Showing papers in "Archives of Toxicology in 1985"

Tumor promotion in the liver.

Abstract: Intensive research during recent years has made the rodent liver one of the best model systems to study chemical carcinogenesis and tumor promotion in vivo. As will be shown in the present paper current knowledge mainly rests on the results of histological and histochemical studies but has reached a state where broader application of the techniques of biochemistry and molecular biology is both possible and necessary for further progress. Such progress will have important implications for the design of future cancer therapies and for the toxicological evaluation of potentially carcinogenic compounds.

Study of inorganic arsenic methylation by rat liver in vitro: relevance for the interpretation of observations in man

Abstract: The biotransformation of inorganic arsenic by rat liver in vitro leads to the production of a monomethylated and a dimethylated arsenic derivative, measured by flameless atomic absorption as monomethylarsonic (MMA) and dimethylarsinic (DMA) acids respectively. The methylating activity is localized in the cytosol and accepts only As3+ as substrate. Its optimum pH lies between 7.5 and 8.0, and reduced glutathione (10−2M) is required for full activity. S-Adenosylmethionine is the essential methyl group donor and corrinoid derivatives act synergistically. An excess of substrate and the addition of mercuric ions prevent the formation of the dimethylated arsenic derivative without affecting that of the monomethylated compound. This indicates that two different enzymatic activities are involved in the methylation of inorganic arsenic in mammals. Previous observations in man (Buchet et al. 1981 b, 1984) and the results of the present study suggest that DMA production results from the subsequent methylation of the MMA precursor, although the possibility that metabolites are also produced by two completely independent pathways cannot yet be conclusively rejected. The kinetics of MMA and DMA production provide an explanation for the observations that in volunteers given increasing amounts of As3+, the urinary excretion of DMA levels off faster than that of MMA and in patients acutely intoxicated with As3+, several days may elapse before DMA becomes the preponderant metabolite. The results of the present study also suggest that the reduction of MMA production associated with an increased synthesis of DMA found in patients with liver diseases given a standard dose of As3+ might be due to a reduction of As3+ uptake by the liver cells.

The comparative toxicology of ethyl- and methylmercury.

Abstract: Neurotoxicity and renotoxicity were compared in rats given by gastric gavage five daily doses of 8.0 mg Hg/kg methyl- or ethylmercuric chloride or 9.6 mg Hg/kg ethylmercuric chloride. Three or 10 days after the last treatment day rats treated with either 8.0 or 9.6 mg Hg/kg ethylmercury had higher total or organic mercury concentrations in blood and lower concentrations in kidneys and brain than methylmercury-treated rats. In each of these tissues the inorganic mercury concentration was higher after ethyl than after methylmercury. Weight loss relative to the expected body weight and renal damage was higher in ethylmercury-treated rats than in rats given equimolar doses of methylmercury. These effects became more severe when the dose of ethylmercury was increased by 20%. Thus in renotoxicity the renal concentration of inorganic mercury seems to be more important than the concentration of organic or total mercury. In methylmercury-treated rats damage and inorganic mercury deposits were restricted to the P2 region of the proximal tubules, while in ethylmercury-treated rats the distribution of mercury and damage was more widespread. There was little difference in the neurotoxicities of methylmercury and ethylmercury when effects on the dorsal root ganglia or coordination disorders were compared. Based on both criteria, an equimolar dose of ethylmercury was less neurotoxic than methylmercury, but a 20% increase in the dose of ethylmercury was enough to raise the sum of coordination disorder scores slightly and ganglion damage significantly above those in methylmercury-treated rats. In spite of the higher inorganic mercury concentration in the brain of ethylmercurythan in the brain of methylmercury-treated rats, the granular layer damage in the cerebellum was widespread only in the methylmercury-treated rats. Thus inorganic mercury or dealkylation cannot be responsible for granular layer damage in alkylmercury intoxication. Moreover, histochemistry demonstrated no inorganic mercury deposits in the granular layer.

