Difference in the Developmental Toxicity of Ethylenethiourea and Three N,N'-Substituted Thiourea Derivatives in Rats

Difference in the Developmental Toxicity of Ethylenethioureaand Thm N,N'-Substituted Thiourea Derivatives in Rats. SAILLENFAIT,A. M., SABATE, J. P., LANGONNE, I., AND DE CUURRIG J. (1991).Fundam. Appl Toxicol 17, 399–408. Sprague-Dawley ratswere administered ethylenethiourea (ETU), 1,3-dimethyl-2-thiourea(DMT), 1,3-dibutyl-2-thiourea (DBT), or 1,3-diphenyl-2-thiourea(DPT) by gavage from Days 6 to 20 of gestation. Daily dosagelevels (mg/kg/day) were ETU at 0, 15, 25 and 35; DMT at 0, 15,25, 50, 100, and 200; DBT at 0, 15,25, 50, 100, and 200; andDPT at 0,25, 50, 100, and 200. There was evidence of maternaltoxlcity at all doses of DMT and at doses 50 mg DBT/kg/day.DPT was embryolethal at 200 mg/kg/day. Fetotoxicity was observedat doses 15 mg DMT/kg/day, 15 mg DBT/kg/day, and 100 mg DPT/kg/day.ETU was the only chemical tested that proved to be teratogenic.     

Prechronic Inhalation Toxicity Studies of Isobutyl Nitrite

Isobutyl nitrite (IBN) is a volatile liquid that has becomeincreasingly popular as an inhaled recreational drug. To investigateshort-term toxic effects and establish exposure parameters forchronic inhalation studies, F344/N rats and B6C3F1 mice wereexposed to IBN vapors on a 6 hr/day + t90, 5 days/week schedule.Twelve exposures were administered at concentrations of 0, 100,200, 400, 600, and 800 ppm IBN. This exposure series resultedmortality in rats exposed to 600 ppm and mice exposed to 800ppm. Animals exposed at the lower concentrations developed hyperplasiaof the bronchiolar and nasal turbinate epithelium (rats andmice) and lymphocytic atrophy in the spleen and thymus (mice).Longer term, 13-week, subchronic exposures were conducted atconcentrations of 0, 10, 25, 75, 150, and 300 ppm IBN. Exposureto 300 ppm IBN reduced the body weight gains in both sexes ofrats and in female mice. IBN-related clinical pathology changesincluded reduced RBC counts accompanied by moderate increasesin mean corpuscular volume and reticulocyte counts, increasedWBC counts, and mildly increased methemoglobin concentration.Bone marrow hyperplasia was observed in all groups of IBN-exposedrats, while in mice only females at l50 ppm IBN displayed thischange. Excessive splenic pulp hematopoiesis was noted in miceat all IBN exposure levels. Respiratory system changes includedincreased lung weights in rats and female mice at 300 ppm, hyperplasiaof the nasal mucosa (male rats at 75 ppm and female rats at150 ppm), and hyperplasia of the lung epithelium (male miceat 150 ppm and female mice at 75 ppm). The results suggestedthat a concentration of 150 ppm could be used as the highestexposure level for subsequent chronic inhalation tests.     

Neuropharmacologic and Neuropathologic Effect of Fenvalerate in Mice and Rats

Neuropharmacologic and Neuropathologic Effect of Fenvaleratein Mice and Rats. PARKER, C.M., ALBERT, J.R., VAN GELDER, G.A.,PATTERSON, D.R., and TAYLOR, J. L. (1985). Fundam. Appl. Toxicol.5, 278–286. B6C3F1 mice and Sprague-Dawley rats displayedthe characteristic signs of pyrethroid intoxication followingsingle oral doses ranging from 56 to 320 and 133 to 1000 mg/kgfenvalerate, respectively. The LD50s for mice and rats were180 and 776 mg/kg, respectively, with corn oil as the vehicle.Signs of neurologic deficit such as splayed gait, tremors, ataxia,and hind limb incoordination were observed at doses of 100mg/kg (mice) and 133 mg/kg (rats) within 1–8 hr afterdosing. These signs had disappeared in most animals within 72hr. Slight peripheral nerve fiber damage was detected in survivingmice and rats sacrificed 10 days after dosing. The incidenceand severity were dose related at doses 56 and 180 mg/kg; however,even at lethal doses, evidence was lacking for the presenceof nerve lesions in several animals. Thus two distinct neurologiceffects were observed: a reversible ataxia/incoordination anda neuropathologic effect manifested as sparse axonal damagein peripheral nerve.     

