Cylindrospermopsin toxicity in mice following a 90-d oral exposure

Cylindrospermopsin (CYN) is a toxin associated with numerous species of freshwater cyanobacteria throughout the world. It is postulated to have caused an episode of serious illnesses in Australia through treated drinking water, as well as lethal effects in livestock exposed to water from farm ponds. Toxicity included effects indicative of both hepatic and renal dysfunction. In humans, symptoms progressed from initial hepatomegaly, vomiting, and malaise to acidosis and hypokalemia, bloody diarrhea, and hyperemia in mucous membranes. Laboratory animal studies predominantly involved the intraperitoneal (i.p.) route of administration and confirmed this pattern of toxicity with changes in liver enzyme activities and histopathology consistent with hepatic injury and adverse renal effects. The aim of this study was designed to assess subchronic oral exposure (90 d) of purified CYN from 75 to 300 µg/kg/d in mouse. At the end of the dosing period, examinations of animals noted (1) elevated organ to body weight ratios of liver and kidney at all dose levels, (2) treatment-related increases in serum alanine aminotransferase (ALT) activity, (3) decreased blood urea nitrogen (BUN) and cholesterol concentrations in males, and (4) elevated monocyte counts in both genders. Histopathological alterations included hepatocellular hypertrophy and cord disruption in the liver, as well as renal cellular hypertrophy, tubule dilation, and cortical tubule lesions that were more prominent in males. A series of genes were differentially expressed including Bax (apoptosis), Rpl6 (tissue regeneration), Fabp4 (fatty acid metabolism), and Proc (blood coagulation). Males were more sensitive to many renal end points suggestive of toxicity. At the end of exposure, toxicity was noted at all dose levels, and the 75 µg/kg group exhibited significant effects in liver and kidney/body weight ratios, reduced BUN, increased serum monocytes, and multiple signs of histopathology indicating that a no-observed-adverse-effect level could not be determined for any dose level.

Dermal Exposure to Cumene Hydroperoxide: Assessing Its Toxic Relevance and Oxidant Potential

Cumene hydroperoxide (CHP) is a high production volume chemical that is used to generate phenol and acetone. Dermal exposure to CHP was hypothesized to result in systemic tissue toxicity, production of free radicals, and consequent decrease in plasma antioxidant levels. To evaluate the hypothesis and characterize the toxicity of CHP, male and female B6C3F1/N mice and F344/N rats were exposed to varying doses of CHP applied topically for 14 or 90 days. No significant changes in survival or body weight of mice and rats were observed following 14 days of exposure. However, 90 days of CHP exposure at the high dose (12 mg/kg) triggered a significant decrease (-15%) in the body weight of the male rat group only. Irritation of the skin was observed at the site of application and was characterized by inflammation and epidermal hyperplasia. In treated animals, histology of liver tissue, free radical generation, and antioxidant levels in blood plasma were not significantly changed as compared to the corresponding controls. Consistent with the lack of systemic damage, no increase in micronucleated erythrocytes was seen in peripheral blood. In conclusion, topical CHP application caused skin damage only at the application site and did not cause systemic tissue impairment.

The course of toxicity in the pregnant mouse after exposure to the cyanobacterial toxin cylindrospermopsin: clinical effects, serum chemistries, hematology, and histopathology

Cylindrospermopsin (CYN) is a toxin produced by a variety of fresh-water cyanobacterial species worldwide and induces significant adverse effects in both livestock and humans. This study investigated the course of CYN-induced toxicity in pregnant mice exposed daily during either the period of major organogenesis (gestation days [GD] 8-12) or fetal growth (GD13-17). Endpoints include clinical signs of toxicity, serum analyses to evaluate hepatic and renal function, histopathology of liver and kidney, and hematology. Study animals were administered 50 μg/kg CYN once daily by ip route and euthanized 24 h after 1, 2, 3, 4, or 5 consecutive doses, or 6 or 13 d after the dosing period. The course of the CYN-induced effects was determined at all euthanasia times for the endpoints just outlined. Results indicated that CYN is a toxin, producing lethality in dams during the early part of gestation, significant weight loss, and bleeding in the gastrointestinal tract, tail tip, and peri-orbital tissues. Effects also included alterations in serum markers for liver function, histopathological changes in liver and kidney tissues, electrolyte abnormalities, leukocytosis, and posttreatment thrombocytopenia and reticulocytosis. The onset of symptoms was rapid, producing reductions in weight gain in GD8-12 animals, bleeding in the vaginal area in GD13-17 animals, and significant increases in sorbitol dehydrogenase (SDH) in both groups after a single dose. Although the GD8-12 dams displayed a 50% lethality, in GD13-17 animals only a single death occurred. Alterations seen in hepatic and renal function or histopathology do not appear to be of sufficient severity to produce death. Evidence indicates that bleeding may play a critical role in the onset of symptoms and eventually, in the observed lethality.

Evaluation of propargyl alcohol toxicity and carcinogenicity in F344/N rats and B6C3F1/N mice following whole-body inhalation exposure

Propargyl alcohol (PA) is a high production volume chemical used in synthesis of many industrial chemicals and agricultural products. Despite the potential for prolonged or accidental exposure to PA in industrial settings, the toxicity potential of PA was not well characterized. To address the knowledge gaps relevant to the toxicity profile of PA, the National Toxicology Program (NTP) conducted 2-week, 14-week and 2-year studies in male and female F344/N rats and B6C3F1/N mice. For the 2-week inhalation study, the rats and mice were exposed to 0, 31.3, 62.5, 125, 250 or 500ppm. Significant mortality was observed in both rats and mice exposed to ≥125ppm of PA. The major target organ of toxicity in both mice and rats was the liver with exposure-related histopathological changes (250 and 500ppm). Based on the decreased survival in the 2-week study, the rats and mice were exposed to 0, 4, 8, 16, 32 or 64ppm of PA in the 14-week study. No treatment-related mortality was observed. Mean body weights of male (≥8ppm) and female mice (32 and 64ppm) were significantly decreased (7-16%). Histopathological changes were noted in the nasal cavity, and included suppurative inflammation, squamous metaplasia, hyaline droplet accumulation, olfactory epithelium atrophy, and necrosis. In the 2-year inhalation studies, the rats were exposed to 0, 16, 32 and 64ppm of PA and the mice were exposed to 0, 8, 16 and 32ppm of PA. Survival of male rats was significantly reduced (32 and 64ppm). Mean body weights of 64ppm male rats were significantly decreased relative to the controls. Both mice and rats showed a spectrum of non-neoplastic changes in the nose. Increased neoplastic incidences of nasal respiratory/transitional epithelial adenoma were observed in both rats and mice. The incidence of mononuclear cell leukemia was significantly increased in male rats and was considered to be treatment-related. In conclusion, the key findings from this study indicated that the nose was the primary target organ of toxicity for PA. Long term inhalation exposure to PA led to nonneoplastic changes in the nose, and increased incidences of respiratory/transitional epithelial adenomas in both mice and rats. Increased incidences of harderian gland adenoma may also have been related to exposure to PA in male mice.

