Dietary pharmacological or excess zinc and phytase effects on tissue mineral concentrations, metallothionein, and apparent mineral retention in the newly weaned pig

Feeding pharmacological zinc (Zn) to weaned pigs improves growth, and dietary phytase improves P and Zn availability. Metallothionein (MT) increases in the duodenum, kidney, and liver of pigs fed 1000 mg Zn/kg with phytase or 2000 mg Zn/kg with or without phytase when fed for 14 d postweaning. The goal of this study was to determine the effects of feeding pharmacological Zn and phytase on tissue minerals, MT, mineral excretion, and apparent retention. Twenty-four newly weaned pigs (20 d; 7.2 kg) were individually fed twice daily, a basal diet supplemented with 0, 1000, or 4000 mg Zn/kg as Zn oxide, without or with phytase (500 phytase units [FTU]/kg) for 14 d, followed by a basal diet (100 mg Zn/kg) without phytase for 7 d. Pigs fed 4000 mg Zn/kg without phytase had higher (p=0.01) plasma, hepatic, renal Zn, renal Cu, and hepatic, renal, and jejunal MT than pigs fed the basal diet or 1000 mg Zn/kg. Duodenal MT was higher (p=0.0001) in pigs fed 1000 and 4000 mg Zn/kg than in pigs fed the basal diet. In pigs fed 1000 and 4000 mg Zn/kg, Zn loading occurred during the first 11 d of supplementation; by d 14, excess Zn was being excreted in the feces.     

Zinc attenuates forskolin-stimulated electrolyte secretion without involvement of the enteric nervous system in small intestinal epithelium from weaned piglets

In a previous study, we found that secretagogue-stimulated electrolyte secretion was attenuated by dietary and serosal zinc in piglet small intestinal epithelium in Ussing chambers. Several studies show that the enteric nervous system (ENS) is involved in regulation of electrolyte and/or fluid transport in intestinal epithelium from many species. The aim of the present study is to examine the mechanisms behind the attenuating effect of zinc on electrolyte secretion and to study whether the ENS is involved in this effect of zinc in vitro. Twenty-four piglets (six litters of four piglets) were allocated randomly to one of two dietary treatments consisting of a basic diet supplemented with 100 mg zinc/kg (Zn(100)) or 2500 mg zinc/kg (Zn(2500)), as ZnO. All the piglets were killed at 5-6 days after weaning and in vitro experiments with small intestinal epithelium in Ussing chambers were carried out. Furthermore, zinc, copper, alkaline phosphatase (AP) and metallothionein (MT) in mucosa, liver, and plasma were measured. These measurements showed that zinc status was increased in the Zn(2500) compared to the Zn(100) fed piglets. The in vitro studies did not confirm previous findings of attenuating effects of dietary zinc and zinc in vitro on the 5-HT induced secretion. But it showed that the addition of zinc at the serosal side attenuated the forskolin (FSK) (cAMP-dependent) induced ion secretion in epithelium from piglets fed with Zn(100) diet. Blocking the ENS with lidocaine or hexamethonium apparently slightly reduced this effect of zinc in vitro, but did not remove the effect of zinc. Consequently, it is suggested that zinc attenuates the cAMP dependent ion secretion mainly due to an effect on epithelial cells rather than affecting the mucosal neuronal pathway.     

Effect of zinc supplementation on metallothionein,copper, and zinc concentration in various tissues of copper-loaded rats

The present study was designed to investigate the effects of Zn administration on metallothionein concentrations in the liver, kidney, and intestine of copper-loaded rats. Male CD rats were fed a diet containing 12 mg Cu and 67 mg Zn/kg body wt. They were divided into either acute or chronic experimental protocols. Rats undergoing acute experiments received daily ip injections of either Cu (3 mg/kg body wt) or Zn (10 mg/kg body wt) for 3 d. Chronic experiments were carried out on rats receiving Cu ip injections on d 1, 2, 3, 10, 17, and 24, Cu injections plus a Zn-supplemented diet containing 5 g Zn/kg solid diet, or a Zn-supplemented diet alone. Rats injected Zn or Cu had increased MT concentrations in liver and kidney. Zn produced the most important effects and the liver was the most responsive organ. Rats fed a Zn-supplemented diet had significantly higher MT concentrations in liver and intestine with respect to controls. Increased MT synthesis in the liver may contribute to copper detoxification; the hypothesis of copper entrapment in enterocytes cannot be confirmed.     

