BIOPERSISTENCE OF SYNTHETIC MINERAL FIBERS AS A PREDICTOR OF CHRONIC INHALATION TOXICITY IN RATS

In December 1997 the European Commission (EC) adopted Directive 97/69/EC (O.J. L 343/19 of 13 December 1997) in which criteria were established for the classification and labeling of synthetic mineral fibers. This directive was derived based upon an extensive program evaluating current scientific knowledge on fiber pathogenicity and its relationship to the biopersistence of long fibers. Within this context, the biopersistence of fibers longer than 20 µm was found to be a good predictor of the lung burden and early pathological changes in chronic inhalation studies with fibers as well as of the tumor response in chronic intraperitoneal studies with fibers. The analysis that provided the scientific basis for the relationship of biopersistence to the chronic inhalation results is presented in detail. Proportional odds regression techniques were used to determine the relationship between both inhalation and intratracheal instillation biopersistence clearance half-times and the collagen deposition at the broncho-alveolar junction as determined following 24 mo in chronic inhalation toxicity studies. The results indicate all the indicators of biopersistence considered are equally good predictors of the early long-term change that occurs in the lung in response to more durable fibers. This change, the collagen deposition at the broncho-alveolar junction, is a precursor of interstitial fibrosis, which has been shown to be associated with tumor response in fiber-exposed animals. The results show that the clearance half-times set in the EC directive are within the baseline for this parameter.     

CHRONIC INHALATION TOXICITY AND CARCINOGENICITY STUDIES ON-CHLOROPRENE IN RATS AND HAMSTERS

Three groups of 100 Wistar rats and Syrian golden hamsters of each sex were exposed by inhalation to 0, 10, or 50 ppm (v/ v)-chloroprene for 6 h/day, 5 days a week for up to 24 and 18 mo, respectively. To maintain the chemical Integrity of this highly reactive material in the exposure chambers,-chloroprene vapor was generated from freshly distilled chloroprene (99.6% -chloroprene; 0.3% -chloroprene and <50 ppm chloroprene dimers) by passing nitrogen through liquid-chloroprene at 0 C. This mixture was then conducted through Teflon and stainless steel transport tubes into the main airflow for the chambers. After 72 wk on test a technical fault in chamber operation procedures resulted in the accidental death of 87 male and 73 female rats at 10 ppm unrelated tochloroprene. Otherwise, survival of the remaining 10 ppm rats and the rats exposed at 50 ppm was unaffected by exposure. Survival among both groups of hamsters exposed to-chloroprene was higher than the controls. All treated rats exhibited slight restlessness during exposure, but only during the first few weeks on test. At 50 ppm, rats also showed an increased incidence of alopecia, slight growth retardation, and an increased incidence of foci of altered liver cells, a change frequently seen in aged rats. Hamsters showed only a slight growth retardation and a slight reduction in amyloidosis at 50 ppm. No serious adverse effects were seen in either species at 10 ppm. Overall, there was no evidence of carcinogenicity related to-chloroprene exposure in either rats or hamsters at vapor concentrations as high as 50 ppm.     