N,N-dimethyl-p-toluidine, a component in dental materials, causes hematologic toxic and carcinogenic responses in rodent model systems

Because of the potential for exposure to N,N-dimethyl-p-toluidine (DMPT) in medical devices and the lack of toxicity and carcinogenicity information available in the literature, the National Toxicology Program conducted toxicity and carcinogenicity studies of DMPT in male and female F344/N rats and B6C3F1/N mice. In these studies, a treatment-related macrocytic regenerative anemia characterized by increased levels of methemoglobin and Heinz body formation developed within a few weeks of DMPT exposure in rats and mice. DMPT induced nasal cavity, splenic, and liver toxicity in rats and mice at 3 months and 2 years. DMPT carcinogenic effects were seen in the liver of male and female rats and mice, the nasal cavity of male and female rats, and the lung and forestomach of female mice. In rodents, DMPT is distributed to many of the sites where toxic and carcinogenic effects occurred. DMPT-induced oxidative damage at these target sites may be one mechanism for the treatment-related lesions. Methemoglobinemia, as seen in these DMPT studies, is caused by oxidation of the heme moiety, and this end point served as an early alert for other target organ toxicities and carcinogenic responses that followed with longer term exposure.

Polg2 is essential for mammalian embryogenesis and is required for mtDNA maintenance

Mammalian mitochondrial DNA (mtDNA) is replicated by the heterotrimeric Pol γ comprised of a single catalytic subunit, encoded by Polg, and a homodimeric accessory subunit encoded by the Polg2 gene. While the catalytic subunit has been shown to be essential for embryo development, genetic data regarding the accessory subunit are lacking in mammalian systems. Here, we describe the generation of heterozygous (Polg2(+/-)) and homozygous (Polg2(-/-)) knockout (KO) mice. Polg2(+/-) mice are haplosufficient and develop normally with no discernable difference in mitochondrial function through 2 years of age. In contrast, the Polg2(-/-) is embryonic lethal at day 8.0-8.5 p.c. with concomitant loss of mtDNA and mtDNA gene products. Electron microscopy shows severe ultra-structural defects and loss of organized cristae in mitochondria of the Polg2(-/-) embryos as well as an increase in lipid accumulation compared with both wild-type (WT) and Polg2(+/-) embryos. Our data indicate that Polg2 function is critical to mammalian embryogenesis and mtDNA replication, and that a single copy of Polg2 is sufficient to sustain life.

Artifactual changes in Sprague-Dawley rat hematologic parameters after storage of samples at 3 °C and 21 °C

Circumstances can occur that prevent timely analysis of blood samples. The purpose of this study was to characterize artifactual changes in rat hematologic parameters after storage of samples at 3 and 21 °C and to document the effects of storage on peripheral blood smear findings. EDTA-treated blood samples were collected from 12 male Sprague-Dawley rats. Samples were analyzed on an impedance hematology analyzer within 5 min after collection and then at 6, 24, 48, and 72 h after storage at 3 °C or 21 °C. Corresponding blood smears were examined microscopically. RBC count and hemoglobin concentration had not changed after 72 h at either temperature. At 3 °C, the instrument-derived hematocrit and manually measured PCV remained unchanged for 72 h. Compared with 0-h values, platelet counts and MCV at 6 h and MPV at 24 h were higher at either temperature. In general, WBC count and neutrophil and lymphocyte percentages were unchanged for at least 48 h at either temperature. Prominent blood smear findings were smudge cells, pyknotic leukocytes, echinocytes, and spheroechinocytes. Although some observed changes were within analytic variability or clinically negligible, the best practice likely is to measure hematologic parameters within 6 h after collection. In the event of delayed analysis, specimens should be stored in the refrigerator, and care must be taken not to misinterpret artifactual changes as pathologic findings.

Proceedings of the 2011 National Toxicology Program Satellite Symposium

The 2011 annual National Toxicology Program (NTP) Satellite Symposium, entitled "Pathology Potpourri," was held in Denver, Colorado in advance of the Society of Toxicologic Pathology's 30th Annual Meeting. The goal of the NTP Symposium is to present current diagnostic pathology or nomenclature issues to the toxicologic pathology community. This article presents summaries of the speakers' presentations, including diagnostic or nomenclature issues that were presented, along with select images that were used for audience voting or discussion. Some lesions and topics covered during the symposium include: proliferative lesions from various fish species including ameloblastoma, gas gland hyperplasia, nodular regenerative hepatocellular hyperplasia, and malignant granulosa cell tumor; spontaneous cystic hyperplasia in the stomach of CD1 mice and histiocytic aggregates in the duodenal villous tips of treated mice; an olfactory neuroblastoma in a cynomolgus monkey; various rodent skin lesions, including follicular parakeratotic hyperkeratosis, adnexal degeneration, and epithelial intracytoplasmic accumulations; oligodendroglioma and microgliomas in rats; a diagnostically challenging microcytic, hypochromic, responsive anemia in rats; a review of microcytes and microcytosis; nasal lesions associated with green tea extract and Ginkgo biloba in rats; corneal dystrophy in Dutch belted rabbits; valvulopathy in rats; and lymphoproliferative disease in a cynomolgus monkey.

