The induced synthesis of metallothionein in various tissues of rats in response to metals. II. Influence of zinc status and specific effect on pancreatic metallothionein

Metallothionein (MT) of various tissues contains bound zinc (Zn) and any change in Zn status can alter its synthesis and tissue deposition. The changes in MT levels and its inducibility in Zn-injected and Zn-deficient (Zn-D) rats were studied. MT levels in 11 tissues (brain, lung, heart, liver, kidney, stomach, small intestine, pancreas, spleen, testes and muscle) of control and rats injected with different doses of ZnSO₄ (20 mg Zn/kg for 2, 4 or 7 times) were measured by the cadmium-hemolysate (Cd-hem) method. A dose dependent increase in MT levels was observed only in the pancreas, liver, small intestine and kidney after ZnSO₄ injection — the highest level being in the pancreas. A positive correlation was found between Zn and MT concentrations and also the relative inducibility of MT was similar in these 4 tissues (slopes of regression equations were 12.6–15.5). In order to study the effect of Zn-D in MT induction, rats were fed a diet containing 1 ppm Zn for 18 days and CdCl₂ (1 mg Cd/kg) was injected subcutaneously 3 times at 48-h intervals to control and Zn-D rats. Although the tissue distribution of Cd was similar in both the groups, MT concentrations in pancreas and kidney were significantly decreased in Zn-D. The plasma and tissue levels of Zn were also decreased in Zn-D rats injected with CdCl₂. The decrease in both Zn and MT levels was more prominent in pancreas than other organs of Zn-D rats. The results suggest that of all the organs studied, the induction of pancreatic MT is sensitive to Zn status and Zn may be a primary inducer of MT.     

The effect of cadmium on vitamin A metabolism

It has been reported that a number of toxic agents impair normal vitamin A (VA) metabolism (A. D. Bruin, 1976, In Biochemical Toxicology of Environmental Agents, pp. 937–980. Elsevier, Amsterdam). A study was conducted to explore the effect of cadmium chloride (CdCl₂) on VA metabolism. Female rats of the Wistar strain were given drinking water containing 50 ppm of cadmium (Cd) for 237 days. Cadmium ingestion did not affect the food intake and body weight, but a significant decrease in serum VA was observed, concurrently with an increase in liver VA. In studying ingestion of tritiated VA alcohol (all trans-[15-³H]retinol), it was found that the absorption of VA alcohol from the intestine, the release of newly absorbed VA from the liver to serum, and the conversion of VA to water-soluble metabolites in the liver were not influenced by Cd. These findings suggest that Cd interfered with the release of VA, especially stored VA, to serum.     

Acute exposure to cadmium causes severe liver injury in rats

The acute cardiotoxicity of Cd was studied in rats injected iv with 3.9 mg Cd/kg (LD99). Electrocardiogram, blood pressure, and heart rate were recorded intermittently from 9 hr after Cd administration until death. No changes were observed in cardiac indices. Microscopic examination of the major tissues revealed histologically normal myocardium but severely damaged liver. To evaluate further the observed hepatotoxic effects of Cd, time course (1 to 10 hr after 3.9 mg Cd/kg, iv) and dose-response (10 hr after 0.9 to 3.9 mg Cd/kg, iv) studies were conducted. Liver was examined for histopathologic changes; plasma enzyme activities of aspartate (AST) and alanine (ALT) aminotransferases and alkaline phosphatase (AP) were determined to assess liver damage. Pronounced eosinophilia, hepatocyte swelling, and an increase of mitotic figures in hepatocytes were present within 1 hr after Cd. Increased AST and ALT activities were also observed, but AP activity and plasma glucose concentration were unchanged. At later times, severe liver injury was evidenced by necrosis of hepatocytes, striking elevation of serum enzymes (AST, ALT, and AP), and a 50% decrease in plasma glucose concentration. Doseresponse data indicated that doses greater than 1.1 mg Cd/kg produced pathologic changes similar to those observed in the time course study 1 hr after 3.9 mg Cd/kg. Doses above 3.5 mg Cd/kg caused massive hepatic necrosis and increased ALT, AST, and AP activities 60-, 100-, and 3-fold, respectively. A 50% decrease in plasma glucose concentration was also observed at doses above 2.9 mg Cd/kg. These results do not suggest that Cd is cardiotoxic after acute exposure, but rather that the liver is a major target organ for acute Cd toxicity.     

