Functional, biochemical, and histopathological evidence of airway obstruction in rats following a four-hour acute inhalation exposure to n-butyl isocyanate.

Pulmonary function, arterial blood gases, acid-base status, and bronchoalveolar lavage fluid (BALF) composition were assessed in male Wistar rats after a single 4-h exposure to 0, 7.6, 23.5 or 55.2 mg n-butyl isocyanate (n-BIC)/m3 air. No significant changes other than transient clinical signs were observed in the rats exposed to 7.6 mg/m3 air. Four weeks after exposure the animals of the 55.2 mg/m3 group showed significant effects: those were pronounced histopathological changes of airways and parenchyma, and elevated relative lung weight. The neutrophils, LDH, and protein in BALF were elevated. Quasi-static lung compliance, peak expiratory flow rate, mean mid expiratory flow rate were decreased whereas lung resistance, residual volume, and single breath CO-diffusing capacity were increased. Blood gas measurements revealed an elevation in hemoglobin, pH, arterio-alveolar oxygen difference, and venous admixture. Arterial pO2 and pCO2 were decreased. In animals exposed to 23.5 mg/m3 only marginal effects were detectable.

A new method for long-term inhalation toxicity studies for bronchospasmolytic aerosol formulations in dogs.

In routine inhalation toxicity studies laboratory animals are exposed under dynamic exposure conditions to different steady-state concentrations of a test compound. The relevant exposure concentration is the analytically determined time-weighted average concentration in the vicinity of the breathing zone of the animals. If the intended use of a bronchospasmolytic aerosol is taken into account, a non-steady-state exposure regimen might be more appropriate. Using this approach local effects of high aerosol concentrations on the respiratory tract were investigated in dogs by daily head/nose-only exposure for 1 h for 4 weeks. Four groups of four dogs were exposed to 20, 40 and 80 bursts of a bronchodilator formulation using a modified metered dose inhaler. The analytically determined mean concentration of the active ingredient (prostaglandin) in the breathing zone was 43.1, 92.2 and 193.9 micrograms l-1 air, respectively. Maximum concentrations were determined by simulation. The aerosol was in the respirable range (mass median aerodynamic diameter approximately 1.2 microns, geometric standard deviation approximately 1.4). A kinetic model was developed to simulate the mean and maximum non-steady-state concentration for an exposure regimen of 20, 40 and 80 bursts per hour under dynamic exposure conditions. The model was based on first-order inhalation chamber kinetics. The kinetic model was validated experimentally by comparing measured mean and simulated mean concentrations. In all exposure groups the simulated maximum concentrations were ca. 80 mg of test compound (formulation) per litre of air. Plasma levels were elevated in a dose-dependent manner as evidence of the validity of the test model employed.

Methodological aspects of the determination of the acute inhalation toxicity of spray-can ingredients.

Spray-can ingredients, if liberated in confined spaces, are potential health hazards for man. Thus, appropriate inhalation toxicity studies have to be performed in accordance with internationally recognized guidelines, e.g. the US Environmental Protection Agency: Federal Insecticide, Fungicide and Rodenticide Act (FIFRA no. 81-3) or OECD no. 403. One of the essential requirements of such guidelines is that test animals (preferably rats) be exposed to a steady-state concentration in a dynamic inhalation chamber for at least 4 hours. This is not easy to achieve with vapours released from a pressurized spray-can. The method described here makes it possible to expose experimental animals in an inhalation chamber to a steady-state concentration of intermittently released spray jets of constant doses per jet. Animal experiments and theoretical considerations (computer simulations) have shown that the method presented allows an up-to-date determination of the acute inhalation toxicity of spray-can ingredients.

Effects of inhaled cholinesterase inhibitors on bronchial tonus and on plasma and erythrocyte acetylcholine esterase activity in rats.

Young adult male and female Wistar rats were inhalationally exposed head-only for 1 or 4 h to different anticholinesterase aerosols. The compounds tested were dichlorvos, fenamiphos, methamidophos, parathion, a pyrimidine thiophosphate and the carbamate propoxur. These compounds are direct or indirect inhibitors of cholinesterase activity. Immediately after termination of exposure to the compounds, the rats were anesthetized with barbiturate and subjected to pulmonary function tests. An acetylcholine provocation test was performed to correlate the effect of the cholinesterase inhibition and lung resistance. The results basically revealed that by inhalation exposure bronchoconstriction in the absence of acetylcholine provocation did not occur at toxicologically significant doses of the pesticides. An increase in lung resistance was observed only after provocation. However, measurements of plasma cholinesterase activity proved to be more sensitive than the provocation test. With regard to their diagnostic value, the results of the reported study may be summarized as follows (beginning with the most sensitive parameter): plasma cholinesterase activity depression greater than or equal to acetylcholine-induced bronchoconstriction greater than or equal to cholinergic symptoms greater than erythrocyte cholinesterase activity depression greater than pulmonary resistance without acetylcholine provocation.

Reproduction and fertility evaluations in CD rats following nitrobenzene inhalation.

