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Mercury (Hg), a divalent metal, produces adverse effects predominantly in the renal and central nervous systems. The aim of this study was to determine the effectiveness of copper (Cu) in prevention of mercuric mercury (Hg2+)-mediated toxic effects as well as the role metallothioneins (MT) play in this protective mechanism in young rats. Wistar rats were treated subcutaneously with saline (Sal) or CuCl2.2H2O (Cu 2.6 mg/kg/day) from 3 to 7 days old and with saline or HgCl2 (Hg 3.7 mg/kg/day) from 8 to 12 days old. The experimental groups were (1) Sal-Sal, (2) Cu-Sal, (3) Sal-Hg, and (4) Cu-Hg. MTs and metal contents were determined at 13 and 33 days of age. Porphobilinogen synthase (PBG-synthase) activity as well as renal and hepatic parameters were measured at 33 days. At 13 day, Hg2+ exposure increased hepatic MT, Hg, zinc (Zn) and iron (Fe) levels, in kidney elevated Cu and Hg and decreased renal Fe concentrations, accompanied by elevated blood Hg levels. At 33 days, Hg2+ exposure inhibited renal PBG-synthase activity, increased serum urea levels and lowered Fe and Mg levels. Copper partially prevented the rise in blood Hg and liver Fe noted at 13 days; and completely blocked urea rise and diminished renal PBG-synthase activity inhibition at 33 days. In 13-day-old rats, Cu exposure redistributed the Hg in the body, decreasing hepatic and blood levels while increasing renal levels, accompanied by elevated renal and hepatic MT levels in Hg2+-exposed animals. These results suggest that hepatic MT might bind to hepatic and blood Hg for transport to the kidney in order to be excreted. ABBREVIATIONS: MT: metallothioneins; PBG-synthase: porphobilinogen synthase.

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This study examined the effects of inorganic mercury exposure on behavioral and biochemical parameters and investigated the possible preventive effects of zinc on the alterations induced by mercury. Pups were exposed from 3rd to 7th postnatal day to ZnCl2 (27 mg/kg/day, s.c.) and subsequently to HgCl2 (5 doses of 5 mg/kg/day, s.c.). Each litter contained two rats for each treatment. The rats were submitted to behavioral task and litters were killed at 13 or 33 days old for acetylcholinesterase activity assays and for the determination of metal levels. Based on the results obtained from 13-day-old rats, they were divided in two groups of litters that were defined at the end of the experimental period (33 days) as less sensitive rats to mercury and more sensitive rats to mercury in accordance with the recovery of body weight until day 33. The mercury exposure caused accumulation of this metal in cerebrum and cerebellum in all mercury treated rats, and inhibited the cerebellum acetylcholinesterase activity from 13-day-old rats. Besides, the mercury-animals of the most sensitive litters to mercury presented impairment in motor function and muscular strength verified in the beaker test, as well as a reduction of the locomotor and exploratory activities in the open field task. Zinc partially prevented all the alterations induced by mercury exposure and reduced the mercury level accumulated in cerebrum and cerebellum. This study confirms the preventive effect of zinc on behavioral alterations induced by mercury in young rats and demonstrates that the mercury behavioral effects are present even for a long time after the end of the exposure.

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The present study was designed to evaluate the time course changes in peripheral markers of oxidative stress in a chronic HgCl2 intoxication model. Twenty male adult Wistar rats were treated subcutaneously daily for 30 days and divided into two groups of 10 animals each: Hg, which received HgCl2 (0.16 mg kg(-1) day(-1)), and control, receiving the same volume of saline solution. Blood was collected at the first, second and fourth weeks of Hg administration to evaluate lipid peroxidation (LPO), total radical trapping antioxidant potential (TRAP), and superoxide dismutase (Cu,Zn-SOD), glutathione peroxidase (GPx), glutathione-S-transferase (GST), and catalase (CAT). HgCl2 administration induced a rise (by 26%) in LPO compared to control (143 +/- 10 cps/mg hemoglobin) in the second week and no difference was found at the end of the treatment. At that time, GST and GPx were higher (14 and 24%, respectively) in the Hg group, and Cu,Zn-SOD was lower (54%) compared to control. At the end of the treatment, Cu,Zn-SOD and CAT were higher (43 and 10%, respectively) in the Hg group compared to control (4.6 +/- 0.3 U/mg protein; 37 +/- 0.9 pmol/mg protein, respectively). TRAP was lower (69%) in the first week compared to control (43.8 +/- 1.9 mM Trolox). These data provide evidence that HgCl2 administration is accompanied by systemic oxidative damage in the initial phase of the process, which leads to adaptive changes in the antioxidant reserve, thus decreasing the oxidative injury at the end of 30 days of HgCl2 administration. These results suggest that a preventive treatment with antioxidants would help to avoid oxidative damage in subjects with chronic intoxication.

