Methylmercury In Rats Research Articles

Evaluation of toxic effects of a diet containing fish contaminated with methylmercury in rats mimicking the exposure in the Amazon riverside population

This study was designed to evaluate the effects of a diet rich in fish contaminated with MeHg, mimicking the typical diet of the Amazon riverside population, in rats. Animals were randomly assigned to one of three groups with eight rats in each group: Group I—control, received commercial ration; Group II—received a diet rich in uncontaminated fish; Group III—received a diet rich in fish contaminated with MeHg. Treatment time was 12 weeks. Oxidative stress markers were evaluated, as well as the effects of this diet on DNA stability, systolic blood pressure (SBP), nitric oxide (NO) levels and histological damage in different tissues. There was a significant increase in SBP values in rats fed with MeHg-contaminated fish diet after the 10th week of the treatment. As far as oxidative stress biomarkers are concerned, no differences were observed in reduced glutathione and protein carbonyl levels, glutathione peroxidase, catalase, superoxide dismutase or δ-aminolevulinate dehydratase activities between the groups of animals receiving contaminated and uncontaminated fish diets. On the other hand, malondialdehyde levels increased significantly in rats fed with contaminated fish. NO levels were similar in all groups. DNA migration showed augmented in rats exposed to contaminated fish and histopathological analyses showed weak but significant leukocyte infiltration. Thus, we conclude that the MeHg-contaminated fish diet induced a slight lipid peroxidation and genotoxicity. However, these effects seem to be much less pronounced than when rats are exposed to aqueous solution containing CH3HgCl.Our findings support the contention that the chemical form of MeHg in fish or fish nutrients such as polyunsaturated fatty acids, Se or vitamin E could minimize the toxic effects of MeHg exposure in fish-eating communities.

Protective properties of quercetin against DNA damage and oxidative stress induced by methylmercury in rats

Aim of the study was to find out whether consumption of quercetin (QC), an abundant flavonoid in the human diet, protects against DNA damage caused by exposure to organic mercury. Therefore, rats were treated orally with methylmercury (MeHg) and the flavonoid with doses that reflect the human exposure. The animals received MeHg (30μg/kg/bw/day), QC (0.5-50mg/kg/bw/day), or combinations of both over 45days. Subsequently, the glutathione levels (GSH) and the activities of glutathione peroxidase (GPx) and catalase (CAT) were determined, and DNA damage was measured in hepatocytes and peripheral leukocytes in single cell gel electrophoresis assays. MeHg decreased the concentration of GSH and the activity of GPx by 17 and 12%, respectively and caused DNA damage to liver and blood cells, while with QC no such effects were seen. When the flavonoid was given in combination with MeHg, the intermediate and the highest concentrations (5.0 and 50.0mg/kg/bw/day) were found to cause DNA protection; DNA migration was reduced by 54 and 65% in the hepatocytes and by 27 and 36% in the leukocytes; furthermore, the reduction in GSH and GPx levels caused by MeHg treatment was restored. In summary, our results indicate that consumption of QC-rich foods may protect Hg-exposed humans against the adverse health effects of the metal.

Dietary fats altered nephrotoxicity profile of methylmercury in rats

Weanling male Sprague-Dawley rats were administered semi-purified isocaloric diet containing soy oil (SO), seal oil (SE), docosahexaenoic acid (DHA), fish oil (FO) or lard (LA) for 28 days, and then gavaged with 0, 1 or 3 mg MeHg kg(-1) body weight per day and fed the same diet for 14 days. Serum and 24 h urine samples were collected on the day of necropsy, and analyzed for markers of kidney function and diseases. Kidney slices were analyzed for para-amino-hippurate (PAH) and tetraethylammonium (TEA) uptake, total mercury and MeHg content, and examined for pathological lesions. Total mercury and MeHg contents increased significantly and dose-dependently in all dietary groups. MeHg significantly increased relative kidney weight in all groups, serum creatinine in all except SO group, serum uric acid in the DHA and LA groups, serum Mg in all except the LA group, and urinary protein in the SO group. MeHg significantly decreased serum urea nitrogen in SE, FO and LA groups, urinary creatinine in the DHA group, PAH uptake in all except the SE group, and TEA uptake in all groups. MeHg caused nephrosis in all dietary groups. MeHg also significantly increased neutrophil counts in all except the SE group, decreased serum albumin and triglyceride in all except the DHA group, and increased serum total cholesterol in all groups, suggesting a nephrotic syndrome-like outcome. These results confirmed that kidney tubules are major targets of MeHg nephrotoxicity. Treatment with dietary fats did not prevent, but rather altered the profile of, nephrotoxicity of MeHg in rats.

