Acute nose-only inhalation exposure of rats to di- and triphosgene relative to phosgene

Groups of young adult Wistar rats were acutely exposed to trichloromethyl chloroformate (diphosgene) and bis(trichloromethyl) carbonate (triphosgene) vapor atmospheres using a directed-flow nose-only mode of exposure. The exposure duration used was 240?min. The median lethal concentration (LC₅₀) of diphosgene and triphosgene was 13.9 and 41.5?mg/m³, respectively. Based on the molar exposure concentrations, the LC₅₀s of phosgene (previously published), diphosgene, and triphosgene were 0.07, 0.07, and 0.14 mmol/m³, respectively. Although the principal toxic mode of action of the volatile diphosgene was similar to phosgene gas, the vapor phase of triphosgene appeared to be different to that of phosgene and diphosgene based on a more persistent occurrence of signs of respiratory distress and a biphasic onset of mortality. While all substances caused mortality within 1 day postexposure, triphosgene induced a second phase of mortality 11–14 days postexposure. The vapor saturation concentration of triphosgene at ambient temperature is ≈100 times its LC₅₀. In summary, triphosgene-induced lung injury patterns are different from that of phosgene and diphosgene. More research is needed to close the substantial data gaps of triphosgene.     

Respiration of F344 rats in nose-only inhalation exposure tubes

The respiration of naive F344 rats confined in nose-only inhalation exposure tubes was measured to obtain data for normal adult rats of different ages and to evaluate the tubes for exposures lasting several hours. Exposure tubes were modified for use as volume-displacement plethysmographs. Respiration of 10 male and 10 female rats at 3, 6, 12 and 24 months of age was measured in the tubes during simulated exposures of up to 6 h duration. Measurements included respiratory frequency, tidal volume, minute volume and body surface temperature. The mean respiratory frequencies of 3, 6, 12 and 24 month old rats during the first hour of exposure were 172, 152, 123 and 136 breaths min-1, respectively. Minute volumes were 1.40, 0.89, 0.67 and 0.82 ml g-1 body weight, respectively. Both frequency and minute volumes g-1 body weight were significantly greater for the youngest group, declined with age to 12 months and then increased at 24 months. Minute volumes g-1 body weight were similar for males and females. Minute volume and respiratory frequency of 3 and 12 month old rats declined progressively between 1 and 6 h of confinement in the tubes. Surface temperature did not increase after the first hour. The age and sex-specific data provide a basis for predicting respiration of naive tube-confined rats during inhalation exposures to non-irritating materials.     

Lack of effects of nose-only inhalation exposure on testicular toxicity in male rats.

Reductions in testicular mass, sperm motility, and mating frequency have been attributed to the stresses caused by confinement of Sprague-Dawley male rats in nose-only inhalation exposure tubes. Testicular changes, including an increase in testicular atrophy, have been detected at an increased incidence in male rats used in inhalation studies as compared with rats of the same age and strain used in oral toxicity studies. This study was designed to determine whether nose-only exposure of male rats caused testicular toxicity under conditions of cooling of the exposure room and appropriate acclimation to the exposure tubes. In order to acclimate the rats to the nose-only inhalation exposure apparatus, all male rats were placed in the exposure tubes for at least four successively increasing time intervals (15, 30, 45, and 60 min) on 4 separate days, with a rest period of approximately 48 h between the first and second acclimation. Twenty male rats were exposed nose-only to filtered air for approximately 2 h per day for 28 days before cohabitation and continuing throughout a 14-day cohabitation period. To reduce thermal stress, the exposure room temperature was maintained at 64 to 70 degrees F. Twenty control rats were housed in the same room as the exposed rats but were not placed in exposure tubes. End points monitored were body weight, testicular weight, sperm count, sperm motility, and histopathology of the testes, epididymides, prostate, and seminal vesicles. The control rats gained weight more rapidly than the exposed rats. All the rats in both groups mated successfully, and testicular weights, normalized to body weight, were similar for both groups. More importantly, there were no microscopic changes that could be considered an adverse effect on the reproductive tissues in the male rats placed in exposure tubes. Thus, nose-only exposure for up to 2 h per day for a total of 42 days did not cause adverse effects on the reproductive organs, fertility, or reproductive performance of male rats under the conditions of this study.     

