Disposition Of Mercury Research Articles

Prophylactic supplementation with selenium alters disposition of mercury in aged rats.

Mercury (Hg) is a prevalent environmental toxicant to which older individuals are particularly susceptible. Selenium (Se) has been used as an antidote following exposure to Hg. However, little is known about the effect of prophylactic supplementation with Se on the handling of Hg. The current study was designed to test the hypothesis that oral pre-treatment with Se alters the corporal disposition of Hg and reduces the risk of Hg-induced toxicity. Young and aged rats were gavaged for 10days with sodium selenite or saline. On day 11, rats were injected intravenously with 0.5μmol HgCl2·kg-1·2mL-1 normal saline. After 24h, rats were euthanized and organs and tissues were harvested for determination of Hg content. Accumulation of Hg in the kidney was reduced significantly by pre-treatment with Se in both young and aged rats. In the renal cortex, the magnitude of the reduction was greater in aged rats than in young rats but in the outer stripe of the outer medulla, the magnitude of the reduction was similar between groups of rats. Urinary excretion of Hg was also reduced in rats pre-treated with Se. In contrast, the hepatic and hematologic burden of Hg increased in rats pre-treated with Se. Fecal excretion of Hg was decreased significantly by pre-treatment with Se in young rats but not in aged rats. These data suggest that prophylactic supplementation with Se alters the corporal disposition of Hg in a way that may reduce Hg-induced toxicity in target organs.

Chronic kidney disease in pregnant mothers affects maternal and fetal disposition of mercury

Chronic kidney disease (CKD) affects over 15 % of the adults in the United States. Pregnant women with CKD present an additional challenge in that they are at increased risk for adverse events such as preterm birth. Exposure to environmental toxicants, such as methylmercury, may exacerbate maternal disease and increase the risk of adverse fetal outcomes. We hypothesized that fetuses of mothers with CKD are more susceptible to accumulation of methylmercury than fetuses of healthy mothers. The current data show that when mothers are in a state of renal insufficiency, uptake of mercury in fetal kidneys is enhanced significantly. Accumulation of Hg in fetal kidneys may be related to the flow of amniotic fluid, maternal handling of Hg, and/or underdeveloped mechanisms for cellular export and urinary excretion. The results of this study indicate that renal insufficiency in mothers leads to significant alterations in the way toxicants such as mercury are handled by maternal and fetal organs.

Investigation of the Passivation Layers Influence on Capacitance Characteristics of AlGaN/GaN Heterostructures

AlGaN/GaN heterostructures grown by MOCVD method on sapphire and silicon substrates were test subjects. The capacity− voltage characteristic measurements have been run in 200Hz — 1MHz frequency range at planar disposition of mercury and second probe on the sample surface. The shape of typical C−V curves for the heterostructures with the upper undoped i−AlGaN and i−GaN layers at thickness 15—25 A have been analyzed. The appearance of a typical peak on the C−V curves at changing from depletion region to accumulation region has been registered for some structures with thickness of i−GaN layer 50A at low frequencies (f < 50—200 kHz). The height of this peak increased with reduction of frequency. It has been found experimentally that frequency at which the peak is registered can depend on the dislocation density in heterostructures. Possible explanation of the peak formation and band diagram modifications in these structures under an applied electric field have been presented. We show that using a Si3N4 passivation layer results in the formation of additional positive charge.

Absence of Mrp2 leads to differences in severity and pattern of mercury nephrotoxicity in mice

The multidrug‐resistance associated protein 2 (Mrp2) is located on the luminal membrane of proximal tubular epithelial cells and has been shown to mediate the export of numerous endobiotics and xenobiotics such as mercury. Although Mrp2 is present in all proximal tubular cells, there is axial heterogeneity in the magnitude of expression along the three segments of the proximal tubule. The purpose of the current study was to assess differences in renal injury and disposition of mercury between Mrp2−/− and FVB mice following a toxic dose of mercuric chloride (HgCl2). Mrp2−/− and FVB mice were injected intraperitoneally with doses of HgCl2 ranging from 18 – 30 μmol/kg. Mice were sacrificed after 24 h and organs were harvested. The renal burden of mercury was significantly greater in Mrp2−/− mice than in FVB mice. Significant differences in pattern and severity of mercury‐induced injury were observed between Mrp2−/− and FVB mice, with the most severe changes observed in Mrp2−/−mice. Histological analyses showed that degenerative change and necrosis occurred as low as 18.5 μmol/kg HgCl2 and the severity of these changes increased as the dose of HgCl2 increased. Our results suggest that the activity of Mrp2 is an important factor in the disposition and nephrotoxicity of HgCl2. This work was supported by NIH ES019991–01 (NIEHS) awarded to CC Bridges.