Markers of brain selenium status and neurobehavioral effects of perinatal exposure to methylmercury in rats

Markers of brain selenium status and neurobehavioral effects of perinatal exposure to methylmercury in rats

An investigation of the effects of methylmercury in rats fed different dietary fats and proteins: Testicular steroidogenic enzymes and serum testosterone levels

Methylmercury (MeHg) is a testicular toxicant causing reduced steroidogenic enzyme activity, reduced serum testosterone (T) and abnormal spermatogenesis in mammals and fowl. It is also known that certain diets can alter androgen metabolism in rats. Previously we have shown that diets used in the current study impact circulating androgen levels and testicular steroidogenic enzyme activities in Sprague Dawley rats in the absence of MeHg. In the present study, we have investigated the impact of imposing an environmental contaminant (MeHg) commonly found in marine mammals and fish onto the rats’ dietary intake of different proteins and lipids in order to determine if the different diets could modify MeHg toxicity in rats. Therefore, we examined the effects of MeHg on testicular steroidogenic enzymes and serum testosterone in rats fed diets containing either different protein sources (casein, fishmeal, whey) or different lipid sources (soybean oil, docosahexaenoic acid (DHA), seal oil, fish oil, lard). Male rats 42–45 days of age (18 per group) were assigned to different experimental diets for 28 days after which 6 rats in each group were gavaged daily with 0, 1 or 3 mg/kg body weight (BW)/day MeHg chloride in 5 mM Na 2CO 3 solution for 14 days while being maintained on their diets. On the 43rd day of dosing, rats were sacrificed and blood plasma and testes frozen (−80 °C) until analysis. Microsomal steroidogenic enzyme activities (3β-HSD, 17-OHase, C-17, 20-lyase, 17β-HSD) were measured radiometrically. Serum testosterone was determined using ELISA kits. Testis weights were not affected by MeHg. MeHg at 3 mg/kg BW/day caused a reduction (>50%) in the activity of C-17, 20-lyase in all three protein diets and similar reductions in 17-OHase activity were seen in the casein and whey protein fed rats. At 3 mg/kg BW/day, MeHg reduced 17-OHase activity in the DHA diet but had no effect on 3β-HSD activity and no inhibitory effects on 17β-HSD activity. MeHg (3 mg/kg BW/day) caused significant reductions in serum T in the whey, soybean oil and fish oil groups. Interestingly, fishmeal protein but not fish oil offered some protection with respect to maintaining steroidogenic enzyme activities and serum T levels in rats dosed with MeHg. In conclusion, these studies show that different lipid diets can alter the toxic effects of MeHg on male rat steroidogenesis in terms of serum testosterone and steroidogenic enzyme activities.

Co-consumption of selenium and vitamin E altered the reproductive and developmental toxicity of methylmercury in rats