Effect of acute and chronic cadmium treatment on hepatic drug metabolism in male rats

The effect of acute and chronic cadmium administration on hepatic drug metabolism was investigated in the male rat. 3 days after the acute administration of cadmium by either the intraperitoneal (0.84 mg Cd/kg) or the oral (> 80 mg Cd/kg) route, there was a significant potentiation in duration of hexobarbital hypnosis and inhibition of hepatic microsomal metabolism of hexobarbital and aniline. Administration of cadmium in the drinking water at levels of 100 or 200 ppm Cd for periods of 2–12 weeks or at levels of 5 or 20 ppm Cd for 50 weeks did not produce alterations in either drug response or hepatic drug metabolism. Significant levels of metallothionein, a cadmium binding protein, found in the liver of the rats receiving cadmium chronically may offer an explanation for the observed differences in drug metabolism between the acute and chronic administration of cadmium. In additional studies, pretreatment of the rats with subthreshold doses of cadmium (0.21 or 0.42 mg Cd/kg) intraperitoneally produced a tolerance to the alterations in drug metabolism induced by the previous cadmium dose (0.84 mg Cd/kg, i.p.). However, chronic cadmium treatment (5 or 20 ppm Cd for 50 weeks) did not impart any such tolerance to subsequently administered Cd (0.84 mg/kg) by the intraperitoneal route. The hepatic levels of metallothionein induced by the chronic cadmium treatment were only 30–60% of those induced by the subthreshold cadmium and thus may not have bound enough of the large challenge cadmium dose to produce the tolerance phenomenon.     

Maternal cadmium exposure reduces placental zinc transport and induces fetal growth restriction in mice

Cadmium (Cd) is linked with increased risk of fetal growth restriction (FGR). Nevertheless, the mechanism remains unknown. This study established a mouse model of Cd-induced FGR through two exposure methods. Pregnant mice were either administered with CdCl₂ (5, 50 and 250 ppm) throughout pregnancy through drinking water or intraperitoneally injected with CdCl₂ (4.5 mg/kg) on GD9. As expected, fetal weight and crown-rump length were reduced in a gender-independent manner. Interestingly, Mt1 and Mt2, two metallothionein genes, were up-regulated in maternal liver. Correspondingly, Cd accumulated mainly in maternal liver and kidney, and only trace amounts of Cd could pass from dam to placentas and fetuses. Further analysis showed that placental Zn concentration was elevated. Conversely, embryonic Zn concentration was reduced. Moreover, placental Znt1 and Znt2, two zinc transporters, were down-regulated in Cd-exposed mice. These results suggest that maternal Cd exposure during pregnancy reduces placental Zn transport and induces fetal growth restriction.     

Effects of subcutaneous and oral cadmium on iron metabolism: Role of ceruloplasmin and metallothionein

Male ICR mice were either given water containing Cd at a level of 192–200 ppm for 45 days (ingestion group), or were injected subcutaneously once a week with Cd (1 mg/kg) as CdCl₂ for 7 weeks (injection group). The control group was given Cd-free water. In both Cd groups, the hematocrit and hemoglobin values did not change markedly. In the ingestion group, the Fe concentration decreased greatly in the liver, kidney, spleen, and duodenum. These decreases may be due to depression of Fe absorption from the intestine. In the injection group, Fe increased in the liver, spleen, and duodenum, although it decreased in the kidney. By Sephadex G-200 gel filtration, Fe-proteins in the hepatic supernatants were located in the void volume region of this gel column in both Cd groups. Apparently, Fe was not a component of metallothionein (MT) protein. The hepatic MT induction by Cd resulted in an increase in hepatic supernatant Cu. Serum Cu and ceruloplasmin (Cp) activity were stimulated only in the injection group. The enhancement of Cp activity may possibly be due to the increase in hepatic Cu which was accompanied by an increase in hepatic Fe, rather than a decrease. Our observations suggest that Fe metabolism is influenced differentially by the administration route of Cd.     

