Tissue-specific accumulation of metallothionein in chickens as influenced by the route of zinc administration

The effect of the route of zinc (Zn) administration on the induction of metallothionein (MT) in various tissues of chicks was examined. Four-week-old, male chicks were assigned to one of four treatments: 5 mg Zn/kg intraperitoneal (i.p.) injection, 5 mg Zn/kg intravenous (i.v.) injection, 16 mg Zn oral (O) dose or a saline control (C). Chicks were fasted overnight, treated and killed 24 h later. 109Cd radioassay analysis of liver (L), kidney (K) and pancreas (P) showed a significant elevation of MT in all tissues except K of i.v. chicks. Comparing tissue MT accumulation within treatments showed that L was induced to a greater extent than P for the i.p. treatment (P/L ratio = 0.69 +/- 0.04), while the reverse effect was seen for both O (1.51 +/- 0.10) and i.v. (1.67 +/- 0.14) chicks, reflecting greater P than L accumulation. Zn injected i.p. did not result in significantly greater total peritoneal exudate cell (PEC) or macrophage (M) numbers than saline-injected controls. Sephadex, while causing massive increases in PEC and M, did not induce tissue MT, demonstrating the lack of correlation between PECs or Ms and MT accumulation. Feed intake by chicks during the 24-h period following i.p. Zn treatment was only 30% of that by controls. A subsequent experiment demonstrated that a similar restriction in feed intake increased L but not P MT. This increase accounted for 17.8% of the L induction due to i.p. Zn injection. This does not fully account for the reduction in P/L that is characteristic of i.p. treatment.(ABSTRACT TRUNCATED AT 250 WORDS)     

Endotoxin-induced changes in copper and zinc metabolism in the Syrian hamster

The temporal response of zinc and copper metabolism to endotoxin administration was examined in Syrian hamsters over a 144-hour period. Serum copper was significantly elevated at 12, 24 and 72 hours after endotoxin, whereas serum zinc was reduced 4-48 hours after treatment. A brief elevation (8 hours) in liver copper concentration and a sustained (72 hours) increase in liver zinc concentration were also observed. The amount of zinc associated with liver metallothionein (MT) progressively increased with time, to a plateau by 24 hours and persisted at the elevated level until 72 hours after endotoxin treatment. In vitro translation of poly (A)+ RNA from liver polyribosomes showed that following endotoxin treatment MTmRNA activity was maximally elevated 6 hours after endotoxin administration and remained elevated 24 and 48 hours thereafter. Slab gel electrophoresis of serum proteins indicated changes in a stainable protein comigrating with purified ceruloplasmin after endotoxin administration. Pooled gingival tissue from endotoxin-treated hamsters demonstrated a consistently elevated copper content 12-144 hours after treatment. Endotoxin isolated from Bacteroides melaninogenicus was more effective in elevating gingival and serum copper and gingival zinc than Escherichia coli endotoxin. It was concluded that endotoxin administration elicits responses that result in enhanced metaollthionein mRNA activity. In addition, Cu and Zn concentrations in serum, liver and gingival tissue are influenced by different endotoxins to different degrees.     

Comparative study of effect of acute administration of cadmium and silver on ceruloplasmin and metallothionein: Involvement of disposition of copper,iron, and zinc

Male ICR mice were subcutaneously injected with either aqueous Ag (1.5 or 5.0 mg/kg) or Cd (1.5 or 2.5 mg/kg) for 2 consecutive days. Body fluids and livers were collected 24 hr after the second dose. In the hepatic supernatant, Ag and Cd were recovered at 2 and 36–46% of the total dose, respectively. Ag-metallothionein (MT), which is associated with Ag, Cu, and Zn, and Cd-MT, which is associated with Cd, Cu, and Zn, were induced in the liver by the injection of Ag and Cd, respectively. The supernatant Ag and Cd existed in the MT fraction at 34–61 and 97% levels, respectively. Cu concentration in the hepatic supernatant was increased by the Ag and Cd injections. The increased Cu was due to the appearance of Ag-MT and Cd-MT, respectively. Microsomal concentrations of Cu increased in the Cd groups, but decreased in the Ag groups. Serum ceruloplasmin (Cp) activity was remarkably increased by the injection of Cd, but severely decreased by the injection of Ag. These opposing changes in Cp activity induced by Cd and Ag may be due not to the sequestering of Cu in MT, but to the alteration of microsomal Cu concentration and/or the difference in affinity of the induction metals to MT. Hepatic Fe concentration was increased by the Ag injection, but was decreased by the Cd injection. These changes may not be related to induction of MT, but to Cp synthesis in the liver.     