A CHRONIC INHALATION TOXICITY/ONCOGENICITY STUDY OF METHYLETHYLKETOXIME IN RATS AND MICE

To evaluate the oncogenic potential of methylethylketoxime (MEKO), CD-1 mice (50/sex/group) and F-344 rats (50/sex/group) were coexposed 6 h/day, 5 days/wk for 18 mo (mice) or 26 mo (rats) via whole-body inhalation exposures to target vapor concentrations of 0, 15, 75, and 375 ppm (actual concentrations of 0, 15 ± 1, 75 ± 2, or 374 ± 10 ppm). Satellite groups of rats and mice (10/sex/group/interval) were exposed for 12 mo (mice) and 3, 12, or 18 mo (rats) to evaluate chronic toxicity. Methyl ethyl ketone (MEK), a possible hydrolysis product of MEKO, was present at less than 1%. Treatment-related effects included increased body weight (male rats only), methemoglobin formation, hematology and clinical chemistry changes, increased liver weight, and increased spleen and testes weights (rats only). A high incidence of cataracts and corneal dystrophy occurred in both control and MEKO-exposed rats, with an earlier appearance and slightly higher incidence for these ocular lesions in MEKO-exposed animals compared to controls. Degenerative and reparative changes of the olfactory epithelium in the nasal turbinates, primarily limited to the dorsal meatus, occurred in both rats (75 and 374 ppm) and mice (15, 75, and 374 ppm). In addition, in the mice, liver changes included increased incidences of pigment in reticuloendothelial cells, centrilobular hypertrophy, granulomatous inflammation, and a slightly increased incidence of necrosis (75 and 374 ppm). An increase in hepatocellular carcinomas occurred in male mice at 374 ppm. Additional MEKO-related findings in the rat included congestion of the spleen with pigment in reticuloendothelial cells and extramedullary hematopoiesis and a decreased incidence of lymphoreticular mononuclear cell leukemia. Effects observed in the liver of the rats included decreases in the incidence of both peribiliary fibrosis and hyperplasia/proliferation of the biliary duct, an increase of spongiosis hepatis in males, and an increase in the incidence of intracytoplasmic vacuoles and hepatocellular basophilic foci. The effects on the liver were generally most profound in the high-exposure groups and, with the exception of the spongiosis hepatis, occurred in both sexes. An increase in hepatocellular adenomas occurred in the male rats at 75 and 374 ppm, and hepatocellular carcinomas in the male rats at 374 ppm. In both species, the liver tumors appeared relatively late in the life of the animals, with no significant increase in tumors at 12 mo of exposure in mice and at 18 mo of exposure in rats. Lifespan shortening was not observed, as MEKO-exposed animals survived generally as well as, or slightly better than, the controls.     

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 twoweek 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.     

INHALATION TOXICITY OF POTASSIUM OCTATITANATE FIBERS (TISMO) IN RATS FOLLOWING 13 WEEKS OF AEROSOL EXPOSURE

One hundred and forty male and 140 female rats were divided into 1 control and 3 test groups of 35 rats each, per sex, and exposed by whole-body inhalation to test compound at target concentrations of 0, 1 mg/m³ (1700 fibers/cm³, 123 WHO fibers/cm³), 10 mg/m³ (5900 fibers/cm³, 952 WHO fibers/cm³), and 100 mg/m³ (112,700 fibers/cm³, 7440 WHO fibers/cm³) for 6 h/day, 5 days/wk for 13 wk. Ten rats from each group were killed after 13 wk of exposure and 13 wk of recovery, respectively, for histopathological evaluation. The other 15 rats from each group were killed to study lung clearance after 91 days of exposure, and approximately 1.5 and 3 mo of recovery following the end of the 13 wk of exposure. The mean fiber length of the chamber atmosphere was 2.8, 2.7, and 2.8 µm, while the mean fiber width was 0.48, 0.48, and 0.45 µm for the 1-, 10-, and 100-mg/m³ chambers, respectively. In the 1-mg/m³ (123 WHO fibers/cm³) exposure group, inhaled particles were mostly retained in a few fiberladen alveolar macrophages (AMs) within the alveoli adjacent to alveolar ducts without any adverse tissue response throughout 13 wk of exposure and following 13 wk of recovery. This exposure concentration was considered to be a no-observable-adverse-effect level (NOAEL), since the alveoli containing fiber-laden AMs preserved normal structure. After 13 wk of exposure to 10 mg/m³ (952 WHO fibers/cm³), fiber-laden AMs were mainly retained at the alveoli adjacent to the alveolar ducts. Infrequently, slight fibrotic thickening was observed in the alveolar ducts and adjoining alveoli, with proliferating fibroblasts and hyperplastic Type II pneumocytes, and microgranulomas. Occasionally, trace amounts of collagenous material were deposited in the thickened alveolar ducts and adjoining alveolar walls. In addition, minimal alveolar bronchiolarization was occasionally found in the alveoli adjacent to the terminal bronchioles. The peribronchial lymphoid tissue and thymic lymph nodes contained migrated fiber-laden AMs. After 13 wk of recovery, fiber-laden AMs had mostly disappeared from alveoli located in the peripheral acini, but they localized in the alveolar ducts region, suggesting there was active lung clearance of fibers by the AMs via airways. Thickened alveolar ducts and adjacent alveoli were decreased in thickness, a reversible change manifested by reduction of proliferating Type II pneumocytes and fibroblasts. Collagenized fibrosis was slightly more pronounced in the thickened alveolar ducts and adjoining alveoli. The lung response following 13 wk of exposure to 100 mg/m³ (7440 WHO fibers/cm³) and after 13 wk of recovery was similar to those findings of the 952 WHO fibers/cm³ group but more pronounced, demonstrating a clear concentration-related response. Alveolar ducts and adjoining alveolar walls in the central acini were irregularly thickened with more frequent evidence of minimal collagenized fibrosis. The lung burden and clearance of fibers were estimated by measuring the total content of titanium (Ti) in the lungs, but high variability of Ti content in control and exposed groups prevented meaningful lung clearance analysis.     

