Metabolism and Disposition of Phenolphthalein in Male and Female F344 Rats and B6C3F1 Mice

A recent 2-year carcinogenicity/toxicology study determinedthat phenolphthalein (PHTH) is a multisite carcinogen in bothmice and rats at all doses evaluated. In response to this findingthe metabolism and disposition of PHTH has been evaluated inboth F344 rats and B6C3F1 mice at a single oral dose of 800mg/kg. This dose fell within the range previously found to becarcinogenic in rats and mice. Studies were also performed using1 and 50 mg/kg doses. At 800 mg/kg recovery of [¹⁴C]PHTH after72 h was near 100% in females but closer to 75% in males. Radioactivitywas primarily recovered in the feces in rats (>90%), whilemice excreted 30–40% of administered activity in the urine.There was no significant retention of radioactivity in tissuesby 72 h and no significant accumulation of radioactivity inany tissue at any time point. Covalent binding to protein intarget tissues, bone marrow and ovary, was at or less than thepmol/mg protein range. The major metabolite was PHTH glucuronide.Three minor metabolites were detected. A sulfate conjugate andand a hydroxylated metabolite were identified by comparisonof retention times and ¹H NMR and/or mass spectra with syntheticstandards. A diglucuronide conjugate was tentatively identified.Biliary elimination was extensive in rats (35% of dose within6 h); the only product detected in bile was phenolphthaleinglucuronide.     

Carcinogenicity of Chloroform in Drinking Water to Male Osborne-Mendel Rats and Female B6C3F1 Mice

Carcinogenicity of Chloroform in Drinking Water to Male Osborne-MendelRats and Female B6C3F1 Mice. JORGENSON, T. A., MEIERHENRY, E.A., RUSHBROOK, C. J., BULL, R. J.AND ROBINSON, M. (1984). Fundam.Appl. Toxicol. 5, 760–769. The carcinogenic activity ofchloroform administered at 0, 200, 400, 900, and 1800 mg/literin drinking water was studied in male Osborne-Mendel rats andfemale B6C3F1 mice. A second control group was included in thestudy and was restricted to the water consumption of the high-dosegroup. Animals were maintained on study for 104 weeks. Groupsizes were adjusted at low doses such that a detectable tumorresponse would result at the lowest dose if there was a linearrelationship with dose, and the higher doses produced responsessimilar to previous carcinogenesis bioassays of chloroform.The primary finding was that chloroform increased the yieldof renal tubular adenomas and adenocarcinomas in male rats ina dose-related manner. For the high-dose group, which correspondedto a time-weighted average dose of 160 mg/kg per day for 104weeks, there was a 14% incidence of renal tubular adenomas andadenocarcinomas, vs 1% in the control group. This compares toa 24% incidence observed when 180 mg/kg per day of chloroformwas administered for 78 weeks in earlier studies. In contrast,chloroform in the drinking water of mice failed to increasethe incidence of hepatocellular carcinomas in female B6C3F1mice. The highest dose group received a time-weighted averagedose of 263 mg/kg for 104 weeks, resulting in a 5% combinedincidence of hepatocellular adenoma and carcinoma relative toa 6% incidence in the control groups. In a prior National CancerInstitute study an 80% incidence of hepatocellular carcinomaswas observed at 270 mg/kg per day for 78 weeks. These data indicatethat chloroform administered in drinking water is capable ofinducing cancer in the rat kidney. However, the lack of responsein the mouse liver when chloroform is supplied in the drinkingwater suggests that earlier reports of chloroform hepatocarcinogenesismay be related to some interaction with the mode of administration(corn oil gavage).     

Disposition and Pharmacokinetics of Isopropanol in F-344 Rats and B6C3F1 Mice

The absorption, metabolism, disposition, and excretion of isopropanol(IPA) were studied in male and female rats and mice. Animalswere exposed by iv (300 mg/kg) and inhalation (500 and 5000ppm for 6 hr) routes; additionally, IPA was given by gavageto rats only in single and multiple 300 and 3000 mg/ kg doses.In the rat approximately 81–89% of the administered dosewas exhaled (as acetone, CO₂, and unmetabolized IPA); approximately76% of the dose in mice was exhaled after iv bolus but 92% wasexhaled following inhalation. Approximately 3–8% of theadministered dose was excreted in urine as IPA, acetone, anda metabolite tentatively identified as isopropyl glucuronicacid. Small amounts of radiolabel were found in feces and inthe carcass. There were no major differences in the rates orroutes of excretion observed either between sexes or betweenroutes of administration. Additionally, repeated exposure hadno effect on excretion. However, both the route of administrationand the exposure or dose level influenced the form in whichmaterial was exhaled. Following exposure to 5000 ppm, a greaterpercentage of unmetabolized IPA was recovered in the expiredair than following exposure to 500 ppm, implying saturationof metabolism.     

