Search

A two-year feeding study in rats and an 18-month feeding study in mice were conducted to evaluate the potential chronic toxicity and oncogenicity of NMP in Crl:CD® (SD)BR rats and B6C3F1/CrlBR mice. Groups of 62 male and female rats were administered diets containing 0, 1600, 5000, or 15000ppm of NMP for approximately 2 years. Groups of 50 male and female mice were administered diets containing 0, 600, 1200, or 7200ppm NMP for approximately 18 months. In vivo parameters were evaluated weekly during the first 3 months of the study, and every other week or monthly during the remainder of the study. For rats, an ophthalmoscopic examination was conducted prior to study start and near the end of the study. Periodically, blood samples were collected from rats and mice for determination of leukocyte differential counts, and from mice for red blood cell morphology. After approximately 2 years of dietary administration in rats and 18 months in mice, all surviving animals were sacrificed. Selected tissues were processed for morphological evaluation. Over the course of the two-year study in rats, test substance-related decrements in body weight and weight gain occurred in 15000ppm males and females, which correlated with decreased food consumption and food efficiency. A toxicologically significant, test substance-related increase in the incidence of severe chronic progressive nephropathy occurred in 15000ppm males. Several morphological changes noted grossly and/or microscopically were secondary to the increased severity of chronic progressive nephropathy. NMP was not oncogenic in male or female rats at dietary concentrations of 15000ppm and below. A test substance-related decrease in the percentage of 15000ppm males surviving to the end of the two-year study compared to the control group resulted from the higher incidence of severe chronic progressive nephropathy. However, a sufficient population of 15 000 ppm rats were at risk for potential oncogenicity, so the... [ABSTRACT FROM AUTHOR]

Ninety-day feeding studies were conducted to evaluate the repeated dose toxicity of NMP, a widely used industrial solvent, in Crl:CD(R)BR rats and B6C3F1 mice. Groups of 20 to 26 male and female rats each were fed either 0, 3,000, 7,500, or 18,000 ppm NMP for 90 days. Groups of 10 male and female mice were fed either 0, 1,000, 2,500, or 7,500 ppm NMP for 28 or 90 days. In vivo parameters, hematologyand clinical chemistry parameters, ophthalmologic examinations, functional and histopathologic neurologic parameters (rats only), and complete pathology evaluations were conducted after 90 days. Decreases in mean body weights, reflecting decreases in food consumption and efficiency were observed in male and female rats fed either 7,500 or 18,000 ppm NMP. A change in urine coloration was observed at 3,000 ppm and above in both males and females. This was considered to be evidence of systemic availability since it was not associated with any functional or pathological changes. Of 36 neurobehavioral parameters investigated, male rats in the 7,500 and 18,000 ppm groups showed an increase in foot splay, and 18,000 ppm males had a higher incidence of lowarousal and slight palpebral closure suggestive of a sedative effect. Absolute and relative liver weights were increased in 18,000 ppm females which were associated with an increased incidence of centrilobular hepatocellular hypertrophy and were considered to be an adaptive/physiological response. Absolute and relative kidney weights were increased in 18,000 ppm males and females, however, there were no pathological or functional changes associated with the increases. In mice, there were no effects on body weight or food consumption. As observedin rats, mice fed 2,500 or 7,500 ppm exhibited a change in urine coloration which was not associated with morphological changes in the kidney. In 2,500 and/or 7,500 ppm mice, changes in cholesterol, triglycerides, calcium, and alkaline phosphatase occurred at 28 days but not90 [ABSTRACT FROM AUTHOR]