INHALATION TOXICITY OF 4-ETHOXYANILINE (p -PHENETIDINE): CRITICAL ANALYSIS OF RESULTS OF SUBACUTE INHALATION EXPOSURE STUDIES IN RATS

This article addresses results from a single 4-h and repeated 1- and 4-wk inhalation exposure studies in Wistar rats with vapor and/or aerosol atmospheres of 4-ethoxyaniline (p -phenetidine). Groups of 10 rats/sex were exposed nose-only to mean analytical concentrations of 11.1, 86.2, and 882.6 mg p -phenetidine/m 3 using an exposure regimen of 6 h/day, 5 days/wk for 4 wk. Concentrations were selected based on results from a pilot study in which rats were exposed under identical conditions on 5 consecutive days for 6 h/day to mean analytical concentrations of 38.2, 133.0, and 1247.6 mg/m 3. In repeated exposure studies, the focus of endpoints was on hematotoxicity. The LC50 was not determined, but no rats died following a single 4-h exposure to 5085 mg/m 3 as a mixture of vapor and aerosol. No mortality was observed either in the 1- or 4-wk studies. Rats exposed to 882.6 mg/m 3 and above evoked characteristic signs of toxicity that included cyanosis, with no apparent progression of findings during the exposure period. Animals exposed to 86.2 mg/m 3 and above exhibited a concentration-dependent, significant increase in blood methemoglobin and reticulocyte counts as well as a significant decrease in hemoglobin, hematocrit, and red blood cell counts. Spleen weights were significantly increased in groups exposed to 133.0 mg/m 3 and above. Microscopic changes demonstrated an increased hematopoiesis (bone marrow smears) and splenic hemosiderosis at 86.2 and 882.6 mg/m 3 and a hepatic hemosiderosis only at 882.6 mg/m 3. These data suggest that the toxicity of p -phenetidine is similar to that of its structural analog aniline. Based on the erythrocytotoxicity occurring at 86.2 mg/m 3 and above, including the apparent reactive changes in bone marrow (increased erythropoiesis) and spleen (increased erythroclasia), the no-observed-adverse-effect level (NOAEL) of the 4-wk study was 11.1 mg/m 3 air and that of the 1-wk study was 38.2 mg/m 3 air. This difference in NOAELs is considered to be related to the selection of exposure concentrations rather than cumulative toxicity.     

