitor 9-hydroxyellipticine inhibited conversion of pentachlorophenol to tetrachlorobenzenediols by HCB and beta-naphthoflavone induced micromes. In addition to hydroxylation reactions, evidence was obtained for the conjugation of HCB with glutathione catalysed by a microsomal glutathione transferase. Radioactivity from [14C]HCB was bound to microsomal protein during aerobic incubations. Binding was inhibited by GSH and N-acetyl-cysteine. Preliminary studies suggested that the reactive species was derived from tetrachloro-1,4-benzoquinone. No correlation was found between levels of metabolites or covalent binding produced by the two sexes and the marked sex dependent hepatic porphyrogenic and carcinogenic effects of HCB.     

Effects of pentachlorophenol on rat liver changes induced by hexachlorobenzene,with special reference to porphyria,and alterations in mixed function oxygen ases

Hexachlorobenzene (HCB, 1000 ppm) and 500 ppm pentachlorophenol (PCP) were fed separately or in combination to female Wistar rats. A control group was provided with standard food without HCB or PCP. Subgroups of 4 rats were killed after 1,2,4,6 and 8 weeks. No significant difference was found between the amounts of HCB accumulated in the livers of the HCB and HCB + PCP fed rats. Administering HCB together with PCP caused a noticeable accumulation of PCP in the liver, compared to the results after administering HCB and PCP separately. In the HCB and HCB + PCP fed groups liver weight increased continuously during the experiments. Microsomal cytochrome P-450, NADPH-cytochrome c reductase, ethoxyresorufin O-de-ethylase, aminopyrine N-demethylase, and glucuronyl transferase increased to a maximum in 2–4 weeks in HCB and HCB + PCP fed rats. Pentachlorophenol accelerates the onset of HCB porphyria, in other words it increases the total urinary porphyrin excretion and causes an earlier disturbance of the porphyrin pattern.     

The role of type I and type II 5' deiodinases on hexachlorobenzene-induced alteration of the hormonal thyroid status

Treatment of male Wistar rats with hexachlorobenzene (HCB) (1000 mg/kg b.w.) for 3-30 days decreases circulating levels of thyroxine (T4) but does not affect triiodothyronine (T3). Time courses were determined for 5' deiodinase type I (5' D-I) activity in thyroid, liver, and kidney and 5' deiodinase type II (5' D-II) activity in brown adipose tissue (BAT) to test the possibility that increased deiodinase activity might contribute to the maintenance of the serum T3 level. Specific 5' D-I activity was increased in the thyroid at 21 days and thereafter. No significant changes were observed in the liver, however, total 5' D-I activity in this tissue was increased at 30 days of treatment as a consequence of liver weight enhancement. HCB decreased kidney 5' D-I activity after 15 days, and BAT 5' D-II activity after 21 days of treatment. Total body 5' D-I activity was significantly increased by 30 days of HCB-treatment. HCB increased the activity of hepatic T4 uridine diphosphoglucuronosyl transferase (UDPGT) in a time-dependent manner, without changes in T3 UDPGT. We propose that increased T4 to T3 conversion in the thyroid and in the greatly enlarged liver may account for the maintenance of serum T3 concentration in hypothyroxinemic HCB-treated rats.     

Induction of rat cytochrome P-450 3 and its mRNA by 3,4,5,3',4',5'-hexachlorobiphenyl

Rat cytochrome P-450 3 (P-450 3) is a constitutive hepatic steroid hormone 7 alpha-hydroxylase which is relatively unresponsive to a number of monooxygenase-inducing agents. The present study demonstrates that a polyhalogenated aromatic hydrocarbon inducer, 3,4,5,3',4',5'-hexachlorobiphenyl (HCB), induces P-450 3 in livers of adult male rats, and that the increase is the result of an increase in the mRNA for this enzyme. Cytochrome P-450 3 and its mRNA were increased more slowly and to a lesser extent than cytochrome P-450c (P-450c) and its mRNA, indicating that these enzymes are not regulated coordinately in liver. The maximum increase in P-450 3 and P-450 3-dependent androstenedione 7 alpha-hydroxylase activity (2- to 3-fold) occurred 7 days after administration of HCB, in contrast to the increase in P-450c (greater than 200-fold) which was maximal by 3-5 days. The rate of induction of P-450 3 mRNA was also slower [maximum increase (9-fold) at 5 days after HCB administration] than that of P-450c mRNA [maximum increase (30-fold) at 2-3 days]. Moreover, a higher dose of HCB was required to produce maximum induction of P-450 3 (50 mg/kg) than that required to produce maximum induction of P-450c (10 mg/kg). P-450 3 was not detected on Western blots of lung, kidney, or prostate microsomes isolated from control or HCB-treated rats (less than or equal to 2% of that found in livers of HCB-treated rats). Moreover, P-450 3-dependent steroid 7 alpha-hydroxylase activity was not detected in these extrahepatic tissues of control or HCB-treated rats (less than or equal to 1% of that found in the corresponding liver microsomes of untreated or HCB-treated rats). In contrast, P-450c was increased dramatically by HCB in lung, kidney, and prostate tissues, indicating differential expression of P-450c and P-450 3 in extrahepatic tissues.     