Young Scientists Award Lecture 1984 : Species Differences in Carcinogenicity and Peroxisome Proliferation due to Trichloroethylene: A Biochemical Human Hazard Assessment

Abstract: Trichloroethylene (TRI) administered to mice by gavage for 10 consecutive days at doses of 50–2000 mg/kg body weight elicited dose-dependent increases (up to 700 % of control values) of hepatic cyanide insensitive palmitoyl CoA oxidation (a marker of peroxisomal β-oxidation). No effect was seen on catalase; the other peroxisomal marker examined. Similar experiments with rats demonstrated no effect of TRI on either cyanide insensitive palmitoyl CoA oxidation or catalase. A major metabolite of TRI, trichloroacetic acid (TCA) when administered by gavage for 10 consecutive days at doses of 10–200 mg/kg body weight, stimulated hepatic cyanide insensitive palmitoyl CoA oxidation in both mice (up to 500 % of control) and rats (up to 650 % of control). Again, no effect upon catalase activity was apparent. The kinetics of biotransformation of TRI to TCA in isolated hepatocytes was markedly species dependent. The ‘intrinsic clearance’ values (Vmax/Km) for TRI in mouse, rat and human hepatocytes were 3.8 × 10−6, 1.2 × 10−7 and 3.25 × 10−8 L/min/106 cells respectively. TCA induced peroxisomal β-oxidation in mouse and rat hepatocytes, but had no effect upon this enzyme activity in cultured human hepatocytes. It is postulated that the species difference in hepatocarcinogenicity of TRI (mouse positive ; rat negative) is due to species differences in peroxisome proliferation which in turn is a result of differences in the rate of formation of TCA from TRI. On this basis it is proposed that TRI presents no significant human hepatocarcinogenic hazard since, (1) human hepatocytes produced TCA at a rate even lower than that of the rat, and (2) TCA was not a peroxisome proliferator in human hepatocytes.

Reduction and binding of arsenate in marmoset monkeys.

Abstract: The metabolism of 74As-arsenate (As V, 0.4 mg As/kg body weight, IV) in marmoset monkeys (two males and two females) was studied. Unlike all other animal species studied so far, the marmoset was found to be unable to metabolize the arsenate to dimethylarsinic acid. Most of the absorbed arsenate was reduced to arsenite (As III) in vivo. Only 20% was excreted in the urine as unchanged As V. A further 20% of the dose was excreted as As III. The rest of the As III produced was bound to the tissues, giving a distribution picture very similar to that reported earlier for marmoset monkeys given arsenite. The tissues with longest retention of arsenic were the liver, upper gastrointestinal tract (oral cavity and esophagus), skin, kidneys and gall bladder. The pronounced accumulation in the liver resulted from specific binding of arsenic to the rough microsomal membranes, unique to this animal species.

The relationship between exposure duration, carboxyhemoglobin, blood glucose, pyruvate and lactate and the severity of intoxication in 39 cases of acute carbon monoxide poisoning in man.

Abstract: The relationship between exposure duration, COHb, blood glucose, pyruvate and lactate and the severity of intoxication was investigated in a group of 39 cases of acute CO poisoning treated in the Clinical Toxicology Center in Lodź, Poland. On the basis of clinical criteria the patients were classified into cases of mild, moderate, severe and very severe CO poisoning. COHb and carbohydrate metabolites were estimated in venous blood taken immediately after admission of the patient to hospital prior to treatment. The severity of intoxication did not correlate with blood COHb; variation in exposure duration seems to be responsible for this phenomenon. Severe and very severe poisonings were associated with longer exposures and were accompanied by a markedly higher blood lactate level, compared to mild and moderate cases. Blood pyruvate depended less than lactate on the severity of intoxication. Blood glucose depended neither on exposure duration nor on the severity of intoxication. Among the carbohydrate metabolic parameters studied, blood lactate determination can be helpful in the evaluation of the severity of CO poisoning in man.

On the Embryotoxic Effects of Benzene and Its Alkyl Derivatives in Mice, Rats and Rabbits

Abstract: Groups of CFY rats were exposed to inhalation of ethylbenzene at 600, 1200 or 2400 mg/m3 or xylene at 250, 1900 or 3400 mg/m3 or Aromatol at 500, 1000 or 2000 mg/m3 atmospheric concentration for 24 h/day from day 7 to day 15 of pregnancy, or for 2–4 hours only on the 18th or 20th day of gestation. CFLP mice and NZ rabbits were exposed to inhalation of 500 mg/m3 or 1000 mg/m3 benzene, toluene, ortho-, meta-, para-xylene, ethylbenzene, xylene or Aromatol for 24 h/day from day 6 to day 15 of pregnancy. Untreated animals and groups inhaling pure air served as controls. All components of the xylene and Aromatol crossed the placenta and were present in fetal blood and amniotic fluid, as well. The maternal toxic effects at all solvents were moderate and dose dependent. All solvents (at higher concentrations) brought about skeletal and weight retardation in fetuses of rats and mice. At highest concentration some solvents increased the post-implantation loss in rats and mice. All solvents caused spontaneous abortion in rabbits at 1000 mg/m3 atmospheric concentration. Only ethylbenzene and Aromatol increased the malformation rate in rats and mice. No other solvent applied proved to be teratogenic either in mice, rats or rabbits.