Methylmercury (MeHg), an environmental contaminant primarily found in fish and seafood, may pose long-term health risks to pregnant women and their developing children. The objective of this study was to determine whether co-consumption of nutritional supplements would alter the effects of MeHg on reproductive and developmental toxicity using a rodent model. Adult female rats were fed a diet containing additional selenium (1 ppm), additional vitamin E (225 IU/kg) or a combination of the two for 4 weeks before oral dosing of MeHg (1.25 mg/kg/day). Treatment with MeHg and dietary supplementation continued throughout pregnancy after which the dams were allowed to deliver their offspring. In addition to routine evaluations including periodic body weight measurements and daily clinical signs observations, dams and pups were evaluated for auditory startle habituation and pups were evaluated for developmental landmarks and reflexology. The dams and offspring were euthanized approximately 4 weeks after birth of the offspring. Results indicated that treatment with MeHg caused adverse effects on both reproduction of the dams and decreased progeny survival. However, the dams showed significant improvement in body weight gain during lactation and average auditory startle response time when the diet was enriched with both selenium and vitamin E. The combination of both vitamin E and Se also resulted in a significant increase in post-natal survival when compared to MeHg-treated group. There was no nutrient effect on the MeHg toxicity shown in offspring physical landmarks, performance in reflex tests and assessment of simple auricular startle response. Also, accelerated development as indicated by earlier opening in the pups of the supplemental diet groups was observed. These results suggest that antioxidant nutrients in the diet may alter MeHg reproductive and developmental toxicity. The underlying and human health implications warrant further investigations.

Spatial Alternation Deficits Following Developmental Exposure to Aroclor 1254 and/or Methylmercury in Rats

Spatial Alternation Deficits Following Developmental Exposure to Aroclor 1254 and/or Methylmercury in Rats

Spatial alternation deficits following developmental exposure to Aroclor 1254 and/or methylmercury in rats.

Polychlorinated biphenyls (PCBs) and methylmercury (MeHg) are ubiquitous environmental contaminants that alter cognitive function in both humans and animals. Because PCBs and MeHg often occur together in the environment, it is important to understand whether these two contaminants have the potential to interact, causing additive or greater than additive effects. The current study examined the combined effects of gestational and lactational exposure to Aroclor 1254 (A1254), a commercial PCB mixture, and MeHg on a series of spatial alternation tasks including cued spatial alternation (CA), non-cued spatial alternation (NCA), and delayed spatial alternation (DSA) in rats using standard two-lever operant testing chambers. Pregnant Long-Evans rats received either 6 mg/kg A1254 pipetted onto a Keebler Vanilla Wafer cookie (PCB-only group), 0.5 ppm. MeHg dissolved in the drinking water (MeHg-only group), 6 mg/kg A1254 + 0.5 ppm. MeHg (PCB + MeHg group), or corn oil vehicle and normal tap water (control group) beginning 28 days prior to mating and continuing through postnatal day 16. One male and one female from each litter began testing on spatial alternation at approximately 110 days of age. Animals were reinforced for pressing the lever opposite that pressed on the previous trial. In general, animals exposed to A1254 and/or MeHg were impaired relative to control rats on the NCA and DSA tasks. Significant reductions in NCA performance were observed in the MeHg-only and PCB + MeHg groups, while significant reductions in DSA performance were observed in the PCB-only and MeHg-only groups. The PCB + MeHg group showed a similar magnitude reduction in performance on DSA, but this difference was not statistically significant due to increased variability in that group. The reductions in DSA performance were observed across most of the delays, indicating that memory impairments were not likely the cause of the deficit. Instead, the DSA deficits following exposure to A1254 and/or MeHg are indicative of either an associative or attentional impairment. The results from the current study indicate that combined exposure to PCBs and MeHg does not exacerbate the PCB- or MeHg-induced impairments on spatial alternation tasks.

Prenatal exposure to methyl mercury in rats: focus on changes in kynurenine pathway

Previous studies showed learning and memory deficits following prenatal exposure to methyl mercury (MMC) in rats. Considering the described dysfunction in several neurotransmission systems after MMC exposure, one can surmise that changes in the kynurenine pathway could also be involved in an altered brain functional development. Thus we focused our attention on the potential alteration in the production of tryptophan metabolites by prenatal MMC exposure. For this purpose, brains were removed, at postnatal days 21 and 60, from rats treated, at gestational day 8, with saline or a single dose of MMC (8 mg/kg). The levels of tryptophan, glutamic, aspartic, kynurenic, anthranilic, and quinolinic acids were determined in hippocampal tissues of both groups of rats. No change was detected in the concentration of aspartic, glutamic, and kynurenic acids in 21- and 60-day-old exposed rats in comparison with age-matched controls. On the contrary, at 21 days of age but not at 60 days, we found a very significant reduction of anthranilic acid and, in parallel, an increase of quinolinic acid levels in MMC-exposed rats in comparison with control animals. Finally in the same brain area, tryptophan levels were significantly increased both at 21 and 60 days of postnatal life. These results suggest that an imbalance in the kynurenine pathway could be involved in the toxic effects induced by MMC on brain development.