Plasma clearance of cadmium and zinc in non-acclimated and metal-acclimated trout

Adult rainbow trout were pre-exposed to a sublethal concentration of waterborne cadmium (Cd, 26.7 nmol/l) or waterborne zinc (Zn, 2294 nmol/l) for 30 days to induce acclimation. A single dose of radiolabeled Cd (64.4 nmol/kg) or Zn (183.8 nmol/kg) was injected into the vascular system of non-acclimated and Cd- or Zn-acclimated trout through indwelling arterial catheters. Subsequently, repetitive blood samples over 10 h and terminal tissue samples (liver, heart, bile, stomach, intestine, kidney, gills, muscle, and spleen) were taken to characterize the effect of metal acclimation on clearance kinetics in vivo. Plasma clearance of Cd in Cd-acclimated fish (0.726+/-0.015 and 0.477+/-0.012 ml/min per kg for total and newly accumulated Cd, respectively), was faster than that in non-acclimated trout (0.493+/-0.013 and 0.394+/-0.009 ml/min per kg). Unlike plasma Cd, the levels of Cd in red blood cells (RBCs) were 1.2-2.2 times higher in Cd-acclimated fish than in non-acclimated fish. At 10 h post-injection, the liver accumulated the highest proportion ( approximately 22%) of the injected Cd dose in both non-acclimated and Cd-acclimated fish but did not account for the difference in plasma levels of Cd between two groups. Plasma clearance of Zn ( approximately 0.23 ml/min per kg for new Zn) was substantially lower than Cd clearance. Pre-acclimation to waterborne Zn reduced the new Zn levels in RBCs, but did not affect the clearance of Zn from blood plasma or tissue burdens of Zn in fish. Bile concentrations of both Cd and Zn were elevated in acclimated fish, but total bile burden accounted for <1% of the injected metal dose. The results suggest that the detoxification process of injected plasma Cd is stimulated by pre-acclimation to waterborne Cd, and that Zn levels are homeostatically controlled in both non-acclimated and acclimated trout.     

钙和镉对金属硫蛋白在小鼠肝合成中的影响

研究了小鼠经口给于钙盐和镉盐后，钙和镉在小鼠肝金属硫蛋白合成中的相互影响。结果发现：单独给于钢（８ｍｇ／ｋｇ）时，镉能诱导肝金属硫蛋白的合成；单独给于钙（２０ｍｇ／ｋｇ）时，肝ＭＴ的含量无明显的增加；但同时经口给于钙和镉（２０＋８ｍｇ／ｋｇ），则肝ＭＴ含量比单独给于镉时的肝ＭＴ含量明显增加（Ｐ＜０．０５），Ｃａ＋Ｃｄ组的肝Ｚｎ浓度大大高于Ｃｄ组。     

Role of intestinal metallothionein in absorption and distribution of orally administered cadmium

The effects of mucosal metallothionein (MT) preinduced by Zn on the intestinal absorption and tissue distribution of Cd were studied. 109CdCl2 was administered to control and Zn-pretreated rats. The total amount of Cd distributed to the liver and the kidney in the group pretreated with 100 mg/kg of Zn was about 70% that of the control group. In the control group, the Cd concentration in the intestinal mucosa reached a maximum 16-24 hr after its administration and then gradually decreased with time, unlike that in the liver and the kidney. The concentration of intestinal Cd in the pretreated group reached a maximum earlier than it did in the control group and most of the Cd was in the MT fraction. Pretreatment with Zn (100 mg/kg or higher, po) caused a reduction in the Cd concentration in the liver and an increase in the kidney. Pretreatment with Zn (5 X 10 mg/kg, sc) or Cd (5 mg/kg, po) also increased renal Cd concentration. This was effective at 24 hr but not at 0.5 hr after pretreatment. These effects of pretreatment with Zn (100 mg/kg, po) on tissue distribution of Cd were also observed after an intraintestinal injection of Cd but not after an iv injection. The results indicate that MT in intestinal mucosa plays a significant role not only in the absorption of Cd but also in its transport to the kidney.     

