Developmental variation in copper,zinc and metallothionein mRNA in brindled mutant and nutritionally copper deficient mice

The concentrations of copper, zinc and metallothionein-I (MT-I) mRNA were determined in the liver, kidney and brain of the brindled mutant mouse from birth until the time of death. Despite accumulation of copper in the kidney of the mutant, MT-I mRNA concentrations were normal. There was no difference between the MT-I mRNA in the brain of mutant and normal in the first 10 days of life, but after day 10 metallothionein mRNA levels were increased in the mutant. The concentration of copper was very low in the liver of the mutant, and on day 6 after birth the metallothionein mRNA was also reduced by about 50%. This reduction was not seen in copper-deficient 6-day-old pups, despite very low hepatic copper levels. This suggests that the lower hepatic MT-I mRNA in the day 6 brindled mouse was not simply due to the reduction in hepatic copper and also that hepatic copper is not regulating metallothionein gene expression the liver of neonatal mice. After day 12 hepatic MT-I mRNA levels were elevated in mutant and in copper deficient mice, both of which die at 14 to 16 days. These increases and the increase in brain MT-I mRNA in older mutant mice are likely to be caused by stress. Overall the results support the conclusions that the brindled mutation does not cause a constitutive activation of the metallothionein genes, and that the differences in metallothionein mRNA between mutant and normal are most probably secondary consequences of the mutation.     

Developmental variation in copper, zinc and metallothionein mRNA in brindled mutant and nutritionally copper deficient mice.

The concentrations of copper, zinc and metallothionein-I (MT-I) mRNA were determined in the liver, kidney and brain of the brindled mutant mouse from birth until the time of death. Despite accumulation of copper in the kidney of the mutant, MT-I mRNA concentrations were normal. There was no difference between the MT-I mRNA in the brain of mutant and normal in the first 10 days of life, but after day 10 metallothionein mRNA levels were increased in the mutant. The concentration of copper was very low in the liver of the mutant, and on day 6 after birth the metallothionein mRNA was also reduced by about 50%. This reduction was not seen in copper-deficient 6-day-old pups, despite very low hepatic copper levels. This suggests that the lower hepatic MT-I mRNA in the day 6 brindled mouse was not simply due to the reduction in hepatic copper and also that hepatic copper is not regulating metallothionein gene expression the liver of neonatal mice. After day 12 hepatic MT-I mRNA levels were elevated in mutant and in copper deficient mice, both of which die at 14 to 16 days. These increases and the increase in brain MT-I mRNA in older mutant mice are likely to be caused by stress. Overall the results support the conclusions that the brindled mutation does not cause a constitutive activation of the metallothionein genes, and that the differences in metallothionein mRNA between mutant and normal are most probably secondary consequences of the mutation.     

Metabolism of zinc and copper in the neonate: Zinc thionein in developing rat brain,heart, lung,spleen, and thymus

In a continuing study of the importance of metallothionein (MT) in the growth and development of neonates, zinc and copper metabolism in rat brain, heart, lung, spleen, and thymus has been analyzed in 5, 10, 15, 20 and 25 day old rats. Total, cytosol, and MT zinc and copper concentrations and organ contents were determined. Zinc, but very little, if any copper was associated with MT in these organs. Concentrations ranged from 0.03 to 3.3 μg Zn in MT/g; organ contents ranged from 0.003 to 2.2 μg Zn in MT/organ. Brain exhibited the highest concentrations and contents of zinc in MT, approaching the levels found in kidneys. Rank order of organ contents of zinc in MT was brain > lung > heart, spleen, thymus, during this neonatal growth period. When organ growth was rapid, a large percentage (20–95%) of the cytosolic zinc present in these organs was associated with MT, as has been previously observed with liver, kidneys, and testes. None of these organs undergoes the dramatic changes in zinc and copper metabolism previously observed in neonatal rat liver and gastrointestinal tract, and in maturing testes. They are more comparable to kidneys in their concentrations of zinc in MT. Like testes, little copper is found in these organs.     