Inducibility and amounts of metallothionein as influenced by cadmium and zinc in the developing rat

Information on the accumulation and/or depletion of Zn in metallothionein (MT) of rat fetus, rat pup, and maternal rat liver at various ages was obtained with pregnant rats fed a basal casein diet or this diet plus either 100 ppm Zn or 50 ppm Cd. Rats fed each of the respective diets were sacrificed on 12, 16, and 20 d of gestation and 0, 7, 14, and 28 d post-partum. No Cd was detected in the placenta or fetal tissue and the Cd did not affect the accumulation of Zn in the fetal MT, but it did increase the Zn content in liver MT of the dams. Very little Zn in MT was found on day 12 of gestation, but Zn rapidly increased in MT to a maximum at time of birth. The accumulation of Zn in MT was independent of the diet for the fetuses, but the Zn accumulation in the dam and pup tissues was diet dependent. In order to study age-dependent difference in the inducibility of MT, newborn, 5-week-old, or 24-week-old rats were injected with zinc at the levels of 0, 3, 6, or 9 mg/kg and 5 h later injected with³⁵S-cystine. In rats sacrificed 1 h later, the amount of radioactivity in liver MT demonstrated that this protein in older animals was more readily induced by Zn than in younger animals.     

Regional distribution of metallothionein and zinc in the mouse gut

Gut Zn homeostatic responses to low, replete, and excess dietary Zn (10, 150, and 400 mg Zn/kg, respectively) were compared in mice with (MT+/+) and without (MT?/?) metallothionein (MT) expression. MT concentrations decreased progressively from stomach (12.9 nmol Cd bound/g) to colon (4.6 nmol Cd bound/g). Small intestinal MT was increased in mice fed the 400-mg Zn/kg diet (+130%, duodenum; +56%, jejunum; +29%, terminal ileum), but not in the stomach, cecum and colon. Zn concentrations were much higher in the distal gut at increasing Zn intakes in MT+/+ mice but to a lesser extent in MT?/? mice. On the 10-mg Zn/kg diet, MT?/? mice had 45% more Zn in the jejunum/ileum than MT+/+ mice. In fasted (20 h) mice, Zn concentrations in all gut regions were similar to those of MT+/+ mice fed the 10-mg Zn/kg diet, irrespective of prior Zn intake or genotype. Liver MT quadrupled in mice fasted after the 10-mg Zn/kg diet but only doubled after the 400-mg Zn/kg diet, a trend also present in gut MT. Glucagon administration stimulated gut as well as liver MT, implicating it as a major component of the MT response to fasting. MT?/? mice had five times more variation than MT+/+ mice in plasma Zn over all dietary groups. Together, these findings demonstrate that without MT, there is little modification of regional gut Zn concentrations in response to extremes of dietary Zn and poorer regulation of Zn homeostasis.     

Zinc availability from zinc lipoate and zinc sulfate in growing rats

The purpose of this study was to investigate the effect of zinc lipoate and zinc sulfate on zinc availability in growing rats. 6 . 6 male albino rats were fed purified diets based on corn starch, egg albumen, sucrose, soy bean oil and cellulose over a 4-week period (diet Ia: 10 mg Zn/kg as zinc sulfate, diet Ib: 10 mg Zn/kg as zinc lipoate, diet IIa: 10 mg Zn/kg as zinc sulfate +0.4% phytic acid, diet IIb: 10 mg Zn/kg as zinc lipoate +0.4% phytic acid, diet IIIa: 20 mg Zn/kg as zinc sulfate + 0.4% phytic acid, diet IIIb: 20 mg Zn/kg as zinc lipoate + 0.4% phytic acid). Zinc lipoate and zinc sulfate both proved to be highly available zinc sources. When 0.4% phytic acid were present in the diets, apparent zinc absorption was generally depressed but was higher from zinc lipoate in tendency than from zinc sulfate. Comparable results were evident for femur zinc, plasma zinc and metallothionein concentrations in liver tissues. This indicates that zinc lipoate could be a valuable zinc source under conditions of low zinc availability. Nevertheless the absence or presence of phytic acid was a more important factor influencing zinc availability than the type of zinc source investigated.     