Evaluation of newly developed nose-only inhalation exposure chamber for nanoparticles

In this study, a direct-flow-type nose-only exposure chamber developed for inhalation toxicity experiments using a numerical analysis and experiments is evaluated. Maintaining a uniform flow rate and test article concentration are the critical factors when designing an inhalation exposure chamber. Therefore, this study evaluated whether the flow rate and particle size distribution at the injection nozzles at each port could be maintained with a deviation below 10%. To achieve this requirement, a nose-only exposure chamber flow field was simulated using a numerical analysis method, i.e. computational fluid dynamics (CFD) code FLUENT 6.3.26. Based on the simulation results, a test chamber was built and tested. The flow velocity was measured at the injection nozzle of the chamber and the aerosol particle size distribution was also measured at each port while inserting the test material into the exposure chamber. The results indicated that a uniform flow field distribution at each stage and port, the deviation of the flow velocity, and particle size distribution were all within 10%. Thus, the resulting nose-only exposure chamber could be described as well-designed.     

Acute nose-only exposure of rats to phosgene. Part I: concentration x time dependence of LC50s, nonlethal-threshold concentrations, and analysis of breathing patterns

Groups of young adult Wistar rats were acutely exposed to phosgene gas using a directed-flow nose-only mode of exposure. The exposure durations used were 10, 30, 60, and 240 min and the corresponding C x t products bracketed a range from 1538 to 2854 mg/m3 x min. The postexposure period was 2 wk. Subgroups of rats were subjected to respiratory function measurements. With few exceptions, mortality occurred within 24 h after exposure. The median lethal concentration (LC50) and the estimated nonlethal threshold concentrations (LC01) for 10, 30, 60, and 240 min were 253.3 (105.3), 54.5 (29.2), 31.3 (21.1), and 8.6 (5.3) mg/m3, respectively. With regard to the fixed outcome Cn x t product, the exponent n was found to be approximately 0.9 for both the LC50 and the LC01. Due to an apparent rodent-specific transient depression in ventilation, results from 10-min exposures were excluded for the calculation of average C x t products. The average LCt50 (and confidence interval 95%) and LCt01 were 1741 (1547-1929) mg/m3 x min and 1075 mg/m3 x min, respectively, with a LCt50/LCt01 ratio of 1.6. Respiratory function measurements revealed an increased apnea time (AT), which is typical for lower respiratory tract irritants. This response was associated with transiently decreased respiratory minute volumes. Borderline, although distinct, changes in AT occurred at 1.2 x 30 mg/m3 x min and above, which did not show evidence of recovery during a 30-min postexposure period at 47.6 x 30 mg/m3 x min and above. In an ancillary study, one group of rats was exposed to 1008 mg/m3 x min (at 4.2 mg/m3 for 240 min; postexposure period 4 wk). Emphasis was on the time course of nonlethal endpoints (bronchoalveolar lavage, BAL) and histopathology of the lungs of rats sacrificed at the end of the 4-wk postexposure period. The climax of BAL protein was on the first postexposure day and exceeded approximately 70 times the control without causing mortality. The changes in BAL protein resolved within 2 wk. Histopathology did not show evidence of lung remodeling or progressive, potentially irreversible changes 4 wk postexposure. In summary, the analysis of the C x t dependent mortality revealed a steep C x t mortality relationship. The C x t product in the range of the nonlethal threshold concentration (1008 mg/m3 x min) caused pulmonary injury as indicated by markedly increased protein in BAL. Changes resolved almost entirely within the 4-wk postexposure period.     

Acute nose-only exposure of rats to phosgene. Part II. Concentration x time dependence of changes in bronchoalveolar lavage during a follow-up period of 3 months