The toxicity of parenteral copper in the chick: dependence on route of administration

Preliminary work in our laboratory suggested that the route of parenteral copper administration influences the acute toxicity of copper (Cu). The present work examined the effects of Cu given either intraperitoneally (i.p.) or intravenously (i.v.) on mortality, feed intake, peritoneal fluid and hepatic accumulation of Cu and zinc (Zn) in chicks. We also studied the potential interaction of prior Zn loading on these parameters. Four-wk-old chicks were pretreated by injection (subcutaneous) with Zn acetate (5 mg Zn/kg) or sodium acetate 24 h prior to Cu treatments. Copper as Cu acetate was given either i.p. or i.v. at a dose of 1.84 mg Cu/kg. Mortality was markedly greater in those chicks given Cu i.p. compared to those given Cu i.v. (46.1% vs. 3.9%). Zinc pretreatment had no effect on any of the parameters associated with copper treatments. The accumulation (24 h) of copper in either total hepatic tissue or cytosol was comparable for both routes of injection. However, marked differences in Cu-induced hepatic Zn accumulation were observed. Massive peritoneal fluid (41% of total plasma volume) was observed 1 to 3 h following the administration of Cu i.p. None was observed in those given Cu i.v. Thus, this effect was associated with the route-dependent mortality observed in the present study. We suggest that our data highlight the gratuitous effects of reactive agents given intraperitoneally.     

甘草甜素和齐墩果酸对大鼠镉中毒性肝损伤的防护作用与机理

为探讨甘草甜素（ＧＬ）和齐墩果酸（ＯＡ）对大鼠镉中毒性肝损伤的防护作用及其作用机理,给大鼠腹腔注射ＣｄＣｌ２溶液（０．８ｍｇＣｄ＾２＋／ｋｇ体重）,两组染镉大鼠分别同时皮下注射ＧＬ的生理盐水溶液（２０ｍｇ／ｋｇ,每周３次）和ＯＡ的吐温－生理盐水混悬液（６０ｍｇ／ｋｇ,每周５次）,测定血清转氨酶、肝镉（Ｃｄ）、金属硫蛋白（ＭＴ）含量,检查肝组织病理形态学。结果显示：ＧＬ和ＯＡ延缓、降低了镉引起的血清     

Effect of cadmium on hepatic metallothionein level in early development of the rat

The induction of hepatic metallothionein (MT) was investigated 24 hr after an intraperitoneal injection of 0.75 mg/kg Cd as CdCl₂ · H₂O in rats of 7, 14, 21, and 90 days. Metallothionein in liver cytosolic fractions collected on Sephadex G-75 was characterized in terms of sulfhydryl, total protein, Cd, and Zn contents. Most of the cytosolic Cd was associated with MT and the concentration of Cd was equal in the different age groups. The higher contents of sulfhydryl, protein, and Zn both in control as well as in Cd-injected rats of 7 and 14 days than in those of 21 and 90 days indicate the presence of more native Zn-thionein in immature pups. However, the increase in sulfhydryl and protein contents showed more prominent induction of MT in Cd-exposed animals of 21 and 90 days than in those of 7 and 14 days. The concentration of Cd was highest in liver followed by the other tissues. While hepatic accumulation of Cd was similar in all age groups, the renal accumulation increased significantly with age. The intestine and spleen of immature pups concentrated more Cd than those of mature animals. The accumulation of the metal did not differ significantly in heart and brain of the animals among the four groups.     

