The morphological effects of chronic cadmium administration on the renal vasculature of rats given low and normal calcium diets

Effects of Low-Level Cadmium Intake on the Contractility and Morphology of the Rat Aorta

Female Long Evans hooded rats with an initial mean (± SE) weight of 85.7 ± 1.2 g were exposed to 5 ppm cadmium (Cd) in drinking water for 6 months. Rats which received no Cd in the drinking water served as untreated controls. Weights, systolic blood pressures (tail cuff method), several aspects of aortic ultrastructure, and isolated aortic contractile responses to epinephrine, angiotensin, and potassium chloride at 0, 1, 2, 3, and 6 months were observed in both groups. At none of the testing times was there a significant difference between the weights or systolic blood pressures of the control and Cd-treated groups. Analysis of variance indicated that aortas from control and Cd-treated rats showed similar age-related changes in maximum tension development (contractility) and similar threshold doses. However, Cd-treated aortas developed significantly less maximum tension than control aortas when compared at the same time intervals in response to all of the vasoconstrictors tested. This decreased contractility was apparent at one month and persisted at about the same level (20%) at 2, 3, and 6 months. There were also expected age-related changes in aortic ultrastructure of both groups, and although the 6-month Cd-treated aortas showed more degenerating endothelial cells, differences that might explain the consistent decreases in contractility of the Cd-treated aortas were not observed. The results of this study indicate that chronic low-level Cd treatment causes decreases in aortic contractility, as have previously been reported for acute exposure to Cd, but that this change is not associated with the development of hypertension or with structural changes in the aorta.

Accumulation and detoxification of metals and arsenic in tissues of cattle (Bos taurus), and the risks for human consumption

The aim of this study was to investigate metal accumulation and detoxification processes in cattle from polluted and unpolluted areas. Therefore dairy cows from farms and free ranging Galloway cows from nature reserves were used as study animals. The concentrations of Ag, Cd, Pb, Al, Cr, Mn, Fe, Co, Ni, Cu, Zn and As were determined in muscle, kidney, liver and lungs of cattle from polluted and reference areas in Belgium. In kidney and liver also the metallothionein concentrations were measured. For Ag, Mn, Co, Cu, Zn and As the concentrations in the different tissues were significantly higher in the sampled Galloways than in the sampled dairy cows. On the other hand Cd and Pb were significantly higher in tissues of both cattle breeds from polluted sites. Cadmium seemed to be the most important metal for metallothionein induction in kidneys whereas Zn seemed to be the most important metal for the induction of metallothionein in the liver. This study also suggested that only for Mn and Cd a significant part of the uptake occurs via the lungs. Although in muscle none of the Cd and Pb levels exceeded the European limits for human consumption, 40% of the livers and 85% of the kidneys of all examined cows were above the European limit for cadmium. Based on the existing minimum risk levels (MRLs) for chronic oral exposure, the present results suggested that a person of 70kg should not eat more than 150g cow meat per day because of the Cr levels in the muscles.

The Effects of Chronic Cadmium Toxicity on the Hemostatic System

Cadmium, a highly toxic heavy metal, is distributed widely in the general environment. The characteristic clinical manifestations of chronic cadmium intoxication include renal proximal tubular dysfunction, osteomalacia and anemia. Accumulating evidence suggests that cadmium toxicity may also affect various organs such as the liver, lung, testis and hematopoietic system. The aim of this study was to determine the effect of chronic cadmium exposure on the anticoagulant system in rats. Fourty-five adult Wistar albino rats were randomly allocated into 2 groups. While the control group was given tap water, the animals in the cadmium group were treated with 15 ppm CdCl(2) for 4 weeks. Blood cadmium concentration, prothrombin time, activated partial thromboplastin time, plasma protein C and antithrombin activity, and platelet count were determined in the rats. Blood cadmium concentrations increased in the experiment group compared to the control group (p < 0.001). Results also show that cadmium exposure shortened prothrombin time (p < 0.05) and activated partial thromboplastin time (p < 0.01) in rats. Protein C (p < 0.001) and antithrombin (p < 0.001) decreased to statistically significantly lower levels in rat plasma after cadmium exposure when compared to the control group. When the number of thrombocytes was compared between 2 groups, a decrease was observed in the group treated with CdCl(2), which was, however, not statistically significant (p > 0.05). In conclusion, when the parameters of the hemolytic system are considered, the decrease in protein C and antithrombin activities and the shortening of prothrombin time and activated partial thromboplastin time suggests the presence of a hypercoagulable state during chronic cadmium intoxication. Therefore, it may be stated that chronic cadmium toxicity sets the stage for hypercoagulation and hence increases the risk of thrombosis.