Groups of young adult male Wistar rats were acutely exposed to phosgene gas for either 30 or 240 min using a directed-flow nose-only mode of exposure. In 30-min exposed rats the concentrations were 0.94, 2.02, 3.89, 7.35, and 15.36 mg/m3, which relate to C x t products of 28.2, 60.6, 116.7, 220.5, and 460.8 mg/m3 x min. In 240-min exposed rats the concentrations were 0.96, 0.387, 0.786, 1.567, and 4.2 mg/m3, which relate C x t products of 47.0, 92.9, 188.6, 376, and 1008 mg/m3 x min. Six rats/group were sacrificed on postexposure days 1, 3, 7, 14, and 84, while the rats of the 1008 mg/m3 x min group where sacrificed on postexposure days 1, 7, 14, and 28. The focus of measurements was directed toward indicators of inflammatory response and increased transmucosal permeability in bronchoalveolar lavage (BAL), including lung weights. Lungs from rats sacrificed at the end of the postexposure period were additionally examined by histopathology. Mortality did not occur at any C x t product. The most pronounced changes were related to C x t-dependent increases in the following markers in BAL: protein, soluble collagen, polymorphonuclear leukocytes (PMN) counts, and alveolar macrophages with foamy appearance. These indicators were maximal on the first postexposure day, while total cell counts and alveolar macrophages containing increased phospholipids reached their climax around post-exposure day 3. At 1008 mg/m3 x min the most sensitive indicators in BAL, that is, protein, PMN, and collagen, resolved within 2 wk, whereas at lower C x t products they reached the level of the control by postexposure day 7. At 1008 mg/m3 x min (day 28), histopathology revealed a minimal to slight hypercellularity in terminal bronchioles with focal peribronchiolar inflammatory infiltrates and focal septal thickening. At lower C x t products (day 84) the rats from all groups were indistinguishable and Sirius red-stained lungs did not provide evidence of late-onset sequelae, such as fibrotic changes or collagen deposition. At similar C x t products the changes in BAL were slightly less pronounced using 30-min exposure periods when compared to 240-min exposure periods. In summary, the phosgene-induced transmucosal permeability caused a C x t-dependent increase of several BAL indicators, of which those of protein, PMN, and soluble collagen were most pronounced. Exposure intensities up to 116.7 mg/m3 x min did not cause changes different from those observed in controls, while at 188.6 mg/m3 x min distinct differences to the control existed. Despite the extensively increased airway permeability, histopathology did not provide evidence of lung tissue remodeling or irreversible sequelae.     

Evaluation of newly developed nose-only inhalation exposure chamber for nanoparticles

In this study, a direct-flow-type nose-only exposure chamber developed for inhalation toxicity experiments using a numerical analysis and experiments is evaluated. Maintaining a uniform flow rate and test article concentration are the critical factors when designing an inhalation exposure chamber. Therefore, this study evaluated whether the flow rate and particle size distribution at the injection nozzles at each port could be maintained with a deviation below 10%. To achieve this requirement, a nose-only exposure chamber flow field was simulated using a numerical analysis method, i.e. computational fluid dynamics (CFD) code FLUENT 6.3.26. Based on the simulation results, a test chamber was built and tested. The flow velocity was measured at the injection nozzle of the chamber and the aerosol particle size distribution was also measured at each port while inserting the test material into the exposure chamber. The results indicated that a uniform flow field distribution at each stage and port, the deviation of the flow velocity, and particle size distribution were all within 10%. Thus, the resulting nose-only exposure chamber could be described as well-designed.     

Adaptation to stress induced by restraining rats and mice in nose-only inhalation holders

There are limited data on the efficacy of procedures for adapting rodents to restraint in nose-only holders. We examined: (1) What effect does restraint in nose-only holders have on heart rate and body temperature? (2) Does a gradual increase in the duration of restraint facilitate adaptation? (3) How long does it take for rodents to become fully adapted to nose-only holders? (4) Do rats and mice respond and adapt similarly to restraint in nose only holders? Heart rate and body temperature were monitored as measures of stress using electrocardiograph (ECG) transmitters in male C57Bl/6J mice and Sprague-Dawley rats. In naive animals during the first hour of restraint, heart rate increased by 58 beats per minute (BPM) (18.6%) in rats and by 174 BPM (32.3%) in mice as compared to cage controls. Temperature increased by 2 degrees C in mice and was unchanged in rats compared to cage controls. Heart rate and temperature values remained within normal physiologic values during restraint. In rats, the response to restraint in nose-only holders was the same after 4 days regardless of whether the duration of restraint was increased gradually to 4 h/day or kept constant at 4 h/day. In mice, the group that was gradually adapted had a statistically significant higher heart rate and temperature after 4 days than the fixed-duration adapted group. Rats and mice restrained for 4 h/day every day showed a gradual decrease in heart rate and temperature over time. Full adaptation to restraint required 14 days of fixed-duration daily restraint.     