Stimulation of calmodulin by cadmium ion

Abstract: Cd2+, a serious environmental pollutant in certain industrial regions, accumulates in mammalian tissues with a very slow turnover. Using various criteria, we studied the ability of Cd2+ to substitute for Ca2+ in calmodulin (CaM), a ubiquitious Ca2+-binding protein that mediates many of the Ca2+ effects. CaM bound Cd2+ with a Kd of 4.5 μM, presumably to the Ca2+-binding sites. Binding of Cd2+ allowed CaM to bind 2 moles chlorpromazine, or to form a complex with skeletal muscle troponin-I, troponin-T, or phosphodiesterase. Complex formation with phosphodiesterase led to its activation, which was observed even in the presence of glutathione or cysteine, agents known to chelate Cd2+. This raises the possibility that one manifestation of Cd2+ toxicity may be through its activation of CaM, thus upsetting its normal regulation by a cellular flux of Ca2+.

The median lethal dose and its estimation.

Abstract: An important paper by Zbinden and Fluri-Roversi (1981) has shown the many weaknesses in any policy or regulatory system that regards an estimated LD50 in an animal species as an adequate guide to toxicity in man. The present paper draws attention to some statistical aspects of LD50 estimation that are too often neglected or misunderstood when this quantity is wanted. It is solely concerned with practice when a LD50 must be estimated, and deliberately does not approach the broader issues of whether the LD50 should be estimated. A first need is clear distinction between the true but unknown form of dependence of mortality on dose and the estimate of it (or of a particular property such as the LD50) that is obtainable from an experiment. Some assumptions are necessary before any estimation is possible. The graphical and semi-graphical methods that once were popular because of their simplicity and speed are today only reasonable as a last resort, when data are wholly inadequate and all that can be found is a very rough preliminary indication. Many "simple" arithmetical methods have been shown to be inherently bad, in that equally simple alternatives are usually more precise and less subject to bias. The Spearman-Karber method remains as a useful possibility, demanding little knowledge of the form of the response curves but often needing other unverifiable assumptions. For most purposes, maximum likelihood estimation of a parametric formulation of the response curve is the best choice, not only because of theoretical merits but also because it can now be performed on a microcomputer in a very few seconds.

Low level chromium (VI) inhalation effects on alveolar macrophages and immune functions in Wistar rats.

Abstract: In inhalation chambers, 5-week-old male Wistar rats of the strain TNO-W-74 were continuously exposed to submicron aerosols of sodium dichromate in concentrations from 25 (low level) to 200 micrograms/m3 Cr (high level). Subacute exposure (28 days) to 25 and 50 micrograms/m3 Cr resulted in "activated" alveolar macrophages with stimulated phagocytic activities, and significantly elevated antibody responses to injected SRBC's. After subchronic (90 days) low level exposure there was a more pronounced effect on activation of the alveolar macrophages, with increased phagocytic activities. However, at high Cr (VI) exposure level (200 microgram/m3), inhibited phagocytic function of the alveolar macrophages was seen. In rats which were exposed to this chromium aerosol concentration for 42 days, the lung clearance of inert iron oxide was reduced significantly. The humoral immune system was still stimulated at subchronic low chromium aerosol concentrations of 100 micrograms/m3, but significantly depressed at 200 micrograms/m3 Cr. These results show that respiratory defence and immunologic functions were stimulated or inhibited depending on dose and time of chromium (VI) inhalation.

Modification and standardization of the culture of early postimplantation embryos for toxicological studies.