The effect of heavy metals on vitamin A metabolism

Three kinds of divalent ions were injected subcutaneously to rats. Copper at the total dose of 6.2 mg/kg and zinc at the total dose of 12.6 mg/kg did not alter the plasma or liver vitamin A (VA) concentrations. The liver concentration of both had returned to control levels by 2 weeks after the final injection. Cadmium, at the total dose of 6.2 mg/kg, decreased significantly the plasma level of VA, although the liver VA content was not affected. This effect persisted till 2 weeks after the final injection.     

Zinc-induced tolerance to cadmium hepatotoxicity

Pretreatment with Zn is known to produce tolerance to several toxic effects of Cd. This study was designed to determine if zinc pretreatment decreased Cd-induced lethality and hepatotoxicity. Rats given 4.0 mg Cd/kg, iv, died within 10 to 20 hr while there was no mortality in rats pretreated with Zn (12 mg Zn/kg, sc, 48 and 24 hr prior to Cd challenge). Ten hr after Cd, plasma aspartate aminotransferase and sorbitol dehydrogenase activities were markedly elevated and extensive histopathologic lesions of the liver were evident in control rats while such injury was not evident in Zn-pretreated rats. To examine the mechanism of this tolerance, distribution of Cd to 14 organs and the subcellular distribution in 6 organs (liver, kidneys, intestines, heart, spleen, and testes) was determined in control and Zn-pretreated rats. Two hours after challenge (3.5 mg Cd/kg, iv, 7 μCi ¹⁰⁹Cd/mg Cd), the distribution of Cd to the liver markedly increased after Zn pretreatment without concomitant decreases in other tissues. Zn pretreatment resulted in distribution of more Cd to hepatic cytosol and less associated with endoplasmic reticulum. Gel filtration chromatography indicated that most cytosolic Cd was bound to metallothionein. These data suggest that Zn pretreatment reduces Cd-induced hepatotoxicity which prevents the lethal effects of Cd possibly by altering the hepatic subcellular distribution of Cd.     

Acute effects of lead on the renal handling of zinc in dogs

Urinary zinc excretion was monitored in anesthetized dogs before and during 4 hr after acute exposure to lead (doses: 0.3 mg Pb (as acetate)/kg as iv prime, followed by infusion of 0.057 mg Pb/min; 3mg Pb/kg, followed by 0.57 mg Pb/min as infusion; or equimolar sodium acetate in the control group). Zinc excretion in time controls was relatively constant over the 4 hr, but it rose above baseline values an average of 140 ng/min in 0.3 mg Pb/kg injected animals, and an average of 300 ng/min in 3 mg Pb/kg injected animals. Other indices of renal function, including excretion of protein, Na, K, and Mg, were relatively constant. Plasma Zn concentration was stable in time control and low Pb-administered animals, but rose significantly after the higher Pb dose. Clearance experiments using ⁶⁵Zn and in vitro ultrafiltration of plasma were performed in another series of dogs under antidiuretic conditions. Zn excretion (monitored by ⁶⁵Zn) was sevenfold higher in Pb-treated dogs; plasma Zn concentration was slightly, but not significantly, elevated. Ultrafiltrable Zn concentration was 2.5-fold higher and fractional Zn excretion was three times higher in Pb-treated dogs. The stop-flow pattern for Zn after Pb treatment showed no change in the distal tubular handling of Zn, but revealed prominent net proximal tubular secretion of Zn in all animals, a frequency statistically different from that observed in control animals. Thus, acute Pb treatment in dogs produced an increase in urinary Zn excretion which was related both to an increase in ultrafilterable plasma Zn and a change in renal tubular Zn transport. The plasma concentrations of insulin and glucagon were not altered by lead.     