Subacute toxicity of hexachlorobenzene in the rat

Male and female rats of the Charles River strain were fed a commercial diet supplemented with 5% corn oil. Hexachlorobenzene (HCB) was added to the corn oil to give 0, 0.5, 2, 8, or 32 mg of HCB/day/kg/body weight. Subgroups of four rats of each sex were killed at 3, 6, 9, 12, and 15 weeks of feeding. To measure the reversibility of changes noted and the decline of HCB residues, the rats remaining at 15 weeks were fed an HCB-free diet and subgroups were killed after 1, 2, 4, 7, 16, and 33 weeks. Tissue residues of HCB reached a plateau before 15 weeks and were dose related, with concentrations in adipose tissue liver brain serum. In both sexes at the two highest dose levels, relative liver weight was increased when compared to control rats for most of the treatment period. Histopathological changes were confined to the liver and spleen. In the liver, there was an increase in the size of centrilobular hepatocytes. Serum sorbitol dehydrogenase activity, an indicator of liver damage, was maximally increased at 6 weeks at the highest dose level in males. Histochemically, this was related to a depletion of this enzyme in the liver. A change in distribution of other enzymes in the liver also was noted. Females developed porphyria, with high porphyrin values persisting after the rats were placed on an HCB-free diet. Pathological examination of the other organs indicated no changes. Females were more sensitive than males to the toxic effects of HCB. The overall results indicated a sex difference in the response to HCB.     

Dose-response relationships in hexachlorobenzene-induced porphyria

The rate of development of hexachlorobenzene (HCB)-induced porphyria in female Wistar rats was determined using HCB dosage and porphyrin analysis protocols designed to determine factors which contribute to the delay commonly observed between initial exposure to HCB and the detection of porphyria. Measurements were made of HCB and porphyrin concentrations in the livers, kidneys, and spleens of female Wistar rats exposed continuously (up to 56 days) or for 1 day to HCB (at dietary concentrations of 1000 ppm and 100 ppm). The experiments showed that when a corn oil solution of HCB was added to the diet at a concentration of 1000 ppm, HCB accumulated rapidly in all organs, and the delay in appearance of elevated liver highly carboxylated porphyrins (HCPs) was at most 4 days (approximately 8-fold elevation of HCPs on day 4). One day of exposure to this diet was sufficient to cause elevated liver HCPs, thus showing that continuous exposure to HCB was not required to cause porphyria in this species. Solid HCB added directly to the diet (1000 ppm) resulted in less rapid HCB accumulation and less rapid development of porphyria. The experiments demonstrated that the appearance of a delay in HCB-induced porphyria in the Wistar rat is caused by the rate at which HCB is absorbed, and by using total hepatic porphyrins (rather than HCPs) as the indicator of the disorder. The experiments also showed that HCB-induced liver enlargement and neurotoxicity are not necessarily associated with the severity of porphyria.     

Glutathione depletion and resynthesis in laboratory animals

The availability of tissue glutathione (GSH) appears to depend upon a balance between tissue concentrations, the rate of reactive metabolite formation and the re-synthesis of GSH. To test this hypothesis, diethyl maleate (DEM, 5.8 mmol/kg bw) was administered intraperitoneally to male and female mice, hamsters, rats and guinea pigs. The regeneration of hepatic and renal GSH was examined at 0.5, 1, 2, 4, 8 and 24 hr post-treatment. DEM caused a rapid and marked depletion of tissue GSH but re-synthesis began to occur by 4 hr post-treatment in all species with the exception of the guinea pig. By 24 hr after treatment, the mouse, hamster and rat had tissue levels of GSH in excess of usual values but, in the guinea pig, recovery of hepatic GSH was still significantly reduced. Considering the reported species differences in S-alkenetransferases which detoxify DEM, the present results revealed that the conjugation of DEM proceeded rapidly in all four species but that the toxicity elicited in the guinea pig may have arisen from the unavailability of GSH during the slow re-synthesis stage following maximal depletion of this agent.     