Chronic progressive nephropathy in male F344 rats in 90-day toxicity studies: its occurrence and association with renal tubule tumors in subsequent 2-year bioassays

The occurrence and severity of spontaneous chronic progressive nephropathy (CPN) in control male F344 rats as well as the frequency of treatment-related CPN exacerbation were histopathologically reevaluated. A series of 43 National Toxicology Program (NTP) 90-day toxicity studies comparing the influence of NIH-07 or NTP-2000 diets was examined. Relationships between the histopathologic findings at 90 days and renal tubule proliferative lesions recorded in subsequent 2-year bioassays for 24 chemicals were statistically analyzed. CPN lesions were observed in 100% of the control male rats regardless of diet, but CPN was more severe in control rats fed NIH-07. Approximately one-third of the 90-day studies demonstrated a treatment-related exacerbation of CPN severity, which was independent of diet. For chemicals that proceeded to 2-year bioassays, all studies with a statistically significant increase in renal tubule tumors (RTT) at 2 years had treatment-related exacerbation of CPN in the 90-day and 2-year studies. These findings indicate that CPN occurs ubiquitously in young male F344 rats and that treatment-related exacerbation of CPN in 90-day studies is a relatively common occurrence, having the potential to be predictive of an increased incidence of RTT in subsequent 2-year bioassays.

Effects of buprenorphine, meloxicam, and flunixin meglumine as postoperative analgesia in mice

C57BL/6NCrl male mice (n = 60; age, 6 to 7 wk) underwent partial hepatectomy or no surgery and were given 1 of 3 analgesics pre- and postoperatively. Food and water consumption, body weight, running wheel activity, locomotor activity, and serum corticosterone concentrations were measured before and after surgery. Mice that were surgically manipulated weighed significantly less on days 1 through 3 after surgery than did mice not manipulated surgically. On the day of surgery, the surgery groups consumed significantly less feed (-1.5±0.35 g) than did nonsurgery groups. There were no differences in water consumption on any day between surgery and nonsurgery groups or among the 3 analgesic groups. For running wheel activity, significant decreases in the surgery groups were seen at day 1 after surgery compared with baseline. Surgery groups that received buprenorphine and meloxicam returned to baseline activity levels on day 2 after surgery. Open-field testing revealed no significant differences in locomotor activity in any groups; however, posttreatment locomotor activity in the buprenorphine nonsurgery group was increased compared with baseline, and posttreatment locomotor activity in the flunixin meglumine surgery group was decreased compared with baseline. Serum corticosterone concentrations were within normal limits regardless of treatment in all groups. Comparison of the overall results indicated that meloxicam and buprenorphine, at the dose given, appear to be suitable postoperative analgesics for partial hepatectomy in mice. Flunixin meglumine at the given dosage (2.5 mg/kg) may not provide adequate analgesia for partial hepatectomy.

Variation in the hepatic gene expression in individual male Fischer rats

A new tool beginning to have wider application in toxicology studies is transcript profiling using microarrays. Microarrays provide an opportunity to directly compare transcript populations in the tissues of chemical-exposed and unexposed animals. While several studies have addressed variation between microarray platforms and between different laboratories, much less effort has been directed toward individual animal differences especially among control animals where RNA samples are usually pooled. Estimation of the variation in gene expression in tissues from untreated animals is essential for the recognition and interpretation of subtle changes associated with chemical exposure. In this study hepatic gene expression as well as standard toxicological parameters were evaluated in 24 rats receiving vehicle only in 2 independent experiments. Unsupervised clustering demonstrated some individual variation but supervised clustering suggested that differentially expressed genes were generally random. The level of hepatic gene expression under carefully controlled study conditions is less than 1.5-fold for most genes. The impact of individual animal variability on microarray data can be minimized through experimental design.

Absence of toxic effects in F344/N rats and B6C3F1 mice following subchronic administration of chromium picolinate monohydrate

Chromium picolinate monohydrate (CPM) is a synthetic compound heavily marketed to consumers in the United States for use as a dietary supplement for muscle building and weight loss. The National Toxicology Program (NTP) tested the toxicity of this compound based on the potential for widespread consumer exposure and lack of information about its toxicity. Groups of 10 male and 10 female F344/N rats and B6C3F(1) mice were exposed to 0, 80, 240, 2000, 10,000, or 50,000 ppm CPM in feed for 13 weeks. CPM administration produced no effect on body weight gain or survival of rats or mice. Organ weights and organ/body weight ratios in exposed animals were generally unaffected by CPM. No compound-related changes in hematology and clinical chemistry parameters were observed. There were no histopathological lesions attributed to CPM in rats or mice.

Toxicology and carcinogenesis studies of microencapsulated citral in rats and mice

Citral, a widely used natural ingredient, is added to foods and cosmetics as a flavoring and fragrance agent. Male and female F344/N rats and B6C3F1 mice were exposed to microencapsulated citral in the feed for 14 weeks or two years. All studies included untreated and vehicle control groups. In the 14-week studies, rats and mice were given diets containing 3,900, 7,800, 15,600, or 31,300 ppm citral. In rats, food consumption was reduced in the two highest dose groups. In mice an apparent increase in food consumption was observed, but was due to mice scattering the feed. Body weights of all treated animals were less than controls. All rats and four male mice were killed moribund in the high dose groups. In rats, forestomach and kidney lesions were observed. At the higher doses, lesions observed in the bone marrow, testes, and thymus in rats and in the ovary in mice were considered related to inanition and resultant moribundity. In the two-year studies, rats were exposed to 1,000, 2,000, or 4,000 ppm citral. Body weights were reduced in the 4,000 ppm rats. Mice were exposed to 500, 1,000, or 2,000 ppm citral. Body weights in the 1,000 and 2,000 ppm groups were reduced. No neoplasms were attributed to citral in rats or mice. Malignant lymphoma occurred with a positive trend and was significantly greater than controls in female mice in the 2,000 ppm group. However, the incidences were within the NTP historical control range and could not be clearly related to citral administration.