Changes in hepatic glutathione concentration modify cadmium-induced hepatotoxicity

Cd has a strong affinity for sulfhydryl groups and is hepatotoxic. Thus, to further understand the mechanism of Cd-induced liver injury, the effect of increased and decreased hepatic glutathione (GSH) concentration on Cd-induced liver injury was examined. Liver GSH was lowered by pretreating rats with phorone (250 mg/kg, ip) or diethyl maleate (0.85 mg/kg, ip) 2 hr prior to challenge with various doses of Cd. Ten hours after Cd (1) 40–80% of the rats pretreated with phorone or diethyl maleate and challenged with 1.0–2.0 mgCd/kg died whereas no mortality was observed in the control group; (2) plasma enzyme activities of alanine (ALT) and aspartate (AST) aminotransferase and sorbitol dehydrogenase (SDH) were markedly increased in phorone and diethyl maleate-pretreated rats challenged with Cd (0.7–2.0 mg/kg) versus control rats; and (3) moderate changes in liver histology were observed in corn oil pretreated and Cd challenged rats, while prior depletion of GSH potentiated histopathologic changes in liver produced by Cd alone. Another group of rats received cysteine (1.9 g/kg, po) 3 hr prior to injection of a lethal dose of Cd. Cysteine pretreatment increased liver GSH levels by 22% 3 hr after administration and attenuated Cd-induced liver injury as evidenced by marked decreases in plasma ALT, AST, and SDH activities. Pathological changes in liver were also reduced. These data indicate that liver reduced GSH concentration is important in modulating Cd-induced hepatotoxicity.     

Protective roles of metallothionein and glutathione in hepatotoxicity of cadmium.

The protective roles of metallothionein (MT) and glutathione (GSH) in acute hepatotoxicity of cadmium (Cd) were investigated in an in vitro system. Liver slices were incubated in a buffer containing cadmium chloride (20-50 ppm) at 37 degrees C for 3 h. Viability of the slices was monitored by measuring intra-cellular potassium (K) content and GSH concentrations. A dose-dependent decrease of intracellular K content of GSH concentrations was observed. Pre-induction of MT (100-fold increase) by injection of zinc sulphate (30 mg Zn/kg body weight) showed protection against decrease in both intracellular K and GSH concentrations in liver slices. Decrease of hepatic GSH (90%) by an injection of buthionine sulfoximine (BSO)(4 mmol/kg body weight) to the rats further enhanced the Cd toxicity in the liver slices. This enhanced toxicity resulting from BSO treatment can be totally overvome by induction of MT by Zn pre-treatment. The cellular uptake of Cd remained unaltered in all experiments. These results demonstrate that hepatic toxicity of Cd may be due to its binding to intracellular sulfhydryl groups and both intracellular GSH and MT levels may provide protection against cytotoxicity of Cd in liver. Moreover, even at low GSH levels, MT could partially protect the hepatic cells from Cd cytotoxicity.     

Comparison of metallothionein determination by polarographic and cadmium-saturation methods

Metallothionein is a low-molecular-weight protein with a large cysteine content and a high affinity for metals. These properties were utilized in the determination of metallothionein by a polarographic method and by a cadmium saturation method. In this study, these two methods were compared for the estimation of metallothionein from rat liver and kidney after injection with CdCl₂ and ZnSO₄. Rats were injected ip with CdCl₂ (0.6 mg Cd/kg) or ZnSO₄ (10 mg Zn/kg); liver and kidneys were removed after 16 or 32 hr for metallothionein estimation by both methods. Comparison of the results showed good agreement in liver and kidney (correlation coefficient, r = 0.92 and r = 0.95, respectively). The values obtained by the polarographic method were slightly higher than those by the Cd-saturation method. A dose-dependent increase in metallothionein levels was also observed by both methods when the rats were injected repeatedly (1, 3, 5, or 10 times) with CdCl₂ (1 mg Cd/kg). There was relatively good agreement between these two methods on the determination of both hepatic and renal metallothioneins containing zinc and cadmium.     