Effect of DMPS and DMSA on the Placental and Fetal Disposition of Methylmercury

Methylmercury (CH 3Hg +) is a serious environmental toxicant. Exposure to this metal during pregnancy can cause serious neurological and developmental defects in a developing fetus. Surprisingly, little is known about the mechanisms by which mercuric ions are transported across the placenta. Although it has been shown that 2,3-dimercaptopropane-1-sulfonate (DMPS) and 2,3-dimercaptosuccinic acid (DMSA) are capable of extracting mercuric ions from various organs and cells, there is no evidence that they are able to extract mercury from placental or fetal tissues following maternal exposure to CH 3Hg +. Therefore, the purpose of the current study was to evaluate the ability of DMPS and DMSA to extract mercuric ions from placental and fetal tissues following maternal exposure to CH 3Hg +. Pregnant Wistar rats were exposed to CH 3HgCl, containing [ 203Hg], on day 11 or day 17 of pregnancy and treated 24 h later with saline, DMPS or DMSA. Maternal organs, fetuses, and placentas were harvested 48 h after exposure to CH 3HgCl. The disposition of mercuric ions in maternal organs and tissues was similar to that reported previously by our laboratory. The disposition of mercuric ions in placentas and fetuses appeared to be dependent upon the gestational age of the fetus. The fetal and placental burden of mercury increased as fetal age increased and was reduced by DMPS and DMSA, with DMPS being more effective. The disposition of mercury was examined in liver, total renal mass, and brain of fetuses harvested on gestational day 19. On a per gram tissue basis, the greatest amount of mercury was detected in the total renal mass of the fetus, followed by brain and liver. DMPS and DMSA reduced the burden of mercury in liver and brain while only DMPS was effective in the total renal mass. The results of the current study are the first to show that DMPS and DMSA are capable of extracting mercuric ions, not only from maternal tissues, but also from placental and fetal tissues following maternal exposure to CH 3Hg +.

MRP2 involvement in renal proximal tubular elimination of methylmercury mediated by DMPS or DMSA

2, 3-Dimercaptopropane-1-sulfonic acid (DMPS) and meso-2, 3-Dimercaptosuccinic acid (DMSA) are dithiols used to treat humans exposed to methylmercury (CH 3Hg +). After treatment, significant amounts of mercury are eliminated rapidly from the kidneys and are excreted in urine. In the present study, we extended our previous studies by testing the hypothesis that MRP2 mediates the secretion of DMPS or DMSA S-conjugates of CH 3Hg +. To test this hypothesis, the disposition of mercury was assessed in control and Mrp2-deficient (TR −) rats exposed intravenously to a 5.0-mg/kg dose of CH 3HgCl. Twenty-four and 28 h after exposure, groups of four control and four TR − rats were injected with saline, DMPS, or DMSA. Tissues were harvested 48 h later. Renal and hepatic contents of mercury were greater in saline-injected TR − rats than in controls. In contrast, the amounts of mercury excreted in urine and feces by TR − rats were less than those by controls. DMPS and DMSA significantly reduced the renal and hepatic content of mercury in both groups of rats, with the greatest reduction in controls. A significant increase in urinary and fecal excretion of mercury (which was greater in the controls) was also observed. Our findings in inside-out membrane vesicles prepared from hMRP2-transfected Sf9 cells show that uptake of DMPS and DMSA S-conjugates of CH 3Hg + was greater in the vesicles containing hMRP2 than in control vesicles. Overall, these dispositional findings indicate that MRP2 does play a role in DMPS- and DMSA-mediated elimination of mercury from the kidney.