Variability of selected nutrients and contaminants monitored in rodent diets: a 6-year study

The results are given from monitoring a commercial closed-formula cereal-based rodent diet (Purina 5010), two open-formula cereal-based diets (NIH-31 and NIH-07), and one purified diet (AIN-76) for selected nutrients and contaminants. The observed concentrations of nutrients (protein, fat, vitamin A, and thiamine) approximated the manufacturer specifications for closed-formula cereal diet, while the average concentrations of nutrients found in the open-formula cereal diets were well above the nominal concentrations. Nominal concentrations for these open-formula diets tended to be close to the minimum values that were observed. Except for protein levels, greater variation in nutrient concentrations was found in the purified diet than in the cereal diets, but the variation of contaminants was about equal in the two types of diets. Open- and closed-formula cereal diets appear to be very similar to each other in the degree of variation of nutrients and contaminants. Cadmium, lead, and selenium are the constituents of greatest concern in assuring the quality of the rodent diets that were evaluated.

Female reproduction and pup survival and growth for mice fed a cadmium-containing purified diet through six consecutive rounds of gestation and lactation

Female CF1 mice were bred for 6 consecutive, 42-d rounds of gestation-lactation. Their purified diets contained cadmium added at either 0.25, 5.0, or 50.0 ppm Cd; at each cadmium level, the diets were either sufficient or deficient in certain vitamins, minerals, and fat. The deficient diet at 5 ppm cadmium was designed to simulate conditions implicated in the etiology of itai-itai disease among multiparous women in Japan. Fertility, litter size, pup survival, and pup growth (weaning weight) are reported for mice on the six diets during each of the six rounds of gestation/lactation. Except for fertility, decreases in reproductive measures that occurred in response to dietary deficiencies or cadmium during round 1 of reproduction were repeated, unchanged in magnitude, in each successive round. For sufficient diet groups, 50 ppm cadmium had no effect on fertility or pup survival during lactation, but caused a 15% decrease in litter size at birth and a 25% decrease in pup growth. Dietary deficiencies alone decreased all four measures of reproductive performance: fertility by 12%, litter size by 30%, pup survival by 18%, and pup growth by 42%. In addition, dietary deficiencies strikingly decreased the incidence of consecutive pregnancies. Combined effects of 50 ppm cadmium and dietary deficiencies were additive for all reproductive measures except fertility; for fertility, cadmium caused no decrease in the fertility of sufficient-diet animals, but caused a striking 45% decrease in deficient-diet animals. Relating our results to humans, women who contracted itai-itai disease (analogous to mice on the deficient, 5 ppm cadmium diet), in addition to their characteristic bone disease, could have experienced decreases in fertility and in growth of their offspring related to their dietary deficiencies. In addition, their diet-related decreases in fertility could have been enhanced by their combined exposure to cadmium.