The interaction of zinc and cadmium in the synthesis of hepatic metallothionein in rats

The interaction of injected zinc salts (Zn) and cadmium salts (Cd) with regard to the synthesis of metallothionein (MT) in adult rat liver was investigated. Male rats received an i.p. injection of Zn (20 mg/kg) or Cd (0.6 mg/kg) with or without pretreatment with Zn (20 mg/kg 16 h prior to the second injection). It was found that both metals, when administered singly, induced the synthesis of significant levels of hepatic MT, but that, when the Cd injection followed the Zn injection, synthesis of MT was not additive. When Zn pretreatment was followed by a second Zn injection, MT accumulation was additive (approx. 2-fold of that observed after a single Zn injection). Also, a highly significant positive correlation, (r = 0.97, P less than 0.01) was noted between hepatic Zn concentration and hepatic MT concentration, a relationship which was independent of the mode of MT induction. The results of the investigation indicate that: (1) in the presence of pre-existing hepatic Zn--MT, the ability of Cd to induce new MT synthesis is greatly reduced; rather, Cd is sequestered by the pre-existing MT; and (2) Zn may play a major role in the induction of MT synthesis both after Zn administration and after Cd administration.     

Cadmium accumulation and metallothionein concentrations after 4-week dietary exposure to cadmium chloride or cadmium-metallothionein in rats.

The distribution of cadmium was examined in rats fed diets containing either cadmium-metallothionein (CdMt) or cadmium chloride (CdCl2) for 4 weeks. The test diets contained 3, 10, or 30 mg Cd/kg diet (3, 10, or 30 ppm) as CdMt or 30 mg Cd/kg diet (30 ppm) as CdCl2. A second study was performed to establish the Cd content in liver and kidneys after exposure to low doses of both CdMt and CdCl2 (1.5 and 8 ppm Cd). The feeding of CdMt resulted in a dose- and time-dependent increase of the Cd concentration in liver, kidneys, and intestinal mucosa. Rats fed 30 ppm CdMt consistently showed less Cd accumulation in liver and intestinal mucosa than did rats fed 30 ppm CdCl2. However, renal accumulation in rats fed 30 ppm was similar until Day 28 regardless of Cd form. At lower dietary Cd levels (1.5 and 8 ppm), relatively more Cd is deposited in the kidneys, although even at these doses the kidney/liver ratio of Cd is still higher with CdMt than with CdCl2. Tissue metallothionein (Mt) levels in the intestinal mucosa were relatively constant but always higher after CdCl2 exposure than after CdMt exposure. Mt levels in both liver and kidney increased after CdCl2 or CdMt exposure during the course of study. Although Mt levels in liver were higher after CdCl2 intake (30 ppm) than after CdMt intake (30 ppm), renal Mt concentrations were the same for both groups. In fact on Day 7, CdMt administration resulted in slightly higher Mt levels than CdCl2 administration, suggesting a direct accumulation of exogenous CdMt in the kidneys. In conclusion, after oral exposure to CdMt in the diet there is a relatively higher Cd accumulation in the kidneys. However, the indirect renal accumulation via redistribution of Cd from the liver might be lower than after CdCl2 exposure. Which of these two phenomena is decisive in the eventual level of renal toxicity of Cd after long-term oral intake could determine the toxicological risk of the chronic intake of biologically incorporated Cd.     