Effects of Zinc Glycinate on Productive and Reproductive Performance,Zinc Concentration and Antioxidant Status in Broiler Breeders

An experiment was conducted to investigate the effects of zinc glycinate (Zn-Gly) supplementation as an alternative for zinc sulphate (ZnSO₄) on productive and reproductive performance, zinc (Zn) concentration and antioxidant status in broiler breeders. Six hundred 39-week-old Lingnan Yellow broiler breeders were randomly assigned to 6 groups consisting of 4 replicates with 25 birds each. Breeders were fed a basal diet (control group, 24 mg Zn/kg diet), basal diet supplemented with 80 mg Zn/kg diet from ZnSO₄ or basal diet supplemented with 20, 40, 60 and 80 mg Zn/kg diet from Zn-Gly. The experiment lasted for 8 weeks after a 4-week pre-test with the basal diet, respectively. Results showed that Zn supplementation, regardless of sources, improved (P?<?0.05) the feed conversion ratio (kilogram of feed/kilogram of egg) and decreased broken egg rate, and elevated (P?<?0.05) the qualified chick rate. Compared with the ZnSO₄ group, the 80 mg Zn/kg Zn-Gly group significantly increased (P?<?0.05) average egg weight, fertility, hatchability and qualified chick rate, whereas it decreased (P?<?0.05) broken egg rate. The Zn concentrations in liver and muscle were significantly higher (P?<?0.05) in 80 mg Zn/kg Zn-Gly group than that in ZnSO₄ group. Compared with ZnSO₄ group, 80 mg Zn/kg Zn-Gly group significantly elevated (P?<?0.05) the mRNA abundances of metallothionein (MT) and copper-zinc superoxide (Cu-Zn SOD), as well as the Cu-Zn SOD activity and MT concentration in liver. Moreover, the 80 mg Zn/kg Zn-Gly group had higher (P?<?0.05) serum T-SOD and Cu-Zn SOD activities than that in the ZnSO₄ group. This study indicated that supplementation of Zn in basal diet improved productive and reproductive performance, Zn concentration and antioxidant status in broiler breeders, and the 80 mg Zn/kg from Zn-Gly was the optimum choice for broiler breeders compared with other levels of Zn from Zn-Gly and 80 mg/kg Zn from ZnSO₄.     

Dietary zinc attenuates renal lead deposition but metallothionein is not directly involved

Chronic lead exposure irreversibly damages the kidneys and may be associated with hypertension and renal insufficiency at sub-clinically toxic levels. Zinc supplementation reduces lead absorption and tissue retention in rodent models but the mechanisms are unknown. Metallothionein (MT) may function in lead detoxification. Our objective was to investigate the effects of marginal zinc (MZ) and supplemental zinc (SZ) intakes on renal lead and zinc accumulation, renal MT immunolocalization and levels. Weanling Sprague Dawley rats were assigned to MZ (8 mg Zn/kg diet), zinc-adequate control (CT; 30 mg Zn/kg), zinc-adequate diet-restricted (DR; 30 mg Zn/kg) or SZ (300 mg Zn/kg) groups, with and without lead acetate-containing drinking water (200 mg Pb/L) for 3 weeks. Kidneys were analyzed for lead and zinc by inductively coupled plasma spectroscopy and MT by immunolocalization and Western blotting. MZ had higher renal lead and lower renal zinc concentrations than CT. SZ was more protective than CT against renal lead accumulation. Renal MT levels reflected dietary intake (SZ ≥ DR ≥ CT ≥ MZ) but lead had no effect on MT staining intensity, distribution, or relative protein amounts. In summary, while SZ lowered renal lead concentration, MT did not appear to function in renal lead accumulation. Future studies should explore alternate mechanisms of renal lead detoxification.     

Effect of cis-diamminedichloroplatinum (II) on metallothionein induction and trace element metabolism in rats fed different amounts of dietary zinc