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The present study was designed to evaluate the time course changes in peripheral markers of oxidative stress in a chronic HgCl2 intoxication model. Twenty male adult Wistar rats were treated subcutaneously daily for 30 days and divided into two groups of 10 animals each: Hg, which received HgCl2 (0.16 mg kg-1 day-1), and control, receiving the same volume of saline solution. Blood was collected at the first, second and fourth weeks of Hg administration to evaluate lipid peroxidation (LPO), total radical trapping antioxidant potential (TRAP), and superoxide dismutase (Cu,Zn-SOD), glutathione peroxidase (GPx), glutathione-S-transferase (GST), and catalase (CAT). HgCl2 administration induced a rise (by 26 percent) in LPO compared to control (143 ± 10 cps/mg hemoglobin) in the second week and no difference was found at the end of the treatment. At that time, GST and GPx were higher (14 and 24 percent, respectively) in the Hg group, and Cu,Zn-SOD was lower (54 percent) compared to control. At the end of the treatment, Cu,Zn-SOD and CAT were higher (43 and 10 percent, respectively) in the Hg group compared to control (4.6 ± 0.3 U/mg protein; 37 ± 0.9 pmol/mg protein, respectively). TRAP was lower (69 percent) in the first week compared to control (43.8 ± 1.9 mM Trolox). These data provide evidence that HgCl2 administration is accompanied by systemic oxidative damage in the initial phase of the process, which leads to adaptive changes in the antioxidant reserve, thus decreasing the oxidative injury at the end of 30 days of HgCl2 administration. These results suggest that a preventive treatment with antioxidants would help to avoid oxidative damage in subjects with chronic intoxication.

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Mercuric chloride (HgCl2) is a well-known renal toxic that causes acute renal failure. The effect of HgCl2 treatment and the protection by thyroxine were studied in rat renal papilla (P), outer medullary inner stripe (OMIS), outer medullary outer stripe (OMOS) and cortical phospholipids (PhLs). HgCl2 brought about an increase in the total phospholipid content in P and OMIS but a drop in OMOS and cortex. Only phosphatidylcholine (PtdCho) and phosphatidylethanolamine (PtdEtn) accounted for such changes. Thyroxine, injected on HgCl2-treated rats, partially reversed the effect of the toxic metal in P and OMIS while completely reversed the PtdCho drop in OMOS and cortex. However, the hormone failed to recover the sphingomyelin increase in P, the PtdEtn shortage in OMIS, OMOS and partially reversed the drop in the cortex. When thyroxine was injected without toxic treatment, no effect was observed in the phospholipid content of any kidney zone. Results obtained by using 32P as a precursor to study the PhL de novo synthesis were consistent with those of the phospholipid content. Thus a radioactivity increase--associated with PtdCho and PtdEtn--was observed in the kidney zones where said endogenous PhLs had risen. But in OMOS and cortex, where PtdCho and PtdEtn had dropped, they were also accompanied by a decrease in radioactivity. The thyroxine-induced recovery phase also paralleled the phospholipid content results with those of the de novo synthesis. We suggest that the decrease in the renal phospholipid de novo synthesis may constitute one biochemical explanation of the selective renal toxic effect exerted by HgCl2 and that the increase observed in the renal phospholipid metabolism--induced by the toxic treatment in OMIS and P--may represent a protective mechanism of these zones against toxic injury. Moreover, recovery promoted by thyroxine treatment in OMOS and cortex was accompanied by the reversion of the corresponding PtdCho decrease induced by HgCl2.

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Thyroxine (T4) seems to accelerate recovery from various forms of acute renal failure. The mechanisms of this effect are still debated. We decided to evaluate if thyroxine enhances the recovery of HgCl2 renal failure through an increment in the mitotic activity or through an increase in membrane phospholipid biosynthesis of the regenerating tubular cells. Male Wistar rats were allocated to four groups: one group received 0.4 mg/100 g BW HgCl2 SC and saline IP (HgCl2 group); the second received the toxin and 24 and 48 h after it, T4 15 micrograms/100 g BW IP (HgCl2 + T4 group); a third group received saline SC and T4 IP (T4 group), and the last group received saline SC and IP (control group). On the third day GFR was evaluated by 24-h creatinine clearance and afterward rats were sacrificed and the kidneys removed. Some of them were studied histologically, evaluating the severity of the tubular lesion using a semiquantitative score (0-4) and the mitotic index (N mitotic figures per 10 high-power fields). In the other kidneys we studied phospholipid synthesis through the incorporation of 32 P into the different renal phospholipids of the several kidney regions. The T4-treated group had a better recovery of GFR after the toxin (HgCl2 + T4: 0.44 +/- .09 vs. HgCl2: 0.23 +/- .06, p < .05). Both HgCl2-treated groups had similar lesional scores and mitotic indexes.(ABSTRACT TRUNCATED AT 250 WORDS)

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