The Chronic Hepatotoxic, Tumor-Promoting, and Carcinogenic Effects of Acetaminophen in Male B6C3F1 Mice

The Chronic Hepatotoxic, Tumor-Promoting, and Carcinogenic Effectsof Acetaminophen in Male B6C3F₁ Mice. HAGIWARA, A., AND WARD,J.M. (1986). Fundam. Appl. Toxicol. 7, 376-386. Acetaminophen(ACT), the most commonly used analgesic and antipyretic in theUnited States, was previously demonstrated to be a hepatocarcinogenin one mouse study but not in rats. In order to help elucidatethe potential mechanisms of carcinogenesis by this nongen-otoxicchemical and its relationship to hepatotoxicity, ACT was fedto groups of 60-120 male B6C3F₁ mice at dietary concentrationsof 5000 or 10,000 ppm from 6 weeks of age for periods of upto 70 weeks to study the hepatotoxic effects of ACT. To testfor potential liver tumor-promoting effects of ACT, N-nitrosodiethylamine(DEN) was injected intraperitoneally at 40 mg/kg into additionalgroups of 30-60 male B6C3F₁ mice at 4 weeks of age. Two weekslater some mice received ACT at dietary concentrations of 5000or 10,000 ppm. Mice were sacrificed either at 24 weeks afterDEN injection or after 22 or 70 weeks of ACT exposure. The liverswere weighed and prepared for qualitative and quantitative histologicalevaluation of focal hepatocel-lular proliferative lesions (FHPL)including microscopic hyperplastic foci and neoplasms by automatedimage analysis. At 24 weeks the incidence and number of FHPLper square centimeter were significantly increased only in DEN-treatedmice receiving 10,000 ppm ACT. Chronic hepatotoxicity was mildat this time. At 72 weeks ACT alone had no effect on the incidenceor number of naturally occurring liver tumors despite severechronic hepatotoxicity and suppression of body weight gain inmice receiving 10,000 ppm and only mild toxicity at 5000 ppm.There were histological findings suggesting that the chronichepatotoxicity had, in part, a vascular pathogenesis. This studyprovided evidence against the hypothesis that chronic hepatotoxicity,in and of itself, results in an increased incidence of naturallyoccurring liver tumors in mice.     

The Toxicity of Dimethylamine in F-344 Rats and B6C3F1 Mice following a 1-Year Inhalation Exposure

The Toxicity of Dimethylamine in F-344 Rats and B6C3F1 Micefollowing a 1-Year Inhalation Exposure (1985). BUCKLEY, L. A.,MORGAN, K. T., SWENBERG, J. A., JAMES, R. A., HAMM, T. E., JR.,and BARROW, C. S. Fundam. Appl. Toxicol. 5, 341–352. Dimethylamineis a widely used commodity chemical, for which there are fewchronic toxicity data. Male and female F-344 rats and B6C3F1mice were exposed by inhalation to 0, 10, 50, or 175 ppm dimethylamine(DMA) for 6 hr/day, 5 days/week for 12 months. Groups of 9–10male and female rats and mice were necropsied after 6 and 12months of exposure. No male mice were sacrificed at 12 monthsdue to a high incidence of early deaths in that group. The meanbody weight gain of rats and mice exposed to 175 ppm DMA wasdepressed to approximately 90% of control after 3 weeks of exposure.The only other treatment-related changes were concentration-relatedlesions in the nasal passages. Two distinct locations in thenose were affected: the respiratory epithelium in the anteriornasal passages, and the olfactory epithelium, especially thatlining the anterior dorsal meatus. There was focal destructionof the anterior nasoturbinate and nasal septum, local inflammation,and focal squamous metaplasia of the respiratory epitheliumin rats and mice. Mild goblet cell hyperplasia was observedonly in rats. The olfactory epithelium exhibited extensive lossof sensory cells with less damage to sustentacular cells. Therewas also loss of olfactory nerves, hypertrophy of Bowman's glands,and distension of the ducts of these glands by serocellulardebris in regions underlying degenerating olfactory epithelium.At the 175-ppm exposure level, rats had more extensive olfactorylesions than mice, with hyperplasia of small basophilic cellsadjacent to the basement membrane being present in rats butnot mice. After 12 months of exposure to 10 ppm DMA, minimalloss of olfactory sensory cells and their axons in olfactorynerve bundles was observed in the nasal passages of a few ratsand mice. These results indicate that the olfactory sensorycell is highly sensitive to the toxic effects of DMA, with minorlesions being produced in rodents even at the current thresholdlimit value of 10 ppm.     