Subchronic nose-only inhalation study of propylene glycol in Sprague-Dawley rats

Groups of nineteen Sprague-Dawley rats of each sex were exposed by a nose-only inhalation to 0.0, 0.16, 1.0 or 2.2 mg propylene glycol/litre air, for 6 hr/day, 5 days/wk for 90 days. There were no significant differences in respiratory rates, minute volumes or tidal volumes between any of the groups during aerosol exposure. The uniformity of respiratory parameters between dose groups implied that the delivered doses were proportional to the exposure concentrations. The mean terminal body weights were not significantly different from controls for any group of male animals. The mean body weights of the females exposed to 2.2 mg/litre were significantly less than those of female controls from day 50 onwards. This effect, in female rats, was consistent with a decrease in feed consumption for the high-exposure female rats beginning on study day 43. Statistically significant differences between the treated and control groups in certain haematological parameters, serum enzyme activities, other serum chemistry parameters and organ weights did not show clear dose relationships. There was a significant increase in the number of goblet cells or an increase in the mucin content of the existing goblet cells in the nasal passages of the medium- and high-exposure animals. Exposure to the above concentrations of propylene glycol caused nasal haemorrhage and ocular discharge in a high proportion of animals, possibly as a result of dehydration of the nares and eyes.     

Influence of exhaled air on inhalation exposure delivered through a directed-flow nose-only exposure system

In order to conserve material that is available in limited quantities, "directed-flow" nose-only exposure systems have at times been run at flow rates close to the minute ventilation of the animal. Such low-flow-rate conditions can contribute to a decrease of test substance concentration in inhaled air; near the animal nose, exhaled air and the directed flow of exposure air move in opposite directions. With a Cannon "directed-flow" nose-only exposure system (Lab Products, Maywood, NJ), we investigated the extent to which exposure air plus exhaled air can be inhaled by an animal. A mathematical model and a mechanical simulation of respiration were adopted to predict for a male Fischer 344 rat the concentration of test substance in inhaled air. The mathematical model was based on the assumption of instantaneous mixing. The mechanical simulation of respiration used a Harvard respirator. When the system was operated at an exposure air flow rate greater than 2.5 times the minute ventilation of the animal, the concentration of test substance in the inhaled air was reduced by less than 10%. Under these conditions, the circular jet of air exiting the exposure air delivery tube tended to reach the animal's nose with little dispersion. For exposure air flow rates less than 2 times the minute ventilation, we predict that the interaction of exhaled air and exposure air can be minimized by proportionally reducing the delivery tube diameter. These findings should be applicable to similar "directed-flow" nose-only exposure systems.     

Acute pulmonary toxicity following inhalation exposure to aerosolized VX in anesthetized rats

ABSTRACT

This study evaluated acute toxicity and pulmonary injury in rats at 3, 6 and 24?h after an inhalation exposure to aerosolized O-ethyl S-[2-(diisopropylamino)ethyl] methylphosphonothioate (VX). Anesthetized male Sprague-Dawley rats (250–300?g) were incubated with a glass endotracheal tube and exposed to saline or VX (171, 343 and 514?mg×min/m³ or 0.2, 0.5 and 0.8?LCt₅₀, respectively) for 10?min. VX was delivered by a small animal ventilator at a volume of 2.5?ml?×?70 breaths/minute. All VX-exposed animals experienced a significant loss in percentage body weight at 3, 6, and 24?h post-exposure. In comparison to controls, animals exposed to 514?mg×min/m³ of VX had significant increases in bronchoalveolar lavage (BAL) protein concentrations at 6 and 24?h post-exposure. Blood acetylcholinesterase (AChE) activity was inhibited dose dependently at each of the times points for all VX-exposed groups. AChE activity in lung homogenates was significantly inhibited in all VX-exposed groups at each time point. All VX-exposed animals assessed at 20 min and 3, 6 and 24?h post-exposure showed increases in lung resistance, which was prominent at 20 min and 3?h post-exposure. Histopathologic evaluation of lung tissue of the 514?mg×min/m³ VX-exposed animals at 3, 6 and 24?h indicated morphological changes, including perivascular inflammation, alveolar exudate and histiocytosis, alveolar septal inflammation and edema, alveolar epithelial necrosis, and bronchiolar inflammatory infiltrates, in comparison to controls. These results suggest that aerosolization of the highly toxic, persistent chemical warfare nerve agent VX results in acute pulmonary toxicity and lung injury in rats.     