14-Week toxicity and cell proliferation of methyleugenol administered by gavage to F344 rats and B6C3F1 mice

Methyleugenol, a food flavor and fragrance agent, was tested for toxicity in male and female F344/N rats and B6C3F1 mice. Groups of 10 males and 10 females per sex per species were administered 0, 10, 30, 100, 300 or 1000 mg methyleugenol/kg body weight in 0.5% aqueous methylcellulose by gavage, 5 days per week for 14 weeks. Additional groups of rats and mice of each sex were dosed similarly and used for hematology and clinical chemistry studies. Groups of 10 male and 10 female rats and mice received the vehicle by gavage on the same dosing schedule and served as vehicle controls. For serum gastrin, gastric pH and cell proliferation studies groups of 10 female rats were given 0, 37, 75 or 150 mg/kg, once daily 5 days per week for 30 or 90 days or 300 or 1000 mg/kg for 30 days; male mice were given 0, 9, 18.5, 37, 75, 150 or 300 mg/kg for 30 or 90 days. For the gastrin, pH and cell proliferation studies, groups of 10 female rats and 10 male mice were given the vehicle for 30 or 90 days and served as controls. Methyleugenol administration to rats induced erythrocyte microcytosis and thrombocytosis in male and female rats. It also caused an increase in serum alanine aminotransferase and sorbitol dehydrogenase activities and bile acid concentration, suggesting hepatocellular injury, cholestasis or altered hepatic function. Additionally, methyleugenol induced hypoproteinemia and hypoalbuminemia, evidenced by decreased total protein and albumin concentrations in both male and female rats, suggesting in inefficiency of dietary protein utilization due to methyleugenol-induced toxic effects on the liver and glandular stomach of rats and mice. The increase in gastrin and gastric pH of rats and mice given methyleugenol suggests that gastrin feedback was impaired and resulted in conditions not conducive to protein digestion. In rats, methyleugenol caused an increase in the incidences of hepatocyte cytologic alteration, cytomegaly, Kupffer cell pigmentation, mixed foci of cellular alteration and bile duct hyperplasia of the liver and atrophy and chronic inflammation of the mucosa of the glandular stomach. In mice, it caused an increase in the incidence of cytologic alteration, necrosis, bile duct hyperplasia and subacute inflammation of the liver and atrophy, degeneration, necrosis, edema, mitotic alteration, and cystic glands of the fundic region of the glandular stomach. The increased incidences of adrenal gland cortical hypertrophy and/or cytoplasmic alteration in the submandibular salivary glands, adrenal glands, testis and uterus of rats were considered secondary to the chemical-related effects observed in the liver and glandular stomach. Based on mortality, body weight gain, clinical chemistry and gross and microscopic evaluation of tissues of rats and mice, the no-observed-effect level (NOEL) of methyleugenol for both species was estimated at 10 mg/kg.

Toxicology and carcinogenesis studies of p,p'-dichlorodiphenyl sulfone in rats and mice

p,p'-Dichlorodiphenyl sulfone (DDS) is used as a starting material in the production of polysulfones and polyethersufones, a family of thermoplastics. DDS was studied because of its high production volume and use. In toxicology studies, 10 Fischer 344 rats and 10 B6C3F1 mice/sex/group were fed diets containing 0, 30, 100, 300, 1,000 or 3,000 ppm DDS for 14 weeks. All animals survived until the end of the studies. Mean body weights of groups exposed to 300 ppm or greater were significantly decreased. Liver and kidney in rats and liver in mice were the major target organs of DDS toxicity. Dose-related increases in liver weights and incidences of centrilobular hepatocyte hypertrophy were observed in DDS-exposed groups. Nephropathy was seen in male and female rats only at and above 300 ppm. Neurotoxicity evaluations were negative in DDS-treated animals. Clinical chemistry and hematology parameters were minimally affected. In the 2-year toxicity and carcinogenicity studies, 50 rats and 50 mice/sex/group were fed diets containing 0, 10 (male rats), 30, 100, or 300 ppm DDS for 104 to 105 weeks. Survival of exposed groups was not affected. There were no clinical signs of toxicity related to DDS exposure. Final mean body weights were 2-17% lower in DDS-treated groups. Liver was the only target organ of DDS-induced toxicity. The incidence of centrilobular hepatocyte hypertrophy in mice and rats, and the incidence of bile duct hyperplasia and centrilobular degeneration in female rats was significantly greater than in controls. A no-observed-adverse-effect level (NOAEL) of 30 ppm DDS in the diet (1.5 mg/kg body weight) was established for rats. DDS was not carcinogenic in these studies.

Subchronic sodium chlorate exposure in drinking water results in a concentration-dependent increase in rat thyroid follicular cell hyperplasia

Chlorine dioxide (ClO2) is an effective drinking water disinfectant, but sodium chlorate (NaClO3) has been identified as a potentially harmful disinfection by-product. Studies were performed to describe the development of thyroid lesions in animals exposed to NaClO3 in the drinking water. Male and female F344 rats and B6C3F1 mice were exposed to 0, 0.125, 0.25, 0.5, 1.0, or 2.0 g/L NaClO3 for 21 days. Additional male F344 rats were exposed to 0, 0.001. 0.01. 0.1, 1.0. or 2.0 g/L NaClO3 for 90 days. Female F344 rats were exposed to 0, 0.5, 1.0, 2.0, 4.0, or 6.0 g/L of NaClO3 for 105 days. Thyroid tissues were processed by routine methods for light microscopic examination, and follicular cell hyperplasia was diagnosed using a novel method. Thyroid hormone levels were altered significantly after 4 and 21 days. NaClO, treatment induced a concentration-dependent increase in the incidence and severity of thyroid follicular cell hyperplasia. Male rats are more sensitive to the effects of NaClO3 treatment than females. Follicular cell hyperplasia was not present in male or female B6C3F1 mice. These data can be used to estimate the human health risk that would be associated with using ClO2, rather than chlorine, to disinfect drinking water.

The effect of short intermittent light exposures on the melatonin circadian rhythm and NMU-induced breast cancer in female F344/N rats

