Time- and concentration-dependent increases in cell proliferation in rats and mice administered vinyl acetate in drinking water.

Chronic administration of vinyl acetate (VA) in drinking water to rats and mice has produced upper digestive tract neoplasms. These tumors were believed to arise from the intracellular metabolism of VA by carboxylesterases to cytotoxic and genotoxic compounds. We hypothesized that prolonged VA exposure at high concentrations would induce cytotoxicity and a restorative cell proliferation (CP). These endpoints were measured in F-344 rats and BDF1 mice administered drinking water containing 0, 1000, 5000, 10,000, or 24,000 ppm VA for 92 days. On test days, Days 1, 8, 29, and 92, upper digestive tract histopathology and oral cavity CP (pulsed 5-bromodeoxyuridine [BrdU] to measure S-phase DNA synthesis) were evaluated. Analysis of test solutions showed that VA spontaneously hydrolyzed, slowly releasing acetic acid and thereby lowering pH. Statistically significant, concentration-related increases in CP occurred in basal cells of the mandibular oral cavity mucosa of mice at 10,000 and 24,000 ppm but only after 92 days. CP increases were approximately 2.4- and 3.4-fold above controls and were considered to be toxicologically significant. Some statistically significant increases in CP were also measured in the oral cavity mucosa of rats; however, these changes were considered to be of equivocal biological relevance. No histopathological evidence of mucosal injury was seen in either species. The absence of cytotoxicity in the upper digestive tract mucosa suggests that the increased CP at high administered VA concentrations may be due to a mitogenic response, ostensibly from the loss of cell growth controls in oral cavity mucosa.

Inhalation toxicity of cyclooctadiene in rats.

Groups of 20 male Crl:CDBR rats each were exposed, whole-body, for six hours/day, for a total of nine exposures over a two-week period to concentrations of 52, 150, or 500 ppm of 1,5-cyclooctadiene vapor. A control group of 20 male rats was exposed simultaneously to houseline air. Ten rats per group were used for standard toxicological evaluations and ten rats per group for neurotoxicity testing. In the standard toxicology group, at the end of the exposure period, blood and urine samples were collected for clinical analyses, and five rats per group were sacrificed for pathologic examination. After a two-week recovery period, the surviving rats in the standard groups were also given clinical and pathological examinations. The neurotoxicity group was given a functional observational battery (FOB) test and motor activity evaluations after the fourth and ninth exposures. In addition, six of ten neurotoxicity rats per exposure group were given neuropathology evaluations at the end of the exposure period. In rats exposed to 500 ppm of 1,5-cyclooctadiene there was an absence of alerting response toward the end of the daily six-hour exposures. These rats appeared to recover within 1/2 hour after exposure. This effect was not observed in the other test groups. The FOB evaluation showed an increase in the number of rats found sleeping in the 500 and 150 ppm groups compared to controls after the last exposure, but there were no treatment-related effects in the motor activity evaluation. Since there were no other neurobehavioral findings and no toxicity findings in the 150 ppm group, the sleeping behavior in the 150 ppm group was considered insufficient evidence of an adverse effect. Clinical laboratory evaluation of the 500 ppm group showed urinary pH decreases at the end of the exposure period but not after the two-week recovery period. There were no other toxicologically important changes in urine analysis, hematologic, or blood chemistry evaluations attributable to the test compound. Histologic effects were found in the nose and kidneys of rats in the 500 ppm group. There was a mild degeneration/necrosis of nasal olfactory epithelium observed immediately after the exposure period and a mild degeneration/regeneration in this area observed after the two-week recovery. In addition, there were increased kidney weights in the 500 ppm group immediately after exposure along with increased hyaline droplets in the kidneys. These effects were reversible after the two-week recovery period. There were no significant nasal or kidney effects observed in the 150 and 52 ppm test groups, and no other organ weight or histological effects attributable to the test compound observed in the standard toxicology groups at either evaluation time. The neuropathologic evaluation showed only one minor lesion in one 500 ppm-group rat and this was not considered to be attributable to exposure to 1,5-cyclooctadiene. Based on the decreased alerting response observed in rats during exposure at 500 ppm, and on the effects observed in the nose, kidney, and urine in rats at this concentration, the no-observed-adverse-effect (NOAEL) level in this study was considered to be 150 ppm.

Subchronic inhalation toxicity of the chlorinated propane 1,1,1,3,3,3-hexachloropropane (HCC-230fa).