Analysis of hepatic copper, zinc, metallothionein and metallothionein-Ia mRNA in developing sheep

The concentrations of zinc, copper, metallothionein and metallothionein-Ia mRNA in sheep livers during development was determined. It was found that early sheep foetuses (30-40 days gestation) had very high concentrations of hepatic zinc (2305 +/- 814 micrograms/g dry mass), and that these levels declined steadily to 644 +/- 304 micrograms/g near to term. The copper concentrations in the foetal livers were not higher than those in the adult. The concentrations of metallothionein and metallothionein-Ia mRNA were also very high in the foetal livers and declined steadily during gestation from 261 +/- 94 molecules/pg RNA to 71 +/- 18 molecules/pg near to term. Metallothionein-Ia mRNA concentrations were closely correlated with hepatic zinc concentrations but not with copper. Metallothionein concentrations also decreased during gestation: e.g. 3044 micrograms/g (wet mass) in one foetus on day 34 of gestation to 862 micrograms/g on day 125. After birth, however, the concentrations of metallothionein declined to less than 100 micrograms/g and this decline occurred despite the presence of significant quantities of mRNA. The ratio of metallothionein/metallothionein-Ia mRNA decreased from 1.3 to 3.2 x 10(5) molecules metallothionein/molecule of metallothionein-Ia mRNA during gestation to between 0.28-0.64 x 10(5) molecules/molecule in the postnatal animals. We conclude that the major function of metallothioneins in the foetal liver is protection of the liver against the potentially toxic accumulation of zinc. In the postnatal sheep there appears to be a decreased synthesis or increased degradation of metallothionein.     

Chronological changes in tissue copper, zinc and iron in the toxic milk mouse and effects of copper loading

The toxic milk (tx) mouse is a rodent model for Wilson disease, an inherited disorder of copper overload. Here we assessed the effect of copper accumulation in the tx mouse on zinc and iron metabolism. Copper, zinc and iron concentrations were determined in the liver, kidney, spleen and brain of control and copper-loaded animals by atomic absorption spectroscopy. Copper concentration increased dramatically in the liver, and was also significantly higher in the spleen, kidney and brain of control tx mice in the first few months of life compared with normal DL mice. Hepatic zinc was increased with age in the tx mouse, but zinc concentrations in the other organs were normal. Liver and kidney iron concentrations were significantly lower at birth in tx mice, but increased quickly to be comparable with control mice by 2 months of age. Iron concentration in the spleen was significantly higher in tx mice, but was lower in 5 day old tx pups. Copper-loading studies showed that normal DL mice ingesting 300 mg/l copper in their diet for 3 months maintained normal liver, kidney and brain copper, zinc and iron levels. Copper-loading of tx mice did not increase the already high liver copper concentrations, but spleen and brain copper concentrations were increased. Despite a significant elevation of copper in the brain of the copper-loaded tx mice no behavioural changes were observed. The livers of copper-loaded tx mice had a lower zinc concentration than control tx mice, whilst the kidney had double the concentration of iron suggesting that there was increased erythrocyte hemolysis in the copper-loaded mutants.     

Cholangioma in white perch (Morone americana) from the Chesapeake Bay

Cholangiomas found in two of 21 wild-caught white perch (Morone americana) from the Chesapeake Bay are described. The two fish were part of a study investigating a condition of abnormal hepatic copper storage in this species. The tumors were superficial, solitary masses consisting of cuboidal to columnar cells in tubuloglandular arrangement. Mild to marked peribiliary inflammation and fibrosis was seen also. Environmental pollution, the condition of abnormal copper storage, peribiliary fibrosis, and/or parasites may have contributed to the development of these tumors.     

Presence of acute phase changes in zinc, iron, and copper metabolism in turkey embryos

Acute phase changes in trace mineral metabolism were examined in turkey embryos. An endotoxin injection resulted in increased concentrations of serum copper and liver zinc and decreased concentrations of serum zinc in embryos incubated either in ovo or ex ovo. Changes in zinc and copper metabolism occurred when endotoxin either was injected intramuscularly, into the amnionic fluid, or administered onto the chorioallantoic membrane. Unlike poults, embryos did not respond to an inflammatory challenge with decreased serum iron concentrations. Acute phase changes in embryo serum zinc and copper as well as liver zinc concentrations were similar to those in poults. Increased liver zinc concentrations were associated with increased zinc in metallothionein (MT). An injection of a crude interleukin 1 preparation into embryos resulted in similar increases in hepatic zinc and MT concentrations as an endotoxin injection, suggesting a role for this cytokine in mediating the acute phase changes in embryonic zinc metabolism.     