Maintenance of zinc-dependent hepatic functions in rat hepatocytes cultured in medium without added zinc

Hepatocytes were cultured with Waymouth's media containing zinc at concentrations of 1 (the endogenous zinc concentration of basal medium), 16 and 48 mumols Zn/L to examine the effects of extracellular zinc on a variety of zinc-related functions. The zinc concentrations were chosen with the intention of simulating zinc-deficient, adequate and excess extracellular conditions. Basal medium had no effect on cell zinc, metallothionein (MT) or MTmRNA for up to 48 h but reduced delta-aminolevulinic acid dehydratase (delta-ALA-D) activity to 75% of the initial level by 3 h. The addition of zinc at 16 or 48 mumols Zn/L during the initial 3 h of culture did not prevent the decrease in delta-ALA-D activity. Reintroducing zinc at concentrations of 16 or 48 mumols Zn/L to hepatocytes after the initial 3 h of culture in basal medium significantly increased cell zinc, MT and MTmRNA levels and fully restored delta-ALA-D activity by 24 h. Medium zinc had no apparent effect on membrane integrity assessed as leakage of lactate dehydrogenase activity into culture media or de novo protein synthesis as examined by two-dimensional gel electrophoresis of 35S-labeled proteins. Hepatocytes cultured in basal medium resisted losses in cell zinc concentration even when EDTA and bovine serum albumin were present in culture medium. Kinetic experiments using 65Zn suggest hepatocytes maintain zinc concentrations by reducing zinc efflux. The ability of hepatocytes cultured in basal (1 mumol Zn/L) medium to maintain cell zinc content and some zinc-dependent functions underscores the difficulty of producing zinc deficiency in primary hepatocyte culture.     

Dietary zinc deficiency and repletion modulate metallothionein immunolocalization and concentration in small intestine and liver of rats

Metallothionein (MT) functions in zinc (Zn) homeostasis and dietary Zn affects tissue MT concentration. The objective of this study was to investigate the effects of dietary Zn deficiency and 24-h Zn repletion on MT immunolocalization and concentration in the small intestine and liver of growing rats. Three-week-old rats fed Zn-deficient diet (< 1 mg Zn/kg) for 16 d had no MT staining in either small intestine or liver. After 24-h Zn repletion with control diet (30 mg Zn/kg), strong MT staining was observed in intestinal Paneth cells and surface epithelial cells in the proliferative regions of villi. Pair-fed control rats had strong MT staining in liver that was localized around central veins. After 24-h energy repletion, the hepatic MT staining diminished. Furthermore, Zn-deficient rats had significantly reduced intestinal (57%) and hepatic (61%) MT concentrations but unaffected Zn concentrations compared with controls that consumed food ad libitum. Zn repletion for 24 h restored intestinal and hepatic MT concentrations and reduced hepatic Zn concentration. Pair-fed control rats had elevated MT concentration in liver that was normalized by energy repletion. There was a significant positive correlation between tissue Zn and MT concentrations in liver (r = 0.60, P = 0.0001), but not in small intestine. In summary, MT immunolocalization and concentration in rat small intestine and liver were responsive to changes in Zn status, supporting the role of MT in Zn metabolism. Cell-type-specific localization of MT in small intestine after dietary Zn manipulations indicates a function of Zn and MT in gut immunity and intestinal mucosal turnover, and the pattern of hepatic MT distribution with energy restriction may be linked to detoxification processes.     

The effect of endotoxin and turpentine administration on intestinal permeability in the rat