Subchronic Toxicity of Triethylenetetramine Dihydrochloride in B6C3F1 Mice and F344 Rats

Triethylenetetramine dihydrochloride (trien-2HCl; CAS No. 38260-01-04),a chelating agent used to treat Wilson's disease patients whoare intolerant of the drug of choice, was tested for subchronictoxicity in B6C3F1 mice and F344 rats. Mice and rats receivedtrien-2HCl in the drinking water at concentrations of 0, 120,600, or 3000 ppm for up to 92 days. Twenty mice and 18 ratsof each sex were assigned to each dose group fed either a cereal-based(NIH-31) or a purified (AIN-76A) diet, both containing nutritionallyadequate levels of copper. An additional control group of ratsand mice received a Cu-deficient AIN-76A diet. This low copperdiet resulted in Cu-deficiency symptoms, such as anemia, liverperiportal cytomegaly, pancreatic atrophy and multifocal necrosis,spleen hematopoietic cell proliferation, and increased heartweight, together with undetectable levels of plasma copper inrats but not in mice. Trien-2HCl lowered plasma copper levelssomewhat (at 600 and 3000 ppm) in rats fed the AIN-76A diet,but did not induce the usual signs of copper deficiency. Trien-2HClcaused an increased frequency of uterine dilatation at 3000ppm in rats fed AIN-76A diet that was not noted in females fedthe Cu-deficient diet. Trien-2HCl toxicity occurred only inmice in the highest dose group fed an AIN-76A diet. Increasedfrequencies of inflammation of the lung interstitium and liverperiportal fatty infiltration were seen in both sexes, and hematopoieticcell proliferation was seen in the spleen of males. Kidney andbody weights were reduced in males as was the incidence of renalcytoplasmic vacuolization. There were no signs of copper deficiencyin mice exposed to trien-2HCl. The only effect of trien-2HClin animals fed the NIH-31 diet was a reduced liver copper levelin both rat sexes, noted at 3000 ppm.     

Two-Year Inhalation Exposure of Female and Male B6C3F1 Mice and F344 Rats to Chlorine Gas Induces Lesions Confined to the Nose

Chlorine gas is a respiratory irritant in both animals and humansthat produces concentration-dependent responses ranging fromminor irritation to death. Female and male B6C3F1 mice and F344rats were exposed to chlorine gas for up to 2 years to determinechronic toxicity and carcinogenicity. Groups of approximately70 each of female and male mice and rats were exposed to 0,0.4, 1.0, or 2.5 ppm chlorine gas for 6 hr/day, 5 days/week(mice and male rats), or 3 alternate days/week (female rats)for 2 years, with an interim necropsy of rats at 12 months (10rats/sex/concentration group). A complete necropsy was performedon all animals. Histological examination was performed on allorgans from high-concentration and control animals and selectedtarget organs from mid-and low-concentration groups. Exposure-dependentlesions were confined to the nasal passages in all sex and speciesgroups. Chlorine-induced lesions, which were most severe inthe anterior nasal cavity, included respiratory and olfactoryepithelial degeneration, septal fenestration, mucosal inflammation,respiratory epithelial hyperplasia, squamous metaplasia andgoblet cell hypertrophy and hyperplasia, and secretory metaplasiaof the transitional epithelium of the lateral meatus. Intracellularaccumulation of eosinophilic proteinaceous material was alsoa prominent response involving the respiratory, transitional,and olfactory epithelia, and in some cases the squamous epitheliumof the nasal vestibule. Many of these nasal lesions exhibitedan increase in incidence and/or severity that was related tochlorine exposure concentration and were statistically significantlyincreased at all chlorine concentrations studied. Male miceand female rats appeared more sensitive to chlorine than femalemice and male rats, respectively. The reasons for the sex differenceswithin a species were not determined. Interspecies differencesin regional dosimetry and site-specific tissue susceptibilityto chlorine exposure should be taken into account when usingthese data for accurate assessment of potential human healthrisks. The incidence of neoplasia was not increased by exposure,indicating that inhaled chlorine in rats and mice is an upperrespiratory tract toxicant but not a carcinogen.     