Simultaneous Coexposure to Inorganic Mercury and Cadmium: A Study of the Renal and Hepatic Disposition of Mercury and Cadmium

This study was designed to evaluate the effects of simultaneous coexposure to inorganic mercury and cadmium on the renal and hepatic disposition of each metal. Dispositional changes were assessed in rats 1 h and 24 h after the coexposure to relatively low doses of the metals (which individually are nonnephrotoxic in rats). The rational for studying mercury and cadmium is that both of these metals are encountered frequently in the same contaminated areas. Coadministration of a 0.5-µmol/kg dose of mercuric chloride with a 10-µmol/kg dose of cadmium chloride resulted in a decrease in the net renal accumulation of inorganic mercury at 1 and 24 h after exposure. Assessment of the disposition of both metals in renal zones indicates that the decreased renal accumulation of inorganic mercury was due specifically to changes in the accumulation of mercury in the renal cortex. Coexposure to inorganic mercury and cadmium also caused both the hepatic accumulation of mercury and the urinary excretion of mercury to increase during the initial 24 h after coexposure. During the initial 1 h after coexposure, the content of mercury in the blood was enhanced significantly. However, by the end of the first 24 h after exposure, the content of mercury in the blood was lower than that in animals treated with only inorganic mercury, likely due to the increased urinary excretion of mercury. Interestingly, with the exception of decreased fecal excretion of cadmium, no other changes in the disposition of cadmium were detected in the animals treated with both mercury and cadmium. These novel findings indicate that at the doses of inorganic mercury and cadmium used in the present study, cadmium has profound effects on the renal and hepatic handling of mercury. Based on the present findings, it appears that cadmium [by some currently unknown mechanism(s)] interferes with the luminal and/or basolateral uptake and/or net accumulation of mercury along S 1 and S 2 segments of the proximal tubules, which results in an overall decrease in the renal burden of mercury and an increased rate in the urinary excretion of mercury.

Disposition of Inorganic Mercury Following Biliary Obstruction and Chemically Induced Glutathione Depletion: Dispositional Changes One Hour after the Intravenous Administration of Mercuric Chloride

Influences of biliary obstruction and systemic depletion of glutathione (GSH) on the disposition of a low nontoxic iv dose of inorganic mercury were evaluated in rats in the present study. Specifically, the disposition of mercury in the kidneys, liver, small and large intestines, and blood was assessed 1 h after the injection of 0.5 μmol/kg mercuric chloride in control rats and rats pretreated with acivicin, buthionine sulfoximine (BSO), or diethylmaleate (DEM) that did or did not undergo acute biliary ligation prior to the injection of mercury. Among the groups that did not undergo biliary ligation, the pretreatments used to alter GSH status systemically had varying effects on the disposition of inorganic mercury in the kidneys, liver, intestines, and blood. Biliary ligation caused the net renal accumulation of mercury to decrease under all pretreatment conditions. By contrast, biliary ligation caused significant increases in the hepatic burden of mercury in all pretreatment groups except the acivicin-pretreated group. Blood levels of mercury also increased as a result of biliary ligation, regardless of the type of pretreatment used. Evidence for a secretory-like movement of mercury into the lumen of the intestines is also provided in the animals that underwent biliary ligation. The present findings indicate that biliary ligation combined with methods used to alter GSH status systemically have additive effects with respect to causing reductions in the net renal accumulation of mercury. In addition, the findings indicate that at least some fraction of the renal accumulation of inorganic mercury is linked mechanistically to the hepatobiliary system.

BASOLATERAL UPTAKE OF MERCURIC CONJUGATES OF N-ACETYLCYSTEINE AND CYSTEINE IN THE KIDNEY INVOLVES THE ORGANIC ANION TRANSPORT SYSTEM

Renal uptake and disposition of administered inorganic mercury were studied in rats that had undergone an acute bilateral ureteral ligation shortly before being injected intravenously with a nontoxic 0.5 mumol/kg dose of inorganic mercury with or without 2 mumol/kg N-acetylcysteine or cysteine. Bilateral ureteral ligation was performed in an attempt to reduce glomerular filtration to negligible levels, which in turn permitted the study of the basolateral uptake of inorganic mercury. The disposition of mercury was studied in the kidneys, liver, and blood 1 h after treatment. In rats given only mercuric chloride, the renal burden of mercury was approximately 20% of the administered dose of mercury. This confirms previous observations implicating a basolateral mechanism in the renal uptake of inorganic mercury. Coadministration of inorganic mercury with either N-acetylcysteine or cysteine caused a significant increase in the renal uptake of mercury 1 h after treatment, particularly in the rats treated with inorganic mercury plus N-acetylcysteine. The enhanced uptake of mercury in the kidneys was due to increased uptake of mercury in the renal cortex and outer stripe of the outer medulla. Interestingly, the rate of uptake of mercury was so great in the rats treated with inorganic mercury plus N-acetylcysteine that the renal burden of mercury was virtually equivalent to that generally detected in normal animals administered the same dose of inorganic mercury as mercuric chloride. Pretreatment with para-aminohippuric acid (PAH) (which is a potent inhibitor of the organic anion transport system) caused significant reductions in the renal uptake and burden of inorganic mercury in all the rats administered inorganic mercury, regardless of whether the inorganic mercury was coadministered with N-acetylcysteine or cysteine. Overall, the findings from the present study provide additional evidence that there is basolateral uptake of inorganic mercury in the kidneys, and that the primary or sole mechanism is dependent on the activity of the organic anion transporter. The present findings also show that cysteine and N-acetylcysteine enhance the basolateral uptake of mercuric ions in the kidney when they are coadministered with inorganic mercury, presumably in the form of mercuric conjugates. Moreover, it appears that mercuric conjugates of N-acetylcysteine are taken up more avidly at the basolateral membrane than mercuric conjugates of cysteine. Furthermore, the basolateral uptake of mercuric conjugates of N-acetylcysteine or cysteine in the kidney is due primarily to a mechanism involving the organic anion transport system.