Recent studies have suggested that the induction of metallothionein synthesis in kidneys of mice by the acute administration of bismuth and other trace elements might protect against cis-diamminedichloroplatinum (II) nephrotoxicity. The present study was designed to determine the effects of dietary zinc and cis-diamminedichloroplatinum (II) on the induction of liver and kidney metallothionein and its subsequent effect on nephrotoxicity and trace element metabolism in rats. Male rats were fed diets containing 5, 20, 80, or 320 mg zinc/kg diet for 3 weeks. Each dietary group was subdivided into 3 groups. In one group, each rat received an i.p. injection of 7.5 mg cis-diamminedichloroplatinum (II)/kg b.w. All other rats received saline. During the next three days a second group of rats was pair-fed to the cis-diamminedichloroplatinum (II) injected group. A third group received no treatment and was allowed to eat ad libitum. Results showed that when dietary zinc was increased from 5 mg/kg diet to higher amounts, kidney metallothionein concentration increased twofold. cis-diamminedichloroplatinum (II) treatment increased kidney metallothionein even further, but elevated metallothionein gave no protection from the toxic effects of the drug. Serum copper concentration and ceruloplasmin activity were significantly lower with higher concentrations of dietary zinc, which indicated that these rats were mildly copper-deficient. There was a small but significant depression of superoxide dismutase activity and a highly significant increase in thiobarbituric acid reactive substances in kidneys of rats treated with cis-diamminedichloroplatinum (II) compared to either pair-fed or ad libitum controls. This supports the hypothesis that part of the mechanism for cis-diamminedichloroplatinum (II)-induced toxicity might be caused by free-radical generation. However, the data do not support the hypothesis that metallothionein induction protects the kidney from cis-diamminedichloroplatinum (II) toxicity.     

日本沼虾MT基因克隆、组织差异性表达及与饲料铜、锌含量的相关性

为了更全面理解日本沼虾(Macrobrachium nipponense)的铜/锌营养生理作用,研究利用RACE技术从日本沼虾肝胰腺中克隆获得一金属硫蛋白基因cDNA全长(mn-MT),并对该基因分子特征、组织表达谱和饲料铜/锌水平对其表达的影响进行分析。结果显示:(1)mn-MT cDNA全长665 bp,含编码59个氨基酸的180 bp的开放阅读框,预测该多肽的理论分子量为6.085 kD,等电点为7.73。该蛋白中半胱氨酸含量最高(30.5%),其次是赖氨酸(16.95%)和丝氨酸(10.17%)。相似性分析显示mn-MT氨基酸序列与美洲海螯虾、斑节对虾和中华绒螯蟹MT的相似性分别达到78%、75%和75%。(2)qRT-PCR分析显示, mn-MT mRNA在肝胰腺、血细胞、鳃、胃、卵巢、肠和肌肉中都有表达,其中肝胰腺中表达量最高。(3)用4组铜添加量分别为0、20、40及160 mg/kg的饲料和3组锌添加水平分别为0、35和210 mg/kg的饲料饲喂初重为(0.1010.002) g日本沼虾56d后,分析各组虾肝胰腺的mn-MT mRNA表达。mn-MT mRNA表达随饲料铜水平的提高而升高,到40 mg/kg组达到最高(P0.05),而后开始下降;饲料中高锌(210 mg/kg)显著提高mn-MT表达(P0.05), 0和35 mg/kg组间差异不显著(P0.05)。结果表明饲料中铜/锌均可影响mn-MT表达,且呈现不同的剂量依赖效应。       

Zinc status does not affect aluminum deposition in tissues of rats

To examine whether zinc deficiency would increase the toxicity of dietary aluminum, weanling, male Sprague-Dawley rats were fed purified diets containing either 2 or 30 mg Zn/kg diet, with or without 500 mg Al/kg diet for 28 d. Individually pair-fed rats were fed the 30 mg Zn/kg diet with or without added aluminum to control for inanition secondary to zinc deficiency. Rats fed the 2 μg Zn/kg diet showed evidence of zinc deficiency, including anorexia, growth retardation, and depressed concentrations of zinc in tibias and livers. Zinc deficiency did not significantly increase the concentrations of aluminum in the tibias, livers, kidneys, or regions of the brain examined (cerebrum, cerebellum, midbrain, and hippocampus). Inclusion of aluminum in the diet did not alter aluminum concentrations in the various tissues. Under the conditions of this study, zinc deficiency did not result in greater sensitivity to dietary aluminum exposure.     

Biochemical interactions among silicon, iron and ascorbic acid in the rat

A 2 x 2 x 2 factorial experiment was conducted using two dietary levels each (mg/kg of diet) of silicon, 0 and 500; iron, 35 and 187; and ascorbic acid, 0 and 900, to identify biochemical interactions occurring among these nutrients. Supplemental silicon, in conjunction with the higher dietary-iron level, prevented the plasma-iron decreasing effect observed for the higher level of iron in the absence of silicon. In the absence of ascorbic acid, silicon also increased iron concentration in the liver. Lower growth of the silicon and iron-supplemented rats is believed to be a response to a subsequent iron-imposed aberration of copper or zinc metabolism. This is supported by decreased intestinal metallothionein, increased weights (g/100 g body weight) of liver, heart, and testes, and decreased packed-cell volume and hemoglobin concentration. The lower plasma-iron level associated with the higher level of dietary iron appeared to be an expression of the iron-imposed reduction of liver copper stores. Ascorbic acid decreased plasma-iron concentration and prevented the silicon-related increase in liver iron.     