BIOPERSISTENCE OF SYNTHETIC MINERAL FIBERS AS A PREDICTOR OF CHRONIC INTRAPERITONEAL INJECTION TUMOR RESPONSE IN RATS

In December 1997 the European Commission (EC) adopted Directive 97/69/EC (O.J. L 343/19 of 13 December 1997), in which criteria were established for the classification and labeling of synthetic mineral fibers. This directive was derived based upon an extensive program evaluating current scientific knowledge on fiber pathogenicity and its relationship to the biopersistence of long fibers. Within this context, the biopersistence of fibers longer than 20 µm was found to be a good predictor of the lung burden and early pathological changes in chronic inhalation studies with fibers as well as of the tumor response in chronic intraperitoneal studies with fibers. The analysis that provided the scientific basis for the relationship of biopersistence to the chronic intraperitoneal (ip) results is presented in detail. Analysis of the relationship of biopersistence clearance half-times to ip tumor response shows a statistically significant relationship of ip tumor response to not only the number of fibers injected, but also the median length of the fibers injected and their solubility (clearance half-time). The results show that the biopersistence half-times as determined by intratracheal instillation (T 1/2 of WHO fibers or weighted T 1/2 of fibers with L > 20 µm) and as determined by inhalation (weighted T 1/2 of fibers with L > 20 µm) are equivalent predictors of the ip results. From these ip studies, fibers that can be exonerated from classification as carcinogens in Europe have a relative tumorigenic potency in the ip cavity of between 66 and 2500 times less than fibers that have been shown to produce a significant increase in tumors following chronic inhalation exposure. In addition, based upon the ip results, there is no statistical difference between the EC and the other fiber exoneration criteria, such as the German Gefahrstoffverordnung of 1999.     

STUDIES ON THE INHALATION TOXICOLOGY OF TWO FIBERGLASSES AND AMOSITE ASBESTOS IN THE SYRIAN GOLDEN HAMSTER. PART II. RESULTS OF CHRONIC EXPOSURE

Fiberglass (FG) is the largest category of man-made mineral fibers (MMVFs). Many types of FG are manufactured for specific uses-building insulation, air handling, filtration, and sound absorption. In the United States, > 95% of FG produced is for building insulation. Several inhalation studies in rodents of FG building insulation have shown no indication of pulmonary fibrosis or carcinogenic activity. However, because of increasing use and potential for widespread human exposure, a chronic toxicity/carcinogenicity inhalation study of a typical building insulation FG (MMVF 10a) was conducted in hamsters, which were shown to be highly sensitive to the induction of mesotheliomas with another MMVF. A special-application FG (MMVF 33) and amosite asbestos were used for comparative purposes. Groups of 140 weanling male Syrian golden hamsters were exposed via nose-only inhalation for 6 h/day, 5 days/wk for 78 wk to either filtered air (chamber controls) or MMVF 10a, MMVF 33, or amosite asbestos at 250-300 WHO fibers/cm3 with two additional amosite asbestos groups at 25 and 125 WHO fibers/cm3. They were then held unexposed for 6 wk until 10-20% survival. After 13, 26, 52, and 78 wk, various pulmonary parameters and lung fiber burdens were evaluated. Groups hamsters were removed from exposure at 13 and 52 wk and were held until 78 wk (recovery groups). Initial lung deposition of long fibers (> 20 mum in length) after a single 6-h exposure was similar for all 3 fibers exposed to 250-300 fibers/cm3. MMVF 10a lungs showed inflammation (which regressed in recovery hamsters) but no pulmonary or pleural fibrosis or neoplasms. MMVF 33 induced more severe inflammation and mild interstitial and pleural fibrosis by 26 wk that progressed in severity until 52 wk, after which it plateaued. While the inflammatory lesions regressed in the recovery animals, pulmonary or pleural fibrosis did not. A single multicentric mesothelioma was observed at 32 wk. No neoplasms were found in the remainder of the study. Amosite asbestos produced dose-related inflammation and pulmonary and pleural fibrosis as early as 13 wk in all 3 exposure levels. The lesions progressed during the course of the study, and at 78 wk severe pulmonary fibrosis with large areas of consolidation was observed in the highest 2 exposure groups. Progressive pleural fibrosis with mesothelial hypertrophy and hyperplasia was present in the thoracic wall and diaphragm in most animals and increased with time in the recovery hamsters. While no pulmonary neoplasms were observed in the amosite exposed hamsters, a large number of mesotheliomas were found; 25 fibers/cm3, 3.6%; 125 fibers/cm3, 25.9%; and 250 fibers/cm3, 19.5%. For the 3 fiber types, the severity of the lung and pleural lesions generally paralleled the cumulative fiber burden, especially those >20 mum length, in the lung, thoracic wall, and diaphragm. They also inversely paralleled the in vitro dissolution rates; that is, the faster the dissolution, the lower were the cumulative lung burdens and the less severe the effects.     