P1G183 - Comparative efficacy of I.V. Pralidoxime vs. NaHCO 3 in rats lethally poisoned with O-P insecticide

2, 3-Dimercaptopropane-1-sulfonic acid (DMPS) and meso-2, 3-Dimercaptosuccinic acid (DMSA) are dithiols used to treat humans exposed to methylmercury (CH3Hg+). After treatment, significant amounts of mercury are eliminated rapidly from the kidneys and are excreted in urine. In the present study, we extended our previous studies by testing the hypothesis that MRP2 mediates the secretion of DMPS or DMSA S-conjugates of CH3Hg+. To test this hypothesis, the disposition of mercury was assessed in control and Mrp2-deficient (TR−) rats exposed intravenously to a 5.0-mg/kg dose of CH3HgCl. Twenty-four and 28 h after exposure, groups of four control and four TR− rats were injected with saline, DMPS, or DMSA. Tissues were harvested 48 h later. Renal and hepatic contents of mercury were greater in saline-injected TR− rats than in controls. In contrast, the amounts of mercury excreted in urine and feces by TR− rats were less than those by controls. DMPS and DMSA significantly reduced the renal and hepatic content of mercury in both groups of rats, with the greatest reduction in controls. A significant increase in urinary and fecal excretion of mercury (which was greater in the controls) was also observed. Our findings in inside-out membrane vesicles prepared from hMRP2-transfected Sf9 cells show that uptake of DMPS and DMSA S-conjugates of CH3Hg+ was greater in the vesicles containing hMRP2 than in control vesicles. Overall, these dispositional findings indicate that MRP2 does play a role in DMPS- and DMSA-mediated elimination of mercury from the kidney.

Basolateral Uptake of Inorganic Mercury in the Kidney

Renal disposition of administered inorganic mercury was studied in rats that had undergone an acute bilateral ureteral ligation shortly before being injected with a nontoxic 0.5-μmol/kg iv dose of inorganic mercury with or without 2.0 μmol/kg glutathione (GSH) or cysteine. Ureteral ligation and induction of “stop–flow” conditions were carried out to decrease glomerular filtration rate to negligible levels prior to the administration of inorganic mercury. The disposition of mercury was studied in the kidneys, liver, and blood 1 h after treatment. In rats given only mercuric chloride, the renal burden of mercury was approximately 20–25% of the administered dose of mercury, which is approximately 50% of the renal burden of mercury detected on average in normal rats. Coadministration of inorganic mercury with GSH or cysteine caused a significant increase in the renal uptake of mercury 1 h after treatment. The enhanced uptake of mercury in the kidneys was due to increased uptake of mercury in the renal cortex and outer stripe of the outer medulla. Pretreatment withpara-aminohippuric acid caused significant reductions in the renal concentration and burden of inorganic mercury in all the rats administered inorganic mercury, regardless of whether the inorganic mercury was coadministered with GSH or cysteine. Overall, the findings from the present study provide additional evidence that there is basolateral uptake of inorganic mercury in the kidneys and that the primary mechanism involved in this basolateral uptake is dependent on the activity of the organic anion transporter. More importantly, the present findings also show that GSH and cysteine enhance the basolateral uptake of mercuric ions in the kidney when they are coadministered with inorganic mercury (presumably in the form of mercuric conjugates). On the basis of the present findings, one is led to believe that mercuric conjugates of GSH and cysteine are taken up at the basolateral membrane following exposure to inorganic forms of mercury.