Aging unmasks adverse effects of gestational exposure to methylmercury in rats

The consequences of developmental exposure to methylmercury on behavior in aged animals were investigated. Methylmercury exposure was arranged by placing 0, 0.5 or 6.4 ppm Hg in the drinking water of female rats at least 4 weeks before mating and continuing until post-natal (PN) day 16. Brain Hg concentrations in cohorts of low- and high-dose offspring were 0.5 and 9.1 ppm at birth and 0.04 and 0.52 ppm at weaning (described in another report). Lever pressing of female offspring was maintained under a Multiple Differential Reinforcement of High Rate 9:4 Extinction schedule of food reinforcement (Mult DRH 9:4 EXT). Under the DRH 9:4 schedule, a food reinforcer was delivered when nine responses occurred within 4 s. Under the Extinction schedule, responding had no programmed consequences. No exposure-related differences in reinforcement rate under the DRH schedule or discrimination between the DRH and extinction components were apparent initially. At 950 days of age, the overall response rates of controls had shown a gradual decline over the previous 500 days to about 80% of their beginning levels, but, otherwise, most controls were healthy. A gradual decline in the reinforcement rate began to appear in low- and high-dose rats at about 500 and 800 days of age, respectively. Microanalyses of the nine-response burst maintained by the DRH schedule revealed that the lever-press duration increased, the inter-response time (IRT) was unaffected, and the time between response bursts increased. Overall, the nine-response burst remained intact as a coherent response unit. The increased time between response bursts caused the decline in reinforcement rate. All rats displayed these effects as they aged, but the mercury-exposed rats did so sooner.

Blood and brain mercury levels after chronic gestational exposure to methylmercury in rats.

Female rats were exposed to 0, 0.5, or 6 ppm Hg (as methylmercuric chloride, 10 rats/group) in drinking water. For half the rats, exposure began 4 weeks before mating and for the others, exposure began 7 weeks before mating. All mating was done with an unexposed male. Maternal exposure continued to post-natal day (PN) 16. Blood and whole-brain mercury concentrations were determined in pups on PN 0 (birth) and PN 21 (weaning). Maternal water consumption was monitored daily during gestation and lactation. Maternal water consumption increased 2- to 3-fold through gestation for all groups. Mercury levels in blood and brain were unrelated to the duration of exposure before mating, although reproductive success appeared to be so related. Mercury levels in both media were closely related to consumption during gestation, but apparently maternal exposure during lactation did not result in exposure to the nursing pups. Brain mercury in offspring decreased between birth and weaning from 0.49 to 0.045 ppm in the low-dose rats and from 9.8 to 0.53 ppm in the high-dose rats. The brain increased in weight only about 5.5-fold during this time, indicating that there was minimal mercury exposure and some net loss from brain during this period. Brain:blood ratios averaged about 0.14 at birth and 0.24 at weaning, suggesting differential loss from neural and non-neural tissue. These ratios are higher than those reported in studies using less chronic exposure conditions or with adult rats. Brain concentrations of mercury in females in the low-dose group were about 10-15% higher than those seen in their male siblings. At the higher dose, the males had slightly higher levels of mercury in the brain than did their female siblings at birth. The relationship between brain concentration (in ppm) and cumulative mercury consumption, also expressed on a ppm basis (cumulative mercury consumed divided by maternal body weight at parturition), was not linear but was well described by a power-function relationship: Hg = A*(cum exposure)b where the exponent, b, was 1.12 and 1.17 for blood and brain, respectively, at birth. This exponent was indistinguishable from 1.0 for both media at weaning, indicating that the relationship between exposure and blood and brain levels became linear.