Assessment of the contribution of chlorinated dibenzo-p-dioxins and dibenzofurans to hexachlorobenzene-induced toxicity, porphyria, changes in mixed function oxygenases, and histopathological changes.

Female rats were fed 30, 100, 300, and 1000 ppm of pure and technical grades of hexachlorobenzene (HCB) for 1 week and 30, 100, and 300 ppm of each for 4 months. Technical HCB was contaminated with 200 ppm decachlorobiphenyl and 4 ppm octachlorodibenzofuran but contained no other chlorinated dibenzofurans or dibenzo-p-dioxins (<0.5 ppm). Pure HCB contained 0.5 ppm decachlorobiphenyl but no detectable amount of any chlorodibenzo-p-dioxins. Pure and technical HCB increased aryl hydrocarbon hydroxylase, aminopyrine N-demethylase, cytochrome P-450, glucuronyl transferase, and liver/body weight ratios comparably at each dose level. Neither grade of HCB shifted the peak of the CO-difference spectrum or altered the 455:430 ratios of the ethyl isocyanide difference spectra appreciably. Livers, lungs, adrenals, and hearts were evaluated histologically. Enlargement of liver cells was seen at 100 and 300 ppm HCB. Marked hypertrophy and proliferation of the lining endothelial cells of the smaller pulmonary blood vessels was observed in rats fed 100 and 300 ppm HCB. At 100 ppm, the number of affected vessels was usually greater in rats fed technical HCB than in those fed pure HCB. At 300 ppm, the pulmonary effects of pure and technical HCB were identical. The porphyria, cutaneous lesions, hyperexcitability, changes in liver enzymes, and morphological changes in the liver were identical in rats fed pure and technical HCB at all dose levels, indicating that these changes were produced by HCB, rather than chlorinated dibenzofuran or dibenzodioxin contaminants.     

Development of an Experimental Model for the Study of Hexachlorobenzene-Induced Hepatic Porphyria in the Rat

Development of an Experimental Model for the Study of Hexachlorobenzene-InducedHepatic Porphyria in the Rat. KRISHNAN, K., BRODEUR, J., ANDCHARBONNEAU, M. (1991). Fundam Appl. Toxicol 17, 433-441. Hexachlorobenzene(HCB) induces hepatic porphyria in rats. Various protocols ofrepeated cumulative and daily doses of HCB administered forseveral weeks until porphyria develops have been traditionallyused. In order to undertake studies on early biochemical eventsoccurring in HCB-induced porphyria, we have designed an experimentalmodel involving the administration of a minimal amount of HCBinducing a fully developed porphyria in a well defined and predictabletime frame. Groups of Sprague-Dawley rats were given (po, in10 ml/kg of corn oil) a cumulative dose of 1500 mg HCB/kg as50 mg/kg for 6 weeks (5 days/week) or 100 mg/kg for 3 weeks(5 days/week). In female, but not male, rats treated for 6 weeks,HCB caused a porphyria as measured by urinary uroporphyrin andhepatic porphyrin levels: this total dose given to female ratsin 3 weeks was not, however, porphyrinogenic. Female rats weregiven 12 consecutive daily doses of 50 mg HCB/kg followed bya no-treatment period of 30 days: this cumulative dose of 600mg HCB/kg induced a porphyria after 6 weeks. The approximateminimally effective cumulative dose inducing porphyria was determinedto be 400 mg HCB/kg, regardless of the magnitude of the dailydose (25, 50, or 100 mg/kg). Finally, the administration ofa cumulative dose of 500mg HCB/kg (50 mg/kg, 5 days/week for2 weeks or 100 mg/kg/day for 5 days) induced after 5 to 6 weeksa porphyna that persisted for more than 500 to 600 days. Theseresults suggest that induction of porphyria is dependent uponthe administration of a threshold cumulative dose of HCB duringan initial phase followed by a delay period with no furthertreatment during which full development of biochemical alterationsin the heme synthesis cycle occurs.     