Inhalation Toxicity of Phosphine for Fischer 344 Rats and B6C3F1 Mice

Abstract

Because of the potential increased use of phosphine (PH₃) as a fumigant and the lack of adequate toxicity data, short-term inhalation studies were conducted to characterize the toxicity of PH₃ for Fischer 344 (F344) rats and B6C3F1 mice. Male rats and mice were exposed to 0, 1, 5, or 10 ppm PH₃ for up to 4 days, and males and females to 0, 1.25, 2.5, or 5 ppm for 2 wk. In the 4-day study, all rats died by the end of the third exposure to 10 ppm, and all mice were euthanized in moribund condition after the fourth exposure to 10 ppm. Clinical pathology data were obtained only for mice, due to early mortality of rats. There were no significant treatment-related effects in hematological indices in mice exposed to 1 or 5 ppm; at 10 ppm there was a moderate anemia, and leukocyte counts were significantly decreased. There were significant biologically relevant increases in serum activity of alanine aminotransferase (ALT) and sorbitol dehydrogenase (SDH) and in the concentration of urine nitrogen (UN) at 10 ppm. Flectrophoretic evaluation of hemoglobin from mice exposed to 10 ppm did not reveal any differences in banding patterns from controls. Moribund mice euthanized after 4 exposures to 10 ppm had minimal to mild degeneration and necrosis of the renal tubule epithelium, minimal myocardial degeneration, and minimal to mild subcapsular foci of hemorrhage and necrosis in the liver. Bound PH₃ could not be detected in blood, lung, liver, or kidney of mice or lungs of rats exposed to 10 ppm for 3–4 days. There were no treatment-related mortalities in rats or mice exposed for 2 weeks. Lung weights of male rats and mice were significantly decreased and heart weights of female rats and mice were significantly increased after 2 wk of exposure to 5 ppm. Slight but statistically significant increases were observed in serum UN in male mice exposed to 5 ppm. There was no microscopic evidence of treatment-related effects in any of the tissues examined from rats or mice exposed to 5 ppm for 2 wk. Bound PH₃ could not be detected in blood, lung, liver, or kidney of mice or rats exposed to 5 ppm for 2 wk. These studies demonstrated that PH₃ inhalation does not cause a specific target organ toxicity in the B6C3F1 mouse or F344 rat, and that the primary hazard of subchronic inhalation in these species is lethality.     

A 90-Day Chloroform Inhalation Study in Female and Male B6C3F1 Mice: Implications for Cancer Risk Assessment

High doses of chloroform induced liver cancer in male and femaleB6C3F₁ mice when administered by gavage, kidney cancer in maleOsborne-Mendel rats when given by gavage or in the drinkingwater, and kidney cancer in male BDF₁ mice when administeredby inhalation. The weight of evidence indicates that chloroformis acting through a nongenotoxic-cytotoxic mode of action. Thepresent study was designed to investigate the dose-responserelationships for chloroform-induced lesions and regenerativecell proliferation in B6C3F₁ mice as the basis for formulationof a biologically based risk assessment for inhaled chloroform.Different groups of female and male B6C3F₁ mice were exposedto atmospheric concentrations of 0, 0.3, 2, 10, 30, and 90 ppmchloroform 6 hr/day, 7 days/week for exposure periods of 4 daysor 3, 6, or 13 consecutive weeks. Some additional exposure groupswere exposed for 5 days/week for 13 weeks or were exposed for6 weeks and then examined at 13 weeks. Bromodeoxyuridine wasadministered via osmotic pumps implanted 3.5 days prior to necropsy,and the labeling index (LI, percentage of nuclei in S-phase)was evaluated iminunohistochemically from histological sections.Complete necropsy and microscopic evaluation revealed treatment-induceddose- and time-dependent lesions only in the livers and nasalpassages of the female and male mice and in the kidneys of themale mice. Large, sustained increases in the liver LI were seenin the 90-ppm groups at all time points. The female mice weremost sensitive, with a no-observed-adverse-effect level (NOAEL)for induced hepatic cell proliferation of 10 ppm. The hepaticLI in the 5 days/week groups were about half of those seen inthe 7 days/week groups and had returned to the normal baselinein the 6-week recovery groups. Induced renal histologic changesand regenerative cell proliferation were seen in the male miceat 30 and 90 ppm with 7 days/week exposures and also at 10 ppmwith the 5 days/week regimen. Nasal lesions were transient andconfined to mice exposed to 10, 30, or 90 ppm for 4 days. Ina previous cancer bioassay, a gavage dose of 477 mg/kg/day produced a 95% liver tumor incidence in female B6C3F₁ mice. Thisgavage dose is equivalent to a daily 6 hr/day inhalation exposureof approximately 80 ppm, based on the observed induced increasesin the LI as an internal dosimeter. The United States EnviromnentalProtection Agency currently uses the linearized multistage modelapplied to the mouse liver tumor data from the chloroform gavagestudy to estimate a virtually safe dose (VSD) as a one in amillion increased lifetime risk of cancer. The resulting valueis an airborne exposure concentration of 0.000008 ppm. Assumingthat chloroform-induced female mouse liver cancer is secondaryto events associated with necrosis and regenerative cell proliferation,then no increases in liver cancer in female mice would be predictedat the NOAEL of 10 ppm or below based on the results reportedhere. Applying an uncertainty factor of 1000 yields an estimateof a VSD at 0.01 ppm. This estimate relies on inhalation dataand is more consistent with the mode of action of chloroform.     