Inhibitory Effect of Selenium on Biliary Secretion of Methyl Mercury in Rats

The inhibitory effect of sodium selenite on biliary secretion of methyl mercury was examined in rats. The biliary secretion of methyl mercury in rat treated with 1 μmol/kg of methyl mercury was significantly decreased by administration of selenite at doses of 0.05 μmol/kg or higher. In rats given 10 μmol/kg of methyl mercury, marked depression of biliary secretion of mercury was observed when selenite was injected at a dose of 0.2 μmol/kg. On the other hand, secretion of substantial amounts of selenium was observed when biliary secretion of mercury was depressed. When the concentration of selenium in the bile was higher than 5 nmol/ml, biliary secretion of mercury was markedly depressed independently of the dose of methyl mercury administered (1 μmol/kg or 10 μmol/kg). These results suggest that the degree of inhibitory effect of selenite may be determined by the selenium concentration in the liver or the bile after treatment with selenite rather than the molar ratio of the dose of methyl mercury and selenite. We concluded that the decrease in biliary secretion of methyl mercury induced by selenite may result from inhibition of pathway for secretion of methyl mercury from liver to bile rather than the direct formation of a compex between methyl mercury and selenium. Methyl mercury has been considered to be secreted from liver to bile as a complex with glutathione (GSH). However, administration of selenite did not affect biliary secretion of GSH or hepatic glutathione S-transferase activity. Moreover, gel filtration of liver cytosol demonstrated that the distribution pattern of hepatic methyl mercury between macromolecules and GSH was not significantly changed by administration of selenite. These results suggest that selenite does not affect complex formation of methyl mercury with GSH at least in the liver. Selenite might specifically inhibit the activity of the canalicular transporter(s) which transport complexes of methyl mercury and GSH from the liver to bile.

Chronic effects of methylmercury in rats. II. Pathological aspects.

Chronic effects of methylmercury (MeHg) were examined pathologically in male Wistar rats fed on diet containing 0, 1 or 5 ppm Hg (as MeHg) for two years. Organs including the central nervous tissues were examined histopathologically using hematoxylin and eosin (H & E), Klüver-Barrera (KB), PAS or phenol-congo red stains. The peripheral nerve system tissues were also examined, using H & E and trichrome stains. Furthermore, immunoglobulins of renal specimens were demonstrated by direct immunofluorescence microscopy. Localization of mercury in the paraffin-embedded sections of the nervous tissue, kidney, liver, pancreas, spleen and testis was demonstrable by the photoemulsion histochemical method. In the 5 ppm group, mercury was readily detectable in tissues of the rats exposed for one year, one and half years, two years and two and half years. Mercury was detected in the cells of the brain such as neurons, neuroglial cells, and phagocytes, and also in most organs, particularly in the epithelium of renal tubules, liver cells, myocardium, in the macrophages of pancreas, spleen and testis. In the 1 ppm group, mercury was detectable in the epithelium of renal tubules and liver cells. Fibrosis of the glomeruli was found in the rat group given a high dose of methylmercury with all experimental methods. Granular IgG, IgM and C3 deposits were demonstrated in the glomeruli by direct immunofluorescence microscopy. The etiology of the pathological changes of glomeruli was suspected to be autoimmune glomerulopathy due to inorganic mercury filtration for a long time. It was difficult to determine the clinical signs and symptoms and pathological changes in the nervous system in spite of the deposition of mercury in the brain.

Chronic Effects of Methylmercury in Rats. I. Biochemical Aspects.