We investigated the effects of altered endogenous nighttime melatonin concentrations on mammary tumor production in an N-nitroso-N-methylurea (NMU)-induced breast cancer model in female Fischer 344 (F344)/N rats. Experiments were designed 1) to evaluate whether short-duration intermittent exposures to light at night would affect the nocturnal rise of melatonin, resulting in a decrease in nighttime serum melatonin concentrations, 2) to evaluate whether any suppression of nighttime serum melatonin concentrations could be maintained for a period of weeks, and 3) to determine the effects of suppressed serum melatonin concentrations on the incidence and progression of NMU-induced breast cancer. In vivo studies were used to assess serum melatonin concentrations after 1 day and 2 and 10 weeks of nightly administration of short-duration intermittent light exposure at night and incidence of NMU-induced tumors. Five 1-minute exposures to incandescent light every 2 hours after the start of the dark phase of the light: dark cycle decreased the magnitude of the nocturnal rise of serum melatonin concentrations in rats by approximately 65%. After 2 weeks of nightly intermittent light exposures, an average decrease of the peak nighttime serum melatonin concentrations of approximately 35% occurred. The amelioration continued and, at 10 weeks, peak nighttime serum melatonin concentrations were still decreased, by approximately 25%. Because peak endogenous nighttime serum melatonin values could be moderately suppressed for at least 10 weeks, a 26-week NMU mammary tumor study was conducted. Serum melatonin concentrations and incidence, multiplicity, and weight of NMU-induced mammary tumors were assessed. A group of pinealectomized (Px) animals was also included in the tumor study. No effect on the development of mammary tumors in an NMU-induced tumor model in rats occurred when endogenous nighttime serum melatonin concentrations were moderately suppressed by short-duration intermittent light exposures at night. At necropsy, there were no alterations in mammary tumor incidence (28/40 NMU controls, 28/40 NMU + light, 31/40 NMU + Px), multiplicity (2.18 tumors/tumor-bearing NMU control, 1.89 NMU + light, 2.39 NMU + Px), or average tumor weight (1.20 g NMU control, 1.19 g NMU + light, 0.74 g NMU + Px). Tumor burden had no effect on the serum melatonin cycle. At 26 weeks, however, animals exposed to intermittent light at night exhibited approximately 3-fold higher serum melatonin concentrations as compared with controls. Additionally, rats that had been pinealectomized at 4 weeks of age had serum melatonin concentrations that were markedly higher than the expected baseline concentrations for pinealectomized rats (<15 pg/ml), suggesting the reestablishment of a melatonin cycle. This finding was unexpected and suggests that melatonin can be produced by an organ or tissue other than the pineal gland.

Disseminated thrombosis and bone infarction in female rats following inhalation exposure to 2-butoxyethanol

Groups of 10 male and 10 female F344/N rats were exposed to 0, 31, 62.5, 125, 250, and 500 ppm of 2-butoxyethanol (BE) by inhalation, 6 hr/day, 5 days/wk, for 13 wk. Four moribund female rats from the 500 ppm group were sacrificed during the first 4 days of exposure, and 1 moribund female from the same group was sacrificed during week 5. Dark irregular mottling and/or loss of the distal tail were noted in sacrificed moribund rats. Similar gross lesions were noted in the terminally sacrificed females exposed to 500 ppm BE. Histologic changes noted in the day 4 sacrificed moribund rats included disseminated thrombosis involving the coccygeal vertebrae, cardiac atrium, lungs, liver, pulp of the incisor teeth, and the submucosa of the anterior section of the nasal cavity. Alterations noted in coccygeal vertebrae from the 500 ppm sacrificed moribund rats included ischemic necrosis and/or degeneration of bone marrow cells, bone-lining cells, osteocytes (within cortical and trabecular bone), and chondrocytes (both articular and growth plate), changes that are consistent with an infarction process. The moribund female rat that was sacrificed during week 5 and those female rats treated with 500 ppm and sacrificed following 13 wk of treatment lacked thrombi, but they had coccygeal vertebral changes consistent with prior infarction and transient or complete bone growth arrest. No bone lesions or thrombi were noted in the male rats treated with the same doses of BE. In conclusion, exposure to 500 ppm BE vapors caused acute disseminated thrombosis and bone infarction in female rats. Possible pathogenic mechanisms are discussed.

Toxicity of 3,3',4,4'-tetrachloroazoxybenzene in rats and mice

The toxicity of 3,3',4,4'-tetrachloroazoxybenzene (TCAOB) was evaluated in 13-week gavage studies in male and female F344/N rats and B6C3F1 mice. In addition to histopathology, evaluations included clinical chemistry, hematology, thyroid hormone analyses, and effects on sperm morphology and estrous cycle length. Groups of 10 rats and 10 mice of each sex were exposed to TCAOB at dose levels of 0, 0.1, 1, 3, 10, or 30 mg/kg 5 days a week for 13 weeks. In the rat studies, the major effects included death in the 30 mg TCAOB/kg dose group; at lower exposure levels, a decrease in body weight gain, a decrease in thymus weight, an increase in liver weight, an increase in hematopoietic cell proliferation in the spleen and liver, a responsive anemia, a decrease in platelet counts, a chronic active inflammation of the vasculature in the lung, an increase in cardiomyopathy, hyperplasia of the forestomach, and a marked decrease in circulating thyroxine concentrations were observed. In male rats a decrease in sperm motility in the epididymides was observed. In addition, in female rats an increase in lung, spleen, kidney, and heart weights and nephropathy was observed. Furthermore, the estrous cycle length was increased. In the mouse studies, the major effects for males and females included a decrease in thymus weights, an increase in liver and kidney weights, centrilobular hypertrophy in the liver, hematopoietic cell proliferation, hyperplasia of the forestomach, and dilatation of hair follicles. The spectrum of effects in both rats and mice after exposure to TCAOB indicates that dioxin-like effects occur in addition to effects that have not been observed with dioxin-like compounds. No no-observed-adverse-effect level was reached in male or female rats or mice.

Toxicity of 3,3',4,4'-tetrachloroazobenzene in rats and mice

The toxicity of 3,3',4,4'-tetrachloroazobenzene (TCAB) was evaluated in 13-week gavage studies in male and female F344/N rats and B6C3F1 mice. In addition to histopathology, evaluations included clinical chemistry, hematology, thyroid hormone analyses, and reproductive parameters. Groups of 10 rats and 10 mice of each sex were exposed to TCAB at dose levels of 0, 0.1, 1, 3, 10, or 30 mg/kg for 5 days a week for 13 weeks. In the rat studies, the major effects for both males and females included a 10% decrease in terminal body weight at 30 mg/kg/day, an increase in hematopoietic cell proliferation in the spleen at 10 and 30 mg/kg/day, and a responsive anemia at 10 and 30 mg/kg/day. A 15 to 30% decrease in platelet counts and a 20 to 40% decrease in thymus weights was observed at 10 and 30 mg/kg/day. An increase in liver weight up to 15% was found at 3 mg/kg/day and higher doses in males and at 10 and 30 mg/kg/day in females, respectively. An increase in spleen weights up to 15% was observed at 10 and 30 mg/kg/day in males and at 30 mg/kg/day in females. A marked decrease in circulating total thyroxine (TT4) was found in both males and females at all dose levels tested. TT4 could hardly be detected at 10 and 30 mg TCAB/kg/day. In addition, hyperplasia of the forestomach was increased at 3 mg/kg/day and higher doses in males and at 30 mg/kg/day in females. In the mouse studies, an increase in liver and spleen weight was observed up to approximately 25% in both males and females at 10 and 30 mg/kg/day. Hyperplasia of the forestomach was observed at 1 mg/kg/day and higher doses in both males and females. In males, a 30% decrease in thymus weights at 30 mg/kg/day and a 60% decrease in epididymal sperm density at 3 and 30 mg/kg/day was observed. Also in males, centrilobular hypertrophy of hepatocytes and an increase in hematopoietic cell proliferation in the spleen was observed at 3 mg/kg/day and higher doses. Based on the current study and information in the literature, TCAB has dioxin-like properties. Comparison of the effects of TCAB in the present study and in the literature to those with 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD) indicates that TCAB is from two to six orders of magnitude less potent than TCDD depending on the end point.