INTESTINAL HANDLING OF MERCURY IN THE RAT: IMPLICATIONS OF INTESTINAL SECRETION OF INORGANIC MERCURY FOLLOWING BILIARY LIGATION OR CANNULATION

Three sets of experiments were carried out to determine if there is an intestinal secretory component in the fecal excretion of administered inorganic mercury. In the first set of experiments the disposition of a nontoxic 0.5-mumol/kg intravenous dose of inorganic mercury was evaluated in control rats and rats whose bile duct had been ligated. Data collected 24 h after the administration of mercuric chloride indicated that some inorganic mercury had moved from the blood across the epithelium into the lumen of the stomach, small intestine, and large intestine. This secretory movement of mercury was most prominent in the small intestine. Interestingly, the renal uptake and accumulation of mercury were diminished significantly in the rats whose bile duct had been ligated. A time-course experiment showed that the maximum amount of secretory movement of mercury into the lumen of the small intestine occurred during the initial 12 h after the injection of mercuric chloride. By the end of 24 h after the injection of mercuric chloride, much of the inorganic mercury secreted in the small intestine appeared to have moved down into the large intestine. In a third experiment, the disposition of mercury was evaluated in control rats and rats who had their bile duct cannulated. The rationale for this third experiment was to study the disposition of mercury under conditions where obstruction of biliary outflow from the liver would not be as much of an issue as with ligation of the bile duct. Evidence for movement of mercury into the lumen of the intestines was also obtained from the rats whose bile duct had been ligated. Eighteen hours after the injection of mercuric chloride the amount of mercury in the luminal compartment of the small intestine was not statistically different between the two groups of rats. Approximately 1.7-2.1% of the administered dose was present in the luminal contents of the small intestine. Decreased renal uptake of mercury was also detected in the rats whose bile duct had been cannulated. The findings from the present study show that when bile flow is obstructed or diverted, clear evidence for secretory movement of mercury into the lumen of the gastrointestinal (GI) tract can be demonstrated. These findings also indicate that the secretory movement of mercury into the lumen of the GI tract is a mechanism that contributes significantly to the pool of mercury that is excreted in the feces.

Small Aliphatic Dicarboxylic Acids Inhibit Renal Uptake of Administered Mercury

We evaluated the effects of pretreating rats intravenously with small aliphatic dicarboxylic acids on the renal disposition of injected inorganic mercury. Three different sets of experiments were carried out. When rats were pretreated with succinic acid, glutaric acid, or adipic acid 5 min prior to the injection of a 0.5-μmol/kg dose of mercuric chloride, there was a significant dose-dependent inhibitory effect on the renal disposition of mercury during the first hour after the administration of mercuric chloride. Both glutaric and adipic acid, at a dose of 1.0 mmol/kg, caused the greatest level of inhibition in the renal tubular uptake of inorganic mercury. By the end of the first hour after the injection of mercuric chloride, the renal burden of mercury in rats pretreated with either glutaric or adipic acid was 27–35% lower than in corresponding control rats. Malonic acid at a dose of 1.0 mmol/kg had no effect on the renal disposition of inorganic mercury. The inhibitory effect of succinic, glutaric, or adipic acid on the overall renal uptake of mercury was due to effects in both the cortex and outer stripe of the outer medulla. Findings from an experiment in which rats had their ureters ligated showed that the inhibitory effect of glutaric acid on the renal tubular uptake of mercury was due to inhibition of the uptake of mercury at the basolateral membrane. Our findings confirm that one of the mechanisms involved in the proximal tubular uptake of inorganic mercury is located on the basolateral membrane. According to findings from our previous studies, this mechanism appears to involve the activity of the organic anion transporter. The inhibitory effects of dicarboxylic acids on the renal tubular uptake of administered inorganic mercury, especially in rats whose ureters had been ligated, are consistent with the hypothesis that the organic anion transport system is involved in the basolateral uptake of inorganic mercury along the proximal tubule.

