Tissue distribution, excretion, and urinary metabolites of dichloroacetic acid in the male Fischer 344 rat.

The disposition of dichloroacetic acid (DCA) was investigated in Fischer 344 rats over the 48 h after oral gavage of 282 mg/kg of 1- or 2-[14C]-DCA (1-DCA or 2-DCA) and 28.2 mg/kg of 2-DCA. DCA was absorbed quickly, and the major route of disposition was through exhalation of carbon dioxide and elimination in the urine. The dispositions of 1- and 2-DCA at 282 mg/kg were similar. With 2-DCA, the disposition differed with dose in that the percentage of the dose expired as carbon dioxide decreased from 34.4% (28.2 mg/kg) to 25.0% (282 mg/kg), while the percentage of the radioactivity excreted in the urine increased from 12.7 to 35.2%. This percentage increase in the urinary excretion was mostly attributable to the presence of unmetabolized DCA, which comprised more than 20% at the higher dose and less than 1% at the lower dose. The major urinary metabolites were glycolic acid, glyoxylic acid, and oxalic acid. DCA and its metabolites accumulated in the tissues and were eliminated slowly. After 48 h, 36.4%, 26.2%, and 20.8% of the dose was retained in the tissues of rats administered 28.2 and 282 mg/kg of 2-DCA and 282 mg/kg of 1-DCA, respectively. Of the organs examined, the liver (4.9-7.9% of dose) and muscle (4.5-9.9%) contained the most radioactivity, followed by skin (3.3-4.5%), blood (1.4-2.6%), and intestines (1.0-1.7%). One metabolite, glyoxylic acid, which is mutagenic, might be responsible for or contribute to the carcinogenicity of DCA.

Comparison of the effects of acute and subacute treatment of phenobarbital in different strains of mice.

A strain specificity has been demonstrated for the effect of subsequent administration of phenobarbital (PB), in which diethylnitrosamine (DENA)-initiated hepatocarcinogenesis was promoted in C3H mice, inhibited in B6C3F1 (C57BL x C3H) and not affected in C57BL mice. A correlation has been established between the ability of barbiturates and hydantoins to promote tumor formation and their ability to induce liver growth, hepatic DNA synthesis and mixed function oxidase activities. Therefore, we examined in these 3 strains of mice and in C3B6F1 (C3H x C57BL) mice the effect of PB administered in their drinking water for 4 days or 28 days. The liver weight to body weight ratio was increased by PB in all types of mice. Microsomal protein concentrations were increased in C57BL mice after 28 days of treatment, in C3H after both 4 days and 28 days and in B6C3F1 after 4 days of treatment. No effect upon microsomal protein content was observed in C3B6F1 mice. DNA content was increased in C3H mice, both in the 4-day and 28-day treatment groups, while the other strains showed either a decrease or no difference from control. DNA synthesis was elevated in all strains of mice after 4 days of treatment with PB, however, after 28 days of treatment there was either a much reduced increase (C57BL and C3B6F1) or no difference (C3H and B6C3F1) from controls. In all 4 types of mice after 4 and 28 days of treatment, PB increased the concentration of cytochrome P-450, the activity of aminopyrine-N-demethylase (AmDm) and 7-ethoxyresorufin-O-deethylase (ErDe) and the oxidation of testosterone (T). The oxidative metabolites of T were similar in the 4 types of mice.

Genotoxic properties of haloacetonitriles: drinking water by-products of chlorine disinfection.

Chlorinated and brominated haloacetonitriles (HAN), known drinking water contaminants which form during chlorine disinfection, were investigated for genotoxic activity. The HAN produced DNA strand breaks in cultured human lymphoblastic (CCRF-CEM) cells, bound to the nucleophilic trapping agent 4-(p-nitrobenzyl)pyridine and formed a covalent bond to polyadenylic acid in a cell-free reaction system. Thus, we have demonstrated that these chemicals are genotoxic, which would indicate a potential for carcinogenic activity and for human health hazard.

Glutathione plus cytosol- and microsome-mediated binding of 1,2-dichloroethane to polynucleotides.