Twenty-eight day feeding studies were conducted to evaluate the repeated dose toxicity of NMP, a widely used industrial solvent, in Crl:CD(R)BR rats and B6C3F1 mice. Groups of 5 male and 5 female rats each were fed either 0, 2,000, 6,000, 18,000, or 30,000 ppm NMP; similar groups of mice were fed either 0, 500, 2,500, 7,500, or 10,000 ppm. Invivo parameters, hematology and clinical chemistry parameters, and complete pathology evaluations were conducted after approximately 28 days. Decrements in mean body weight gains, reflecting decreases in food consumption and efficiency, were seen in male rats fed 18,000 ppm and in both sexes fed 30,000 ppm. In rats, clinical chemical changes,indicating possible compound-related alterations in lipid, protein, and carbohydrate metabolism, occurred at 18,000 ppm in males and 30,000 ppm in both sexes. No histopathological changes in rats were judged to be directly related to NMP exposure. Hematological (mild to moderate leukopenia) and histopathological alterations (hypocellular bonemarrow, testicular degeneration and atrophy, and thymic atrophy) were judged to be secondary to nutritional and body weight effects in male and/or female rats at 30,000 ppm. In mice, cloudy swelling of the epithelia of the distal parts of the renal tubuli was observed in 4 males and 3 females at 10,000 ppm and in 2 male mice at 7,500 ppm. Forboth rats and mice, abnormal urine coloration was observed (in mice at 2,500 ppm and above, and in rats at 18,000 ppm and above). This discoloration was interpreted as a sign of systemic availability of thetest substance, but not as an adverse effect. The NOAEL was 6,000 ppm for mate rats and 18,000 ppm for female rats. In mice, the NOAEL was 2,500 ppm based on the kidney histopathology. [ABSTRACT FROM AUTHOR]

After previously examining an estrogen receptor agonist (17beta-estradiol), several additional compounds have been evaluated in a Tier I screening battery for detecting endocrine-active compounds (EACs): an estrogen receptor antagonist (ICI-182,780, ICI), an androgen receptor antagonist (flutamide, FLUT), a testosterone biosynthesis inhibitor (ketoconazole, KETO), a 5alpha-reductase inhibitor (finasteride, FIN), and an aromatase inhibitor (anastrozole, ANA). The Tier I battery incorporates two short-term in vivo tests (a 5-day ovariectomized female battery and a 15-day intact male battery) and an in vitro yeast transactivation system (YTS). The Tier I battery is designed to identify compounds that have the potential to act as agonists or antagonists to the estrogen, androgen, progesterone, or dopamine receptors, steroid biosynthesis inhibitors (aromatase, 5alpha-reductase, and testosterone biosynthesis), or compounds that alter thyroid function. ICI administration decreased uterine estrogen and progesterone receptor number in the female battery, increased serum follicle-stimulating hormone (FSH) levels and caused spermatid retention in the male battery, and activated gene transcription in the YTS containing the estrogen receptor. FLUT administration increased uterine stromal cell proliferation in the female battery and decreased weights for all androgen-dependent tissues, induced Leydig cell hyperplasia, and caused hormonal alterations (increased testosterone (T), estradiol (E2), dihydrotestosterone (DHT), luteinizing hormone (LH), and FSH) in the male battery, and competed for binding to the androgen receptor in the YTS competition assay. In the male battery KETO decreased weights for all androgen-dependent tissues, caused hormonal alterations (decreased T and DHT and increased LH and FSH), and induced spermatid retention. FIN decreased seminal vesicle and accessory sex gland (ASG) unit weight and caused hormonal alterations (decreased DHT and increased LH, and PRL) in the male battery. KETO was judged not to affect any of the endpoints in the female battery. ANA decreased ASG unit weight and serum E2 levels in the male battery. Using the responses obtained for all the endpoints in the Tier I battery, a distinct "fingerprint" was produced for each type of endocrine activity against which compounds with unknown activity can be compared. These data demonstrate that the described Tier I battery is useful for identifying EACs.

This study describes the neural structures damaged following exposure to the nerve agent soman, shows there are time-dependent differences in the extent of damage in certain structures, and relates seizure-induced increases in delta band (0-3.5 Hz) electroencephalographic (EEG) activity with severity of subsequent neuropathology. Rats, instrumented to record cortical EEG activity, were pretreated with the oxime HI-6 (125 mg/kg, i.p.) and then challenged with soman (180 ug/kg, s.c.). All animals developed continuous epileptiform seizures that lasted in excess of 4 hr. Groups of animals were perfused 1, 3, 10 or 30 days following exposure. Paraffin-embedded brains were stained with hematoxylin and eosin; thirty-four neural structures were examined and scored for neural damage. All cortical areas sustained damage, with piriform and perirhinal cortices exhibiting the most severe. Subcortical limbic areas (amygdala, amygdala-piriform transition zone, hippocampus, claustrum) and various thalamic nuclei were most consistently and severely damaged in all animals regardless of survival time. Brainstem structures, cerebellum, spinal cord, and other motor output nuclei were never damaged. It was found that some structures were rated as more severely damaged when evaluated at shorter survival times. Severity of neural damage was related to high levels of EEG delta power recorded 24 hr after exposure; power during the acute seizure or 24 hr body weight loss did not predict lesion severity. Sections between AP -0.8 to -4.8 contain cortical and subcortical structures that can be readily and reproducibly evaluated for brain damage.