Changes in copper and zinc status and response to dietary copper deficiency in metallothionein-overexpressing transgenic mouse heart

Previous studies have shown that cardiac-specific overexpression of metallothionein (MT) inhibits progression of dietary copper restriction-induced cardiac hypertrophy. Because copper and zinc are critically involved in myocardial response to dietary copper restriction, the present study was undertaken to understand the effect of MT on the status of copper and zinc in the heart and the subsequent response to dietary copper restriction. Dams of cardiac-specific MT-transgenic (MT-TG) mouse pups and wild-type (WT) littermates were fed copper-adequate (CuA) or copper-deficient (CuD) diet starting on the fourth day post delivery, and the weanling mice were continued on the same diet until they were sacrificed. Zinc and copper concentrations were significantly elevated in MT-TG mouse heart, but the extent of zinc elevation was much more than that of copper. Dietary copper restriction significantly decreased copper concentrations to the same extent in both MT-TG and WT mouse hearts, and decreased zinc concentrations along with a decrease in MT concentrations in the MT-TG mouse heart. Copper deficiency-induced heart hypertrophy was significantly inhibited, but copper deficiency-induced suppression of serum ceruloplasmin or hepatic Cu,Zn-SOD activities was not inhibited in the MT-TG mice. These results suggest that elevation in zinc but not in copper in the heart may be involved in the MT inhibition of copper deficiency-induced cardiac hypertrophy.     

Cadmium, copper and zinc in tissues of deceased copper smelter workers

Workers at a copper and lead smelter in northern Sweden have a multifactorial exposure to a number of heavy metals. The concentrations of cadmium, copper and zinc in liver, lung, kidney and brain tissues have been determined by atomic absorption spectrometry in 32 deceased long-term exposed male lead smelter workers, and compared with those of 10 male controls. Furthermore, copper and zinc levels in hair and nails were determined by energy-dispersive X-ray fluorescence.

The highest cadmium concentrations among both workers and controls were observed in kidney, followed in order by liver, lung and brain. The levels in kidney, liver and lung were all significantly higher in the workers than in the controls (p < 0.03). Among the workers relatively strong positive correlations (p < 0.03) were observed between cadmium concentrations in liver and lung, liver and kidney, liver and brain, and lung and brain. In the exposed workers a positive correlation was observed between cadmium and zinc concentrations in the kidney (r_s = 0.38; p = 0.034). This is probably mainly due to the protein metallothionein, which is stored in the kidney, binding equimolar amounts of these two metals.

The highest concentrations of copper were found in hair and nails among both workers and controls, followed in order by liver, brain, kidney and lung. The tissue concentrations of copper in brain, lung and kidney were all significantly higher among the smelter workers than in the controls (p ≤ 0.036). Copper levels in lung and age at time of death were positively correlated among the exposed workers (r_s = 0.39; p = 0.029). In the same group, positive correlations between copper and zinc concentrations in kidney (r_s = 0.45; p = 0.009) and nails (r_s = 0.68; p < 0.001) were also observed, reflecting possible biological interactions between these two metals.

Among both workers and controls, the highest zinc concentrations were found in hair, followed in order by nails, liver, kidney, brain and lung. Significantly higher tissue concentrations among the workers as compared with the reference group were noted in kidney, liver and brain (p ≤ 0.033).

Neither copper nor zinc concentrations in hair and nails seemed to provide a useful measure of the trace element status of the smelter workers.     

Developmental changes in hepatic metallothionein, zinc, and copper levels in genetically altered mice.