Cadmium-induced changes in avian renal morphology

The effects of i.m. administered cadmium on growth rate and nephromorphology were studied in young pullets. The growth rate of pullets treated with 0.6 mg Cd2+/kg at 48-h intervals was severely retarded, reaching only 50% of normal growth by 21 days. Such a decrease in growth rate was prevented when cadmium was given with either ferric or magnesium EDTA chelate. Electron micrographs of kidney tissue from cadmium intoxicated birds revealed massive intracellular disorganisation of proximal tubular cells, showing increased vacuolation and dilated endoplasmic reticulum. Mitochondria were few and swollen with reduced cristae. Some disorganisation was noted in the group treated with MgEDTA in conjunction with cadmium, with normal morphology observed in the group treated with FeEDTA plus cadmium. In general, glomerular morphology of intoxicated pullets appeared normal, except that a 25% increase in thickness of the glomerular basement membrane was evident. No such membrane thickening was observed in any of the chelate treated groups. These findings indicate that both chelates can provide certain levels of protection, in terms of growth rate and morphology, from cadmium intoxication. The possible mechanisms by which chelates offer protection have been discussed, but many questions remain unanswered.

Cadmium induced changes in cell organelles: an ultrastructural study using cadmium sensitive and resistant muntjac fibroblast cell lines

A detailed electron microscopy study of cadmium sensitive and resistant muntjac fibroblast cell lines has identified a wide range of intracellular damage following exposure to cadmium. Damaged organelles included cell membrane, mitochondria, Golgi cisternae and tubular network, chromatin, nucleoli, microfilaments and ribosomes. Although cell membrane damage was generally the earliest indication of adverse cadmium action, particularly with continuous cadmium exposures, cells could tolerate extensive membrane loss. Mitochondrial distortion and some damage to Golgi was also tolerated. The turning point at which cadmium became lethal was generally marked by a cascade of events which included damage to both nuclear and cytoplasmic components. These results for fibroblasts are discussed and compared with damage reported in other types of cells.

Inhibition of rat heart mitochondrial respiration by cadmium chloride

Mitochondria were isolated from hearts obtained from adult male Sprague-Dawley rats by two-part differential centrifugation of heart homogenates. Time-dependent (0-120 sec) and concentration-dependent (0-10 microM CdCl2) effects of cadmium on pyruvate-malate-supported state 3 and state 4 respiration were measured in a constant temperature reaction chamber at 37 degrees C, according to established procedures. The ID50 for cadmium chloride on state 3 respiration was determined to be 4.2 microM. The inhibition produced by cadmium chloride in heart mitochondria was compared, using identical procedures, to the effects induced by two compounds, sodium atractyloside and potassium cyanide, which are known to alter mitochondrial respiration at specific sites. The calculated ID50 values for these agents in heart mitochondria were 1.8 and 16 microM, respectively. The concentration-dependent inhibition of mitochondrial respiration induced by either cadmium chloride or potassium cyanide was maintained in the presence of 50 microM carbonyl cyanide m-chlorophenylhydrazone (CCCP), a known uncoupling agent. In contrast, sodium atractyloside did not block the uncoupling effect of 50 microM CCCP. In addition cadmium chloride was also shown to inhibit CCCP-uncoupled mitochondrial respiration. The cadmium-induced inhibition of mitochondrial respiration was reversed partially by cysteine and completely by 2,3-dimercaptopropanol. The results of the present study indicate that, at all concentrations, cadmium chloride acted solely as an inhibitor of rat heart pyruvate-malate-supported mitochondrial respiration. These findings suggest a possible mechanism for the reported disturbances in myocardial metabolism and function that occur in conjunction with acute and chronic cadmium exposure in humans and experimental animals.