Male and female rats were exposed by inhalation (whole body) to HCC-230fa (1,1,1,3,3,3-hexachloropropane) for 6 h/day, 5 days/week over a 15-week period. Concentrations of 0, 0.50, 2.5, and 25 ppm were studied. A total of eight groups/sex were exposed. Four groups of male and four groups of female rats were used to measure clinical signs and growth, clinical pathology, and tissue pathology. The remaining four groups of male rats were used for immunotoxicological and sperm assessment evaluations, and the remaining four groups of female rats were used for immunotoxicological evaluation. Following the exposure period, surviving male rats were kept for a 1- or 3-month recovery period. Male and female rats exposed to 25 ppm had lower mean body weights, mean body weight gains, and food consumption during the exposure period. Male and female rats exposed to 25 ppm and sacrificed immediately after the exposure period had minimally decreased total leukocyte and lymphocyte counts. These changes were considered to be marginally adverse. Pathologic examination revealed hepatocellular hypertrophy in 0-day recovery males and an increased incidence and/or severity in chronic progressive nephropathy in 0-day, 1-month recovery, and 3-month recovery males at 25 ppm. No other pathological changes, including the testis, epididymis, and other accessory sex organs, were noted in rats during the study. Evaluation of sperm parameters at the end of the exposure period showed statistically significant decreases in epididymal sperm number per cauda epididymis, percent motile sperm, and percent normal sperm morphology at 25 ppm. The biological significance of the slight changes observed in the sperm parameters in the absence of histopathological changes is unclear. After a 1-month recovery period, no biologically significant differences in sperm parameters were noted at 25 ppm compared with controls. Exposure to HCC-230fa did not significantly alter the primary humoral immune response to sheep red blood cell (SRBC). Under the conditions of this study, the no-observed-adverse-effect level (NOAEL) was considered to be 2.5 ppm.

Subchronic toxicity of cyclohexane in rats and mice by inhalation exposure.

Inhalation studies were conducted to determine the potential toxicity and/or potential neurotoxicity of cyclohexane. Groups of rats and mice were exposed to 0, 500, 2000, or 7000 ppm concentrations of cyclohexane vapor 6 hr/day, 5 days/week for 14 weeks. Subgroups of rats and mice were further observed during a 1-month recovery period. Functional observational battery (FOB) and motor activity (MA) behavioral tests were conducted on rats. These tests were conducted prior to the exposure series and during weeks 4, 8, and 13 on non-exposure days. Clinical pathology evaluations were conducted after approximately 7, 13, and 18 weeks. Approximately 14 and 18 weeks after study initiation, tissues from rats and mice were histologically processed and evaluated by light microscopy. During exposure to 2000 or 7000 ppm, rats and mice had a diminished response or an absent response to delivery of a punctate auditory alerting stimulus. Immediately following removal of rats from the inhalation chambers, 7000 ppm males and females and 2000 ppm females displayed a compound-related increase in the incidence of wet and/or stained fur (which occurred in the areas of the mouth, chin, and/or perineum). These signs were transient, were not observed during exposure or prior to exposure the following day, and were not associated with any behavioral or morphological changes. During exposure sessions, mice exposed to 7000 ppm exhibited clinical signs of toxicity which included hyperactivity, circling, jumping/hopping, excessive grooming, kicking of rear legs, standing on front legs, and occasional flipping behavior. Clinical signs of toxicity observed in 7000 ppm mice immediately after exposure included hyperactivity, hyperreactivity, ruffled fur (females only), gait abnormalities, spasms in both rear legs, and excessive grooming (males only). The clinical signs observed in mice during and immediately after exposure were transient, and were not present prior to the subsequent exposure. A few mice exposed to 2000 ppm appeared hyperactive during exposure in the latter portion of the study. There were no compound-related changes in mean body weights, body weight gains, food consumption, food efficiency, or mortality; and there were no ophthalmological abnormalities in rats or mice. In addition, there were no compound-related effects on 37 different behavioral parameters assessed during the FOB or during motor activity tests in rats. Male and female mice exposed to 7000 ppm had slight increases in measures of circulating erythrocyte mass (red blood cells, hemoglobin, hematocrit) and plasma protein concentration (males only). Male rats and male and female mice exposed to 7000 ppm had significantly increased relative liver weights, and 7000 ppm male mice also had significantly increased absolute liver weights at the end of the exposure period. At the end of the 1-month recovery period, absolute and relative liver weights of male and female mice were similar to control. However, relative liver weights of 7000 ppm male rats continued to be significantly higher at the end of the recovery period. Male and female rats exposed to 7000 ppm had a significantly increased incidence of hepatic centrilobular hypertrophy at the end of the exposure period, which was not observed at the conclusion of the 1-month recovery period. No microscopic changes were observed in mice. In rats, the no-observed-effect level (NOEL) for acute, transient effects was 500 ppm based on a diminished/absent response to an auditory alerting stimulus at 2000 ppm and above. The NOEL for subchronic toxicity in rats was 7000 ppm based on the lack of adverse effects on body weight, clinical chemistry, tissue morphology, and neurobehavioral parameters. In mice, the NOEL for acute, transient effects was 500 ppm based on behavioral changes during exposure at 2000 ppm and above. The NOEL for subchronic toxicity in mice is 2000 ppm based on hematological changes at 7000 ppm.