Using mice that either overexpress metallothionein 1 (MT-1*) or do not express metallothionein 1 and 2 (MT-null) and a control strain (C57BL/6), the essential metal storage function of hepatic metallothionein and its subcellular localization were investigated during development. Hepatic metallothionein, zinc, and copper levels were measured in all groups from gestational day 20 to 60 days of age. Hepatic metallothionein levels were maximal during the perinatal period in both MT-1* and C57BL/6 mice with levels approximately three times higher in MT-1* mice. MT-null mice had no detectable hepatic metallothionein throughout development. Hepatic zinc levels were highest in the neonatal period of MT-1* and C57BL/6 mice and declined to adult levels by 30 days of age, while hepatic zinc levels in MT-null mice did not vary markedly throughout development. Hepatic copper profiles were very similar in MT-1* and MT-null mice as compared with the C57BL/6 mice. Correlation analysis showed a strong positive correlation between hepatic metallothionein and zinc levels in MT-1* mice, moderate correlation between hepatic metallothionein and metals in C57BL/6 mice, but only a very weak correlation between hepatic metallothionein and copper levels in MT-1* mice. Immunohistochemical localization showed specific nuclear staining in both MT-1* and C57BL/6 mice during the neonatal period with a gradual shift to the cytoplasm. The results show that hepatic metallothionein is a major determinant of zinc but not copper levels during murine development. Additionally, hepatic metallothionein levels and localization are regulated in a similar manner in MT-1* and C57BL/6 mice. The MT-null mice maintain a basel level of zinc sufficient for development, which was found to be 15.9 micrograms/g. This value was similar to the levels of hepatic zinc that was not bound to metallothionein in MT-1* and C57BL/6 mice during development.     

Effect of dietary copper and zinc levels on tissue copper,zinc, and iron in male rats

The interaction between dietary copper and zinc as determined by tissue concentrations of trace elements was investigated in male Sprague-Dawley rats. Animals were fed diets in a factorial design with two levels of copper (0.5, 5 μg/g) and five levels of zinc (1, 4.5, 10, 100, 1000 μg/g) for 42 d. In rats fed the low copper diet, as dietary zinc concentration increased, the level of copper decreased in brain, testis, spleen, heart, liver, and intestine. There was no significant effect of dietary copper on tissue zinc levels. In the zinc-deficient groups, the level of iron was higher in most tissues than in tissues from controls (5 μg Cu, 100 μg Zn/g diet). In the copper-deficient groups, iron concentration was higher than control values only in the liver. These data show that dietary zinc affected tissue copper levels primarily when dietary copper was deficient, that dietary copper had no effect on tissue zinc, and that both zinc deficiency and copper deficiency affected tissue iron levels.     

Effects of sub-chronic low-level lead exposure on the homeostasis of copper and zinc in rat tissues

Information about the health risks or the subtle adverse health effects that might be associated with low-level lead exposure on micronutrient metabolism are scarce in the literature. The present work investigated the subtle adverse health effects of exposure to progressively low levels of lead on the metabolism of two micronutrients, copper and zinc in different tissues of the rat. Rats were exposed to 200, 300 and 400 ppm lead in their drinking water for 12 weeks. Lead, copper and zinc concentrations were determined in blood, liver, kidney, heart, spleen and brain of the animals. While the imbalance in zinc metabolism was characterized by a deposition of zinc in the kidney and to a lesser extent in the heart of the animals, imbalance in copper metabolism was characterized by a depletion of blood and splenic copper concentrations as well as renal and cardiac accumulation of copper. Hepatic and brain copper and zinc contents, together with blood zinc were not affected by the 12-week lead exposure. A linear relationship was observed between lead dose and lead accumulation in the spleen, whereas a non-linear relationship was observed between lead dose and lead accumulation in blood, liver, kidney and heart. Our findings indicate that exposure to progressively low-level lead concentrations results in imbalance in copper and zinc in the organism and this might be a factor in propensity toward behavioral disorders observed in lead exposure.     

Metallothionein accumulation may account for intracellular copper retention in Menkes' disease

Cultured lymphoblasts derived from infants with Menkes' disease exhibit the same increased avidity for copper as do fibroblasts and most extrahepatic tissues from these patients. The Menkes' cells preferentially take up not only copper but also, on exposure to elevated metal concentrations, the other metallothionein-binding metals, zinc and cadmium. Menkes' lymphoblasts contain larger amounts of metallothionein than normal cells following exposure to each of these metals; the amount bound to this protein quantitatively accounted for the total cellular increment in metal in Menkes' cells. Induction of metallothionein synthesis caused both normal and Menkes' cells to subsequently take up increased amounts of 67Cu. These observations suggest that an enhanced capacity of Menkes' cells to accumulate metallothionein may be responsible for their increased uptake and retention of copper.     

Variation in the amounts of hepatic copper, zinc and metallothionein mRNA during development in the rat.