The potential chronic toxicity and oncogenicity of dimethylacetamide (DMAC) was evaluated by exposing male and female rats and mice to 0, 25, 100, or 350 ppm DMAC for 6 hr/day, 5 days/week for 18 months (mice) or 2 years (rats). Clinical pathology was evaluated at 3, 6, 12, 18, and 24 (rats only) months. An interim euthanization for rats occurred at 12 months and hepatic cell proliferation in rats and mice was examined at 2 weeks and 3 and 12 months. No compound-related effects on survival were observed. Rats exposed to 350 ppm had lower body weight and/or body weight gain. There were no compound-related effects on body weight or weight gain in mice at any concentration. There were no compound-related adverse effects on the incidence of clinical signs of toxicity in rats or mice. No hematologic changes were observed in either species. Serum sorbitol dehydrogenase activity was increased in rats exposed to 350 ppm. Serum cholesterol and glucose concentrations were significantly higher in 100 and 350 ppm female rats. Compound-related morphological changes were observed in the liver. In rats, exposure to 100 or 350 ppm produced increased absolute and/or relative liver weights, hepatic focal cystic degeneration, hepatic peliosis, biliary hyperplasia (350 ppm only), and lipofuscin/hemosiderin accumulation in Kupffer cells. In mice, exposure to 100 or 350 ppm produced increased absolute and relative liver weights (350 ppm females only), accumulation lipofuscin/hemosiderin in Kupffer cells, and centrilobular single cell necrosis. Male rats exposed to 350 ppm also had significantly higher absolute and relative kidney weights which correlated with the gross and microscopic changes resulting from a compound-related increase in severity of chronic progressive nephropathy. Female mice exposed to 350 ppm had an increased incidence of bilateral, diffuse retinal atrophy. No increase in hepatic cell proliferation was seen in mice or rats at any exposure concentration. DMAC was not oncogenic under these experimental conditions in either the rat or mouse. The NOAEL for male and female rats and mice is 25 ppm.

A 90-day gavage study was performed to evaluate the subchronic toxicity of 1-methyl-3-propylimidazole-2-thione (PTI) when administered to Crl:CD BR rats. PTI is a chemical catalyst and is structurally similar to the thioureas, which are known to adversely affect the thyroid. Therefore, this study was designed to investigate the effects of PTI on the thyroid. Male and female rats were dosed with 0, 5, 10, 25, or 75 mgPTI/kg/day for 13 weeks. Clinical pathology examinations and pathology examination were performed and the following were measured periodically: serum T3, T4, and TSH, hepatic UDP-glucuronyltransferase activity, and cell proliferation of the thyroid and liver. Under the conditions of this study, the overall no-observed-adverse-effect level (NOAEL) for the subchronic effects of PTI in male and female rats was 10 mg PTI/kg/day. The NOAEL was based on the effects on the thyroid gland in male and female rats dosed with 25 and 75 mg PTI/kg/day, as well as the hepatic centrilobular fatty change, increased severity of chronic progressive nephropathy, fatty change in the adrenal medulla, and the substantial reduction in body weight and body weight gain. The primary target organs were the thyroid and liver. Alterations in thyroid hormones (T3, T4, and TSH) occurred predominantly at 25 and 75 mg/kg/day. Toxicologically significant alterations in T3, T4, and TSH levels, cell proliferation, and UDP-glucuronyltransferase activity occurred in rats dosed with 25 and 75 mg/kg/day, which correlated with organ weight and histopathological effects. Additionally, the effect of PTI on thyroid peroxidase activity, a key step in thyroid hormone synthesis, was evaluated in vitro using microswine thyroid microsomes. PTI was shown to inhibit thyroid peroxidase, with an IC50 of 0.02 M. These data suggest that PTI enhances the excretion of T4 via induction of glucuronyltransferase and inhibits thyroid hormone synthesis via a direct affect on thyroid peroxidase. Both of these effects contribute to the disruption of the hypothalamic-pituitary-thyroid axis and result in sustained elevation of TSH and the corresponding thyroid hypertrophy and hyperplasia.