Effects of fasting on cadmium toxicity, glutathione metabolism, and metallothionein synthesis in rats

Acute oral toxicity of Cd (as cadmium chloride) was enhanced in rats fasted 24 hr, as shown by a markedly decreased LD50. To examine the relationship among Cd toxicity, hepatic glutathione (GSH), and metallothionein (MT) during fasting, rats were administered 75 mg Cd/kg orally 24 hr after fasting and euthanized after a further 4 or 24 hr for various assays. Serum glutamic-pyruvic transaminase activity 24 hr after Cd treatment was higher in fasted rats than in fed rats. Both total GSH and nonprotein sulfhydryl (NPSH) concentrations in liver decreased to 50% of control levels after 28 hr of fasting and returned to 75% of control values by 48 hr. Total hepatic GSH concentration in fed rats decreased 4 and 24 hr after Cd treatment, whereas that in fasted rats remained unchanged at 4 hr and decreased significantly at 24 hr. Cd uptake by the liver (both concentration and content) 24 hr after Cd treatment was higher in fasted rats than in fed rats. Hepatic MT concentration was markedly increased by Cd treatment and higher in fasted rats than in fed rats. There was no relationship between Cd toxicity and hepatic thiobarbituric acid (TBA) value, an indicator of lipid peroxidation. Fasting had no effect on hepatic GSH peroxidase and GSH reductase activities. These enzymes probably are not involved in Cd toxicity. On histological examination, focal degenerative and necrotic changes were observed from the midlobular to the pericentral region in the livers of fed rats 24 hr after Cd treatment. These changes were enhanced by fasting, diffusing from the pericentral to the periportal region. Histochemical examination revealed a heterogeneous distribution of GSH in the livers of fed rats, with strong staining of GSH in the periportal region. This heterogeneous distribution of GSH in liver was not observed in fed rats 4 hr after Cd treatment or in fasted rats at 24 hr. The present results suggest that hepatic GSH plays an important role in protection against Cd toxicity before the onset of MT synthesis. Animals in bad condition, such as that resulting from interruption of nutrient supply, cannot be protected against Cd toxicity even if the hepatic MT level is high.     

Activities of several phase I and phase II xenobiotic biotransformation enzymes in cultured hepatocytes from male and female rats

Hepatocytes were isolated from adult male and female rats and maintained in monolayer culture for up to 24 hr. The degree of preservation of representative phase I and phase II xenobiotic biotransformation enzymes was studied in these cells immediately after isolation, after attachment in culture, and after 24 hr in culture. Regarding phase I pathways, hepatocytes during 24 hr lost 50% of cytochrome P-450, but maintained high mixed function oxidase activities; 75% of aryl hydrocarbon hydroxylase and 65% of benzphetamine demethylase activities were preserved in hepatocytes from males, whereas in hepatocytes from females 70 and 50% of these activities, respectively, were maintained. Of phase II pathways, glutathione transferase activity after 24 hr, tested toward 1,2-dichloro-4-nitrobenzene as substrate, was diminished in male hepatocytes to 20% of the initial liver activity and in female cells, to 35%, whereas the activity tested toward 1-chloro-2,4-dinitrobenzene as substrate was stable. UDP-glucuronosyltransferase activities, tested toward p-nitrophenol and phenolphthalein as substrates, were slightly increased during 24 hr of culture of hepatocytes to levels higher than in liver before perfusion. The level of UDP-glucuronic acid, the endogenous substrate for the enzyme, was reduced after isolation to only 6% of the initial liver value, and then increased during culture to a level approximately 60% of normal. Thus, the changes in xenobiotic biotransformation enzymes and associated constituents in cultured hepatocytes were not uniform, although biotransformation capability remained reasonably intact.     