A MINIREVIEW OF CHRONIC ANIMAL INHALATION STUDIES WITH MAINSTREAM CIGARETTE SMOKE

This work was performed to verify whether or not the inhalation response to cigarette smoke in animal species for assessing carcinogenic potential in humans reflects the strong epidemiological evidence in human smokers. Significant increases in the numbers of malignant tumors of the respiratory tract were not seen in rats, mice, hamsters, dogs, or nonhuman primates exposed for long periods of time to very high concentrations of mainstream cigarette smoke. The results are clearly at variance with the epidemiological evidence in smokers, and it is difficult to reconcile this major difference between observational studies in humans and controlled laboratory studies.     

REPEATED EXPOSURE INHALATION STUDY OF PENTANE IN RATS

Pentane (CAS No. 109-66-0) is a chemical being used as a co-solvent in a polymer production facility with potential for inhalation exposure in humans. To assess the toxicity of pentane, groups of 10 male rats each were exposed by inhalation, 6 hr/day, 5 days/week for 2 weeks to either 0 (control), 1,000, 3,000 or 10,000 ppm. Five rats per group were killed following the 10th exposure; the remaining 5/group were killed after a 14-day post-exposure recovery period. Parameters investigated were clinical signs of toxicity, functional behavior, body weights, clinical pathology, and gross and microscopic pathology including organ weights. No unusual clinical observations were seen in the pentane-treated rats, and body weights were not altered. Test rats generally exhibited normal behavioral responses in the functional observational battery. Increases in serum calcium and phosphorus concentrations were seen in rats exposed to either 3,000 or 10,000 ppm. These were reversible during the 2-week recovery period. No other clinical pathology changes were observed and no pentane-related tissue pathology was seen in any of the groups. The no-observed-adverse-effect level was 1,000 ppm with reversible clinical pathology changes produced at 3,000 and 10,000 ppm.     

ACUTE AND SUBCHRONIC NEUROTOXICOLOGICAL EVALUATION OF TETRAHYDROFURAN BY INHALATION IN RATS

Groups of adult male and female rats received exposure to tetrahydrofuran (THF) vapor by inhalation in acute or subchronic exposure scenarios. Acute exposure concentrations were 0, 500, 2500, or 5000 ppm for 6 hr. Evaluations conducted immediately after exposure included clinical observations, motor activity assessments (MA), and a battery of functional tests (FOB) designed to reveal nervous system dysfunction. During exposure to 2500 and 5000 ppm, rats had a diminished or absent startle response to a punctate auditory alerting stimulus. Following exposure to 5000 ppm, male and female rats were lethargic, exhibited abnormal gait or mobility, and splayed rear feet. Lethargy and splayed rear feet were also observed in females esposed to 2500 ppm. During the subsequent FOB, males exposed to 5000 ppm had a lower incidence of palpebral closure, higher incidences of slow or absent righting reflex, and a biphasic pattern of reduced motor activity followed by increased motor activity. Females exposed to 5000 ppm had increased incidences of palpebral closure in the open field, increased incidences of slow or absent righting reflex, and decreased motor activity.

During the 14-week subchronic exposure series, daily THF exposure concentrations were 0, 500, 1500, or 3000 ppm, and neurobehavioral evaluations occurred on non-exposure days at approximately monthly intervals. Diminished startle responses to an auditory alerting stimulus were observed during exposure to 1500 or 3000 ppm; however, repeated exposures did not cause additional neurobehavioral or pathological effects. This pattern of effects is suggestive of transient sedation. Despite daily reinstatement of acute sedative effects during repeated exposure with up to 3000 ppm, THF did not produce any persistent or cumulative effects on nervous system structure or function. The demonstrated no-observed-effect level of THF for both acute and subchronic exposure was 500 ppm.     