Kinetic Analysis of the Chronology of Patulin- and Gossypol-Induced Cytotoxicity in Vitro

Kinetic analyses of the mechanisms of patulin- and gossypolinduced cellular toxicity in an immortalized rat hepatocytecell line were examined using a battery of vital fluorescencebioassays. Intracellular glutathione (GSH) content and intracellularCa²⁺ ([Ca²⁺]_i) were monitored simultaneously using fluorescentprobes requiring uv excitation (351–363 nm); reactiveoxygen species (ROS) production, mitochondrial and plasma membranepotential, and intracellular pH were monitored simultaneouslywith visible wavelength probes (488 nm). Changes in gap junction-mediatedintercellular communication (GJIC) were monitored using thegap FRAP technique. Cells were exposed to different concentrationsof patulin (0, 1.0, 10, 100, and 1000 µM) or gossypol(0, 1.0, 3.0, and 10 µM). All parameters were monitoreddirectly after addition of toxin for 20 min. The analyses providedthe following chronology of cellular injury caused by patulin:simultaneous suppression of GJIC and GSH depletion ROS generation mitochondrial membrane depolarization simultaneous increasein [Ca²⁺]_i and cytoplasmic acidification depolarization ofplasma membrane. A distinct chronology of gossypol-induced cellularinjury was also identified: simultaneous suppression of GJICand generation of ROS cytoplasmic acidification simultaneouselevation of [Ca²⁺]_i and partial depletion of GSH mitochondrialmembrane depolarization depolarization of plasma membrane.This report indicates the utility of these vital assays as improvedmechanistically based methods for toxicity testing in vitro.     

Differences in the Mode of Lethality Produced through Intravenous and Oral Administration of Organophosphorus Insecticides in Rats

Differences in the Mode of Lethality Produced through Intravenousand Oral Administration of Organophosphorus Insecticides inRats. TAKAHASHI, H., KOJIMA, T., IKEDA, T., TSUDA, S. and SHIRASU,Y. (1991). Fundam. Appl. Toxicol. 16, 459–468. This studywas undertaken to investigate the possibility that mechanismsother than cholinesterase (ChE) inhibition account for the acutetoxicity of organophosphorus insecticide. Both the PO type insecticide(direct ChE inhibitors: chlorfenvinphos and dichlorvos) andthe PS type insecticide (indirect ChE inhibitors: diazinon andfenthion) were employed. Rats treated with lethal doses of intravenousand oral PO type insecticides and oral PS type insecticidesexhibited typical signs of anti-ChE poisoning along with markedinhibition of brain and erythrocyte ChE activity. In contrast,rats given lethal doses of intravenous PS type insecticidesexhibited tonic convulsions and opisthotonos, with only slightinhibition of ChE activities. When PO type insecticides wereintravenously administered to anesthetized and conscious rats,animals exhibited typical anti-ChE poisoning signs in cardiorespiration:hypertension and apnea which were antagonized by atropine. Afteradministration of lethal doses of PO type insecticides, breathingdisappeared before the cessation of heart beats. Rats receivinglethal doses of intravenous PS type insecticides did not showhypertension, but exhibited transient cessation of breathingand heart beats. Breathing was observed after the disappearanceof heart beats. The electroencephalogram (EEG) was characterizedby spike and wave complexes. The EEG and cardiorespiratory changeswere not antagonized by atropine. It was concluded that lethalityfollowing intravenous PS type insecticides may be independentof ChE inhibition.     