Amounts of hepatic metallothionein mRNA were assessed in RNA from foetal and neonatal rat livers by using dot-blot hybridization. Metallothionein mRNA began to increase about day 15 of gestation and reached a foetal maximum of 5-fold higher than adult values between 18 and 21 days of gestation. The amounts fell significantly for the first 3 days after parturition, and rose again to 6-fold above adult values 6 days after birth. By 15 days after birth the metallothionein mRNA had declined to adult amounts. In comparison, amounts of ornithine transcarbamoylase mRNA did not vary greatly during development. Hepatic zinc concentrations increased from day 14 of gestation to a maximum just before birth, and remained above adult values until 30 days after birth. From 14 days of gestation to 8 days after birth, hepatic copper concentrations were about 4-fold higher than in the adult, but a substantial increase (to about 9-fold higher than in the adult) occurs between 10 and 15 days after birth. CdCl2 administered to pregnant rats on day 18 of gestation was shown to block placental transfer of zinc, and we found decreased foetal hepatic zinc concentration after the CdCl2 treatment, but this failed to cause a significant decrease in metallothionein mRNA, suggesting that zinc may not be the primary inducer of hepatic metallothionein mRNA during foetal life.     

Influence of spontaneous diabetes on tissue status of zinc, copper, and manganese in the BB Wistar rat

The concentrations of zinc, copper, and manganese in liver, kidney, duodenum, pancreas, testes, bone, and serum from control and untreated, spontaneously diabetic BB Wistar rats were compared. Chronic insulin deficiency resulted in significant alterations in the concentrations of one or more of these essential micronutrients in several tissues. The amounts of zinc and copper bound to metallothionein in the liver and kidney of untreated spontaneously diabetic rats were also markedly increased. The tissue trace metal status in diabetic rats was altered similarly in both male and female rats. Daily injections of insulin blocked many of the changes in the tissue concentrations of the metals. The effects of spontaneous diabetes on tissue trace metal status are quite similar to those reported for chemically induced diabetes. Thus, these results demonstrate that chronic endocrine imbalance is responsible for a series of tissue specific changes in the transport and metabolism of zinc, copper, and manganese.     

Induction of metallothionein in rat tissues following subchronic exposure to mercury shown by radioimmunoassay

Although the analysis of metallothionein (MT) by radioimmunoassay (RIA) is not a common technique, its use is preferred over other methods since it offers the advantages of sensitivity and specificity. In this paper we present data on the basal levels of MT in rat tissues and physiological fluids of female Sprague-Dawley rats. The mean basal MT concentrations of the following organs and fluids were determined by RIA to be: liver (9.8 μg/g), kidney (68 μ/g), brain (0.8 μg/g), spleen (1.0 μg/g), heart (5.4 μg/g), plasma (11 ng/ml), and urine (200–300 μg/g creatinine). Following subcutaneous exposure to inorganic mercury (0.2 μmol/kg/d, 5 d a week for up to 4 wk), the metal accumulated primarily in the kidney. There was also a simultaneous accumulation of zinc in the liver and of zinc and copper in the kidney. Induction of MT did take place in liver, kidney, brain, and spleen. No increases in the MT contents of blood and urine were noted. The excess zinc and copper in the kidney of exposed animals were found to be associated predominantly with MT. No overt signs of mercury toxicity were noted in these animals and the incidence of proteinurea was nil. The data are discussed with reference to methods of MT determination in animal tissues and in relation to mercury metabolism and toxicity.     

Influence of zinc on copper binding in tissue proteins of steers

Two experiments were conducted with steers fed diets containing 270 ppm copper either with or without 2050 ppm zinc. Liver biopsies were taken from steers biweekly for 10 wk for analysis. The steers were then killed; tissues were removed, homogenized, and centrifuged, and the pellets were extracted with mercaptoethanol (BME), and selected cytosols and extracts were subjected to gel filtration (Sephadex G-75). Copper and zinc were determined on the BME extracts, pellets after extraction, cytosols, and gel-filtration fractions. Copper accumulated at about the same rate in BME extract and in the extracted pellet, with the smallest amount in the cytosol. In contrast, over 70% of the zinc was present in the hepatic cytosols. Gel filtration of BME extracts revealed the greatest amount of copper in a low-molwt (MW) peak in addition to three minor peaks of copper. Within the hepatic cytosols, the greatest amount of copper accumulated in proteins of MW>75,000, the next greatest amount in 30,000-MW proteins, and the least amount with metallothionein (MT) of steers fed the diet with only copper added. In contrast, the greatest amount of copper was present with MT in hepatic cytosols of the steer fed a diet that included copper plus zinc. Hence the zinc status of steers influences the deposition of copper in the cytosolic proteins (as demonstrated by liver, kidney, and pancreas), but not in the intracellular fractions.     