Developmental toxicity in rats after inhalation exposure of di-2-ethylhexylphthalate (DEHP)

Di-2-ethylhexylphthalate (DEHP) was investigated in Wistar rats for developmental toxicity after head-nose exposure to aerosol concentrations of 0, 0.01, 0.05 and 0.3 mg/l for 6 h per day from gestation day 6 through 15. A range finding study revealed peroxisome proliferation in the liver of the dams throughout exposure levels of 0.2, 0.5 and 1.0 mg/l with an increasing trend. 0.3 mg/l was therefore regarded as an exposure level leading to peroxisome proliferation as a marker for maternal effects. All concentrations were tolerated without clinical signs of maternal toxicity. The fetuses of 20 animals per exposure group were investigated for structural defects. Five additional animals per group were allowed to litter and the offsprings were raised and observed for postnatal signs of toxicity. No significant developmental toxicity or changes in the postnatal physical development were observed. DEHP is assumed not to exhibit developmental toxicity under the experimental conditions employed.     

Mosquito coil smoke inhalation toxicity. Part II: subchronic nose-only inhalation study in rats

This paper addresses the results of a subchronic inhalation study in rats exposed to the smoke of burning mosquito coils manufactured in Indonesia. The objective of the study was a comparative assessment of different mosquito coils, including a blank coil, utilizing the OECD No. 413 testing paradigm, however, with the focus on hazard identification at a single maximum tolerated exposure concentration rather than concentration-response. Groups of rats were nose-only exposed 6 h a day, 5 days a week for 13 weeks to an average particulate concentration of 30 mg m(-3) from either blank coils or coils that contain the insecticidal ingredient transfluthrin. Nose-only air-exposed rats served as a control. A range of markers of exposure have been characterized to define the most critical exposure metrics with regard to total suspended particulate matter (TSP) and potentially noxious volatile products of combustion. During the course of the exposure period the smoke-exposed rats showed clinical signs suggestive of acute upper respiratory tract sensory irritation. Body weights were mildly affected in the male rats, but food and water consumption were indistinguishable amongst the groups. Carboxyhemoglobin concentrations were approximately 11% throughout the exposure period in smoke exposed rats. Hematology, clinical pathology and urinalysis as well as the analysis of organ weights and histopathology of extrapulmonary organs and the lung did not reveal any evidence of adverse systemic or local effects, whereas in the anterior region of the nasal passages, and to some extent also in the larynx, irritant-related changes typical for water-soluble upper respiratory irritants were found. Markers of pulmonary inflammation or increased phagocytosis and lysosomal activity in bronchoalveolar lavage were indistinguishable amongst the groups. gamma-Glutamyltranspeptidase was significantly increased in the smoke exposure groups, which is taken as indirect evidence of an adaptive upregulation of the pulmonary antioxidant glutathione. In rats exposed to mosquito coil smoke containing transfluthrin, a somewhat increased frequency of alveolar macrophages with foamy appearance was identified through cytodifferentiation but not histopathology compared with the blank coil. From the specific staining of intracellular phospholipids, the notion is supported that this equivocal finding is probably related to an increased uptake of modified pulmonary surfactant rather than increased engulfment of insoluble particulate matter since pigmentation or clustering or intra-alveolar cells did not occur. The results of this subchronic inhalation study support the conclusion that smoke from burning mosquito coils in concentrations high enough to elicit acute upper respiratory tract irritation due to the presence of common wood-combustion products (such as aliphatic aldehydes) did not cause any adverse effect in the lower respiratory tract or any other extrapulmonary organ. The most critical mode of action is related to acute and readily perceivable sensory irritation. The concentration tested was estimated to be well above that occurring under more realistic exposure conditions. Therefore, overnight exposure to the smoke from burning mosquito coils (manufactured in Indonesia) is unlikely to be associated with any unreasonable health risk.     

Characterization of a nose-only inhaled phosgene acute lung injury mouse model

Abstract

Context: Phosgene’s primary mode of action is as a pulmonary irritant characterized by its early latent phase where life-threatening, non-cardiogenic pulmonary edema is typically observed 6‐24 h post-exposure.

Objective: To develop an inhaled phosgene acute lung injury (ALI) model in C57BL/6 mice that can be used to screen potential medical countermeasures.