Hepatic and Adrenal Toxicity of a Novel Lipid Regulator in Beagle Dogs

PD 138142-15 is a substituted urea hypolipidemic and potentialanti-atherosclerotic agent. To determine the toxicity of PD138142-15, beagle dogs were given oral doses of 1, 10, 30, and100 mg/kg daily for 13 weeks. Two animals at 100 mg/kg wereeuthanized during Week 5 due to poor condition. Clinical findingsincluded decreased serum albumin at mg/kg, and increased ALP(up to 30-fold) and 5'-nucleotidase activities (up to 9-fold)at doses 10 mg/kg. ALT and AST activities were elevated onlyat 100 mg/kg. There was a two- to threefold increase in cytochromeP450 content of hepatic microsomes from all treated animalsand increases in liver weights at 10 mg/kg and above. Hepaticchanges included hepatocellular hypertrophy and increased cytoplasmiceosinophilia at 10 mg/kg; single cell necrosis of hepatocyteswas noted in moribund animals. ACTH-stimulated cortisol levelswere decreased at 30 and 100 mg/kg. Adrenal cholesterol esterswere decreased at 10 mg/kg and above, while total adrenal cholesterolwas decreased at 30 mg/kg. These changes correlated with adrenalcortical zonal atrophy, principally of the zona fasciculataand zona reticularis, present at 30 and 100 mg/kg. Plasma concentrationsof PD 138142-15 increased with increasing dose; plasma levelswere significantly lower during Week 12 than those on Day 1,possibly due to autoinduction. Overt hepatotoxicity occurredat 100 mg/kg, whereas hepatic changes at 10 and 30 mg/kg wereconsistent with cytochrome P450 induction. The hepatic lesionswere reversible within 4 weeks, while adrenal lesions were stillevident after 4 weeks without treatment.     

Inhibition of Human Plasma and Serum Butyrylcholinesterase (EC 3.1.1.8) by {alpha}-Chaconine and {alpha}-Solanine

The purpose of these experiments was to determine the reversibilityof -chaconine and -solanine inhibition of human plasma butyrylcholinesterase(BuChE). For the substrate -naphthylacetate, optimal assay conditionswere 0.50 M sodium phosphate buffer and a substrate concentrationof 3–5 ' 10^–4 M. Dibucaine (1 ' 10^–5 M) indicatedthe usual phenotype for all subjects; -chaconine and -solanineat 2.88 ' 10^–6 M inhibited BuChE about 70 and 50%, respectively.One-and 24-hr incubations at 1 ' 10^–1 M with -chaconine,-solanine, paraoxon, eserine, and ethanol yielded reversibleinhibition with dilution except for paraoxon. Twenty-four-hourdialyses of incubations showed no inhibition except for paraoxon.PAGE enzyme activity gels of 1-and 24-hr incubations also showedno inhibition except for paraoxon. -Chaconine and -solanineare reversible inhibitors of human butyrylcholinesterase. Atestimated tissue levels, -chaconine, -solanine, and solanidineinhibited BuChE 10–86%. In assays which combined -chaconine,-solanine, and solanidine, inhibition of BuChE was less thanadditive. No inhibition of albumin -naphthylacetate esterase(an arylesterase) was noted with any inhibitor. The importanceof these data to adverse toxicological effects of potato alkaloidsis discussed.     

Development of a Mechanism-Based Dosimetry Model for 2,4,4-Trimethyl-2-pentanol-lnduced {alpha}2u-Globulin Nephropathy in Male Fischer 344 Rats

A mechanism-based dosimetry model was developed to describe2,4,4-trimethyl-2-pentanol (TMP-2-OH) dosimetry and renal 2u-globulin(2u) nephropathy in the male Fischer 344 rat. Experimental datawere collected to estimate the chemical-specific parameters(metabolic constants, tissue solubility, and oral absorptionrate) necessary to describe TMP-2-OH dosimetry in male rats.The concentrations of 2u and TMP-2-OH were measured in malerats up to 64 hr after a single oral dose of TMP-2-OH (6, 60,or 600 mg/kg). The model predicted the time course behaviorof TMP-2-OH and 2u in the kidney, but overestimated their renalconcentrations by two or threefold. Simulations of renal 2uconcentration were sensitive to changes in TMP-2-OH-2u-bindingaffinity and degradation rate of the TMP-2-OH-protein complex.In contrast, simulation of the concentration of TMP-2-OH inthe kidney was most sensitive to the amount of protein present.Oral absorption of TMP-2-OH was dose dependent. The model predictedthat 2u and TMP-2-OH concentration in the kidney is sensitiveto changes in the rate of TMP-2-OH absorbed after oral administration.This model permitted a more rigorous evaluation than has previouslybeen possible of the combination of protein characteristicsand chemical dosimetry required for the accumulation of 2u inthe kidney of male rats. The behavior of the model is consistentwith the qualitative aspects of the 2u hypothesis. However,further characterization of 2u distribution and renal hydrolysiswill be required in order to fully characterize the hypothesisat the quantitative level.     