Melatonin does not inhibit estradiol-stimulated proliferation in MCF-7 and BG-1 cells

Melatonin, an indolic pineal hormone, is produced primarily at night in mammals and is important in controlling biological rhythms. Previous research suggested that melatonin can attenuate proliferation in the estrogen-responsive MCF-7 breast cancer cell line. We tested whether these anti-proliferative effects may have physiological consequences upon two estrogen-responsive cell lines, MCF-7 (a breast cancer cell line) and BG-1 (an ovarian adenocarcinoma cell line). Melatonin (10(-9)-10(-5) M) attenuated proliferation of MCF-7 and BG-1 cells by >20% in the absence of estrogen. However, 17beta-estradiol exposure negated the ability of melatonin to inhibit proliferation. To substantiate this finding, cells were estrogen starved followed by multiple treatments with estradiol and melatonin. Melatonin did not inhibit estradiol-stimulated proliferation under this protocol. Estradiol increased MCF-7 and BG-1 cell cycle transition from G1 to S phase, however, melatonin did not inhibit this transition nor did it down-regulate estradiol-induced pS2 mRNA levels measured by northern blotting, further indicating that melatonin was unable to attenuate estradiol-induced proliferation and gene expression. We also examined the effects of melatonin on estradiol-induced proliferation in MCF-7 cell xenografts in athymic nude mice. Melatonin at a dose 28 times greater than 17beta-estradiol did not inhibit estradiol-induced proliferation in vivo. Furthermore, pinealectomy did not increase proliferation. Therefore, we conclude that melatonin does not directly inhibit estradiol-induced proliferation.

Nutritional status modulates rat liver cytochrome P450 arachidonic acid metabolism

Alterations in nutritional status affect hepatic cytochrome P450 levels. Since cytochromes P450 participate in the metabolism of arachidonic acid, we hypothesized that changes in liver P450 arachidonic acid metabolism occur during fasting and refeeding. Male Fisher 344 rats were either fed, fasted 48 hr (F48), fasted 48 hr and then refed 6 hr (F48/R6), or fasted 48 hr and then refed 24 hr (F48/R24). F48 rats had reduced body weight, increased plasma beta-hydroxybutyrate, and reduced plasma insulin compared with the other groups. Although there was no significant change in total liver P450 content, there was a significant 20%, 48%, and 24% reduction in total hepatic microsomal arachidonic acid metabolism in F48, F48/R6, and F48/R24 rats, respectively, compared with fed rats. Epoxygenase activity decreased by 28%, 51%, and 26% in F48, F48/R6, and F48/R24 rats, respectively. In contrast, omega-1 hydroxylase activity increased by 126% in F48 rats compared with fed rats. Immunoblotting revealed that levels of CYP2C11 protein were markedly reduced, whereas levels of CYP2E1 protein were markedly increased in the F48 and F48/R6 groups. In contrast, levels of CYP1A1, CYP1A2, CYP2B1, CYP2J3, CYP4A1, and CYP4A3 were unchanged with fasting/refeeding. Northern blots revealed that levels of CYP2C11 mRNAs were decreased, whereas CYP2E1 mRNAs were increased in F48 and F48/R6 rats. Recombinant CYP2C11 metabolized arachidonic acid primarily to epoxides with preference for the 14(S),15(R)-, 11(R), 12(S)-, and 8(S),9(R)- epoxyeicosatrienoic acid enantiomers. We conclude that (1) nutritional status affects hepatic microsomal arachidonic acid metabolism, (2) reduced epoxygenase activity in F48 and F48/R6 rats is accompanied by decreased levels of CYP2C11, (3) increased omega-1 hydroxylase activity is accompanied by augmented levels of CYP2E1, and (4) the effects of fasting on CYP2C11 and CYP2E1 expression occur at the pretranslational level.

Eight-week toxicity study of 60 Hz magnetic fields in F344 rats and B6C3F1 mice

Toxicity studies were performed by exposing F344/N rats and B6C3F1 mice (10 animals per sex per species per group) to transient-free, linearly polarized 60 Hz magnetic fields for 8 weeks. Targeted magnetic fields strengths used were 0 gauss (G; sham control fields did not exceed 0.001 G), 0.02 G, 2 G, and 10 G. Exposure was whole-body and continuous for 18.5 hr per day, 7 days per week. 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 (rats only), and hematology (rats only). All mice and all male rats survived until the end of the study. One female rat (2-G exposure group) died during Week 7 of the study; the death was not attributed to magnetic field exposure. In both studies, the mean body weight gains of exposed animals were similar to those of the respective controls. There were no gross, histological, hematological, or biochemical lesions attributed to magnetic field exposure. Statistically significant increases in liver weight and liver to body weight ratio occurred in female rats of all exposure groups but only at the termination. These data suggest that, for the variables evaluated in these studies, an 8-week exposure to linear-polarized, transient-free 60 Hz magnetic fields at field intensities of up to 10 G is not associated with significant toxicity in F344/N rats and B6C3F1 mice. Furthermore, there was no toxicity observed in animals receiving intermittent (1 hr on/1 hr off) exposures to 10-G fields. A 2-year study in F344/N rats and B6C3F1 mice is nearing completion of the in-life phase without overt toxicity in any exposed group. It is premature, however, to make any prediction concerning the possible influence of exposure to 60 Hz magnetic fields on cancer rates.