Abstract: 1 The method of culturing “whole” rat embryos (days 95–115 of gestation, ie at the early stage of organogenesis) as modified and standardized in our laboratory is presented; 2 We have succeeded in using bovine serum as culture medium instead of rat serum as recommended in the original procedure Experimental conditions are described for obtaining reproducible results; 3 An improved scoring system was developed which, in connection with a computerized documentation, greatly facilitates the evaluation of the data

Biochemical effects of methyl tertiary-butyl ether in extended vapour exposure of rats.

Abstract: Male Wistar rats exposed to 50, 100 or 300 ppm methyl tertiary-butyl ether vapour for 2–15 weeks, 6 h daily, 5 days a week, showed a dose-dependent blood ether concentration after 2 weeks' exposure. Blood concentrations of teriary-butanol, were also dose dependent indicating metabolic breakdown of the ether in vivo. The blood ether concentrations decreased after 6 weeks of exposure at the 50 ppm dose level and remained unaffected at higher doses while tertiary-butanol concentrations increased after 6 weeks with all doses, and began to decrease thereafter. Exposure caused a transient increase in UDP-glucuronosyltransferase activities in liver and kidney microsomes, almost no effects on hepatic cytochrome P-450 concentrations and a minor induction of kidney microsomal cytochrome P-450 content. Exposure produced almost no effect on brain succinate dehydrogenase, creatine kinase or acetylcholinesterase activities, while early inhibition of muscle creatine kinase activity was noted, accompanied by increased activity at the end of exposure.

Depletion of nasal mucosal glutathione by acrolein and enhancement of formaldehyde-induced DNA-protein cross-linking by simultaneous exposure to acrolein.

Abstract: Incubation of homogenates of rat nasal mucosa with acrolein resulted in the apparent formation of DNA-protein cross-links. However, inhalation exposure of male Fischer-344 rats to acrolein (2.0 ppm, 6 h) did not cause detectable DNA-protein cross-linking in the nasal respiratory mucosa. Simultaneous exposure of rats to both acrolein (2.0 ppm) and formaldehyde (6.0 ppm) for 6 h resulted in a significantly higher yield of DNA-protein cross-links than was obtained following exposure to formaldehyde (6.0 ppm) alone. Acrolein exposure at concentrations of 0.1, 0.5, 1.0, or 2.5 ppm resulted in a concentration-dependent depletion of nonprotein sulfhydryl groups in the nasal respiratory mucosa. A plausible explanation for the enhancement of DNA-protein cross-links by simultaneous exposure to formaldehyde and acrolein may be that depletion of glutathione by acrolein inhibited the oxidative metabolism of formaldehyde, leading to an increase of formaldehyde-induced DNA-protein cross-links.

Fast uptake kinetics in vitro of 51Cr (VI) by red blood cells of man and rat.

Abstract: Fast transport kinetics of 51Cr (VI) into red blood cells (RBCs) in vitro were studied. No significant species differences were found between RBCs of man and rat. The uptake of 51Cr (VI) by RBCs in whole blood was composed of two different first order processes of different velocities (apparent t1/2 of 22.7 s and 10.4 min for man and 6.9 s and 10.1 min for rat, respectively). However, even after longer time periods a fixed portion of approximately 15% of the administered dose remained in the plasma and did not penetrate into RBCs Over the entire concentration range studied (10 μM–50 mM), the fast initial uptake followed Michaelis-Menten kinetics. The maximal capacity of this Cr(VI) transport into RBCs of man and rat was 3.1×108 CrO42− ions × cell−1 × min−1 and 2.5×108 CrO4−2 ions × cell−1 × min−1, respectively. It is likely that Cr(VI) is transported into RBCs via a physiological anion carrier (“band-3-protein”).

Biomonitoring of aniline and nitrobenzene. Hemoglobin binding in rats and analysis of adducts.

Abstract: Covalent binding to hemoglobin was studied to further substantiate the proposal that it may be used for biomonitoring N-substituted aryl compounds (14C)-Labeled acetanilide and nitrobenzene were orally administered to female Wistar rats and binding indices [Binding(mmol/mol Hb)/Dose(mmol/kg)] determined; these were 12±1 and 73±10, respectively After mild acidic or alkaline hydrolysis, 90% of the bound material was released and identified as aniline by radio thin layer chromatography This supports the hypothesis that nitroso aryl derivatives, common intermediates in the metabolism of N-substituted aryl compounds, react with SH-groups of hemoglobin to yield sulfinic acid amides Aniline was furthermore identified and quantified by capillary gas chromatography, using hemoglobin from animals treated with unlabeled aniline and nitrobenzene Binding indices in this case were 30±3 and 85±19, respectively With this method human blood samples may also be analysed