Induction of metallothionein synthesis by zinc in cadmium pretreated rats

The ability of zinc (Zn) salts to induce the synthesis of metallothionein (MT) in liver, kidney and pancreas of rats pretreated with cadmium (Cd) salts was investigated. Twenty-four hours after either CdCl2 (2.0 mg Cd/kg, s.c.) or saline pretreatment, rats were injected with saline, CdCl2 (2.0 mg Cd/kg, s.c.) or ZnSO4 (20 mg Zn/kg, s.c.) and the concentrations of MT and MT-1 mRNA in tissues subsequently measured. After a single injection of Cd salts, concentrations of MT and MT-1 mRNA were significantly increased in liver as compared to control. With two injections of Cd, the accumulation of MT in liver was approximately twice the levels of MT following a single injection of Cd. In kidney, MT and MT-1 mRNA expression were significantly increased only after two injections of Cd and in the pancreas, Cd injections did not alter either MT content or MT-1 mRNA expression. Treatment with Zn salts increased MT concentrations in both liver and pancreas. However, the pancreas was the most responsive to injections of Zn salts as compared to the liver in terms of increases in both protein concentration and MT-1 mRNA expression. When Zn injection was preceded by a Cd injection, induction as measured by MT-1 mRNA and MT concentrations were approximately additive in liver. In kidney, although Cd or Zn treatment separately had no effect on MT or MT-1 mRNA content, injection of Cd followed by Zn resulted in significantly increased levels of renal MT and MT-1 mRNA. Fractionation of liver cytosols on a Sephadex G-75 column revealed that in animals receiving two injections of Cd, virtually all the Cd was associated with MT whereas Zn was distributed between both high molecular weight (HMW) proteins and MT. In animals receiving both Cd and Zn injections, cytosolic Cd was still bound predominantly to the MT fraction, while the proportion of cytosolic Zn associated with MT increased. The results of this study suggest that, treatment with Cd salts followed by Zn salt injection can induce further synthesis of MT in liver, kidney and pancreas with subsequent binding of both Zn and Cd to the intracellular MT.     

Glutathione depletion and oxidative damage in mitochondria following exposure to cadmium in rat liver and kidney.

The dose-dependent effects of cadmium (Cd) on mitochondria and post-mitochondrial supernatant (PMS) of liver and kidney were investigated in adult male albino rats. Two groups of rats were injected intraperitoneally with 0.1 mg Cd/kg body weight and 1 mg/kg body weight, respectively, for a period of 3 months (5 days/week). This resulted in a significant decrease in total glutathione (GSH) levels, irrespective of the doses, in mitochondrial as well as in PMS fractions of liver and kidney. In contrast, end products of lipid and protein were significantly increased in a dose-dependent manner in subcellular fractions of liver and kidney. These results suggest that the depletion of tissue glutathione levels is not a primary reason of the observed oxidative damage in liver and kidney caused by Cd.     

Effects of high doses of vitamin E on dimethylnitrosamine hepatotoxicity and drug metabolism in the rat.

The administration of relatively high doses of vitamin E [55 mg/kg/day, intramuscular (i.m.)] to rats for 3 days resulted in a significant decrease in the acute hepatotoxieity of dimethynitrosamine (DMN). This decrease in toxicity was associated with a decrease in the hepatic metabolism of DMN. Since the metabolism of DMN is mediated by the liver microsomal mixed function oxidase (MFO), the effect of high doses of vitamin E on hepatic MFO was investigated. Rats were treated daily for 3 days with 10, 21, 45 or 100 mg/kg of vitamin E (i.m.), and various parameters of MFO activity were studied in liver cell fractions. DMN demethylase and ethylmorphine demethylase activities and cytochrome P-450 concentration were decreased in animals pretreated with 45 or 100 mg/kg of vitamin E (i.m.). Benzo(a)pyrene hydroxylase activity and cytochrome b₅, concentration were decreased only by pretreatment with the highest dose of vitamin E. NADPH cytochrome c reductase activity was unaffected by vitamin E pretreatment. Inhibition of drug metabolism in the rat was also demonstrated invivo. Pretreatment of rats with vitamin E (100 mg/kg/day, i.m., 3 days) resulted in a significant prolongation of hexobarbital sleeping time. The effect of pretreatment of rats with vitamin E (100 mg/kg/day, i.m., for 3 days) on ethylmorphine demethylase was shown to be reversible after cessation of vitamin E administration. It is concluded that large doses of vitamin E inhibit hepatic microsomal MFO, and thus decrease the hepatoxicity of DMN by inhibiting its metabolism to a presumed active metabolite.