Oncogenicity Testing of 2-Ethylhexanol in Fischer 344 Rats and B6C3F1 Mice

2-Ethylhexanol (2EH) is a weak nongenotoxic hepatic peroxisomeproliferator in the rat. It is a high-volume chemical intermediatein the preparation of the plasticizers bis-(2-ethylhexyl) adipate(DEHA), bis-(2-ethylhexyl) phthalate (DEHP), and tris-(2-ethylhexyl)phosphate (TEHP), which are weak hepatocellular tumorigens infemale mice. In consequence, the oncogenic potential of 2EHwas evaluated in male (M) and female (F) rats and mice (50 animals/sex/group).Oral gavage doses of 2EH in 0.005% aqueous Cremophor EL (polyoxyl-35castor oil) were given five times a week to rats: 0 (water),0 (vehicle), 50, 150, and 500 mg/kg for 24 months, and to mice:0 (water), 0 (vehicle), 50, 200, and 750 mg/kg for 18 months.Statistical comparisons of data were made between vehicle controlsand treatment groups. There were no differences of biologicalsignificance between data from vehicle and water control groups.In rats, there were no dose-related changes at 50 mg/kg. Therewas reduced body weight gain at 150 mg/kg (M, 16; F, 12%) and500 mg/kg (M, 33; F, 31%) and an increased incidence of lethargyand unkemptness. There were dose-related increases in relativeliver, stomach, brain, kidney, and testis weights at sacrifice.Female rat mortality was markedly increased at 500 mg/kg. Therewas marked aspiration-induced bronchopneumonia in rats at 500mg/kg; hematologic, gross, and microscopic changes, includingtumors, were otherwise comparable among all rat groups. In miceat 50 and 200 mg/kg there were no dose-related changes and essentiallyno time-dependent or time-independent adverse trends in livertumor incidence at the 5% significance level. At 750 mg/kg mousebody weight gain was reduced (M, 26; F, 24%), and mortalityincreased (M and F, 30%) versus vehicle controls. At 750 mg/kgthere was a slight increase in nonneoplastic focal hyperplasiain the forestomach of mice (M 5/50, F 4/50) versus vehicle controls(M 1/50, F 1/50). There were increases in mouse relative liver(F, 21%) and stomach (M, 13%; F, 19%) weights at 750 mg/kg.There was a 12% incidence of hepatic basophilic foci and an18% incidence of hepatocellular carcinomas in male mice at 750mg/kg, not statistically significant compared with either controlby Fisher's exact test. There was a 12% incidence of hepaticbasophilic foci and a 10% incidence of hepatocellular carcinomasin female mice at 750 mg/kg, statistically significant (p <0.05) compared with vehicle but not with water controls by Fisher'sexact test. There were no metastases. Time-dependent and -independentstatistical analyses showed an adverse trend in the incidenceof hepatocellular carcinomas in male and female mice, correlatedwith toxicity (expressed as mortality) at 750 mg/kg. The time-adjustedincidence of hepatocellular carcinomas in male mice (18.8%)was within the historical normal range at the testing facility(0–22%), but that in females (13.1%) lay outside the normalrange (0–2%). Under the conditions of these studies 2EHwas not oncogenic in rats, but there were weak adverse trendsin hepatocellular carcinoma incidence in mice at high dose levelswhich may have been associated with toxicity. The major effectsof chronic dosing were mortality in female rats at 500 mg/kgand in male and female mice at 750 mg/kg, accompanied by reductionsin body weight gain in rats at 150 and 500 mg/kg and in miceat 750 mg/kg. Direct comparison of any tumorogenic effects of2EH given alone to female mice with those due to 2EH formedin vivo from DEHA, DEHP, or TEHP is limited by the high mortalitycaused by 2EH in female mice at equivalent doses of 2EH. While2EH may be a contributing factor in the hepatocellular carcinogenesisin female mice associated with the chronic administration ofDEHA and DEHP, it is unlikely to be the entire proximate carcinogen.     

Monochlorodiisobutylene Vapor: Acute and 9-Day Inhalation Studies in Fischer-344 Rats and B6C3F1 Mice

Monochlorodiisobutylene Vapor Acute and 9-Day Inhalation Studiesin Fischer-344 Rats and B6C3F1 Mice. SNELUNGS, W. M., DODD,D. E., GRICE, H. C, AND PHILLIPS, R. D. (1985) Fundam. Appl.Toxicol. 5, 506–514. Acute and 9-day repeated exposuresto monochlorodiisobutylene (CDIB) were conducted in male andfemale Fischer-344 rats and B6C3F1 mice. The 4-hr LC50 valuesfor these animals ranged between 1400 and 2100 ppm. Animalsin the 9-day study were exposed at a mean concentration of 478,97, or 25 ppm of CDIB for 6 hr per day. Treatment-related effectsdiffered between species in this study. Body weight change wasdecreased in rats. Morphologic changes in the kidneys with accompanyingpolyuria and hematuria/hemoglobinuria were observed in malerats. The only effect observed at 25 ppm was a low incidenceof hematuria/hemoglobinuria in male rats. Mice appeared unaffectedby exposure to CDIB at levels as high as 478 ppm     

Carcinogenicity and Toxicity of Inhaled Nitrobenzene in B6C3F1 Mice and F344 and CD Rats