Intestinal permeability in 4-week-old rats has been assessed by the dual sugar (lactulose/mannitol) permeability test before and for two days after induction of systemic inflammation by various endotoxins and turpentine. Evidence of an inflammatory response to these agents was provided by marked reductions in food consumption and growth rate, hypoalbuminaemia, and a large increase in the plasma concentration of the acute-phase protein alpha-2-macroglobin. Abnormal values for intestinal permeability occurred only in animals which had been injected with E. coli 0111:B4 endotoxin. Neither turpentine nor the other endotoxins produced any detectable effect. Within 2-7h of the first exposure to a low dose, (3mg/kg) of either phenol or trichloroacetic extracts of E. coli 0111:B4 endotoxin, the lactulose:mannitol (L M ) ratio was elevated by 32% and 50% respectively (p < 0.05), but the rise was not sustained despite continued twice-daily injections of endotoxin. Administration of a higher dose, (10 mg/kg twice daily, phenol extract) resulted in diarrhoea, and a greater more persistent increase in the L M ratio; 115% (p < 0.05) 2-7h after the first injection, and 49% above control values, (p < 0.01) 24h later. The increase in L M ratio appeared to be due to a decrease in mannitol excretion. Total urinary lactulose also tended to fall, especially in rats given the high dose of endotoxin. It is concluded that a systemic inflammatory response does not necessarily lead to a change in intestinal permeability as measured by the dual sugar permeability test. The transient permeability changes observed following E. coli 0111:B4 administration may be a specific reaction to this material rather than to a more general systemic stimulus.     

Alteration of dissolved cadmium and zinc uptake kinetics by metal pre-exposure in the Black Sea bream (Acanthopagrus schlegeli)

We first examined the uptake kinetics of Cd and Zn in the juvenile marine black sea bream (Acanthopagrus schlegeli) over a wide range of ambient Cd and Zn concentrations, and the relationships with metal accumulation (uptake rate and amount of nonexchangeable surface binding) were established for different fish tissues. Both Cd and Zn accumulation in the body increased linearly with exposure time after the initial metal surface binding. The dissolved Cd and Zn uptake rate constants were 2.64 and 6.50 L/kg/d, respectively, and the kinetics followed a first-order process. No evidence of biphasic transport was found, in contrast to the situation in freshwater fish. Viscera were the most important sites of metal uptake, and gills were the second most important sites. The black sea breams were then acclimated at different Cd or Zn concentrations from either waterborne or dietary source for one week, and the alteration of metal uptake kinetics or subcellular distribution and metallothionein (MT) induction were further quantified. The Cd body burden was enhanced up to 8.6- and 49-fold after waterborne and dietary Cd pre-exposure, respectively. Cadmium pre-exposure also altered the tissue-specific subcellular Cd distribution and significantly elevated tissue MT levels. In contrast, the black sea breams were able to regulate Zn accumulation, and waterborne or dietary Zn pre-exposure had only weak influences on Zn body burden and redistribution. Both Cd and Zn pre-exposures enhanced the metal uptake rate constants, whereas the nonexchangeable surface bindings were less impacted by these pre-exposures. We demonstrated a positive relationship between the Cd uptake rate and Cd or MT concentration in the fish. Pre-exposure to metals may substantially modify the kinetics of metal uptake.     

Combined effects of methylmercury,lead, and cadmium on hepatic metallothionein and metal concentrations in the pekin duck

This study was initiated to determine the effects of combined treatments of methylmercuric chloride (MeHg), lead acetate (Pb) and cadmium chloride (Cd) administered orally on metallothionein (MT) and metal levels in the liver of the pekin duck (Anas platyrynchos). Methylmercury and Pb induced a two-fold increase in MT while Cd caused a seven-fold increase over controls. Concurrent administration of MeHg and Pb caused no increase in MT over single treatments. The hepatic MT content of the MeHg + Cd and MeHg + Pb + Cd groups was not different from the Cdalone group. Hepatic lead levels were lowest followed by Hg and Cd. Lead increased Hg levels when given simultaneously with MeHg, and further addition of Cd increased this effect. In groups given Pb, MeHg increased hepatic levels of this element, but when MeHg was also given with Cd, the combination produced a reduction in levels of Pb. Lead or MeHg had no effect on Cd levels. Methylmercury, Pb, and their combination elevated hepatic Cu over controls. All treatments significantly raised hepatic Zn levels above controls. Combinations of Cd with either MeHg or Pb lowered Zn levels below that caused by Cd alone. The simultaneous administration of all three metals did not produce Zn levels which were additive. The liver content of iron was not significantly altered.     