A RETROSPECTIVE REVIEW OF THE CARCINOGENICITY OF REFRACTORY CERAMIC FIBER IN TWO CHRONIC FISCHER 344 RAT INHALATION STUDIES: An Assessment of the MTD and Implications for Risk Assessment

The purpose of this article is to review previous chronic inhalation studies in rats with refractory ceramic fiber (RCF), the mathematical modeling efforts to describe the deposition, clearance, and retention of RCF fiber in the rat and human, and the concept of ''overload,'' and to assess the possibility that the maximum tolerated dose (MTD) was exceeded. Lastly, based on recent biopersistence and pulmonary clearance studies of several investigators with a particulate-free RCF, we examine the potential impact on the chronic RCF rat bioassay of coexposure to both RCF particulate and RCF fibers. The review concludes, inter alia, that RCF particulate coexposure probably had a major impact on the observed chronic adverse effects, that the MTD was probably exceeded at the highest exposure concentration of 30 mg/m3 in the rat bioassay, and that inclusion of the highest dose in the risk assessment process may overstate human health risk if a linear rather than nonlinear model is used.     

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.     

REGIONAL BRAIN DOSIMETRY OF TRICHLOROETHANE IN MICE AND RATS FOLLOWING INHALATION EXPOSURES

While certain neuroactive volatile organic compounds (VOCs) have been reported to have an uneven distribution in various anatomically distinctive brain regions, this has not yet been reported for the short-chain aliphatic halogenated hydrocarbons. Therefore, the uptake and regional brain distribution of 1,1,1-trichloroethane (TRI) in mice and rats following inhalation exposure were examined. Male Sprague-Dawley rats and CD-1 mice were exposed to TRI at either 3500 or 5000 ppm for 10, 30, 60, or 120 min. Seven brain regions from rats and three from mice were sampled, and TRI concentrations in the blood and brain tissues were determined by headspace gas chromatography. In both species, the medulla oblongata was found to have the highest TRI concentrations, while cortex (in both species) and hippocampus (only sampled in rats) contained the lowest TRI concentrations. Substantial differences were also observed between the two species, as the mice exhibited higher capacity to accumulate TRI in the blood as well as in the brain regions. It appears that lipid content is a main factor influencing the differential disposition of TRI among the brains regions. Physiological differences in the respiratory systems of the two species and the physiochemical properties of the chemical favoring diffusion toward lipid-rich compartments could also have been expected to account for the patterns of regional distribution and species differences.     

DISSOLUTION OF FIBERS INHALED BY RATS

Abstract

This article provides an analysis and an interpretation of the results of an inhalation study of the durability of several man-made vitreous fiber (MMVF) insulation wool samples in rats. The study was sponsored by the Thermal Insulation Manufacturers Association and was conducted by the Research and Consulting Company in Geneva with fiber size measurements made by Schuller Mountain Technical Center in Denver, CO. In this study, rats were exposed for 5 days to 4 types of airborne, respirable-sized MMVF and to crocidolite asbestos fibers. The MMVF included two compositions of glass wool, and one each of rock and slag wool. After exposure, animals were sacrificed at intervals up to 18 mo, and the number, length, and diameter of a representative sample of fibers in their lungs were measured. These data show that the long fibers (>20 μm) are eliminated from the rats' lungs at a rate that is predicted from the dissolution rate measured in vitro for these fiber compositions. In particular, the long MMVF were nearly completely eliminated in several months, whereas the long crocidolite asbestos fibers remained in significant numbers at the end of the study. The number, length, and diameter distributions of fibers remaining in the rats' lungs agreed well with a computer simulation of fiber clearance. This simulation assumed that the long fibers dissolved at the rate measured for each fiber in vitro, and that the short fibers of every type were removed at the same rate as short crocidolite asbestos. The results are strong evidence that long MMVF are cleared by complete dissolution at the rate measured in vitro and that short fibers do not dissolve but are cleared by macrophage-mediated physical removal.     