The potential carcinogenicity and toxicity of inhaled nitrobenzenewere evaluated following chronic (2-year) exposure in mice andrats. Male and female B6C3F1 mice were exposed to 0, 5, 25,or 50 ppm nitrobenzene, while male and female F344 rats andmale CD rats were exposed to 0, 1, 5, or 25 ppm nitrobenzene.All exposures were for 6 hr/day, 5 days/week excluding holidays,for a total of 505 days over 2 years. Survival was not adverselyaffected by nitrobenzene exposure, and only mild exposure-relateddecreases in body weights (<10% of control) were occasionallynoted. Nitrobenaene exposure resulted in increased incidenceof neoplasia in male B6C3F1 mice (pulmonary alveolar/bronchiolarand thyroid follicular cell neoplasms), female B6C3FI mice (mammarygland neoplasms), male F344 rats (hepatocellular and renal neoplasms),female F344 rats (endometrial stromal neoplasms), and male CDrats (hepatocellu lar neoplasms). In addition, there were marginalincreases in the incidence of hepatocellular neoplasia in femaleB6C3F1 mice and thyroid follicular neoplasia in male F344 rats.Groups of nitrobenzene-exposed mice and rats with increasedincidence of renal and thyroid neoplasia also had increasedincidences of hyperplasia in these tissues. Toxicity resultingfrom chronic inhalation of nitrobenzene was manifested by methemoglobinemia,anemia, and adaptive or degenerative changes in the nose, liver,and testis. The results indicate that inhaled nitrobenzene iscarcinogenic and toxic in mice and rats, and that the spectrumof these responses in animals is dependent on species, sex,and genetic background.     

Inhalation Toxicity of 1,6-Hexanediamine Dihydrochloride in F344/N Rats and B6C3F1 Mice

1,6-Hexanediamine (HDA) is a high production volume chemicalwhich is used as an intermediate in the synthesis of paints,resins, inks, and textiles and as a corrosion inhibitor in lubricants.Two- and 13-week studies of the toxicity of the dihydrochloridesalt of HDA (HDDC) were conducted in male and female Fischer344/N rats and B6C3F₁ mice using whole-body inhalation exposure.Both species were evaluated for histopatho-logic and reproductiveeffects, and rats were examined for clinical chemistry and hematologicchanges. In the 2-week inhalation studies, animals were exposedto 10–800 mg HDDC/m³, 6 hr per day. All rats, all femalemice, and two of five male mice in the high-exposure group diedbefore the end of the study. Surviving mice in this group hada dose-dependent depression in body weight gain. Clinical signswere primarily related to upper respiratory tract irritationand included dyspnea and nasal discharge in both species. Treatment-relatedhistopathologic lesions included inflammation and necrosis ofthe laryngeal epithelium of both species and the tracheal epitheliumof mice, as well as focal inflammation and ulceration of therespiratory and olfactory nasal mucosa. In the 13-week inhalationstudies, animals were exposed to HDDC at concentrations of 1.6–160mg/ m³ for 6 hr per day, 5 days per week. In addition to thebase study groups, a supplemental group of rats at each exposurelevel was included to assess the effect of HDDC on reproduction.No treatment-related changes in organ weights or organ-to-body-weightratios occurred in rats, and no treatment-related clinical signsor gross lesions were seen in either species. Chemical-relatedmicroscopic lesions were limited to the upper respiratory tract(larynx and nasal passages) in the two highest exposure groupsand were similar in both species. These lesions included minimalto mild focal erosion, ulceration, inflammation, and hyperplasiaof the laryngeal epithelium, in addition to degeneration ofthe olfactory and respiratory nasal epithelium. HDDC causedno significant changes in sperm morphology or vaginal cytologyand no significant adverse effects on reproduction in rats ormice. Hematologic and clinical chemistry changes in rats wereminor and sporadic and were not accompanied by related histologicfindings. HDDC did not increase the frequency of micronucleatederythrocytes in mice. In summary, the toxicity of HDDC to ratsand mice was a result of the irritant properties of the chemical,was limited primarily to the nasal passages and upper airways,and was consistent with the effects of other irritant chemicalsadministered by inhalation.     