To examine chronic effects of methylmercury (MeHg), male Wistar rats were fed on MeHg-contaminated diet, 0, 1 and 5 ppm Hg, under a restricted feeding schedule of 16 g/rat/day for 6 days a week. Rats were killed at 6-month intervals for examination of Hg accumulation, tissue levels of glutathione, metallothionein and lipid peroxide, as well as anti-oxidative enzyme activities. The survival of the 5 ppm Hg group, 50% of which died by the end of 32nd month of the exposure, was somewhat shorter than control and 1 ppm Hg groups, 50% of which survived for 34 months. Although the rats showed no neurological signs or decreased body weight gain even in 5 ppm Hg-exposed group until the end of the 2nd year, crossing of hind limb was evident after 2.5 years in all three groups. Accordingly, the neurological sign observed here possibly due to aging rather than MeHg toxicity. Tissue Hg levels showed a dose-dependent accumulation except for the kidney, where the highest Hg accumulation was observed among tissues examined. Renal Hg levels in the 1 ppm group showed about 40% of those in the 5 ppm group. Significant effects by MeHg were evident only in the kidney, where glutathione and metallothionein levels increased in both MeHg-exposed groups. However, lipid peroxide levels elevated only in 1 ppm group. Among the antioxidative enzymes examined, the renal glutathione peroxidase was found to be the most labile enzyme against MeHg exposure. Renal dysfunction suggested by increased plasma creatinine levels was also significant in 5 ppm Hg rats at 2 years. Furthermore, anemia which would be caused by reduced erythropoietin production in the kidney was also evident in this group. The present study suggested that the kidney was the most susceptible organ against MeHg toxicity under the present exposure schedule and that the renal dysfunction might at least partly account for the shortened survival in 5 ppm Hg rats.

Impaired biliary excretion and whole body elimination of methylmercury in rats with a congenital defect in biliary glutathione excretion

Biliary excretion of methylmercury, a major route of elimination of this toxic compound, was less than 2% of control in Eisai hyperbilirubinemic (EHBR) rats, a mutant Sprague-Dawley strain with a defect in biliary excretion of a variety of organic anions, including glutathione S-conjugates and reduced glutathione (GSH). Biliary GSH excretion in EHBR rats was also <2% of controls, confirming previous findings. Impaired biliary methylmercury and GSH excretion was not explained by decreased hepatic content of these compounds. Indeed, hepatic methylmercury and GSH concentrations in EHBR rats were actually double those of controls. To assess the significance of the impaired biliary excretion in the whole body elimination of the toxicant, 203Hg excretion was measured over a 17-day period after intraperitoneal administration of either 0.5 or 5 μmol/kg of 203Hg-methylmercury chloride. The results for the two doses were similar. Methyhnercury was eliminated by a first order process; however, the biological half-life was significantly longer in the EHBR rats, 46 to 54 days versus 18 to 22 days. Fecal excretion was the main route of elimination in both control and mutant animals. At necropsy (17 days), 16% to 25% of the 203Hg dose was recovered in the liver of the EHBR rats, whereas livers of control animals contained less than 2% of the administered dose. These findings demonstrate that biliary excretion of methylmercury is markedly impaired in EHBR rats and is associated with a low biliary GSH excretion, providing support for the hypothesis that methylmercury is normally transported across the canalicular membrane by a GSH-dependent mechanism, and presumably as a GSH mercaptide (CH 3Hg-SG). This study also provides a direct measure of the contribution of biliary excretion to the whole-body elimination of methylmercury. The biological half-life of the metal was 2.5 times longer in the mutant animals, indicating a critical role for biliary secretion in methyhnercury detoxification.

Impaired biliary excretion and whole body elimination of methylmercury in rats with a congenital defect in biliary glutathione excretion