Structure and expression of chicken metallothionein

The chicken metallothionein (MT) cDNA and gene were cloned, and their nucleotide sequences determined. The cDNA clones encode a cysteine-rich protein of 63 amino acids which shares extensive structural homology with the mammalian MTs. Southern blot analyses of total genomic DNA, and cloned chicken DNA indicated that the MT gene is a unique gene sequence. The chicken MT gene is structurally homologous with the mammalian MT genes; consisting of three exons separated by two intervening sequences. The placement of the intervening sequences in the chicken gene is nearly identical with that in the mammalian MT genes. Levels of hepatic MT mRNA were rapidly induced by metal ions (Cd2+, Zn2+, Cu2+), glucocorticoids and lipopolysaccharide (LPS). MT mRNA was present in low levels in embryonic liver, but was inducible in ovo by injection of metal ions, glucocorticoids or LPS. Hepatic MT mRNA increased to high levels soon after hatching, before decreasing again to the basal levels found in adult liver. Levels of hepatic MT mRNA in hatched chicks were influenced by dietary metals. The results establish that the structure of the MT protein and gene has been highly conserved between birds and mammals, which suggests a functionally important role(s) for this protein.     

Time-course studies of pancreatic exocrine damage induced by excess dietary zinc in the chick.

Experiments were conducted to determine the time course of Zn-induced changes in the exocrine status of the chick pancreas. In experiments 1 and 2, chicks killed at intervals after the addition of excess Zn (500 mg/kg as ZnO) to a purified diet containing 70 mg Zn/kg showed a rapid increase in plasma Zn concentration that reached a plateau within 1 h. The pancreatic soluble Zn level increased linearly for 24 h, but then its rate of accumulation diminished. The same pattern of accumulation was shown by pancreatic metallothionein (MT), which correlated highly with pancreatic Zn; that is, MT-associated Zn consistently accounted for 70 to 80% of pancreatic Zn. Plasma amylase activity started to increase 8-10 h after Zn introduction and reached a maximum by 24 h. Two critical levels of pancreatic soluble Zn (1 and 2.7 micrograms Zn/mg of protein, respectively) were observed at which amylase activities increased in the plasma and decreased in the pancreas. In experiment 3, feeding excess Zn reduced the incorporation of [3H]leucine into pancreatic amylase protein. This was associated with a reduction of tracer incorporation into total pancreatic proteins, that is, the fraction that is precipitable by trichloracetic acid (TCA). In experiment 4, the enzyme (or potential) activities of the exportable Zn-containing enzymes procarboxypeptidases A and B and ribonuclease were not affected by excess Zn intake, indicating the selective nature of the effect of excess Zn on pancreatic function.     

Metallothionein cDNA cloning, metallothionein expression and heavy metals in Scapharca inaequivalvis along the Northern Adriatic coast of Italy

The aims of this work were: (1) identification of the metallothionein (MT) gene coding sequence in order to prepare an MT probe in Scapharca inaequivalvis and (2) quantification of Cd, Zn, Cu, MT and MTmRNA expression in tissues of molluscs from three areas along the Northern Adriatic coast of Italy. By RT-PCR we cloned the MTcDNA of S. inaequivalvis using the RNA extracted from hepatopancreas of specimens exposed to Cd. The 61 amino acids sequence of MT was deduced and was 70% identical to S. brughtonii MT. Cd concentration in molluscs from the wild was significantly higher in gills from specimens sampled near Ravenna. Zn concentration in the same tissue was significantly higher in Ravenna with respect to Porto Garibaldi while no difference with respect to Cesenatico was detected. Cu levels showed significant differences among sites in gills and mantle whereas values in the hepatopancreas were similar in all sites. The low MT levels were indicative of a low metal exposure; few differences were found in MTmRNA concentrations, which resulted significantly higher in hepatopancreas of molluscs from Porto Garibaldi.     