Reductions in Renal Mass and the Nephropathy Induced by Mercury

The severity of renal injury induced by several graded doses of mercuric chloride and the disposition of mercury were evaluated and compared in control, uninephrectomized (50% NPX), and 75% nephrectomized (75% NPX) rats in an attempt to determine the effect of increased reductions of renal mass on the nephropathy induced by inorganic mercury. Consistent with previously published findings, proximal tubular necrosis (as assessed histopathologically and by the urinary excretion of lactate dehydrogenase (LDH) and total protein) was significantly more severe in 50% NPX rats than in control rats 24 hr after the administration of any of three lowest (1.0, 1.5, or 1.75 μmol/kg) doses of mercuric chloride used in the study. Interestingly, the severity of proximal tubular necrosis in the 75% NPX rats was not greater than that in control rats at these same doses. The reason for this appeared to be due to decreased renal accumulation of mercury, particularly in the renal cortex and outer stripe of the outer medulla. At the highest (8.0 μmol/kg) dose of mercuric chloride used, renal tubular injury was very extensive in all three groups of rats, with the level of injury being greatest in the 50% NPX rats. The injury was so severe in all three groups that acute renal failure was induced within the first 24 hr after the injection of mercury. An important finding that was made at this dose was that the level of blood urea nitrogen (BUN) was significantly greater in the 75% NPX rats than in either the 50% NPX or control rats, which indicates that 75% NPX rats may have entered into acute renal failure sooner than the 50% NPX or control rats. Overall, the findings from the present study indicate that as renal mass is reduced to a level at which renal function is not significantly impaired (50% NPX), the severity of the nephropathy induced by mercury is increased. By contrast, when the reduction of renal mass progresses to a level at which renal function begins to become impaired, the level of proximal tubular injury is not greatly different from that of animals with two kidneys, especially at low nephrotoxic doses of inorganic mercury. In addition, low nephrotoxic doses of inorganic mercury do not appear to affect significantly the reduced glomerular filtration rate in 75% NPX rats. However, it does appear that 75% NPX rats may be at greater risk of entering into acute renal failure at higher toxic doses of inorganic mercury than 50% NPX or control rats.

ENHANCED RENAL OUTER MEDULLARY UPTAKE OF MERCURY ASSOCIATED WITH UNINEPHRECTOMY: IMPLICATION OF A LUMINAL MECHANISM

In the present study, pretreatment with p-aminohippurate (PAH) and induction of stopflow conditions (by ureteral ligation) were used as tools to determine whether the enhanced accumulation of injected inorganic mercury that occurs in the renal outer stripe of the outer medulla in rats following uninephrectomy and compensatory renal growth is due to a luminal and/or basolateral mechanism. The effects of these pretreatments on the disposition of mercury in the liver and blood were also evaluated as a secondary aim. Pretreatment of both uninephrectomized (NPX) and control rats with a 7.5 mmol/kg dose of PAH 5 min prior to the injection of a nontoxic 0.5 mol/kg iv dose of mercuric chloride caused a significant decrease in the renal accumulation of mercury in both control and NPX rats during the initial 3 h after the injection of inorganic mercury. However, the concentration of mercury in the renal outer stripe of the outer medulla was significantly greater in the NPX rats than in the corresponding control rats. Induction of stop-flow conditions (by iv bolus injection of 2.0 mmol/kg mannitol followed 5 min later by ureteral ligation) approximately 75 min prior to the injection of inorganic mercury also resulted in decreased renal accumulation of mercury in both NPX and control rats. In contrast to the effects of PAH, induction of stop-flow conditions resulted in the concentration of mercury in the renal outer stripe of the outer medulla in the NPX rats being statistically equivalent to that in the corresponding control rats 3 h after the injection of mercury. Assuming that glomerular filtration rate was reduced to negligible levels in these animals, the fraction of mercury that was not taken up and accumulated in the outer stripe of both groups of rats represents the fraction of mercury that is taken up by a luminal mechanism. Thus, on the basis of the findings in this study, it appears that the increased accumulation of mercury that occurs in the renal outer stripe of the outer medulla in NPX rats is linked to a luminal mechanism, presumably localized in the epithelial cells lining the proximal tubule. Finally, when pretreatment with PAH and induction of stop-flow conditions were combined, there was additivity with respect to decreased renal accumulation of mercury. This additivity provides further support for the current hypothesis that there are both luminal and basolateral mechanisms involved in the renal uptake of inorganic mercury.

Pretreatment with p-aminohippurate inhibits the renal uptake and accumulation of injected inorganic mercury in the rat