The objective of this study was to examine the feasibility of conducting an immunotoxicological assay for assessing humoral immunity in rats on standard toxicology study. Male CD rats were untreated or dosed intraperitoneally daily for 30 or 90 days, excluding weekends, with vehicle or 2 mg/kg cyclophosphamide (CY). Six days prior to sacrifice, selected rats were injected intravenously with sheep red blood cells (SRBC). One day prior to necropsy, blood samples for hematological and clinical chemical measurements were collected from each rat. On the day of necropsy standard protocol tissues were collected, weighed, processed to slides, and examined microscopically. One-half of each spleen was used to prepare a single cell suspension in order to assess spleen cell numbers. Serum was analyzed for anti-SRBC IgM antibody using an enzyme-linked immunosorbent assay. A second set of studies was performed to examine further the effect of SRBC administration on lymphoid organ weights using 30- and 90-day study age-equivalent naive male CD rats. Exposure of animals to 2 mg/kg CY for 30 or 90 days resulted in a 28% and 61% decrease, respectively, in SRBC-specific serum IgM levels. CY treatment also caused mild alterations in some leukocytic parameters, with significant decreases of 35% and 33% in white blood cell and lymphocyte counts, respectively, observed in 30-day CY-treated animals receiving SRBC. Injection of SRBC alone did not alter hematological or clinical chemistry parameters. With the expected exception of the spleen (increased number and size of germinal centers), administration of SRBC did not significantly alter the weights or morphology of routine protocol tissues. Furthermore, administration of SRBC did not mask the immunosuppressive effects of CY treatment under the conditions of this study. Based on our preliminary findings, a functional assay for assessing humoral immunity may be conducted in animals on standard toxicology study.

The potential chronic toxicity and oncogenicity of dimethyl-formamide (DMF) was evaluated by exposing male and female rats and mice to 0, 25, 100, or 400 ppm DMF for 6 hr/day, 5 days/week for 18 months (mice) or 2 years (rats). Clinical pathology was evaluated at 3, 6, 12, 18, and 24 (rats only) months. An interim euthanasia for rats occurred at 12 months and hepatic cell proliferation in rats and mice was examined at 2 weeks, 3 months, and 12 months. No compound-related effects on clinical observations or survival were observed. Body weights of rats exposed to 100 (males only) and 400 ppm were reduced. Conversely, body weights were increased in 400 ppm mice. No hematologic changes were observed in either species. Serum sorbitol dehydrogenase activity was increased in rats exposed to 100 or 400 ppm. There were no compound-related effects on the estrous cycle of rats or mice at any concentration. Compound-related morphological changes were observed only in the liver. In rats, exposure to 100 and 400 ppm produced increased relative liver weights, centrilobular hepatocellular hypertrophy, lipofuscin/hemosiderin accumulation in Kupffer cells, and centrilobular single cell necrosis (400 ppm only). In mice, increased liver weights (100 ppm males, 400 ppm both sexes), centrilobular hepatocellular hypertrophy, accumulation of lipofuscin/hemosiderin in Kupffer cells, and centrilobular single cell necrosis were observed in all exposure groups. These observations occurred in a dose-response fashion and were minimal at 25 ppm. No increase in hepatic cell proliferation was seen in mice or female rats. Slightly higher proliferation was seen in male rats exposed to 400 ppm at 2 weeks and 3 months but not at 12 months. Dimethylformamide was not oncogenic under these experimental conditions in either the rat or mouse.

A histiocytic sarcoma in an aging female gerbil is described. The neoplasm primarily involved the spleen and liver, and these organs were considered the primary sites of neoplastic origin. No neoplastic infiltration was noted in the uterus or ovaries as is commonly seen in the female mouse. This is the first report of histiocytic sarcoma in gerbils.