Organ-Specific Hematopoietic Changes Induced by a Recombinant Human Interferon-{alpha} in Mice

Organ-Specific Hematopoietic Changes Induced by a RecombinantHuman Interferon- in Mice. ROSENTHAL, G. J., STRANAHAN, R. P.,ILL, THOMPSON, M., BLAIR, P., GERMOLEC, D. R., COMMENT, C. E.,SCHWAB, K., AND LUSTER, M. I. (1990). Fundam. Appl. Toxicol.14, 666–675. Interferon-a (IFN-) is a naturally occurringcytokine that mediates numerous biological activities and hasdemonstrated therapeutic potential in a variety of malignancies.Encouraging activity against HIV-1 replication has also beenobserved with IFN- in the treatment of AIDS, although hematotoxicityhas been a frequently observed side effect. In addition, invitro studies have suggested that IFN- may function as a down-regulatorof myelopoiesis. A recombinant hybrid of subtypes of human IFN-,rHuIFN-A/D, has antiviral activity in mu-rine cells in vitroand In vivo. This study examines the effect of acute and subchronicexposure to rHuIFN-A/D on hemopoietic and immune parametersin C57B1/6 mice. IFN-a was administered ip at 0, 1000, 10,000,and 100,000 units/day for either 1 or 10 consecutive days. Manyof the known effects of IFN- in humans such as anemia, leukopenia,and thrombocytopenia were observed in mice following subchronicexposure, with the latter two effects also manifested followingacute exposure. Further analysis showed that this leukopeniawas not selective. Both splenic and bone marrow cells were examinedfollowing 10 days of dosing with the high dose of IFN-. Lymphocyteswere reduced in both compartments, while granulocytes were increasedin both compartments. Bone marrow cells programmed to differentiateinto granulocytes (CFU-G) were suppressed, while macrophageprogenitors (CFU-M) were stimulated. Erythroid cells decreasedin the marrow but increased in the spleen, suggesting that themicroenvironmerit may play a significant role in the effectof IFN-. The proliferative capacity of both B and T spleniclymphocytes was significantly suppressed in a dose-related fashionfollowing multiple exposure to IFN-a. Clinically, IFN-a is mostoften given in multiple doses and the present data suggest thatsuch a regimen is toxic to both erythroid and myeloid cells,as well as being immunotoxic to splenic B and T lymphocytes.     

Application of Molecular Encapsulation for Toxicology Studies: Comparative Toxicity of p-Chloro-{alpha},{alpha},{alpha}-trifluorotoluene in {alpha}-Cyclodextrin Vehicle versus Corn Oil Vehicle in Male and Female Fischer 344 Rats and B6C3F1 Mice

The application of -cyclodextrin (-CD) as an alternative vehiclefor water insoluble and volatile chemicals was investigatedin toxicity studies of p-chloro-,,-trifluorotoluene (CTFT).Groups of F344 rats and B6C3F1 mice of each sex were administeredCTFT (97% pure) by gavage in either corn oil or -CD aqueousformulations daily for 14 consecutive days. The dose levelsused were 10 (mice only), 50, 400, and 1000 mg/kg for corn oilvehicle and 10, 50, and 400 mg/kg (maximum achievable dose atgavage volume of 5 ml/kg) for -CD vehicle. With both vehiclesCTFT and a_2u-globulin were found to accumulate in the male ratkidney after 14 days of exposure and a dose-related toxic nephropathywas observed at dose of 50 mg/kg or higher. The hepatocellularhypertrophy and cytoplasmic vacuolation of the adrenal cortexwhich appeared in dosed male and female rats were also foundto be independent of vehicle. Clinical pathology findings suggesteda mild anemia and cholestasis in rats. With both vehicles notissue bioaccumulation of CTFT was found in male or female mice.Vehicle-independent hepatocellular hypertrophy and cholestasiswere also observed in mice at doses of 400 and 1000 mg/kg. Inconclusion, the -CD vehicle does not affect the toxic responsesof CTFT in both sexes of both species. The results of the studiessuggest that -CD may be an appropriate alternative vehicle fortoxicity studies.     