Inhalation toxicity of cyclododecatriene in rats.

Cyclododecatriene (CDDT, CAS No. 4904-61-4) was tested for its inhalation toxicity in rats following repeated exposures. Male rats were exposed nose-only to CDDT for 6 hr/day, 5 days/wk for a total of 9 exposures over 2 weeks. Particular attention was paid to neurotoxicologic endpoints. Concentrations of 0 (control), 5, 50, and 260 ppm were studied. The 260 ppm chamber contained both vapor and aerosol while the 5 and 50 ppm chambers were vapor only. Four groups of 10 rats each were used to measure standard clinical signs and growth, clinical pathology (including hematology, biochemistries, and urine analysis), and tissue pathology. Another 4 groups of similar size were used for neurotoxicity testing. In the standard toxicity groups, 1/2 of the rats were sacrificed 1 day following the 9th exposure; the other half underwent a 2-week recovery period prior to being sacrificed (recovery group). During the exposures rats inhaling 260 ppm had a diminished or absent response to an alerting stimulus. Irregular respiration and lethargy were observed in these rats immediately following exposure. These signs were rapidly reversible and were not seen prior to the subsequent exposure. Body weights in rats exposed to either 50 or 260 ppm were significantly lower than the corresponding controls. No compound-related clinical pathology changes were seen in any of the test groups and tissue pathology effects only occurred in the nasal tissue. In rats exposed to 260 ppm, minimal degeneration/necrosis of nasal olfactory epithelium was observed in rats examined immediately following the exposure period. This change was not seen in the recovery rats. Functional observational battery (FOB) assessments and motor activity (MA) evaluations conducted after the 4th and 9th exposures on rats from all test groups, and specific neuropathologic evaluation on perfused brain, spinal cord, and skeletal muscle from rats exposed to 260 ppm failed to demonstrate any specific neurotoxicity. Outward signs of sedation were seen at the top level tested. Under the conditions of this test, the no-observed-adverse-effect level (NOAEL) was determined to be 5 ppm based upon a reduced rate of body weight gain in the 50 ppm group. No specific neurotoxicity was detected and the histopathologic response was limited to reversible changes in the nasal epithelia in rats exposed to 260 ppm.

Complement facilitates macrophage phagocytosis of inhaled iron particles but has little effect in mediating silica-induced lung inflammatory and clearance responses.

Complement-mediated mechanisms are known to play a role in pulmonary inflammation and clearance responses to some types of inhaled particles. The present studies were undertaken to investigate the role of complement in mediating pulmonary inflammation and/or phagocytosis as a function of particle clearance in rats exposed to silica or carbonyl iron (CI) particles. Both particle types were shown to be weak activators of serum complement in vitro. In these studies, normal and complement-depressed (CVF-treated) rats were exposed to aerosols of CI or silica particles for 6 hr at 100 mg/m3. Following exposure, alveolar fluids and cells from sham and dust-exposed animals were recovered by bronchoalveolar lavage (BAL) at several time periods postexposure and measured for a variety of biochemical and cellular indices. In addition, pulmonary macrophages were cultured and studied for morphology and phagocytosis. Our results showed that CI exposure did not produce cellular or biochemical indices of pulmonary inflammation, either in normal or complement-depleted rats. However, fewer phagocytic macrophages were recovered from the lungs of CVF-treated, CI-exposed rats than from normal exposed animals. In contrast, silica inhalation produced a sustained PMN inflammatory response in the lungs of exposed rats, measured up through 1 month postexposure, along with significant increases in BAL fluid levels of LDH, protein, and alkaline phosphatase (P less than 0.05) and deficits in pulmonary macrophage phagocytic functions. Cobra venom factor (CVF) treatment prior to exposure in rats had no significant effect upon the silica-induced parameters, suggesting that complement may not play an important role in the acute pulmonary response to silica. The results indicate that complement may play a role in mediating CI-related macrophage clearance responses but has little effect upon sustained silica-induced pulmonary inflammatory parameters.