1,2-[1,2-14C]Dichloroethane was metabolized by rat hepatic microsomes to products that irreversibly bound polynucleotides. The polynucleotides were then enzymatically hydrolyzed and the products separated by a high-performance liquid chromatograph (HPLC) equipped with an ODS or a SCX column. The products of microsome-mediated binding were identified in the HPLC eluate as 1,N6-ethenoadenosine to polyadenylic acid, 3,N4-ethenocytidine to polycytidylic acid, and two cyclic derivatives to polyguanylic acid. 1,2-[1,2-14C]Dichloroethane was also metabolized in the presence of a glutathione (GSH)-cytosolic fraction and a polynucleotide. After enzymatic hydrolysis of the polynucleotide, the major peak of radioactivity was eluted from a Sephadex G-25 column in the salt volume which would exclude the presence of a product containing both GSH and a nucleoside. Chromatography by ODS-HPLC of the major peak from Sephadex G-25 indicated the presence of a GSH metabolite of 1,2-dichloroethane that did not contain a nucleoside. A similar hydrophilic peak was obtained for the hydrolysis products of polynucleotides from a glutathione plus cytosol incubation in which the polynucleotide instead of being added prior to the incubation was added after the incubation. The products of the glutathione plus cytosol metabolism of 1,2-[1,2-14]dichloroethane appear to be glutathione metabolites that coisolated with the polynucleotides rather than covalently bound adducts. In conclusion, covalently bound adducts were identified for microsome-mediated binding of 1,2-dichlorethane to polynucleotides, while no evidence was obtained for glutathione plus cytosol-mediated covalent binding to polynucleotides.

Haloacetonitrile excretion as thiocyanate and inhibition of dimethylnitrosamine demethylase: a proposed metabolic scheme.

Haloacetonitriles, contaminants present in chlorinated drinking water, were administered orally to rats, and the urinary excretion of thiocyanate was measured as an index of cyanide release. The urinary excretion of thiocyanate accounted for 14.2% of the dose of monochloroacetonitrile; 7.7-12.8% of the dose of bromochloro-, dichloro-, and dibromoacetonitrile; and 2.25% of the dose of trichloroacetonitrile. The haloacetonitriles inhibited rat-liver microsomal dimethylnitrosamine (DMN) demethylase in an in vitro assay system. Dibromo- and bromochloroacetonitrile were the most potent inhibitors of DMN demethylase, with Ki = 3-4 X 10(-5) M; dichloro- and trichloroacetonitrile were the next most potent, with Ki = 2 X 10(-4) M; and monochloroacetonitrile was the least potent inhibitor, with Ki = 9 X 10(-2) M. Trichloroacetonitrile, but not dibromoacetonitrile, when administered orally inhibited hepatic DMN demethylase activity. The relative capacity of the haloacetonitriles to inhibit DMN demethylase and to be excreted as thiocyanate did not correlate.

Pulmonary function and pathology in cats exposed 28 days to diesel exhaust.

Young adult male cats were exposed 28 days, 20 hrs per day, to a 1:14 dilution of diesel exhaust emissions. Following termination of exposure, the following pulmonary function measurements were carried out: lung volumes, maximum expiratory flow rates (MEF), MEF at 50%, 25% and 10% of vital capacity (VC): forced expiratory volume (FEV) after 0.2, 0.3 and 0.4 sec, dynamic compliance, resistance and helium washout at 25, 50, 75, and 100 breaths per min. The only significant functional change was a decrease in MEF at 10% of VC (P x .02). The lungs of the exposed cats appeared charcoal grey with frequent focal black spots visible on the pleural surface. Pathologic changes in the exposed cats included a predominantly peribronchiolar localization of black-pigmented macrophages within the alveoli producing a focal pneumonitis or alveolitis. In general, evidence of serious lung damage was not observed following the 28-day exposure period.

Arterial blood gases, pulmonary function and pathology in rats exposed to 0.75 or 1.0 ppm ozone.

Arterial blood gases, residual lung volume (RV), deflation pressure volume (PV) curves, pulmonary pathology and body weight changes were studied in rats exposed up to 14 days to either 0.75 or 1.0 ppm ozone. Arterial PO2 and body weights decreased progressively with length of exposure while PaCO2 and RV increased. The slope of the PV curve decreased in all groups exposed to ozone. Pathological changes in the lung increased in severity with concentration and length of exposure. The present findings have shown that arterial blood gas measurements represent a sensitive index of altered lung function in rats, a species very sensitive to ozone exposure.