Hepatic responses to dietary stress in zinc- and metallothionein-deficient mice

Metallothionein (MT) and zinc are both reported to be protective against oxidative and inflammatory stress and may also influence energy metabolism. The role of MT in regulating intracellular labile zinc, thus influencing zinc (Zn)-modulated protein activity, may be a key factor in the response to stress and other metabolic challenges. The objective of this study was to investigate the influence of dietary zinc intake and MT on hepatic responses to a pro-oxidant stress and energy challenge in the form of a high dietary intake of linoleic acid, an omega-6 polyunsaturated fatty acid. Male MT-null (KO) and wild-type (WT) mice, aged 16 weeks, were given semisynthetic diets containing 16% fat and either 5 (marginally zinc-deficient [ZD]) or 35 (zinc-adequate [ZA]) mg Zn/kg. For comparison, separate groups of KO and WT mice were given a rodent chow diet containing 3.36% fat and 86.6 mg Zn/kg. After 4 months on these diets, the body weights of all mice were equal, but liver size, weight, and lipid content were much greater in the animals that consumed semisynthetic diets compared to the chow diet. The increase in liver size was significantly lower in ZA but not ZD KO mice, compared with WT mice. Principally, MT appears to affect the diet-induced increase in liver tissue but it also influences the concentration of hepatic lipid. Plasma levels of C-reactive protein (CRP), a marker of inflammation, were increased by zinc deficiency in WT mice, suggesting that marginal zinc deficiency is proinflammatory. CRP was unaffected by zinc deficiency in KO mice, indicating a role for MT in modulating the influence of zinc. Neither zinc nor MT deficiency affects the level of soluble liver proteins, as determined using two-dimensional (2D) gel proteomics. This study highlights the close association between zinc and MT in the manifestation of stress responses.     

Tissue metallothionein, apoptosis and cell proliferation responses in Atlantic salmon (Salmo salar L.) parr fed elevated dietary cadmium

Atlantic salmon parr were reared for 4 months on experimental diets supplemented with 0 (control), 0.5, 5, 25, 125, or 250 mg Cd x kg(-1) feed to establish a threshold concentration for dietary cadmium exposure by assessing early adaptive cellular responses. At the end of the experiment, the lowest dietary Cd concentration that caused significant accumulation in the gut, kidney and muscle was 5 mg Cd x kg(-1) compared to the control group. Over time, dietary Cd accumulated first in the gut (after 1 month), followed by the kidney (2 months), and later by muscle (4 months). Highest Cd accumulation (100-fold) was found in the gut. A significant increase in regulated cell death and proliferation in salmon fed 125 mg Cd x kg(-1) compared to control fish appeared efficient in preventing gross histopathological damage in the intestine. The highest increase in metallothionein levels was found in the kidney, and metallothionein (MT) levels increased disproportionally to Cd accumulation at increased exposure concentrations. It was concluded that MT was not directly associated with long-term Cd accumulation. Atlantic salmon showed increased metallothionein levels in the kidney at a median effective concentration (concentration of dietary Cd giving 50% of the maximum increase in metallothionein, EC50) of 7 mg Cd x kg(-1), indicating toxic exposure at this concentration.     

Gestational zinc deficiency amplifies the regulation of metallothionein induction in adult mice

To determine if prenatal zinc deficiency has a persistent effect on metallothionein (MT) regulation, Swiss-Webster mice were mated and fed a diet containing either control (100 micrograms Zn/g) or low levels of zinc (5 micrograms Zn/g) from Day 7 of gestation to parturition. After birth all mice were given the control diet. Liver zinc and MT levels were 50% lower in newborn pups from dams fed the low zinc diets than in control pups. In control pups, liver zinc and MT concentrations were relatively stable during the first week of postnatal life. In contrast, in pups prenatally deprived of zinc, liver levels of zinc and MT increased such that by Day 3 of postnatal life, the levels were not significantly different from controls. At Day 56, serum IgM concentrations were significantly lower in the low zinc offspring. Liver zinc concentrations in the two groups of mice were similar at Day 70 postnatal, and in both groups liver MT levels were below detection limits. However, when Day 70 mice were given zinc injections to stimulate MT synthesis, the prenatally zinc deprived offspring showed markedly higher liver MT levels than did control mice given similar injections, despite similar liver zinc concentrations in the two groups. These results show that prenatal zinc deficiency has pronounced effects on postnatal MT metabolism which can persist into adulthood.     