RENAL KALLIKREIN IN CHRONIC HYPOXIC RATS

1. We have studied the role of kallikrein (KK) in the maintenance of renal function in chronic hypoxic rats (high altitude; HA), compared with control rats kept at sea level (SL). Hypoxia was induced by placing female Wistar rats (198-290 g) in an altitude chamber (5500m) 15 h/day for 4 weeks. Experiments were also conducted to study the interaction of KK with renal nerve activity and endothelin (ET), two parameters previously shown to be altered in this model. 2. It was found that renal cortex tissue KK activity (TKA) was not significantly different in 10 SL and 10 HA rats. However, the urinary KK activity (UKA) was reduced nearly to half (from 35.2±4.6 to 18.5±1.7 pkat/min) in HA rats after 4 weeks of chronic hypoxia. 3. Acute renal denervated diuresis was accompanied by a significant increase in UKA (from 9±2 to 14±2 pkat/min in HA and denervated HA rats, respectively; P < 0.05) in HA rats. Intrarenal arterial pretreatment of aprotinin reduced the denervated diuresis. 4. Endothelin (600 ng/kg per h) reduced urine flow, sodium and potassium excretion in the ipsilateral kidney in another 10 SL and 10 HA rats. The extent of the drop of these parameters was significantly less in HA rats. Urinary KK activity was correlated significantly with the measured renal functional parameters (r ranging from 0.472 to 0.612) in SL rats, but was insignificant in HA rats (r ranging from 0.032 to 0.192). 5. We have demonstrated that chronic exposure to hypoxia decreases urinary KK excretion and that KK is involved in acute renal denervated diuresis generated in these animals. The present study suggests that KK plays a partial role in the maintenance of renal function in chronic hypoxic rats.     

EFFECT OF CHRONIC TREATMENT WITH AMLODIPINE IN NON-INSULIN-DEPENDENT DIABETIC RATS

We have investigated the effects of amlodipine on streptozotocin- (STZ) induced neonatal non-insulin-dependent diabetes mellitus (NIDDM) rats. NIDDM was induced by intraperitoneal injection of STZ (70 mg kg⁻¹) to 5-day-old rat pups. The animals were weaned at 30 days and maintained with food and waterad libitumfor 3 months. Amlodipine (5 mg kg⁻¹p.o.) was administered for 6 weeks after the animals were confirmed diabetic (3 months after the STZ injection). A group of control animals were also maintained and this group received citrate buffer 5 days after birth. Fasting- and fed-glucose levels in NIDDM rats were significantly higher than control rats. Treatment with amlodipine reduced the elevated fasting- and fed-glucose levels significantly. Results of the oral glucose tolerance test (OGTT) revealed that glucose tolerance is impaired in the NIDDM rats. There was a marked increase in glucose levels after oral administration of glucose in the control NIDDM rats. Increased glucose levels were found to be associated with increased insulin levels. Treatment with amlodipine in the NIDDM rats caused a decrease in insulin release, however, glucose levels were found to be lowered significantly indicating that amlodipine causes an increase in insulin sensitivity. In conclusion, our data indicated that amlodipine increases insulin sensitivity in neonatal-STZ NIDDM rats.     

[~(14)C]亮菌甲素微囊的药动学

报告两种亮菌甲素微囊混悬剂在大鼠im后的药动学,并与溶液剂进行比较.结果表明,两种亮菌甲素微囊平均吸收时间6.9h,为溶液剂的30倍;生物利用度为溶液剂的136%.预计须要达到稳态浓度为10μg/ml时,im微囊混悬剂60mg/kg时的给药间隔为4h,微囊B囊壁成分增加了油酸乙酯,但药动学参数与微囊A没有显著差异.