The effects of zinc deficiency on turnover of cadmium-metallothionein in rat liver

The object of this experiment was to determine the effects of Zn deficiency on the turnover of Cd-induced metallothionein (MT) in rat liver. Male rats were fed a purified Zn-deficient or Zn-adequate diet. After 13 days, the rats were given three daily injections of Cd2+ totaling 1.5 or 3.0 (Zn-deficient) and 3.0 or 6.0 (Zn-adequate) mg Cd/kg body weight. The MT was labeled by injecting the rats with [35S]cystine 2 hours after the final Cd injection. One, 3 or 5 days after labeling, the rats were killed, and their livers were assayed for MT 35S and metal content. The metal composition of MT (mole %) was 41-42% Cd, 51-54% Zn and 4-7% Cu in the Zn-adequate groups and 64% Cd, 27-31% Zn and 6-9% Cu in the Zn-deficient groups. The half-lives of Cd-induced MT in the Zn-deficient rats were 2.6 days (1.5 mg Cd/kg) and 2.8 days (3.0 mg Cd/kg). In the Zn-adequate rats, the half-lives were 3.6 days (3.0 mg Cd/kg) and 3.1 days (6.0 mg Cd/kg). The half-lives of general, soluble hepatic proteins were 4.1 to 4.3 days in all groups. Despite the stabilizing effect of the higher Cd content, the half-life of hepatic MT in the Zn-deficient rats was significantly shorter than in the Zn-adequate rats. These results indicate that hepatic MT degradation is faster in Zn-deficient animals.     

Excess dietary L-cysteine causes lethal metabolic acidosis in chicks

A 72-h time-course study was conducted to elucidate the physiological mechanism underlying cysteine (Cys) toxicity in chicks beginning at 8-d posthatch. Biochemical markers quantified in plasma and liver samples collected from chicks receiving 30 g/kg excess dietary Cys were compared with baseline measurements from chicks receiving an unsupplemented corn-soybean meal diet over a 72-h feeding period. Concomitant with chick mortality were indices of acute metabolic acidosis, including a rapid increase (P < 0.001) in anion gap that resulted from a reduction (P < 0.001) in plasma HCO(3)(-) of approximately 40% and a 2.8-fold increase (P < 0.001) in plasma sulfate in chicks receiving excess Cys. Additionally, provision of 30 g/kg excess Cys resulted in a 1.5-fold increase (P < 0.05) in hepatic oxidized glutathione compared with the 0-h control time-point. Excess dietary Cys did not affect plasma free Met, but plasma free Cys increased (P < 0.05) from 89 to 107 mumol/L at 12 h and remained elevated through 36 h. Strikingly, ingestion of 30 g/kg excess Cys caused more than a doubling (P < 0.001) of plasma free cystine, the oxidized form of Cys, beginning 12 h after initiating the study, and it remained elevated throughout the 72-h feeding period. Taken together, these data suggest that ingestion of 30 g/kg excess l-Cys causes both acute metabolic acidosis and oxidative stress in young chicks when fed a nutritionally adequate, corn-soybean meal diet.     

Variations in metallothionein, Zn, Cu, and Fe concentrations and ceruloplasmin activity in pregnant rat dams and their fetuses

Growing rat fetuses have great need for Zn, Cu, and Fe. In fetal livers (FL) large accumulations of Zn and Cu connected with increased metallothionein (MT) synthesis take place. In dams, serum changes in metals concentrations with increased ceruloplasmin (Cp) activity are observed. The aim of this study was to determine (1) mutual relationships in the accumulation of MT, Zn, Cu, and Fe in fetal livers; (2) changes in Zn, Cu, and Fe concentrations in dam serum; and (3) the day with the maximum Cp activity. Sections of rat dams were taken on 16th-21st day of gestation, twice a day, and MT, Zn, Cu, and Fe concentrations in liver, spleen, kidneys, and placenta of dams and in liver and brain in fetuses were determined. In fetal livers high correlations between MT and Zn and between Zn and Cu were obtained. The investigated Cp activity was always high, reaching its maximum on the 20th day and minimum on the 21st day. Significant correlation between Cp activity and Cu concentration in dam serum was also revealed. In conclusion it is suggested that Zn accumulation in FL is strictly connected with MT synthesis but Cu content in FL is rather dependent on Cp activity in dam serum. Iron accumulation in fetal livers is connected with the diminution of iron concentrations in dam serum.     