Cadmium/zinc relationships in kidney cortex and metallothionein of horse and red deer: histopathological observations on horse kidneys

Cadmium and zinc were determined in kidney cortex of 63 horses and 51 red deer (Cervus elaphus). Cadmium and zinc were also determined in protein fractions obtained by Sephadex chromatography of kidney cortex from 10 horses and 4 red deer. Histopathological parameters in kidney cortex of horses were compared to cadmium content. The metal contents (on wet weight basis) in kidney cortex of the horses were 0.31 +/- 0.22 mmole Cd/kg (range 0.03-1.21) and 0.63 +/- 0.17 mmole Zn/kg (range 0.36-1.23). The Zn content increased with the Cd content, the Zn increase being less at higher concentrations. No significant increase of the Cd content with age of the horses (range 2-19 years) was found. The metal contents in kidney cortex of the red deer were 0.030 +/- 0.031 mmole Cd/kg (range 0.002-0.13) and 0.51 +/- 0.37 mmole Zn/kg (range 0.30-2.82). Here the Zn content did not increase significantly with Cd content, and in this case a positive linear relation of Cd content with age of the deer (range 0-11 years) was observed. The molar Zn/Cd ratio in the metallothionein fractions of horse kidney cortex was less variable at higher Cd contents. All Cd and the increase of Zn above an average basal level of 0.36 mmole Zn/kg was recovered in the metallothionein fractions. No gross histopathological changes could be observed in kidney cortex of the horses. Nevertheless a slight increase of the thickness of the basement membrane of Bowman's Capsule and also of the diameter of Bowman's Capsule in relation to Cd content up to 0.3 mmole/kg could be observed.

Calcium-dependent effects of cadmium on energy metabolism and function of perfused rat heart

Postequilibrated isolated rat hearts were perfused for 60 min with a standard supporting electrolyte buffer containing one of the following calcium concentrations: 0.9, 1.8, 3.5, or 5.0 mM, either with or without added cadmium. Doses of cadmium which proved to be minimally (0.03 microM Cd)--and maximally (3.0 microM Cd)--effective at 0.9 mM Ca were studied at all other calcium concentrations. A dose-dependent positive inotropy that persisted throughout the 60-min perfusion period was induced by the graded increases in the perfusate calcium concentration throughout the range from 0.9 to 5.0 mM. Atrioventricular node conductivity was prolonged significantly in hearts perfused with 0.9 mM Ca as compared to hearts perfused with higher calcium concentrations. Increasing the perfusate calcium concentration caused a dose-dependent increase in heart glycerol 3-phosphorylcholine (GPC) content. The other measured phosphatic metabolites of the heart were not altered significantly by varying the perfusate calcium level. In contrast, cadmium (3.0 microM Cd) induced extensive functional and metabolic aberrations which varied in magnitude as an inverse function of the perfusate calcium concentration. Contractile tension, rate of tension development (dT/dt), heart rate, coronary flow rate, and atrioventricular node conductivity were decreased significantly in response to cadmium perfusion. Moreover, these hearts characteristically had significantly elevated low energy phosphate (inosine monophosphate and inorganic phosphate) and decreased high energy phosphate (ATP, PCr) levels relative to their respective calcium controls. Furthermore, various phosphorylated intermediates of glycolysis (glucose 6-phosphate, fructose 6-phosphate, glucose 1-phosphate), as well as glycerol 3-phosphate, and uridine diphosphoglucose accumulated significantly in hearts perfused with cadmium at certain calcium concentrations below 5.0 mM. The calcium-activated increase in heart GPC was inhibited completely by 3 microM cadmium. At the minimally effective dose of cadmium (0.03 microM), demonstrable changes were apparent only at the lowest perfusate calcium concentration examined (0.9 mM). These findings are consistent with the hypothesis that cadmium interferes with calcium-activated and calcium-mediated physiologic and biochemical processes of the mammalian heart. The primary mechanistic basis for the action of cadmium appears to be linked to a competition with calcium for membrane and possibly intracellular binding and activation sites.