A two-generation reproduction study was performed by exposure of Sprague-Dawley CD rats to concentrations of 40, 10, 1, or 0 (control) ppm of nitrobenzene (NB) vapor. No NB-related effects on reproduction were observed at 10 or 1 ppm. At 40 ppm, a decrease in the fertility index of the F0 and F1 generations occurred, which was associated with alterations in the male reproductive organs. Specifically, weights of testes and epididymides were reduced and seminiferous tubule atrophy, spermatocyte degeneration, and the presence of giant syncytial spermatocytes were observed. The only significant finding in the litters derived from rats exposed to 40 ppm was an approximate 12% decrease in the mean body weight of F1 pups on Postnatal Day 21. Survival indices were unaltered. To examine the reversibility of this selective effect on male gonads, the F1 males from the 40-ppm group were allowed a 9-week nonexposure period and mated to naive females. An almost fivefold increase in the fertility index was observed, indicating at least partial functional reversibility upon removal from NB exposure. Also, the numbers of giant syncytial spermatocytes and degenerated spermatocytes were greatly reduced. The results of this study support the selection of 10 ppm of NB as the no-observable-effect level for reproduction and fertility effects in rats.

Development toxicity evaluation of inhaled nitrobenzene in CD rats.

Pregnant CD (Sprague-Dawley) rats were exposed to nitrobenzene vapor (CAS Registry No. 98-95-3) at 0, 1, 10, and 40 ppm (mean analytical values of 0.0, 1.06, 9.8, and 39.4 ppm, respectively) on gestational days (gd) 6 through 15 for 6 hr/day. At sacrifice on gd 21, fetuses were evaluated for external, visceral, and skeletal malformations and variations. Maternal toxicity was observed: weight gain was reduced during exposure (gd 6-9 and 6-15) to 40 ppm, with full recovery by gd 21, and absolute and relative spleen weights were increased at 10 and 40 ppm. There was no effect of treatment on maternal liver, kidney, or gravid uterine weights, on pre- or postimplantation loss including resorptions or dead fetuses, on sex ratio of live fetuses, or on fetal body weights (male, female, or total) per litter. There were also no treatment-related effects on the incidence of fetal malformations or variations. In summary, during organogenesis in CD rats, there was no developmental toxicity (including teratogenicity) associated with exposure to nitrobenzene concentrations that produced some maternal toxicity (10 and 40 ppm) or that produced no observable maternal toxicity (1 ppm).

Inhalation studies with benzo[a]pyrene in Syrian golden hamsters.

Groups of Syrian golden hamsters were exposed by inhalation to benzo[a]pyrene (BP) in concentrations of 2.2, 9.5, and 45.6 mg/m3 air. Although 45.6 mg BP/m3 air was carcinogenic and toxic, 2.2 mg BP/m3 air led to no neoplastic response. The highest tumor incidence was seen in the group exposed to 9.5 mg BP/m3 air. Average survival times were similar in the controls (not exposed to BP) and in the 2 groups given 2.2 and 9.5 mg BP/m3 air. Exposure-related neoplasms were found in the nasal cavity, larynx, pharynx, esophagus, and forestomach. Bronchogenic tumors did not develop.

Investigation on the carcinogenic burden of air pollution in man. XIX. Effect of inhaled benzo(a)pyrene in Syrian golden hamsters: a pilot study.

In an inhalation study, two groups of male Syrian golden hamsters were exposed to 9.8 and 44.8 mg BP/m3 air respectively for 16 weeks. No significant histological or pathological alterations were seen, and no tumours were found which could be related to BP exposure.

Spontaneous endocrine tumors in Sprague-Dawley rats.

Spontaneous endocrine tumors were found in 81 of 100 Sprague-Dawley rats (42 males and 39 females) which survived for more than 2 years. Most of these tumors were medullary carcinomas of the thyroid, followed by tumors of the anterior pituitary gland, pheochromocytomas and cortical adenomas of the adrenal gland, and islet cell tumors of the pancreas. Multiple occurrence of these tumors was frequently observed. This study describes the morphology of these spontaneous endocrine tumors.

Inhalation studies with polyurethane foam dust in relation to respiratory tract carcinogenesis.

Male and female Sprague-Dawley rats were exposed to freshly generated polyurethane foam dusts, in concentrations averaging 8.65 mg/m3 air, for 6 hours daily 5 days a week over a period of 12 weeks. For comparison the same numbers of rats were exposed to titanium dioxide (TiO2) (15.95 mg/m3 air), which is a known inert dust, and to air alone, as controls for the same exposure period. This exposure caused no noticeable changes in appearance, behavior, or body weight. The average lifespan values were within the normal range. A high tumor rate was seen in all groups, with no significant differences among the groups. No indications of a carcinogenic effect of the inhaled dusts on the respiratory tract could be established. The numerous tumors found in the different organs and groups were of a spontaneous nature. The observed lung-reactions are discussed.

Toxicity of propoxur to rats by subacute inhalation.

Male and female rats were exposed to propoxur (2-isopropoxyphenyl-N-methyl-carbamate) aerosol, concentrations averaging 5.7, 18.7 and 31.7 mg/m3 air, for 6 hours daily on five days in a week over a period of 12 weeks. The effects were depressions of plasma by 20 to 30%, and of erythrocyte and brain cholinesterase activities which were caused by the highest air concentration of 31.7 mg/m3. On the basis of the physical, biochemical, phamacokinetic and metabolic behaviors of propoxur, a maximum allowable concentration of 2.5 mg/m3 air is suggested.