Sparing effect of microbial phytase on zinc supplementation in maize-soya-bean meal diets for chickens

The experiment was conducted to evaluate the sparing effect of microbial phytase on the need for dietary zinc supplementation in chicks. A maize–soya-bean meal basal diet, containing 33 mg of zinc and 16 mg of copper per kg, supplemented with 0, 6, 12, 18, 24, 30 or 60 mg of zinc as sulphate per kg or with 250, 500, 750 or 1000 units (FTU) of microbial phytase (3-phytase from Aspergillus niger, Natuphos®) per kg was given to 1-day-old chicks for 20 days. Sixteen chicks placed in individual cages were assigned to each diet except the unsupplemented basal diet which was assigned to 32 cages. Actual range of phytase supplementation was 280 to 850 FTU per kg diet. Growth performance was not affected by microbial phytase. Chicks given the unsupplemented basal diet and the basal diet supplemented with 60 mg of zinc per kg displayed similar performance. Bone weight, bone ash, liver weight and liver dry matter were independent (P > 0.1) of zinc and phytase supplementations. Plasma, bone and liver zinc concentrations increased linearly (P < 0.001) and quadratically (P < 0.001; P < 0.001 and P < 0.05, respectively) with zinc added. Plasma zinc tended to increase linearly (P = 0.07) and bone zinc increased linearly (P < 0.01) with phytase added but no quadratic response was detected (P > 0.1). Liver zinc was unresponsive to phytase added (P > 0.1). Liver copper decreased linearly (P < 0.001) and quadratically (P < 0.01) with zinc supplementation. Mathematical functions were fitted to the responses of plasma and bone zinc to zinc and phytase added and used to calculate zinc equivalency values of phytase. The models included a linear plateau response to zinc added and a linear response to phytase added. In diets without phytase, plasma and bone zinc concentrations were maximised for a dietary zinc concentration of 55 and 51 mg/kg, respectively. Over the range of 280 to 850 FTU, 100 FTU was equivalent to 1 mg of zinc as sulphate. Consequently, in a maize–soya-bean meal chicken diet formulated to contain 60 mg zinc per kg, zinc ingested, and in turn, zinc excreted may be reduced by around 10% if the diet contains 500 FTU as Natuphos® per kg.     

Iron,copper, and zinc status in rats fed supplemental nickel

Literature data concerning the effect of increasing dietary Ni concentrations on Fe, Cu, and Zn status in rats are sparse and, in part, controversial. Therefore, the effects of the addition of either 0, 3, 50, or 100 mg Ni/kg diet on Fe, Cu, and Zn status of rats were investigated in two separate experiments. Purified diets were used that were composed according to the established nutrient requirements of rats. Ni in kidney was increased with increasing Ni intakes. Dietary Ni did not significantly influence Fe concentrations in plasma, liver, kidney, femur, and spleen. Likewise, the addition of Ni to the diet did not alter Cu status. Zn concentrations in femur were significantly decreased after feeding the diets with 100 mg Ni/kg. However, Zn in plasma, liver, kidney, and spleen was not affected. It is concluded that variations in dietary Ni concentrations have no major impact on Fe, Cu, and Zn status in rats.     

Kidney and liver metallothioneins in rats after administration of an organic compound

Intubation of rats with alpha-mercapto-beta-(2-furyl)-acrylic acid (MFA) for 5 days at 50 mg/kg caused a 7-fold increase in kidney copper concentration, a 2-fold increase in kidney zinc concentration, and a 20% increase in liver zinc concentration. The proteins which bound the increased metals were purified and identified as metallothioneins by their amino acid compositions. Two isoforms were isolated from each organ. Renal thioneins appeared identical to counterpart hepatic apoproteins, but the former bound Cu and Zn in a 2:1 mole ratio and the latter bound only Zn. Kidney contained over 10 times more metallothionein per g of tissue than did liver. In rats previously administered MFA, injection of cadmium sulfate resulted in rapid displacement of liver metallothionein-bound Zn by Cd under conditions where minimal metallothionein was found in Cd-dosed animals not administered MFA. We conclude that MFA induces metallothionein biosynthesis in kidney and liver of normal rats; this is a novel effect for an organic compound.