Effects of methylmercury and some metal ions on microtubule networks in mouse glioma cells and in vitro tubulin polymerization

Mercury compounds and some other metal ions were investigated with respect to their effect on in vitro tubulin polymerization and on cellular microtubules in mouse glioma. In vitro tubulin polymerization was completely inhibited by 2.5 X 10(-5) M Hg2+, 5 X 10(-5) M CH3Hg+, 2 X 10(-4) M Cr3+, 2.5 X 10(-4) M Cu2+, and 5 X 10(-4) M Cd2+. Zn2+ did not affect the polymerization up to 5 X 10(-4) M. Indirect immunofluorescence study with rabbit antiporcine tubulin antibody revealed that methylmercury disrupted the microtubule network at an early stage of growth inhibition. On the other hand, in the presence of Cd2+, Cu2+, and Cr3+ at their growth inhibitory concentrations, no effects on microtubule networks were observed for the first 1 hr. These results indicate that only methylmercury affects cellular microtubules, while other ions seem to interfere with other sites in the cells, although these ions showed the ability to depress in vitro tubulin polymerization.

Investigation for the mechanism of cadmium toxicity at cellular level. II. An electron microscopical study

With quantitative techniques at electron microscopical level chromatin condensation and emptying of the interchromatin space have been established in the nuclei of the endothelial cells of small uterine vessels. The nuclear and cytoplasmic changes after cadmium administration show much similarity between endothelial cells of small uterine vessels and cultured liver parenchymal cells. Cytoplasmic changes in both cell types after cadmium administration are suggestive of a disturbance in ribosomal RNA synthesis as the main cause leading to ultimate cell lysis.

Lung endocrine-like cells in hamsters treated with diethylnitrosamine: alterations in vivo and in cell culture

Diethylnitrosamine is known to cause squamous cell carcinoma and adenocarcinoma of the lung in Syrian golden hamsters. Sections of lungs obtained from hamsters treated with the systemic carcinogen diethylnitrosamine showed a significant increase in the number of argyrophilic cells of neuroepithelial bodies. The hyperplastic response was retained at least 4 weeks after cessation of treatment. To examine whether these affected cells exhibited enhanced survival in vitro, lung cells were dissociated with Pronase and grown in culture. After 7 days, argyrophilia, dense-cored vesicles, and corticotropin-like immunoreactivity were observed in many of the cells derived from hamsters treated for 5 or 8 weeks. These findings suggest that the endocrine-like cells of neuroepithelial bodies are affected by diethylnitrosamine as evidenced by a numerical increase in vivo and by the properties exhibited by cells in vitro. The relationship of this diethylnitrosamine-induced reaction to bronchial carcinoid tumors or small-cell carcinoma of the lung remains to be established.

The chemical form of cadmium in microsomal and mitochondrial fractions from rat liver and kidney after long term administration of cadmium chloride

Wistar rats were given drinking water containing 250 ppm cadmium (Cd) for 12 months. After excising the kidney and liver, the organs were subfractionated into nuclear, mitochondrial, microsomal and cytosol fractions, and the chemical forms of Cd in the subcellular fractions were examined. Although approx. 90% of the total Cd was present in the cytosol, in the form of metallothionein, 3-5% was also present in the mitochondrial fraction and 5-7% in the microsomal fraction from both organs. Each membrane fraction was washed 3 times and there was no contamination of metallothionein from the cytosol according to Cd/protein ratios. By Sephadex G-75 gel filtration, after solubilizing the particulate fractions with sodium deoxycholate, approx. 89% of Cd in the microsomal fraction and 94% in the mitochondrial fraction eluted with the same retention time as that of metallothionein in both liver and kidney, while the remainder was found in a high molecular weight protein fraction. The Cd eluted with the high molecular protein fraction might be involved in dysfunctions in subcellular organelles.

Commercial laboratory animal diets: toxicant and nutrient variability

A commercial rodent feed was analyzed for a series of nutrients and potential contaminants during a 5-yr period. Annual average Cu and vitamin A concentrations were generally at least 12% lower than the approximate concentrations listed by the manufacturer, whereas Ca, protein, and vitamin B1 were within +/- 5% and fat and Zn within +/- 8% of the manufacturer's specifications. Frequently, Se was found at concentrations at which it has been shown to interact with the process of chemical carcinogenesis. DDT, dieldrin, Cd, and Pb were occasionally close to concentrations known to have biological effects.