Inhalation Toxicity Studies of Cobalt Sulfate in F344/N Rats and B6C3F1 Mice

Inhalation Toxicity Studies of Cobalt Sulfate in F344/N Ratsand B6C3F1 Mice. BUCHER, J. R., ELWELL, M. R., THOMPSON, M.B., CHOU, B. J., RENNE, R., AND RAGAN, H. A. (1990). Fundam.Appl. Toxicol. 15, 357–372. Groups of 10 F344/N rats andB6C3F1 mice of each sex were exposed to cobalt sulfate heptahydrateaerosols of 0, 0.3, 1.0, 3.0, 10, or 30 mg/m3, 6 hr per day,5 days per week, for 13 weeks. All rats and female mice andall but 2/10 male mice exposed at the top concentration survivedto the end of the studies. Polycythemia was observed in exposedrats but not in mice. Sperm motility was decreased in mice exposedat 3 mg/m3 (the lowest concentration evaluated) and at higherconcentrations, and increased numbers of abnormal sperm anddecreased testis and epididymal weights occurred in mice exposedto 30 mg/m3. Cobalt content in the urine of rats increased withincreasing atmospheric cobalt exposure. Primary histopathologiceffects were limited to the respiratory tract. Lesions in ratsand mice included degeneration of the olfactory epithelium,squamous metaplasia of the respiratory epithelium, and inflammationin the nose; inflammation, necrosis, squamous metaplasia, ulcers(rats), and inflammatory polyps (rats) of the larynx; metaplasiaof the trachea (mice); and fibro-sis, histiocytic infiltrates,bronchiolar epithelial regeneration, and epithelial hyperplasiain the alveoli of the lung. The most sensitive tissue was thelarynx, with squamous metaplasia observed in rats and mice atthe lowest exposure concentration of 0.3 mg/m3. Thus, a no-observed-adverse-effectlevel was not reached in these studies     

Eight-Week Toxicity Study of 60 Hz Magnetic Fields in F344 Rats and B6C3F1 Mice

Toxicity studies were performed by exposing F344/N rats andB6C3F1 mice (10 animals per sex per species per group) to transient-free,linearly polarized 60 Hz magnetic fields for 8 weeks. Targetedmagnetic fields strengths used were 0 gauss (G; sham controlfields did not exceed 0.001 G), 0.02 G, 2 G, and 10 G. Exposurewas whole-body and continuous for 18.5 hr per day, 7 days perweek. An additional group of rats and mice was exposed intermittently(1 hr on/1 hr off) to 10 G fields for the same period of time.Endpoints evaluated included morbidity, mortality, gross pathology,histopathology, body/organ weights, clinical chemistry (ratsonly), and hematology (rats only). All mice and all male ratssurvived until the end of the study. One female rat (2-G exposuregroup) died during Week 7 of the study; the death was not attributedto magnetic field exposure. In both studies, the mean body weightgains of exposed animals were similar to those of the respectivecontrols. There were no gross, histological, hematological,or biochemical lesions attributed to magnetic field exposure.Statistically significant increases in liver weight and liverto body weight ratio occurred in female rats of all exposuregroups but only at the termination. These data suggest that,for the variables evaluated in these studies, an 8-week exposureto linear-polarized, transientfree 60 Hz magnetic fields atfield intensities of up to 10 G is not associated with significanttoxicity in F344/N rats and B6C3F1 mice. Furthermore, therewas no toxicity observed in animals receiving intermittent (1hr on/l hr off) exposures to 10-G fields. A 2-year study inF344/N rats and B6C3F1 mice is nearing completion of the in-lifephase without overt toxicity in any exposed group. It is premature,however, to make any prediction concerning the possible influenceof exposure to 60 Hz magnetic fields on cancer rates.     

Subchronic Feeding Study of the Mycotoxin Fumonisin B1 in B6C3F1 Mice and Fischer 344 Rats

Fumonisin B1 (FB1) is a mycotoxin produced by Fusarium moniliforme,a common fungus which occurs naturally on corn, and other Fusariumspecies. FB1 and other fumonisins are now recognized as havingpotentially important animal and human health implications.However, few toxicological data are currently available. Maleand female B6C3F1 mice and Fischer 344 rats were fed diets containing0, 1, 3, 9, 27, or 81 ppm FB1 (98% purity) for 13 weeks. Nodifferences in behavior or appearance, body weight or food consumptionbetween control and FB1-fed groups were found. In mice, hepatopathyand altered serum chemical profiles indicative of hepatotoxicitywere found in females fed the 81 ppm diet. No adverse effectswere found in female mice fed 27 ppm FB1 or in male mice atany dietary level studied. In rats, nephrosis involving theouter medulla was found in males fed 9 ppm and, to a lesserdegree, in females fed 81 ppm FB1, while decreased kidney weightwas found in both sexes at dietary levels 9 ppm FB1. Althoughthe liver is a target organ of FB1 in rats, hepatotoxicity wasnot found in rats fed diets containing up to 81 ppm FB1 for90 days. Thus, FB1 was toxic to both species following subchronicoral exposure, although significant interspecies differencesin the no observed effect levels and organ-specific responseswere found.     