Biliary excretion of methylmercury, a major route of elimination of this toxic compound, was less than 2% of control in Eisai hyperbilirubinemic (EHBR) rats, a mutant Sprague-Dawley strain with a defect in biliary excretion of a variety of organic anions, including glutathione S-conjugates and reduced glutathione (GSH). Biliary GSH excretion in EHBR rats was also < 2% of controls, confirming previous findings. Impaired biliary methylmercury and GSH excretion was not explained by decreased hepatic content of these compounds. Indeed, hepatic methylmercury and GSH concentrations in EHBR rats were actually double those of controls. To assess the significance of the impaired biliary excretion in the whole body elimination of the toxicant, 203Hg excretion was measured over a 17-day period after intraperitoneal administration of either 0.5 or 5 mumol/kg of 203Hg-methylmercury chloride. The results for the two doses were similar. Methylmercury was eliminated by a first order process; however, the biological half-line was significantly longer in the EHBR rats, 46 to 54 days versus 18 to 22 days. Fecal excretion was the main route of elimination in both control and mutant animals. At necropsy (17 days), 16% to 25% of the 203Hg dose was recovered in the liver of the EHBR rats, whereas livers of control animals contained less than 2%of the administered dose. These findings demonstrate the biliary excretion of methylmercury is markedly impaired in EHBR rats and is associated with a low biliary GSH excretion, providing support for the hypothesis that methylmercury is normally transported across the canalicular membrane by a GSH-dependent mechanism, and presumably as a GSH mercaptide (CH3Hg-SG).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of Fe-Overload on the Biotransformation of Methylmercury in Rat.

It is well documented that methylmercury (MeHg) in vivo slowly undergoes demethylation reaction to change to inorganic mercury (Hg-i). The cleavage of the C-Hg bond was suggested to occur via a reactive oxygen-mediated process in vitro. To study the possibility of the involvement of hydroxyl radical (·OH) in the demethylation of MeHg in vivo, the combined effect of Fe-overload and carbon tetrachloride (CCl4) treatment on the rate of biotransformation of MeHg was examined in rats. The effects of this treatment on H2O2-scavenging enzyme activities (catalase and glutathione peroxidase) were also studied. Rats were fed 3.5% Fe (II) fumalate-containing diet for 0, 7 or 21 d to load Fe. Feeding of the Fe-containing diet brought about a time-dependent increase of the hepatic Fe levels by nearly 7-fold after 3 weeks. The serum Fe levels showed a maximum on day 7, while the renal levels increased after day 7. TBA-reactive substance levels in the liver significantly increased along with the Fe feeding, and this increase was drastically accelerated by CCl4 treatment, suggesting the effective production of ·OH. The CCl4-induced stimulation of the lipid peroxidation was observed also in serum and kidney, though not as marked as in the liver. The hepatic accumulations of total and inorganic Hg at 72 h after MeHg administration were significantly increased by the Fe-feeding. The proportion of Hg-i to total Hg in this tissue increased markedly by the combined effect of Fe and CCl4 with the concomitant decrease of catalase activity. On the other hand, the renal accumulation of Hg-i drastically decreased by the Fe-load, while the MeHg levels remained unchanged. Since the renal metallothionein levels were found to be lowered after the Fe-feeding, this might account for the reduced retention of Hg-i in the whole kidney. The present results suggest that reactive oxygen species, probably ·OH, induced by Fe and CCl4 treatment may play a critical role in the biotransformation of MeHg in the liver.

Effects of long-term treatment with methyl mercury on the developing rat brain

Sprague-Dawley rats were exposed to low doses of methyl mercury (3.9 mg mercury/kg diet), via their dams during gestation and lactation and directly via their diet until sacrifice at 50 days postpartum, in order to study possible detrimental effects on CNS development. The methyl mercury exposure of the rats resulted in a brain concentration of 1.45 +/- 0.06 mg mercury/kg wet weight (mean +/- SEM). No general toxic effects were observed; body weight was not affected, brain weight was only slightly increased. No discernible general morphological alterations were seen in the brain as evaluated using cresyl violet histology. Furthermore, no effects on GFA-positive astrocytes in brain sections were observed and computerized morphometry of smeared astrocytes from frontal cortex, hippocampus, and cerebellum did not reveal any effects of the methyl mercury treatment. The noradrenaline (NA) and dopamine (DA) systems were also studied. In cerebellum the NA levels were increased (117% of controls, P = 0.008), whereas in other regions analyzed NA and DA levels were unchanged. Thus, long-term low-dosage exposure of methyl mercury in rats during development does not appear to exert any major effects on the morphological maturation of neurons and astrocytes. However, the results indicate that effects may occur in specific transmitter-identified systems, such as the NA input to cerebellum. The results therefore underline the need for detailed biochemical analyses to study the effects of long-term low-dosage exposure to neurotoxic compounds.