Thirteen-week inhalation toxicity of 2- and 4-chloronitrobenzene in F344/N rats and B6C3F1 mice

Toxicity studies were performed by exposing F344/N rats and B6C3F1 mice to 2- and 4-chloronitrobenzene (CNB) by whole-body inhalation 6 hr/day, 5 days/week, for 13 weeks. Animals were evaluated for clinical chemistry (rats), hematology (rats), histopathology, and body/organ weights. Exposure concentrations were 0, 1.1, 2.3, 4.5, 9, and 18 ppm for 2-CNB and 0, 1.5, 3, 6, 12, and 24 ppm for 4-CNB. All rats in the 2-CNB study survived until the end of the study. Two male mice in the 18-ppm group in the 2-CNB study, however, died during Week 12; no deaths attributable to 4-CNB exposure occurred in rats or mice. In both studies, the mean body weight gains of exposed animals were similar to those of the respective controls. In rats, inhalation exposure to 2- or 4-CNB resulted in methemoglobinemia leading to a regenerative anemia and a variety of tissue changes secondary to the oxidative erythrocyte injury. In the 2-CNB study, methemoglobinemia resulted in a normocytic, normochromic, responsive anemia, whereas with 4-CNB, the methemoglobinemia was more severe and resulted in a macrocytic, hyperchromic, responsive anemia. Alterations of erythrocyte morphology were observed in both studies; changes included Heinz bodies, poikilocytes, and polychromasia. In rats, both isomers caused increases in serum activities of alanine aminotransferase and sorbitol dehydrogenase and increased bile acid concentrations. Microscopic liver changes included hemosiderin deposition in Kupffer cells (rats and mice exposed to 4-CNB), hepatocytomegaly (mice), and cytoplasmic basophilia (rats). Hepatocellular necrosis and chronic inflammation observed in mice were rather specific to the 2-CNB isomer, as only slight evidence of focal necrosis in the liver was observed in mice exposed to 4-CNB. Splenic lesions included hemosiderin accumulation capsular fibrosis, and increased hematopoietic cell proliferation. Increased bone marrow hemosiderin and hematopoietic cell proliferation and kidney tubule hemosiderin deposition were also observed. Other findings, attributed to chemical exposure but not to the hematotoxicity, were described. Lesions included hyaline droplet nephropathy and degeneration of the testis in male rats exposed to 4-CNB, inflammation of the harderian gland in rats exposed to 4-CNB, hyperplasia of the nasal cavity epithelium in rats exposed to 2-CNB, and hyperplasia of the forestomach epithelium in mice exposed to 4-CNB; these lesions have not been described previously in studies with these chemicals. Based on the exposure concentrations evaluated, A no-observed-adverse-effect level (NOAEL) for histopathological injury in mice was 4.5 ppm for 2-chloronitrobenzene and 6 ppm for 4-chloronitrobenzene; a NOAEL was not determined for rats.

Frequency and relationships of clinical chemistry and liver and kidney histopathology findings in 13-week toxicity studies in rats

The relative sensitivities of eight commonly used clinical chemistry end points and histopathology to detect potential toxic effects in liver and kidney were evaluated for a series of 61 13-week rat toxicity studies conducted for the National Toxicology Program. The data consisted of 1-,2- to 3-, and 13 week clinical chemistry measurements and 13-week histopathological assessments of liver and kidney. Except for serum alkaline phosphatase, treatment-related alterations of individual clinical chemistry variables occurred in 20-48% of the studies, depending on the analyte, sampling time, and sex. Liver and kidney lesions were reported for 31% and 41% of the studies respectively. There was an association between treatment-related increases in alanine aminotransferase (ALT) and sorbitol dehydrogenase (SDH) activities and histopathological changes in the liver. SDH activity had greater positive and negative predictive values than similar changes in ALT; by week 1 in females and weeks 2-3 in both sexes. SDH predicted morphological hepatic change at study termination with 75% or better accuracy. If increases in activities of both enzymes occurred simultaneously, however, terminal histopathological changes could be predicted, in both sexes, with 75% accuracy by week 1, increasing to 100% by weeks 2-3. There also was an association between treatment-related increases in urea nitrogen (UN) and creatinine (Cre) concentrations and morphological kidney change. Cre concentration had greater positive predictive values than similar changes in UN; by weeks 2-3 in males and week 13 in both sexes. Cre predicted morphological renal change at study termination with 56% or better accuracy. UN concentration was associated and predictive of morphological kidney change only in females at week 13. Depending on time point and sex, serum alkaline phosphatase activity increased in 5-22% of the studies. Increases in total bile acid concentration occurred in 33-48% of the studies. Because both tests are used as markers of cholestasis, this marked discrepancy was unexpected. Treatment-related decreases in alkaline phosphatase activity occurred, however, in 39-56% of the studies; serum alkaline phosphatase may be more useful as an indicator of decreased food intake (decreased activity) than of cholestasis (increased activity). In summary, treatment-related alterations of clinical chemistry and histopathology occurred frequently in this series of toxicity studies in rats. Changes in the chemistry end points also occurred frequently at interim time points, indicating that clinical chemistry evaluations can be useful for detecting potential treatment effects throughout a study. This observation is important, since histopathological evaluations are limited to animal termination and not useful for detecting transient responses or the onset of treatment-related effects.

Early changes in sex hormones are not evident in mice exposed to the uterine carcinogens chloroethane or bromoethane

Chloroethane and bromoethane have been shown to cause a marked uterine tumor response in B6C3F1 mice exposed for 2 years. These chemicals are nearly unique in this regard among the nearly 400 chemicals studied by the National Toxicology Program, and the reasons for this carcinogenic activity are unclear. The possible relationship of changes in blood concentrations of sex hormones to this response was evaluated by examining the estrous cycle of mice prior to and during a 21-day exposure to concentrations of the haloethanes which resulted in the tumorigenic response in the 2-year studies. Serum concentrations of estradiol and progesterone were determined at the termination of the exposures and compared to exposure group and stage of the estrous cycle. No consistent patterns of change were found in estrous cyclicity or in blood concentrations of sex hormones. Thus, the findings suggest that early changes in circulating sex hormones are not important contributing factors in the uterine neoplasia caused by these chemicals.