Occupational lead exposure, nephropathy, and renal cancer

A 48-year-old lead worker was found to have a cystic renal carcinoma during an evaluation of his occupational lead poisoning. Clinical studies showed elevated blood lead levels, impaired urinary concentrating ability, and reduced creatinine clearance. Histologic and electron microscopic studies showed this cystic tumor to be similar to renal carcinomas observed in animals with prolonged lead exposure. Lead content of the tumor was elevated (2.49 micrograms/gm) in comparison with adjacent renal tissue and with normal adult levels. In light of previous animal studies, this case adds increased evidence to the concern over the carcinogenic potential of prolonged lead exposure.

Flow of reducing equivalents into isolated intestinal mitochondria

A system of enzymes is required for the transport of reducing equivalents from reduced nicotinamide adenine dinucleotide (NADH) generated in the cytosol into the mitochondria by the substrate cycles. Also, the intestinal mitochondria must be capable of oxidizing the substrates of the cycles. Both substrate cycle enzymes and permeable mitochondria are necessary for the flow of pyruvate derived from glucose into the mitochondria for oxidative decarboxylation and for the efficient production of adenosine 5'-triphosphate (ATP) for the unique intestinal nutrient transport functions. Mitochondria from hamster intestinal mucosa were prepared exhibiting good respiratory control ratios. The isolated intestinal mitochondria would not oxidize NADH unless N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) was added as a carrier of reducing equivalents. The rates of oxidation of the substrates of the L-glycerol 3-phosphate and the L-malate/1-aspartate substrate cycles were measured with the mitochondria isolated from the small intestinal mucosa. The key enzymes measured in the cytosol and mitochondria from the mucosa were NAD-L-glycerol 3-phosphate dehydrogenase, Fp-L-glycerol 3-phosphate dehydrogenase, L-malate dehydrogenase and L-glutamate-oxaloacetate transaminase. In addition, the substrate cyclase were simulated in vitro by following NADH oxidation by isolated mitochondria in the presence of added cytosolic constituents.

Dose-related alterations in growth and mineral disposition by chronic oral cadmium administration in the male rat

The effect of cadmium (1, 10, or 100 ppm) administered to male rats in drinking water for 13 weeks on body weight and mineral disposition (Cd, Mg, P and Zn) in several body tissues was examined. Most alterations observed in these parameters occurred only at the 100 ppm dose of Cd. Terminal body weight was decreased by 10% in rats ingesting Cd at 100 ppm resulting from decreased food intake since weight gain/food consumption ratio was the same for all treatment groups. In serum, cadmium ingestion resulted in an inhibition of alkaline phosphatase activity at all concentrations and phosphorous was elevated only in animals receiving 100 ppm Cd. No changes were observed in Ca in urea. In bone, Cd decreased zinc content, increased Ca content, but did not influence bone ash, Mg or P and roentgenographic examination revealed no bone abnormalities. In both liver and kidney, cadmium ingestion did not influence intestinal absorption of Ca, Mg, P, or Zn or the renal excretion of Ca, P, or urea. The results of this study indicate that alterations in body weight and tissue mineral disposition resulting from chronic Cd ingestion are dose-related.

The differential response of isolated intestinal crypt and tip cells to the inductive actions of 2,3,7,8-tetrachlorodibenzo-p-dioxin

The cell specific induction of uridine diphosphate(UDP)-glucuronyltransferase by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in intestinal epithelium was studied by administering [14C] TCDD (8 microgram/kg to adult female rats). Intact epithelial cells from the tip and crypt regions were isolated by differential vibration of rat duodenum. Cell separation was monitored by electron microscopy and marker enzymes. UDP-glucuronyltransferase and radioactivity were assayed in both cell types 0 h, 3 h, 10 h, 1 day, 3 days and 5 days after treatment. UDP-glucuronyltransferase activities were not significantly changed in either cell type isolated from TCDD-treated rats until 24 hr after treatment when a three-fold increase in crypt cell activity was evident. No significant changes in UDP-glucuronyltransferase activity were observed in the differentiated tip cells until 3 days after TCDD treatment. UDP-glucuronyltransferase was increased approximately two-fold in both cell types from 3 and 5 days following TCDD treatment. There was a negative correlation between the time-course of UDP-glucuronyltransferase induction and the [14C]TCDD concentrations measured in these cells. These studies suggest that the undifferentiated cells of the intestinal crypt region are more sensitive to TCDD inductive actions than are the absorptive tip cells.