Possible Involvement of Prostaglandins in Increases in Rat Plasma Adrenocorticotropic Hormone and Corticosterone Levels Induced by Radiation and Interleukin-1{alpha} Alone or Combined

Exposing rats to 1–10 Gy of ionizing radiation increasedplasma adrenocorticotropic hormone (ACTH) and corticoste-rone(CORT) levels. In both irradiated and nonirradiated rats, recombinanthuman interleukin-1 (rhIL-1 1 hr before radiation/sham exposure)enhanced plasma ACTH and CORT levels. Indomethacin, a cyclooxygenaseinhibitor, attenuated plasma ACTH and CORT levels induced byradiation. Indomethacin also attenuated ACTH and CORT levelsinduced by radiation and interleukin-1 alone or combined. Theseresults suggest that prostaglandins are involved in the increasein plasma ACTH and CORT levels induced by radiation and rhIL-1alone or combined.     

Acute and Subchronic Toxicity Studies with Detirelix, a Luteinizing Hormone-Releasing Hormone Antagonist, in the Rat and Monkey

Acute and Subchronic Toxicity Studies with Detirelix, a LuteinizingHormone-Releasing Hormone Antagonist, in the Rat and Monkey.CHESTER, A. E., FAIRCHILD, D. G., AND DEPASS, L. R. (1991).Fundam. Appl. Toxicol. 17, 505–518. Acute (single dose),2-week, and 3-month toxicology studies were conducted with detirelix,a luteinizing hormone-releasing hormone (LHRH) antagonist, inrats and cynomolgus monkeys. Acute studies were conducted byintravenous and subcutaneous injection. Subchronic studies wereconducted by daily subcutaneous injection. Clinical signs aftera single intravenous dose included lethargy, edema, cyanosis,pallor, and red ears in rats at 0.3 mg/kg and lethargy andfacial flushing in monkeys at 0.5 mg/kg, In subchronic studies,detirelix at 0.4 mg/kg/day (rats) and at 0.2 mg/kg/day (monkeys)produced atrophy of the reproductive organs, inhibition of ovulationand spermatogenesis, decreased body weight gain in male ratsand monkeys, and increased body weight gain in female rats.In the rat, morbidity and/or mortality occurred throughout thetreatment phase at a subcutaneous dose of 2.0 mg/kg/day. Inboth species, the time to recovery of normal reproductive organmorphology and function was directly related to dose. Exogenoustestosterone decreased the severity of reproductive and bodyweight effects in male rats. In conclusion, the acute effectsof detirelix were consistent with peripheral vasodilation. Subchroniceffects were associated with inhibition of pituitary gonadotropicand gonadal hormone secretion.     

The Developmental Toxicity of Diethylene Glycol Dimethyl Ether in Mice

The Developmental Toxicity of Diethylene Glycol Dimethyl Etherin Mice. PRICE, C. J., KIMMEL, C. A., GEORGE, J. D., AND MARR,M. C. (1987). Fundam. Appl. Toxicol. 8, 115–126. Diethyleneglycol dimethyl ether (diEGdiME) is structurally related toseveral compounds which produce reproductive and developmentaltoxicity, including teratogenicity in laboratory animals. Inthe present study, diEGdiME (0, 62.5, 125, 250, or 500 mg/kg/day)was administered by gavage in distilled water to timed-pregnantCD-1 mice during major organogenesis [gestational days (gd)6–15]. Clinical status of treated females was monitoreddaily during treatment and on gd 17. At sacrifice (gd 17), pregnancywas confirmed by uterine examination for 20–24 dams pergroup; each live fetus was examined for external, visceral,and skeletal malformations. No maternal deaths, morbidity, ortreatment-related clinical signs were observed. Reduced maternalweight gain during treatment at 250 mg/kg/day was primarilyattributed to compromised pregnancy status resulting in reducedgravid uterine weight. Maternal weight gain during gestationcorrected for gravid uterine weight, and relative liver weight(% body weight) were not affected. Average fetal body weight/litterwas significantly reduced at 125 mg/kg/day. The percentageof postimplantation loss/litter (5, 8, 7, 12, and 50% for controlthrough high dose) and the percentage of malformed live fetuses/litter(0.4, 0, 2, 24, and 96%) were significantly increased at 250mg/kg/day. Developmental defects involved primarily the neuraltube, limbs and digits, craniofacial structures, abdominal wall,cardiovascular system, urogenital organs, and both the axialand appendicular skeleton. In summary, oral administration ofdiEGdiME during major organogenesis did not produce any distinctivesigns of maternal toxicity, but did produce selective and profoundadverse effects upon fetal growth, viability, and morphologicaldevelopment at 125 mg/kg/day.     