Toxicity and Carcinogenicity of 2,3-Dibromo-1-propanol in F344/N Rats and B6C3F1 Mice

2,3-Dibromo-1-propanol is a metabolite of the flame retardanttris(2,3-dibromopropyl) phosphate, previously shown to be amutagen and carcinogen in experimental animals. Toxicology andcarcinogenesis studies of 2,3-dibromo-1-propanol were conductedby applying the chemical in 95% ethanol to the interscapularskin of male and female F344/N rats and B6C3F₁ mice 5 days aweek for 13 weeks in the prechronic study and 48–55 weeks(rats) or 36–42 weeks (mice) in the carcinogenicity study.In the 13-week study, 10 rats and 10 mice of each sex receiveddoses of 0, 44, 88, 177, 375, or 750 mg/kg. Deaths associatedwith chemical application occurred only in the high-dose (750mg/kg) male mice. Chemical-related lesions were seen in thekidney of male rats, liver of female rats, and liver and lungof both sexes of mice. Based on the toxicity observed in the13-week study, 50 rats of each sex received doses of 0, 188,or 375 mg/kg and 50 mice of each sex received 0, 88, or 177mg/kg in the carcinogenicity study. The planned 2-year studywas terminated early because of reduced survival of rats relatedto chemical-induced neoplasia and because of the appearanceof antibodies to lymphocytic choriomeningitis virus in sentinelmice. Nearly all dosed rats had malignant neoplasms at one ormore sites, while only one control male and one control femalehad malignant neoplasms. In rats, neoplasms induced by 2,3-dibromo-1-propanoloccurred in the skin, nasal mucosa, Zymbal's gland, oral mucosa,esophagus, forestomach, intestines, liver, kidney, mammary gland(females), clitoral gland (females), spleen (males), and mesothelium(males). In mice, chemical-induced neoplasms occurred in theskin, forestomach, liver (males), and lung (males).     

Chronic Nephropathy and Renal Carcinogenicity of o-Benzyl-p-chlorophenol in F344/N Rats and B6C3F1 Mice

o-Benzyl-p-chlorophenol, an aryl halide biocide, was evaluatedin male and female F344/N rats and B6C3F₁ mice in a series ofsubchronic and 2-year toxicity and carcinogenicity studies.Kidney was the primary target of toxicity in the 13-week gavagestudies in rats and mice, with increased nephropathy noted aslow as 240 mg/kg in male rats. Considering the nephropathy tobe dose-limiting, the chronic (2-year) study was conducted atlower doses (male rats: 30, 60, or 120 mg/kg; female rats: 60,120, or 240 mg/kg; male and female mice: 120, 240, or 480 mg/kg;in corn oil; n=50/group). Survival and body weights of dosedrats were similar to controls in the 2-year study. Survivalof high-dose male and female mice, and body weights of all dosedmale and mid- and high-dose female mice, were lower than controls.The incidence and severity of nephropathy increased with doseand length of treatment in both rats and mice. There was anincreased incidence of renal tubule adenomas or carcinomas inboth the mid- and high-dose male mice. Despite similar evidenceof nephropathy, however, there were no increased incidencesof neoplasms in female mice or in male or female rats. Thisstudy suggests therefore that while nephrotoxicity may havebeen a necessary component, factors other than the marked nephrotoxicityof o-benzyl-p-chloro-phenol were critical to the developmentof renal carcinogenesis induced in only male mice.     

Four-Day Repeated Inhalation and Recovery Study of Methyl lsocyanate in F344 Rats and B6C3F1 Mice

F344 rats and B6C3F1 mice of both sexes were exposed by inhalationto 0, l,and 3 ppm methyl isocyanate (MIC) for 4 consecutivedays (6 hr/day) followed by a recovery period of 91 days. Fivemice and rats/sex/group except the 3 ppm group (5 rats/ sexon Day 7 and 2 males on Day 28) were killed on Days 7, 28, 49,and 91 after the exposure and examined histopathologically.Forty-nine of 56 male rats, 51 of 56 female rats, and 1 of 56male mice in the 3 ppm group died by 28 days; early death animalswere also examined histologically. Exposure-related changesoccurred in rats and mice of both sexes in the 3 ppm group only.Lesions of the nasal cavity in rats and mice were characterizedby regeneration of the olfactory and respiratory epithelia secondaryto epithelial erosion. By Day 28 the olfactory and respiratoryepithelia in mice appeared normal, while in rats incompleteregeneration of the olfactory epithelium was still present.Regeneration of the respiratory epithelium in the trachea ofrats occurred in the 3 ppm group and the epithelium appearedto return to normal by Day 28. Lung lesions in rats consistedof mural and/or intraluminal fibrosis secondary to extensiveerosion of the respiratory epithelium in the major bronchi tothe terminal bronchioles. Acute inflammation of the small airways,occasional hyaline membranes of alveolar walls, and pulmonaryatelectasis were also seen. Alveolar fibrosis was observed inrats found dead from Day 14 on and in male rats killed on Day28. Atrophy of the thymus and spleen, atrial thrombosis of theheart, and hepatocellular necrosis were frequently seen in ratsdying following MIC exposure. The lung lesions in mice werequalitatively similar to those in rats, but were restrictedto the major bronchi. Minimal intraluminal or mural fibrosiswas still present in mice on Day 91. In a separate study, asingle 6-hr exposure of five male rats to 3 ppm MIC was followedby a recovery period of 7 days. The lesions of the respiratorysystem were essentially the same as those in the 3 ppm groupkilled on Day 7 after the 4-day repeated exposure of MIC, butthe alveolar lesions were more severe.