Arsenic uptake, cytotoxicity and detoxification studied in mammalian cells in culture

Abstract: The cytotoxicity of trivalent and pentavalent inorganic arsenic salts was determined in mouse fibroblasts in vitro Concentrations of As (III) in the μM range led to a reduction of proliferation and viability with a concomitant increase in LDH release and stimulation of lactic acid production Similar effects were noted with approximately 10-fold greater molar concentrations of As(V) Cells pretreated with a low As(III) concentration are less sensitive to toxic doses of As(III) or As(V)

Toxicokinetics of labeled amatoxins in the dog.

Abstract: Radioactivities were measured in serum, urine, and bile of dogs at different times after intravenous injection of 14C-methyl-gamma-amanitin (14C-A) and 3H-O-methyl-dehydroxymethyl-alpha-amanitin (3H-A). For either substance, the relation between the specific plasma activity C and the time t could be best described with the function C = C1 X e- lambda 1 X t + C2 X e- lambda 2 X t. Therefore the linear open two-compartment system was selected as an adequate toxicokinetic model. Most important, the distribution volumes (in the steady state) were in the range of the extracellular space, and the total body clearances were in the range of the dog creatinine clearance. In accordance with former findings for 3H-A, 14C-A was not bound to plasma proteins. More than 80% of 14C-A was eliminated in the urine; less than 10% was found in the bile. From these data, two suggestions may be derived for the therapy of Amanita intoxication in man. First, detection in the urine of amatoxins 2 or 3 days after mushroom ingestion points to an ongoing amatoxin absorption or reabsorption from the intestine, and should lead to therapy with adsorbents and, in the absence of diarrhea, with laxatives. Second, hemoperfusion will remove significant amounts of amatoxins during the time of ongoing absorption or reabsorption and a few hours thereafter.

Species differences in the formation of butadiene monoxide from 1,3-butadiene.

Abstract: When 1,3-butadiene is incubated with liver postmitochondrial fractions from mouse, rat, monkey or man and a NADPH-regenerating system, the formation rate of butadiene monoxide is different in the four species. With the exception of the rhesus monkey, the amount of epoxide is proportional to the monooxygenase activity. The sequence of epoxide formation is B6C3F1 mouse, Sprague Dawley rat, man, rhesus monkey. The ratio between mouse and monkey was about 7∶1. When 1,3-butadiene is incubated with homogenates from lung tissue, only tissues from mouse and rat produce measurable butadiene monoxide concentrations. The monooxygenase activity in lung tissue of the mouse was only 1/30 that in mouse liver. By contrast, lung tissue formed epoxide concentrations comparable to those formed by liver tissue, whereas monkey and human lung tissue did not produce any measurable levels of butadiene monoxide. The data might suggest that the results of recent rodent inhalation studies with 1,3-butadiene could not automatically be extrapolated to man.

Accidental exposure to sarin: vision effects

Abstract: Two men were accidentally exposed to vapors of sarin, a cholinesterase inhibitor and extremely toxic nerve gas. Diagnosis was confirmed by depressed cholinesterase activity, and fixed extremely miotic pupils. No other signs or symptoms developed and neither man required treatment. Recovery to normal cholinesterase activity was gradual over a 90-day period. Pupillary reflexes were not detectable until 11 days after exposure; the miotic pupils dilated slowly over a 30–45 day-period. Eye pain and blurred vision did not occur; visual acuity and amplitude of accommodation were improved for several weeks. Other functions not affected significantly were intraocular pressure, visual fields, color vision, heterophorias, and vergences.

Brain manganese accumulation following systemic administration of different forms

Abstract: The content and retention of manganese in the blood and brain of mice exposed to different forms of the metal was compared. Mice received an acute sc injection of manganese as the chloride or oxide (Mn3O4) or as the organic MMT. A single injection markedly elevated brain manganese concentrations within 1 day and elevated levels were maintained for at least 21 days. Repeated injections led to further increases in both brain and blood, although the levels in the brain appeared to persist at consistently high levels for longer periods. The chloride form produced higher brain levels than either of the other two forms. These results appear to suggest that the slowly developing neurotoxicity in response to manganese exposure may be due to a persistent retention of manganese by the brain.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and 2,3,7,8-tetrachlorodibenzofuran (TCDF) in pregnant C57BL/6N mice: distribution to the embryo and excretion.