Comparison of hexachlorobenzene-induced alterations of microsomal membrane composition and monooxygenase activity in male and female rats

The effect of hexachlorobenzene (HCB) on microsomal cytochromes P-450 and b5, monooxygenase activity and membrane composition was examined in male and female Fischer rats. Cytochrome P-450 was induced more in male than in female animals while cytochrome b5 was induced only in males. Analysis of patterns of induction of microsomal monooxygenases showed that aminopyrine-N-demethylase activity doubled in both sexes after treatment while aryl hydrocarbon hydroxylase activity was 16 times the control value in the females and 1.5 times in the males. After HCB treatment the phospholipid content of microsomal membranes per gram of liver was increased in both sexes while cholesterol was unchanged. Analysis of the phospholipids (PL) pattern showed that the percentage of sphingomyelin (SPH) decreased significantly (50% of the control value) while phosphatidylcholine (PC), phosphatidylinositol (PI) and phosphatidylethanolamine (PE) did not change. These changes resulted in a reduction of membrane microviscosity and indicate that HCB interferes with the biosynthesis of phospholipids containing choline. Free fatty acid (FFA) content also dropped in both sexes but females were more affected; free arachidonic acid rose in females. HCB induction of microsomal cytochromes and monooxygenases is thus accompanied by marked modifications of membrane composition. Comparing the 2 sexes, HCB showed more pronounced features of 'PB type' inducers in males.     

Sex difference in the stereoselective metabolism of a new dihydropyridine calcium channel blocker, in rat studies in vivo and in vitro

1. After oral dosing with a new racemic dihydropyridine calcium channel blocker (I), plasma levels of (+/-)-I, the 3-desisopropyl metabolite (M-2), the pyridine metabolite (M-3) and the 5-desmethyl metabolite (M-10) in female rats were higher than in males, and plasma levels of (+)-I were higher than those of the (-)-enantiomer in both sexes. 2. Plasma levels of M-2 after oral dosing with (-)-I were much higher than those after dosing with (+)-I, in both male and female rats. 3. Stereoselective metabolism of I by rat liver microsomes was shown in the formation of the 3-(2'-hydroxy-1'-methylethyl) ester metabolite (M-1), and metabolites M-2 and M-10. 4. Marked sex differences were seen in the formation of M-1 and M-3 in adult rats (7 weeks of age), but not in immature rats (3 weeks of age). 5. In liver microsomes of rats pretreated with phenobarbital, the formation of M-1 was decreased in adult male rats, and formation of M-2 and M-3 was increased in adult rats of both sexes.     

The involvement of iron and lipid peroxidation in the pathogenesis of HCB induced porphyria

Hexachlorobenzene (HCB) induces a porphyria characterized by a diminished activity of the enzyme uroporphyrinogen decarboxylase (URO-D), presumably due to inactivation by reactive metabolites of HCB. We studied the effect of iron on HCB porphyria in female rats, to determine whether the iron dependent process of lipid peroxidation was involved in the pathogenesis of porphyria. We showed that malondialdehyde formation is increased in rat liver tissue of porphyric rats and that high molecular weight proteins due to cross-linking are formed. We also showed that the induction of porphyria by HCB is dependent on the presence of iron. Our findings suggest that lipid peroxidation is involved in the toxicity of HCB and that the aggravating effects of iron on HCB are mediated by lipid peroxidation.     

An investigation of sex-linked differences to the toxic and to the pharmacological actions of difenacoum: studies in mice and rats

We have investigated the actions of the coumarin anticoagulant, difenacoum, in male and female rats and mice. In our first experiment difenacoum (0.5 mg kg-1) killed 50% of male mice within 9 days of its administration, whereas no female mice died during this study. In a second group of experiments, the anticoagulant effect of difenacoum in male and female rats was determined. Under resting conditions, the prothrombin complex activities (PCA) of male and female rats were not significantly different. Over the first 24 h after administration of difenacoum (0.4 mg kg-1 i.p.), there was a monoexponential fall in PCA in both sexes. However, 6, 12 and 24 h after difenacoum, the PCA in male rats was significantly (P less than 0.05) lower than in female rats. PCA began to recover over the subsequent 48 h in both sexes, during which time there was marked variability in recovery in female rats. The difference between the onset of action of difenacoum in male and female rats did not appear to be due to a greater rate of elimination of the drug in female rats, since the plasma concentrations of difenacoum 24 h after its administration were the same in both sexes. The concentration of vitamin K1 in rat liver was also investigated. Vitamin K1 levels were 35.1 +/- 18.6 ng (g liver)-1 (male), and 29.4 +/- 5.4 ng (g liver)-1 (females) in control rats, but 24 h after difenacoum, vitamin K1 levels were either very low, or undetectable in all rats.(ABSTRACT TRUNCATED AT 250 WORDS)