Developmental Toxicity of Boric Acid in Mice and Rats

Boric acid (BORA), an ingredient of many cosmetics, pharmaceuticals,and pesticides, was tested for developmental toxicity in timed-pregnantSwiss mice and Sprague-Dawley rats (n = 26–28/group).BORA (0, 0.1, 0.2, or 0.4% in feed) was provided throughoutgestation to attain steady-state exposure as early as possibleduring prenatal development. Average doses (mg/kg/day) were248, 452, or 1003 in mice, and 78, 163, or 330 in rats. To limitprenatal mortality, BORA (0.8% or 539 mg/kg/day) was providedto an additional group of rats on Gestational Days (GD) 6 to15 only. On GD 17 (mice) or 20 (rats), fetuses were weighedand examined for malformations (external, visceral, skeletal).Mouse dams exhibited mild renal lesions (0.1%), increased waterintake and relative kidney weight (0.4%), and decreased weightgain (0.4%) during treatment. There was a reduction of fetalbody weight (0.2%) and an increased incidence of resorptionsand malformed fetuses per litter (0.4%). Morphological changesincluded an increased incidence of short rib XIII (a malformation)and a decreased incidence of rudimentary or full rib(s) at lumbarI (an anatomical variation). Maternal rats exhibited increasedliver and kidney weights at 0.2%, altered water and/or foodintake at >0.2%, and decreased weight gain at >0.4%. Averagefetal body weight/litter was reduced at all doses. Prenatalmortality was increased only at 0.8%. The incidence of fetalmalformations was significantly increased at 0.2%. The mostfrequently observed malformations were enlarged lateral ventriclesof the brain and agenesis or shortening of rib XIII. In rats,the no-observable-adverse-effect level (NOAEL) for maternaltoxicity was 78 mg/kg (0.1%), while in mice the low dose of248 mg/kg (0.1%) approached the maternal NOAEL with mild renallesions in only 2 of 10 females. Embryo/fetal toxicity occurredin all groups of rats at 78 mg/kg (0.1%) while the NOAEL fordevelopmental toxicity in mice was 248mg/kg (0.1%). Thus developmentaltoxicity occurred below maternally toxic levels in rats as wellas in the presence of maternal toxicity in mice and rats.     

NCI-Black-Reiter (NBR) Male Rats Fail to Develop Renal Disease following Exposure to Agents That Induce {alpha}-2u-Globulin ({alpha}2u) Nephropathy

NCI-Black-Reiler (NBR) Male Rats Fail to Develop Renal Diseasefollowing Exposure to Agents That Induce _2u-Globulin (_2u) Nephropathy.Dietrich, D. R., and Swenberg, J. A. (1991). Fundam. Appl. Toxicol16, 749–762. The NCI-Black-Reiter (NBR) rat is the onlystrain of male rat known not to synthesize the hepatic formof the low molecular weight protein, _2u-globulin. In previousstudies, NBR rats were shown not to develop renal disease whenexposed to decalin, a compound known to induce _2u-globulin nephropathyin other rat strains. The objective of this study was to showthat the presence of _2u-globulin (_2u-) is essential for thedevelopment of this syndrome in rats exposed to 2,2,4-trimethylpentane(TMP), 1,4-dichlorobenzene (DCB), isopho-rone (IP), PS-6 unleadedgasoline (UG), and d-limonene (d-L). The induction of _2u-nephropathyin F344 male rats with lindane was used as a positive controland this response was contrasted to male NBR and female F344rats treated with lindane. Five to seven 11-week-old male NBRrats were exposed to TMP (500 mg/kg/day), DCB (500 mg/kg/day),IP (1000 mg/kg/day), UG (500 mg/kg/day), d-L (1650 mg/kg/day),or lindane (10 mg/kg/day) and five 11-week-old male and femaleF344 rats were exposed to lindane (10 mg/kg/day) by oral gavageon 4 consecutive days. NBR male and F344 male and female ratsgavaged with corn oil were incorporated in the study as vehiclecontrols. The presence of hyaline droplets was assessed in perfusion-fixedkidneys by staining paraffin sections with Mallory-Heidenheinstain and in GMA sections with Lee's methylene basic blue fuchsinstain. Paraffin sections were also analyzed immunohistochemicallyfor the presence of _2u-. Under exposure conditions that clearlyinduce _2u-nephropathy in male F344 rats, no lesions, hyalinedroplets, or _2u- were detectable in treated or control maleNBR and female F344 rats. It is thus concluded that the presenceof _2u is causal to the development of renal disease in ratsexposed to TMP, DCB, IP, UG, d-L, and lindane.     