Methods: A Cannon style nose-only inhalation exposure tower was used to expose mice to phosgene (8?ppm) or air (sham). An inhalation lethality study was conducted to determine the 8?ppm median lethal exposure (LCt₅₀) at 24 and 48 h post-exposure. The model was then developed at 1.2 times the 24 h LCt₅₀. At predetermined serial sacrifice time points, survivors were euthanized, body and lung weights collected, and lung tissues processed for histopathology. Additionally, post-exposure clinical observations were used to assess quality of life.

Results and discussion: The 24-hour LCt₅₀ was 226?ppm*min (8?ppm for 28.2?min) and the 48-hour LCt₅₀ was 215?ppm*min (8?ppm for 26.9?min). The phosgene exposed animals had a distinct progression of clinical signs, histopathological changes and increased lung/body weight ratios. Early indicators of a 1.2 times the 24-hour LCt₅₀ phosgene exposure were significant changes in the lung-to-body weight ratios by 4 h post-exposure. The progression of clinical signs and histopathological changes were important endpoints for characterizing phosgene-induced ALI for future countermeasure studies.

Conclusion: An 8?ppm phosgene exposure for 34?min (1.2?×?LCt₅₀) is the minimum challenge recommended for evaluating therapeutic interventions. The predicted higher mortality in the phosgene-only controls will help demonstrate efficacy of candidate treatments and increase the probability that a change in survival rate is statistically significant.     

Acute inhalation exposure to cyclohexane and schedule-controlled operant performance in rats: comparison to d-amphetamine and chlorpromazine

Adult male rats pressed a lever on a multiple fixed ratio-fixed interval (FR20-FI120 sec) schedule of food presentation, and after attaining a stable baseline subjects received an acute inhalation exposure to cyclohexane vapor (0 ppm, 500 ppm, 2000 ppm, or 7000 ppm) for 6 hr. During the operant session that began 30 min after termination of exposure, FR running rate for the 7000 ppm group decreased 11% relative to performance on the previous day. FR post-reinforcement pause duration and the rate and pattern of FT performance were unaffected. Cyclohexane exposures of 500 or 2000 ppm had no detectable effects. No enduring effects of cyclohexane occurred up to 2 weeks after exposure. An independent set of rats, trained under nominally identical conditions, received various doses (i.p.) of d-amphetamine (AMPH) or chlorpromazine (CPZ) at 1-2 week intervals. Effective doses of AMPH decreased FR running rate, decreased FR post-reinforcement pause duration and increased FI rate of response. AMPH also decreased the FI index of curvature, indicating a change from an accelerating rate during the FI to a more constant rate. Effective doses of CPZ decreased FR rate, increased FR pause duration, decreased FI rate, and decreased FI index of curvature. Thus, schedule-controlled operant procedures that were sensitive to the effects of psychoactive drugs were able to identify only a minor and transient effect of the highest concentration (7000 ppm) of cyclohexane vapor on operant performance.     

A simple approach to validation of directed-flow nose-only inhalation chambers

Directed-flow nose-only exposure systems are designed and operated so that the genuine test atmosphere is dynamically delivered to each exposure port and exhaled air from exposed animals is immediately exhausted without the possibility of other animals rebreathing this atmosphere. This technique is particularly useful for preventing uncontrolled changes of exposure atmospheres, stimulating breathing activity due to the rebreathing of exhaled carbon dioxide, and the conserving a test material that is available only in limited quantities. The intricate relationship of the delivered flow of air at each exposure port relative to the respiratory minute volume of the exposed animal appears to be critical for the state-of-the-art performance of directed-flow nose-only exposure systems. This analysis revealed that the determination of carbon dioxide concentrations at different inhalation chamber locations, including exposure ports, is a simple and cost-effective procedure to evaluate whether the rebreathing of atmospheres can be excluded. It has been shown that directed-flow systems need to be operated at an exposure air flow rate greater than 2.5 times the respiratory minute volume of the exposed animal or optimally approximately 0.75 l min(-1) per rat exposure port ( approximately 3.75 times the minute volume of young adult rats) to prevent higher CO(2)-concentrations occurring.     