The effects of intravenous pretreatment with the organic anion p-aminohippurate (PAH) on the disposition of intravenously administered inorganic mercury in the kidneys, liver and blood were evaluated in rats. In dose-response experiments, the renal uptake (and/or accumulation) of mercury, 1 h after the injection of a nontoxic 0.5 μmol/kg dose of mercuric chloride (HgCl 2), was significantly reduced in rats when a 1.0, 3.3 or 10 mmol/kg dose of PAH was administered 5 min prior to the injection of HgCl 2. This reduction was due to reduced uptake of mercury in both the renal cortex and outer stripe of the outer medulla. Near maximal inhibition appeared to be achieved with the 10 mmol/kg dose of PAH. Inhibition of the uptake (and/or accumulation) of mercury in the renal cortex and outer stripe of the outer medulla, 1 h after the injection of the nontoxic dose of HgCl 2, was also detected in experiments where HgCl 2 was injected 5, 30, 60 or 180 min after pretreatment with a 10 mmol/kg dose of PAH. The renal uptake of mercury was inhibited significantly when the nontoxic dose of inorganic mercury was administered 5, 30 or 60, but not 180 min after pretreatment with the 10 mmol/kg dose of PAH. In another experiment, the renal burden of mercury was significantly reduced for 24 h when pretreatment with a 10 mmol/kg dose of PAH was administered 5 min prior to the injection of HgCl 2. Pretreatment with PAH did not have an effect on the hepatic disposition of mercury, but it did cause a significant increase in the fraction of mercury present in the plasma of blood. In summary, the findings in the present study indicate that pretreatment with PAH inhibits the renal uptake of injected inorganic mercury in a dose-dependent and time-dependent manner. In addition, the findings tend to indicate that some fraction of the mercury that enters into renal tubular epithelial cells is by a mechanism involving the organic anion transport system.

Luminal and basolateral mechanisms involved in the renal tubular uptake of inorganic mercury.

The principle aim of the present study was to provide evidence for the existence of both a luminal and a basolateral mechanism involved in the renal tubular uptake of inorganic mercury. To accomplish this aim, we examined individually and collectively the effects of a "stop-flow" technique designed to reduce glomerular filtration to negligible levels and pretreatment with the organic anion p-aminohippurate (PAH) on the renal uptake and disposition of administered inorganic mercury. More specifically, we compared the disposition of inorganic mercury in groups of surgical control rats, rats that underwent a unilateral ureteral ligation, and rats that underwent a bilateral ureteral ligation that were pretreated with either normal saline or a 7.5 mmol/kg intravenous dose of PAH 5 min prior to receiving a nontoxic 0.5-mumol/kg intravenous dose of mercuric chloride. The disposition of mercury was evaluated at both 1 h and 24 h after the dose of inorganic mercury had been administered. In brief, the "stop-flow" conditions induced by either unilateral or bilateral ureteral ligation caused a significant reduction in the uptake and content of mercury in the kidneys (whose ureter was ligated) both at 1 h and 24 h after the intravenous injection of the nontoxic dose of mercuric chloride. This decreased renal uptake of mercury was due specifically to decreased uptake of mercury in the renal cortex and outer stripe of the outer medulla. Assuming that glomerular filtration was reduced to negligible levels, the amount of mercury not taken up during ureteral ligation represents the portion of mercury that is presumably taken up by a luminal mechanism. Pretreatment with PAH also caused a significant reduction in the renal uptake of mercury, specifically in the cortex and outer stripe of the outer medulla. The effects were most prominent 1 h after the injection of inorganic mercury. When either unilateral or bilateral ureteral ligation was combined with PAH pretreatment, an additive inhibitory effect occurred with respect to the renal uptake of mercury. In fact, the renal uptake of mercury was reduced by approximately 85% at 1 h after the injection of mercuric chloride. Since the luminal uptake of mercury was blocked by ureteral ligation, the effect of PAH on the renal uptake of mercury must have occurred at the basolateral membrane. Thus, the findings from the present study indicate that there are two distinct mechanisms involved in the uptake of mercury, with one mechanism located on the luminal membrane and another located on the basolateral membrane (presumably on proximal tubular epithelial cells).

Organic anion transport and action of gamma-glutamyl transpeptidase in kidney linked mechanistically to renal tubular uptake of inorganic mercury.