The pathogenesis of Rift Valley fever in adult rats from 3 inbred strains (LEW, MAXX, WF) was investigated. WF rats all died by day 2 postinoculation with viral tissue titers reaching 9 log10 PFU/g. LEW and MAXX rats were resistant to liver disease, but fatal necrotising encephalitis developed in 16 and 44% of the rats, respectively. Detection of serum neutralising antibody on day 3 coincided with clearance of virus from serum and liver, although infectious virus was detected in spleen homogenates as late as day 19 postinfection. Viral titers in LEW and MAXX rats did not exceed 4.5 log10 PFU/g. Cyclophosphamide immunosuppression of LEW rats led to death 5-9 days postinfection; early patterns of viral replication were not affected, but continued growth in the liver resulted in fatal hepatitis. These animals could be protected by passive antibody therapy administered on days 2-5 postinfection to mimic the serum neutralising antibody pattern seen in unmanipulated infected LEW rats. Thus, RVF virus replication and spread is rapid in the WF rats tissues, whereas in LEW and MAXX rats viral growth is less due to an intrinsic mechanism which allows sufficient time for an immune response to terminate infection. A slightly diminished immune response may lead to the development of encephalitis more frequently in MAXX than LEW rats. These rat strains should be useful in elucidating those mechanisms of resistance which limit RVFV-induced hepatitis and encephalitis.

A formalin-inactivated Rift Valley fever (RVF) vaccine prepared in cell culture for human use was immunogenic in sheep. Vaccine was administered as a single dose of diluted (1:5) or undiluted vaccine with or without an adjuvant. Serum-neutralizing antibodies induced by RVF vaccine persisted for at least 7 months. Seven of 11 vaccinated sheep with prechallenge plaque-reduction neutralization (PRN80) antibody titers of less than or equal to 10 were protected against challenge exposure with 10(6) plaque-forming units of Zagazig 501 strain of RVF virus. Challenge exposure induced abortion in 2 of 2 pregnant sheep. Five sheep with PRN80 titers greater than or equal 1:20 were protected from detectable viremia after challenge exposure. Additionally, 5 of 6 lambs (3 months old) were protected (by maternal antibodies) against challenge exposure. Challenge control sheep developed clinical disease and detectable viremia after exposure. Virus was isolated from saliva of 1 challenge control sheep and virus was transmitted by contact exposure to 1 of 4 seronegative contact-control sheep. Immunization of sheep with formalin-inactivated RVF vaccine induced a priming effect against RVF viral antigens. Challenge exposure with RVF virus resulted in significantly higher neutralizing titers in vaccinated sheep than in nonvaccinated sheep.

Rift Valley fever virus (RVFV), a member of the family Bunyaviridae, extended its range from sub-Saharan Africa into Egypt in 1977. Its clinical spectrum is recognized to include severe manifestations such as hemorrhagic fever and encephalitis. For these reasons, as well as the limited knowledge of specific therapy for Bunyaviridae infections, we investigated several prophylactic regimens for RVF in a mouse model. Rimantadine, thiosemicarbazone, and inosiplex were ineffective. Pretreatment with glucan was of some use, but the most encouraging results were obtained with the antiviral drug ribavirin, passive antibody, or an interferon inducer polyriboinosinic-polyribocytidylic acid complexed with poly-L-lysine and carboxymethylcellulose (poly[ICLC]). Ribavirin and poly(ICLC) were also shown to be efficacious in preventing disease in hamsters. Ribavirin (loading dose of 50 mg/kg followed by 10 mg/kg at 8-h intervals for 9 days) suppressed viremia in RVF-infected rhesus monkeys. Ribavirin also reduced virus yield in infected cell cultures; sensitivity varied markedly with cell type but not with virus strain. Immune mouse ascitic fluid, with a plaque reduction neutralization titer of 1:1024, was effective in a dose of 4 ml/kg, a volume approximately equivalent to administration of a unit of convalescent plasma to a human. Poly(ICLC) may well have functioned through interferon induction, since RVFV was shown to be sensitive to interferon in cell culture, and since another macrophage activator (glucan) was only marginally effective. These studies suggest that ribavirin, poly(ICLC), and convalescent plasma may have a role in prevention or therapy of human RVF.