Metallothionein-null mice absorb less Zn from an egg-white diet, but a similar amount from solutions, although with altered intertissue Zn distribution

The influence of metallothionein (MT) on Zn transfer into non-gut tissues was investigated in MT-null (MT-/-) and normal (MT+/+) mice 4 h after oral gavage of aqueous 65ZnSO4solution at doses of 154, 385, 770 and 1540 nmol Zn per mouse. Zn transfer was not significantly different between MT+/+ and MT-/- mice and was directly proportional to the oral dose (slope = 0.127, r = 0.991; 0. 146, r = 0.994, respectively). Blood 65Zn and plasma Zn concentrations increased progressively in MT-/- mice at doses >154 nmol Zn, reaching levels of 2.4% of oral dose and 60 micromol/L, respectively, at the 1540 nmol Zn dose. The corresponding values for MT+/+ mice were approximately half, 1.0% and 29 micromol/L. Intergenotypic differences were found in tissue distribution of 65Zn within the body; MT-/- mice had higher 65Zn levels in muscle, skin, heart and brain, whereas MT+/+ mice retained progressively more Zn in the liver, in conjunction with a linear increase in hepatic MT up to the highest Zn dose. MT induction in the small intestine reached its maximum at an oral dose of 385 nmol Zn and did not differ at higher doses. Absorption of a 770 nmol 65Zn dose from a solid egg-white diet was only one fourth (MT+/+) and one eighth (MT-/-) of the Zn absorption from the same dose of 65Zn in aqueous solution. MT+/+ mice had greater (P < 0.05) Zn absorption from the egg-white diet than did MT-/- mice, indicating that gut MT confers an absorptive advantage, but only when Zn is incorporated into solid food.     

Influence of diethyldithiocarbamate on nickel-induced hepatic metallothionein in rats

The influence of sodium diethyldithiocarbamate (DDC) on 63nickel chloride-induced metallothionein (MT) and alterations in essential metal levels in the liver of rats was investigated. The induction of MT, Zn and Cu levels of the hepatic cytosolic "heat stable fraction" (HSF) by DDC increased with time up to 24 hr. Although MT, Zn and Cu were significantly greater at 17 hr than those at 6.5 hr after 63Ni administration, the Ni level decreased. The treatment with DDC at 6 hr, but not at 10 min, prior to 63Ni administration increased significantly the MT, Zn and Cu contents 17 hr after 63Ni administration over that caused by 63Ni alone at 17 hr., showing a synergistic effect. The induction of hepatic MT by 63Ni or DDC alone was prevented by cycloheximide but not by actinomycin D and seemed to be regulated at the protein synthesis level.     

Zn-depleted mice absorb more of an intragastric Zn solution by a metallothionein-enhanced process than do Zn-replete mice

The influence of metallothionein (MT)(2) on Zn absorption was investigated in MT-null (MT-/-) and normal (MT+/+) mice fed Zn-depleted (ZnD) diets for 7 d and compared with those fed Zn-replete (ZnR) diets in a previous study. Mice were starved for 20 h, then administered an oral gavage of aqueous (65)ZnSO(4) solution at doses of 154, 770 or 1540 nmol of Zn, and the amount transferred into nongut tissues was determined 4 h later. (65)Zn transfer did not differ between genotypes in ZnR mice. However ZnD MT+/+ mice had a 30-40% greater transfer from the 154 and 770 Zn doses compared to ZnR MT+/+ mice. This was not observed in MT-/- mice. In MT+/+ mice, Zn depletion enhanced the induction of MT by Zn in the intestine and pancreas. (65)Zn uptakes in the liver and pancreas were greater in MT+/+ than MT-/- mice, and this was greater (50%) at the 154 and 770 doses in mice fed ZnD diets. Plasma Zn concentrations were raised to a similar extent in ZnR and ZnD MT-/- mice. ZnR MT+/+ mice had significantly lower plasma Zn levels than MT-/-mice; this difference was less marked in the ZnD mice. We conclude that a MT-facilitated enhancement in Zn absorption occurs in response to dietary Zn deficiency.