Toxicity and carcinogenicity of riddelliine following 13 weeks of treatment to rats and mice

Toxicity studies of riddelliine, a member of a class of pyrrolizidine alkaloids, were conducted because riddelliine has been found to contaminate human food sources. Groups of male and female Fischer rats were administered riddelliine by gavage in phosphate buffer at doses up to 10 mg/kg, and B6C3F1 mice at doses up to 25 mg/kg, five times a week. The animals were necropsied after 13 weeks of treatment or after a 7 or 14 week recovery period. Body weight gains were inversely related to dose in both rats and mice. Body weight of the 1.0 and 3.3 mg/kg female rats and 10.0 and 25.0 mg/kg mice remained depressed during the 14 week recovery period. At 13 weeks, significant findings included dose-related hepatopathy and intravascular macrophage accumulation in rats and hepatocytomegaly in mice. During the 14 week recovery period these lesions persisted and hepatic foci of cellular alteration in male rats and bile duct proliferation in female rats and male and female mice increased in severity. In the 10 mg/kg group of female rats adenomas of the liver occurred in two of ten at 13 weeks and in one of five at the 14 week recovery period. In separate studies, the frequency of micronucleated erythrocytes in peripheral blood was increased in male mice administered a single dose (150 mg/kg) of riddelliine. Increases in unscheduled DNA and S-phase syntheses were detected in primary hepatocytes from rats and mice treated with riddelliine at doses up to 25.0 mg/kg for 5 or 30 days. In mating trials in rats and mice, pup weights from treated dams at birth and during suckling were lower than controls. Thus, riddelliine is genotoxic and carcinogenic and may cross the placenta and/or be found in milk, causing developmental toxicity in rodents.

Subchronic toxicity of cupric sulfate administered in drinking water and feed to rats and mice

The effects of acute poisoning by cupric sulfate in a number of species are well known; however, the effects of chronic low-level ingestion of cupric sulfate are less well characterized. Because exposure of humans to cupric sulfate may occur through drinking water, food, soil, or ambient air, subchronic toxicity studies were conducted in male and female F344/N rats and B6C3F1 mice by the drinking water (2-week exposure) and dosed feed (2- and 13-week exposure) routes. Animals were evaluated for histopathology, clinical pathology, reproductive toxicity, and tissue metal accumulation, and target organs were examined by a variety of special stains and by electron microscopy to characterize the observed lesions. In drinking water, cupric sulfate concentrations of 300 to 100 ppm produced no ill effects, whereas concentrations of 3000 to 30,000 ppm were lethal to rats and mice within 2 weeks. In feed, cupric sulfate concentrations of 4000 to 16,000 ppm caused significant reductions in body weight gain in both species in the 2- and 13-week studies. Hyperplasia and hyperkeratosis of the limiting ridge of the forestomach were present in both species in the 2- and 13-week studies. Rats in the dosed feed studies had a dose-related increase in inflammation in the liver and changes in clinical chemistry parameters which were indicative of hepatocellular damage and cholestasis. Histologic changes in the kidneys of rats consisted of a dose-related increase in the number and size of eosinophilic protein droplets in the epithelial cytoplasm and the lumina of the proximal convoluted tubules. Droplets were larger and more numerous in males than in females. Urinalysis results were suggestive of renal tubular epithelial damage. Iron staining of spleens from treated animals indicated a marked depletion of iron stores in both male and female rats, but not in mice, while hematologic and clinical chemistry alterations in rats in the 13-week study, along with histologic changes in bone in the 2-week dosed feed study, were indicative of a microcytic anemia. Cupric sulfate produced no adverse effects on any of the reproductive parameters measured in rats or mice of either sex. These results indicate that cupric sulfate at high exposure levels is a hepatic and renal toxicant, as well as an inducer of anemia in rodents, with rats more sensitive than mice following subchronic exposure.

Inhalation toxicity of 1,6-hexanediamine dihydrochloride in F344/N rats and B6C3F1 mice

1,6-Hexanediamine (HDA) is a high production volume chemical which 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 dihydrochloride salt of HDA (HDDC) were conducted in male and female Fischer 344/N rats and B6C3F1 mice using whole-body inhalation exposure. Both species were evaluated for histopathologic and reproductive effects, and rats were examined for clinical chemistry and hematologic changes. In the 2-week inhalation studies, animals were exposed to 10-800 mg HDDC/m3, 6 hr per day. All rats, all female mice, and two of five male mice in the high-exposure group died before the end of the study. Surviving mice in this group had a dose-dependent depression in body weight gain. Clinical signs were primarily related to upper respiratory tract irritation and included dyspnea and nasal discharge in both species. Treatment-related histopathologic lesions included inflammation and necrosis of the laryngeal epithelium of both species and the tracheal epithelium of mice, as well as focal inflammation and ulceration of the respiratory and olfactory nasal mucosa. In the 13-week inhalation studies, animals were exposed to HDDC at concentrations of 1.6-160 mg/m3 for 6 hr per day, 5 days per week. In addition to the base study groups, a supplemental group of rats at each exposure level was included to assess the effect of HDDC on reproduction. No treatment-related changes in organ weights or organ-to-body-weight ratios occurred in rats, and no treatment-related clinical signs or gross lesions were seen in either species. Chemical-related microscopic lesions were limited to the upper respiratory tract (larynx and nasal passages) in the two highest exposure groups and were similar in both species. These lesions included minimal to mild focal erosion, ulceration, inflammation, and hyperplasia of the laryngeal epithelium, in addition to degeneration of the olfactory and respiratory nasal epithelium. HDDC caused no significant changes in sperm morphology or vaginal cytology and no significant adverse effects on reproduction in rats or mice. Hematologic and clinical chemistry changes in rats were minor and sporadic and were not accompanied by related histologic findings. HDDC did not increase the frequency of micronucleated erythrocytes in mice.(ABSTRACT TRUNCATED AT 400 WORDS)

Two histopathologic types of inflammatory vascular disease in MRL/Mp autoimmune mice. Model for human vasculitis in connective tissue disease

We have recently described 2 histopathologic types of inflammatory vascular disease (IVD) in patients with Sjögren's syndrome (SS): neutrophilic IVD (NIVD) and mononuclear IVD (MIVD). Autoimmune MRL/Mp mice, which have many features of SS, spontaneously develop IVD which is histopathologically indistinguishable from that observed in human SS patients. Both MRL/Mp-+/+ and MRL/Mp-lpr/lpr mice develop MIVD which evolves into NIVD and results in decreased survival; the transition to NIVD is accelerated by the lpr gene. The presence of the lpr gene on other genetic backgrounds does not result in a similar acceleration of IVD and associated decreased survival. Thus, the spontaneous autosomal recessive mutation lpr appears to modulate the development of IVD in a strain of mice with an underlying propensity for vasculitis. Based on our observations on IVD in SS patients and MRL/Mp mice, we propose a new model which may enhance our understanding of the immunopathogenesis of IVD in connective tissue disease.