Abstract: The distribution and excretion of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 2,3,7,8-tetrachlordibenzofuran (TCDF) were studied in pregnant C57BL/6N mice following an oral dose of 30 micrograms/kg 14C-TCDD and 800 micrograms/kg 14C-TCDF on gestation day 11. The distribution in maternal blood and liver and excretion in urine and feces was similar to that previously reported in males of the same strain. However, the rates of elimination were more rapid in pregnant females for both chemicals. This was more pronounced for TCDD than for TCDF. At all time points examined, the levels of radioactivity in the individual embryos were below 0.5% of the total TCDD dose and below 0.05% of the total TCDF dose. Assuming that all radioactive material found in embryos was unmetabolized compound, no more than 2.6 ng (8 pmoles) TCDD and 6.4 ng (21 pmoles) TCDF per g tissue were detected. In light of recent findings which strongly suggest a direct effect of TCDD and related compounds on embryonic palatal tissue, our data clearly support the potent teratogenic effect of TCDD and TCDF on the development of the secondary palate.

The octanol/water distribution of mercury compounds.

Abstract: Lipophilicity plays an important role in the biological action of mercurials. The distribution of one inorganic and five organic mercury compounds was determined in an n-octanol/water system. Lipophilicity decreased in the order CH3HgCl, bromomercurihydroxypropane, HgCl2, chlormerodrin, p-chloromercuribenzoic acid (PCMB), p-chloromercuriphenylsulfonic acid (PCMBS). The toxicity of mercurials, as reported in the literature, appears to parallel their lipophilicity.

Lead and cadmium in breast milk higher levels in urban vs rural mothers during the first 3 months of lactation

Abstract: Breast milk from 10 women each from the city of Hamburg and from a rural area was analyzed by atomic absorption spectrometry for contamination with lead and cadmium. Samples were examined at regular intervals for 3 months after birth. On day 5 a diurnal profile was analyzed; on the other days milk was taken before and after the morning feed.

Teratogenesis and reproductive safety evaluation of the retinoid etretin (Ro 10-1670).

Abstract: Reproduction and teratology studies were performed with etretin, the free acid analog of the retinoid etretinate. The lowest teratogenic dose of etretin in mice, rats and rabbits was 3, 15 and 0.6 mg/kg, respectively. In all three species, the lowest dose which was embryolethal, fetolethal or reduced the survivability of the pups during lactation was 2–3 times higher than the above doses. In rats, the lowest effective dose of etretin was 3 mg/kg in both the study for fertility and general reproductive performance and the peri- and postnatal study. The main adverse effect in these two experiments was a reduced survival of the F1-generation.

Formation, toxicity and inactivation of acrolein during biotransformation of cyclophosphamide as studied in freshly isolated cells from rat liver and kidney

Abstract: In the present study the formation and the effects of cyclophosphamide-derived acrolein were investigated using isolated cells from rat liver and kidney, with particular regard to the protective action of low molecular weight thiols against cellular toxicity. The results may be summarized as follows: (a) Cyclophosphamide (CTX)-mediated toxicity to isolated cells is dependent on cytochrome P-450 activity; (b) Loss of viability in cells incubated with cyclophosphamide is preceded by a depletion of cellular GSH; (c) Stimulation of cellular GSH synthesis or the presence of low molecular weight thiols in the incubation medium protects against cyclophosphamide-induced toxicity; (d) Acrolein is probably formed extracellularly as well as intracellularly and can be detoxified by thiol compounds, forming a thiochemiacetal or a thioether.

Assessment of the teratogenicity of di(2-ethylhexyl)phthalate and mono(2-ethylhexyl)phthalate in mice.