Concentrations of copper, iron, and zinc in the major organs of the wistar albino and wild black rats: a comparative study

The concentrations of copper, iron, and zinc in the major organs of Wistar albino (Rattus norvegicus) and wild black rats (Rattus rattus) were measured by means of atomic absorption spectroscopy. The copper levels in the kidneys and liver of the Wistar albino rats (WARs) were significantly higher (p<0.05) than in the wild black rats (WBRs). There were no significant differences in the concentrations of zinc in the liver, lungs, kidneys, and brain between the two study groups, but zinc was significantly higher in the spleen (p<0.05) and lower in the heart (p<0.05) of WAR, compared to WBRs. Iron was significantly higher (p<0.05) in the heart and spleen of WBRs, compared to WARs.There were no extreme differences in the organ concentrations of trace elements between the two species, but, cumulatively, the WARs tend to have higher metallic concentrations in their system than the WBRs. The potential of these differences on the experimental results should not be overlooked and will serve as basis to further consider the complex interrelationships of these animals in their microenvironments and macroenvironments.     

The effects of cadmium and copper on the renal uptake and metallothionein binding of gold in the rat and hamster

Rats and hamsters, (pre)-treated with copper and cadmium, were used to investigate whether species-differences in renal metallothionein synthesis in response to gold were determined by changes in the kidney concentrations of other metals. The effects of both dietary copper limitation and excess on the renal metabolism of gold also were studied in the rat. In this species, all of the pre-treatments affected the renal concentrations of total and metallothionein-bound copper, but none of them altered either the kidney uptake or thionein-binding of gold. Incorporation of zinc into the metallothionein, which accompanied the binding of gold in this fraction of the kidney, however, was influenced slightly by the pretreatments. In hamsters, pretreatment with cadmium, which increased the concentrations of total and thionein-bound zinc in the kidneys, also did not affect the renal uptake of gold, although it increased significantly the binding of gold to the metallothionein fraction of the renal cytosol. This increased binding of gold also was accompanied by further increases in the zinc and copper contents of the metallothionein; the contents of total and thionein-bound cadmium, however, remained essentially unchanged. Concentrations of copper and zinc in the hamster kidney were not affected significantly by subcutaneous administration of copper alone (five daily doses, each of 3.2 mg Cu/kg body wt.), but were increased when gold was given during the copper-treatment. The concentrations of gold, copper and zinc in the renal metallothionein fraction also were increased under these conditions. From these results it seems that kidney metallothionein synthesis in response to gold may be related to the changes in either the concentration or distribution of zinc, rather than copper.     

Effect of acute administration of mercuric chloride on the disposition of copper, zinc, and iron in the rat

The present study was designed to investigate the effect of mercuric chloride administration on copper, zinc, and iron concentrations in the liver, kidney, lung, heart, spleen, and muscle of rats. The results showed that after dose and time exposure to mercuric chloride, the concentration of mercury in the six tissues was significantly elevated. Data showed that there were no interaction between mercury and tissue iron. There was a considerable elevation of the content of copper in the kidney and liver. The most significant changes in the copper concentration took place in the kidneys. About a twofold increase in the copper content of the kidney was noted after exposure to mercuric chloride (3 mg and 5 mg/kg). Only slight elevations in the copper content occurred in the liver, especially in high dose and longer exposure time. In the remaining organs, the copper content was not changed significantly (p>0.05). The most significant changes in the zinc concentration took place in liver, kidney, lung, and heart (5 mg/kg). Marked changes in kidney zinc concentrations were observed at any of the specified doses. Zinc concentrations were significantly increased in kidney of rats sacrificed 9–48 h after sc injection of HgCl₂ (5 mg/kg); in liver obtained from rats at 18, 24, or 48 h after injection; and in lung after 24 or 48 h of treatment. The heart and spleen zinc concentrations were elevated at 24 and 48 h after injection of HgCl₂ (5 mg/kg), respectively. The results of this study implicate that effects on copper and zinc concentrations of the target tissues of mercury may play an important role in the pathogenesis of acute mercuric chloride intoxication.