In the present study, the roles of renal tubular gamma-glutamyl transpeptidase and renal organic anion transport on the renal uptake and accumulation and intrarenal distribution of injected inorganic mercury were investigated. The renal (and general) disposition of injected inorganic mercury (Hg2+) was evaluated in control rats, rats pretreated with two 10 mg/kg doses of acivicin, rats pretreated with a 10 mmol/kg dose of p-aminohippurate (PAH), and rats pretreated with both acivicin and PAH. The dose(s) of acivicin were used to inhibit the activity of renal gamma-glutamyl transpeptidase to a near maximal level and the dose of PAH (which is a water-soluble organic anion) was used to competitively inhibit the renal organic anion transport system to a near maximal level. Dispositional data were obtained at both 1 and 24 hr after a nontoxic, 0.5 mumol/kg iv dose of mercuric chloride had been administered. Radiolabeled inorganic mercury (203Hg2+) was added to the injection solution containing the mercuric chloride to make it possible to quantitate the accumulation and disposition of mercury using standard isotopic methods. The renal concentration and content of mercury were significantly lower in the rats pretreated with either acivicin or PAH than in the control rats at both times after the injection of inorganic mercury. Pretreatment with acivicin mainly affected the content of mercury in the renal cortex, while pretreatment with PAH affected the content of mercury in both the renal cortex and the outer stripe of the outer medulla. Interestingly, the renal concentration and content of mercury in the rats pretreated with both acivicin and PAH were significantly lower than in any of the other three groups at both times after injection of inorganic mercury. Evaluation of the intrarenal distribution of mercury indicated that the renal cortex was the main zone in which the uptake of mercury was significantly affected by both acivicin and PAH. The findings from this study indicate that the renal tubular uptake of administered inorganic mercury is linked both to the transport of organic anions and to the action of gamma-glutamyltransferase. Thus, at least two mechanisms appear to be involved in the renal tubular uptake of inorganic mercury.

Renal disposition of mercury in rats after intravenous injection of inorganic mercury and cysteine

The disposition of mercury in the blood, kidneys and liver was evaluated and compared in rats 5 min, 1 h, and 24 h after the intravenous administration of a 0.25 mumol/kg dose of inorganic mercury or a 0.25 mumol/kg dose of inorganic mercury plus a 0.5 mumol/kg dose of cysteine to determine the possible role of extracellular cysteine and complexes of cysteine and inorganic mercury in the renal uptake and transport of inorganic mercury. More inorganic mercury was present in the blood of the rats injected with inorganic mercury alone than in the blood of the rats injected simultaneously with both the inorganic mercury and cysteine during the first hour after injection. In addition, significantly more mercury was in the plasma fraction of blood in the rats injected with both inorganic mercury and cysteine than in the rats injected with inorganic mercury alone. These findings indicate that much of the mercury injected with cysteine was in some form of a complex that allowed the mercury to be cleared from the blood more readily and prevented the mercury from entering readily into the cellular components of blood. The renal concentration of mercury was significantly greater in the rats injected with both inorganic mercury and cysteine than in the rats injected with inorganic mercury alone 1 h, but not 24 h, after injection. This increased renal accumulation of mercury during the initial hour after injection was due mainly to enhanced uptake and/or retention of mercury in the renal cortex, although some of the enhanced accumulation of mercury also occurred in the outer stripe of the outer medulla during the first hour after injection. These data indicate that coadministration of a nontoxic dose of inorganic mercury with a twofold higher amount (in moles) of cysteine increases significantly the clearance of mercury from the blood and increases the accumulation of inorganic mercury in the renal cortex and outer stripe of the outer medulla during the initial 1 h after injection. In conclusion, the data in this study are consistent with the hypothesis that complexes of inorganic mercury and cysteine in the blood and/or ultrafiltrate probably play a role in the renal uptake of some of the mercury in blood after exposure to mercuric compounds.

Effects of dietary lipids on whole-body retention and organ distribution of organic and inorganic mercury in mice

The effect has been investigated of dietary lipids on the whole-body retention and organ distribution of organic and inorganic mercury in mice. A single oral dose of methylmercury chloride or mercuric chloride labelled with 203Hg was given to female NMRI mice fed semi-synthetic diets containing varying amounts (5, 10, 20 or 50%) of energy derived from lipid (coconut oil, soya oil, or cod liver oil). The whole-body retention and relative organ distribution of mercury depended on diet composition. Thus, a significant reduction of the whole-body retention of mercury was seen in mice fed a diet containing 50% cod liver oil compared with mice fed a diet containing 50% coconut oil. After oral administration of mercuric chloride the relative deposition of mercury in the kidneys increased while that in the liver decreased with increasing concentrations of soya oil or coconut oil in the diet. The whole-body retention of mercury after treatment with methylmercury chloride was significantly decreased in mice fed cod liver oil compared with mice fed coconut oil; there was no difference between mice fed cod liver oil and those fed soya oil. The relative disposition of mercury was significantly higher in all organs of mice fed a diet containing 20% energy from cod liver oil compared with mice fed a diet containing 20% energy from soya oil. The present study demonstrates that diet composition is of major importance to the toxicokinetics of methylmercury and mercuric mercury.