Cadmium feeding: apparent depression of atrioventricular-his-Purkinje conduction system

Male rats were exposed to 0, 10 and 130 p.p.m. cadmium administered in 0.5% saline drinking water for 71 days. Biweekly records of ECGs, Hct, body weight and blood levels of cadmium were made. Rats exposed to 130 p.p.m. cadmium showed slower growth rates and declining Hct indicative of acute cadmium poisoning. At the end of the experimental period, carotid artery blood pressures and whole heart cadmium levels were determined. Although no significant blood pressure changes were observed in the experimental groups, the cadmium content of the hearts of the higher dose group was significantly higher than in the hearts of the lower dose group. The PR interval of the ECG was lengthened progressively and to the same extent in both experimental groups with continued cadmium feeding. These experiments offer evidence that the accumulation of even moderate amounts of cadmium will be manifested in marked changes in cardiac conduction without overt signs of cadmium poisoning.

Blood cadmium level and hypertension in humans

Blood cadmium level was determined in 29 nontreated hypertensive male subjects and 29 controls. All were individually matched for sex, age, and smoking habits. No differences were found between hypertensives (3.3 +/- 0.4 ng/ml) and normotensives (2.6 +/- 0.4 ng/ml).

Semichronic oral toxicity of cadmium. I. Studies on rats

Cadmium (in the form of CdCl2) was fed to groups of 20 male and 20 female rats each over a period of 3 months in concentrations of 0, 1, 3, 10 and 30 ppm. Appearance, behaviour, food consumption, growth and mortality of the treated rats of all groups were not affected during the 3-month period. The cadmium concentrations did not cause blood, liver or kidney damage. The systolic blood pressure of the treated animals was not increased. Autopsies and histopathological investigation of the animals showed no sign of any alterations. Cadmium accumulated dose-dependently in the kerated by rats over a period of 3 months without harm.

Biomedical responses of rats to chronic exposure to dietary cadmium fed in ad libitum and equalized regimes

Forty 100 g male rats were fed, in groups of eight, either 0, 5, or 25 ppm cadmium in a purified diet for 14 wk. Three groups were fed each of the levels of cadmium on an ad libitum basis. Two other groups were fed either 0 or 5 ppm cadmium in amounts that were equalized to that consumed by the 25 ppm group fed ad libitum. Cadmium ingestion decreased daily diet consumption, weight gain, and terminal body weight. These parameters were not significantly different in rats whose diet consumption was equalized. Packed cell volume and serum iron as well as serum zinc were decreased in the rats fed 25 ppm cadmium. These effects were not related to diet intake. No major differences were observed in serum ceruloplasmin, glucose, protein, leucine aminopeptidase activity, or copper in any of the groups. Blood urea nitrogen and renal leucine aminopeptidase activity were decreased by cadmium ingestion in the rats fed ad libitum only. In contrast, serum alkaline phosphatase activity was elevated by cadmium in the equalized-intake groups only. Cadmium and zinc concentrations were elevated and the iron concentration was decreased in the kidney, liver, and intestinal mucosa of the cadmium-fed rats irrespective of level of diet consumption. The increased uptake of cadmium in these tissues was coincident with the increased content of the cadmium-binding protein, metallothionein, in the cytosol fraction. The results indicate that some parameters of chronic cadmium toxicity are associated with diet consumption whereas others are not.