Prechronic Inhalation Toxicity Studies of 2-Mercaptobenzimidazole (2-MBI)in F344/N Rats

2-Mercaptobenzimidazole (2-MBI), used in rubber processing,is a suspect carcinogen structurally related to ethylene thiourea.The inhalation toxicity of 2-MBI was evaluated in male and femaleF344/N rats exposed 6 hr/day, 5 days/week to respirable aerosolsgenerated by spray atomization of aqueous suspensions of the2-MBI powder and subsequent drying of the resulting aerosols.Twelve exposures at target concentrations of 0, 6.3, 12.5, 25.0,50.0, or 100 mg/m³ of 2-MBI produced a dose-related reductionin body weight gains, thyroid follicular cell hyperplasia, adrenalcortex fatty change, and pituitary atrophy. Sub-chronic exposureswere conducted at target concentrations of 0, 3.1, 6.2, 12.5,25.0, and 50.0 mg/m³ of 2-MBI. Rats at 25 mg/m³ displayed hunchedposture, hypoactivity, and reduced body weight gain, with compoundrelated mortality at the highest exposure level. Anemia; increasedSGPT, SGOT, alkaline phosphatase, sorbitol dehydrogenase, BUN,and cholesterol; and reduced free fatty acid were seen in ratsat 25 mg/m³. Increased thyroid weight and thyroid follicularcell hyperplasia were noted in both sexes at 6.2 mg/m³, withreduced triiodothyronine and thyroxine levels in both sexesat > 12.5 mg/m³. Thyroid follicular cell hyperplasia wasalso seen in rats at 3.1 mg/m³. Thymus weights were significantlyreduced in both sexes at all exposure levels with liver weightincreases at 6.2 mg/m³. Exposure-related histopathologic changesincluded pituitary cytoplasmic vacuolization, adrenal cortexnecrosis, lymphoid depletion, thymic atrophy, liver cell hypertrophy,renal mineralization and tubular atrophy, and hypocellularityof the bone marrow.     

Nephrotoxicity of Pravadoline Maleate (WIN 48098-6) in Dogs: Evidence of Maleic Acid-Induced Acute Tubular Necrosis

Single oral administration of pravadoline maleate (WIN 48098-6),the maleic acid salt of WIN 48098, induced acute tubular necrosis(ATN) in male and female beagle dogs at dosages 40 mg/kg (WIN48098 base (31 mg/kg) and maleic acid (9 mg/kg)). Subsequentoral studies were conducted with equimolar dosages of maleicacid and WIN 48098-7, the ethanesulfonate salt of WIN 48098,to determine the nephrotoxic moiety of WIN 48098-6. ATN wasobserved for dogs given only maleic acid at single oral dosages9 mg/kg. This result provided evidence that maleic acid wasresponsible for the nephrotoxicity observed in dogs given singleoral dosages of WIN 48098-6. The induction of maleic acid-relatednephrotoxicity in dogs may confound the interpretation of toxicologicstudies of maleic acid salts of basic pharmaceutics, if thedosage of test article results in the delivery of dosages ofmaleic acid 9 mg/kg. Furthermore, the results of these studiesunderscore the importance of establishing maximum no-observed-effectdosages and target organ toxicity profiles for acids and basesthat are commonly used in the development of salts of pharmaceutics.