Blood pharmacokinetics of tertiary amyl methyl ether in male and female F344 rats and CD-1 mice after nose-only inhalation exposure

Interest in understanding the biological behavior of aliphatic ethers has increased owing to their use as gasoline additives. The purpose of this study was to investigate the blood pharmacokinetics of the oxygenate tertiary amyl methyl ether (TAME), its major metabolite tertiary amyl alcohol (TAA) and acetone in rats and mice following inhalation exposure to TAME. Species differences in the area under the curve (AUC) for TAME were significant at each exposure concentration. For rats, the blood TAME AUC increased in proportion with an increase in exposure concentration. For mice, an increase in exposure concentration (100-500 ppm) resulted in a disproportional increase in the TAME AUC. Mice had greater (two- to threefold) blood concentrations of TAA compared with rats following exposure to 2500 or 500 ppm TAME. Mice had a disproportional increase in the TAA AUC with an increase in exposure concentration (100-500 ppm). This difference could result from saturation of a process (e.g. oxidation, glucuronide conjugation) that is involved in the further metabolism of TAA. For each species, gender and exposure concentration, acetone increased during exposure and returned to control values by 16 h following exposure. The source of acetone could be both as a metabolite of TAA or an effect on endogenous metabolism produced by exposure to TAME.     

A 13-week nose-only inhalation toxicity study for perfluoro-n-butyl iodide (PFBI) in rats with recommended occupational exposure levels

A 13-week study was conducted to develop occupational exposure limits (OELs) for the solvent perfluoro-n-butyl iodide (PFBI). Fischer 344 rats (15 males & 10 females per group) were exposed for 6?h/day to 0 (air control), 500, 1500, or 5000?ppm PFBI vapor for 5 days/week for 13 consecutive weeks (at least 65 exposures) followed by a 4-week recovery period. Clinical observations, body weights, clinical pathology, organ weights, and histopathology as well as detailed evaluations of neurotoxicity and thyroid function parameters were conducted at the end of the treatment period for up to 10 animals/sex/group with 5 males/group held for a 4-week recovery period. Findings in the thyroid target tissue consisted of a minimal thyroid follicular cell hypertrophy occasionally accompanied by hyperplasia, but without an increase in thyroid weight in the 500, 1500, and 5000?ppm males. At ≥500?ppm, there was also increased thyroid stimulating hormone in females and increased T₃ and T₄ in animals of both sexes. These effects resolved following a 4-week recovery period in the males evaluated. Minor clinical pathology variations in all PFBI exposure groups were not considered biologically significant. A 9.4% reduction in absolute body weight in the 5000?ppm males was observed. Dosimetric adjustments for daily exposure time and uncertainty factors were selected to provide a basis for the proposed OELs. For acute (single event) exposures, a ceiling OEL of 3900?ppm, and for repeated exposures, an 8-h time-weighted average of 40?ppm PFBI were proposed.     

Comparisons of acute inflammatory responses of nose-only inhalation and intratracheal instillation of ammonia in rats

Objective: To establish a rat model with respiratory and pulmonary responses caused by inhalation exposure to non-lethal concentrations of ammonia (NH₃) that can be used for evaluation of new medical countermeasure strategies for NH₃-induced acute lung injury (ALI). This is of great value since no specific antidotes of NH₃-induced injuries exist and medical management relies on supportive and symptomatically relieving efforts.

Methods: Female Sprague-Dawley rats (8–9?weeks old, 213g?±?2g) were exposed to NH₃ using two different exposure regimens; nose-only inhalation or intratracheal instillation. The experiment was terminated 5?h, 24?h, 14 and 28?days post-exposure.

Results: Nose-only inhalation of NH₃ (9000–15 000?ppm) resulted in increased salivation and labored breathing directly post-exposure. Exposure did not increase inflammatory cells in bronchoalveolar lavage fluid but exposure to 12 000?ppm NH₃ during 15?min reduced body weight and induced coagulation abnormalities by increasing serum fibrinogen levels. All animals were relatively recovered by 24?h. Intratracheal instillation of NH₃ (1%) caused early symptoms of ALI including airway hyperresponsiveness, neutrophilic lung inflammation and altered levels of coagulation factors (increased fibrinogen and PAI-1) and early biomarkers of ALI (IL-18, MMP-9, TGFβ) which was followed by increased deposition of newly produced collagen 14?days later. Histopathology analysis at 5?h revealed epithelial desquamation and that most lesions were healed after 14?days.

Conclusions: This study demonstrates that intratracheal instillation can reproduce several early hallmarks of ALI. Our findings therefore support that the intratracheal instillation exposure regimen can be used for new medical countermeasure strategies for NH₃-induced ALI.