Lipid peroxidation induced by methylmercury in rats

The ability of methylmercury (MMC) to induce lipid peroxidation was tested in rats. One group of 5 rats (MMC group) took a diet to which 10 ppm of methylmercury was added while another group of 5 rats was fed a diet containing no MMC as a control. During the experimental period of 14 weeks (98 days) on these diets, body weight gain and amount of food consumption were checked individually for each two-day interval. Samples of expired air and blood were obtained every two weeks and analysed for ethane and pentane production and for plasma fatty acid composition, respectively. Results obtained were as follows: 1. During the first half of the 14-week experimental period, there was no significant difference in the amount of food consumption between the MMC group and the control group. However, a significantly smaller amount of food consumption was found in the MMC group as compared to the control group during the latter half of the experiment. The amount of food consumption was directly reflected in the body weight gain throughout the experimental period. 2. The amount of expired ethane was generally higher in the MMC group than in the control group throughout the experimental period. During the last 2 weeks of the experimental period, the difference in the amount of expired ethane between the two groups was statistically significant. 3. The amount of expired pentane was also higher in the MMC group than in the control group during all the weeks of the experimental period.(ABSTRACT TRUNCATED AT 250 WORDS)

Combined toxicity of ethanol and methylmercury in rat

The hepatotoxic and nephrotoxic effects of methylmercury (CH 3Hg) and ethanol (EtOH) are well known; however, their interaction in vivo is not clearly understood. In order to investigate the combined effects of these 2 substances, 4 groups of male Wistar rats with an initial weight of approximately 190 g were treated for 7 weeks. Each group consisting of 8 rats was gavaged as follows: Group 1 with 5.0 ml/kg body weight of double distilled water, Group 2 with 5.0 ml/kg body weight of 25% EtOH, Group 3 with 2.5 mg/kg of CH 3Hg in water, and Group 4 with 2.5 mg/kg of CH 3Hg in 25% EtOH. At the termination of the experiment the mean body weights of the rats in Group 3 (372.5 ± 10.8 S.E.) and Group 4 (383.4 ± 13.4) were significantly lower than that of Group 1 (433.0 ± 7.8). Linear regression showed a positive feed conversion efficiency for Groups 1 and 2 (1.07 and 0.83, respectively), and a negative score for this parameter for Groups 3 and 4 (−1.43, −1.53). At necropsy, rat livers from Group 3 exhibited random multifocal tan spots. The relative liver weights were similar to those of controls. Semithin sections of liver revealed an increase in lipid droplets in Groups 2 and 3 compared to those in the other 2 groups while vacuolization was more striking in CH 3Hg treated rats (Groups 3 and 4). Severe hepatolysis and portal canal edema were noted in the groups of rats exposed to either EtOH alone or in combination with mercury. The relative weight of left kidney in Group 3 (0.70 ± 0.03) and Group 4 (0.51 ± 0.04) rats was significantly greater than of the control (0.39 ± 0.03). In gross appearance the kidney was pale and the urine production was significantly higher ( P<0.05) in Group 3 compared to that of Group 1. Group 4 rats had significantly more ( P <0.50) Hg in the kidney than Group 3; however, the inorganic percentages in both groups were similar. Morphological examination of the kidney proximal tubules from CH 3Hg treated rats (Groups 3 and 4) revealed an increase in lipid droplets, vacuoles, cell sloughing and tubular degeneration compared to Groups 1 and 2. These histological changes in the proximal tubules of Groups 4 rats indicate an additive effect of EtOH on the kidney pathology caused by CH 3Hg. This present study seems to suggest that ethanol in combination with mercury enhances the retention of mercury in the kidney and increases the nephrotoxicity while it has no effect on the neurotoxicity of mercury. EtOH and CH 3Hg combination (Group 4) showed increased fibroblast infiltration and fibrosis in the kidney cortex, and larger and more numerous dense bodies and swollen mitochondria in the tubular cells. However, these alterations of nephrotoxicity by EtOH require further study.