Abstract: Di(2-ethylhexyl)phthalate (DEHP) and mono(2-ethylhexyl)phthalate (MEHP) were administered PO or IP to pregnant ICR mice at varying doses on days 7, 8, and 9 of gestation. In groups given DEHP orally, resorptions and malformed fetuses increased significantly at 1,000 mg/kg. Fetal weights were also significantly suppressed. Anterior neural tube defects (anencephaly and exencephaly) were the malformations most commonly produced. No teratogenic effects were revealed by IP doses of DEHP and PO or IP doses of MEHP, although high doses were abortifacient and lethal to pregnant females. Thus DEHP is highly embryotoxic and teratogenic in mice when given PO but not IP. The difference in metabolism, disposition, or excretion by the route of administration may be responsible for the difference in DEHP teratogenicity. Although MEHP is a principal metabolite of DEHP and is several times more toxic than DEHP to adult mice, it seems that MEHP and its metabolites are not teratogenic in ICR mice.

Metabolism and pharmacokinetics of vinyl acetate.

Abstract: The hydrolysis of vinyl acetate (formation of acetic acid) has been studied in vitro with rat liver and lung microsomes, rat and human plasma and purified esterases (such as acetylcholine esterase, butyrylcholine esterase, carboxyl esterase). Characterization of the kinetic parameters revealed that rat liver microsomes and purified carboxyl esterase (from porcine liver) displayed the highest activity. In order to establish the rate of metabolism of vinyl acetate in vivo, rats were exposed in closed desiccator jar chambers, and gas uptake kinetics were studied. The decay of vinyl acetate was dose-dependent, indicating possible saturation of metabolic pathway(s). The maximal clearance (at lower concentrations) of vinyl acetate from the system (30 000 ml/h per kg body weight) was similar to the maximal ventilation rate in this species. This indicated that under conditions when metabolic enzymes are not saturated the metabolic rate is mainly determined by pulmonary uptake. The exposure of rats to vinyl acetate resulted in a transient exhalation of significant amounts of acetaldehyde into the closed exposure system. This indicates the presence of this metabolic intermediate of vinyl acetate in the organism in vivo.

The interaction of aluminum and other metal ions with calcium-calmodulin-dependent phosphodiesterase.

Abstract: In the search for the mode of action of aluminum ions in dialysis encephalopathy, their interaction with calmodulin has been assessed, and compared with those of Ca2+, Pb2+, Mn2+, Hg2+ and Cd2+. The basal and calmodulin-dependent activity of phosphodiesterase was measured in the presence of the ions, and their binding to calmodulin was assessed by competition with 45Ca2+ in flow dialysis. Al3+, Mn2+, Hg2+, and Cd2+ cannot be regarded as exclusive calmodulin antagonists or agonists, but rather interact with the phosphodiesterase itself. Pb2+ however, mimicks Ca2+ in every system tested, and is active in the same concentration range as Ca2+. Our results indicate that the assumed role of Al3+ ions in dialysis encephalopathy or other neurological disturbances is not linked with calmodulin.

Effects of ethylbenzene, toluene, and xylene on the induction of micronuclei in bone marrow polychromatic erythrocytes of mice

Abstract: Genotoxic effects of five widely used aromatic industrial solvents, ethylbenzene, methylbenzene (toluene), o-, m-, and p-dimethylbenzene (xylene), on bone marrow cells of male NMRI mice were studied using micronucleus test. Each compound was given to animals by IP administration of two similar doses 24 h apart. Increased formation of micronuclei within polychromatic erythrocytes of femoral bone marrow 30 h after the first injection was conducted to be due to the clastogenic effect of the test compound. Of the chemicals tested, only toluene gave a dose-dependent increase in the frequency of micronucleated polychromatic erythrocytes. This genotoxic activity of toluene was confirmed in male B6C3F1 mice.

Effect of oral cadmium administration to female rats during pregnancy on zinc, copper, and iron content in placenta, foetal liver, kidney, intestine, and brain.

Abstract: Cadmium chloride was administered in drinking water at a concentration of 50 ppm cadmium to female rats for 20 days of gestation. The foetuses were then removed from the uteri of the dams. Gestational exposure to oral cadmium resulted in decreased zinc, copper, iron, metallothionein, and thionein-bound zinc content in foetal liver as well as in reduced copper content in placenta and foetal intestine, brain and kidney. Subcellular fractionation of the foetal liver revealed decreased nuclear and cytoplasmic zinc content as well as decreased microsomal iron content. Pregnant rats exposed to oral cadmium revealed decreased serum zinc and iron concentration as well as reduced ceruloplasmin activity. The decreased zinc, copper, and iron content in foetal organs is suggested to be causally connected with the diminished availability of these metals in the maternal circulation.