Influence of ozone on pentobarbital-induced sleeping time in mice,rats, and hamsters

Studies were conducted to investigate the effect of ozone (O₃) in prolonging pentobarbital (PEN)-induced sleeping time (S.T.). Since O₃ is a common air pollutant, an O₃-induced alteration of mechanisms of drug action could have public health implications. It was shown that a 5-hr exposure to 1960 μg O₃/m³ (1 ppm) caused an increased PEN-induced S.T. in female mice (three strains), rats, and hamsters. This response was not observed in male rats or in male mice even when the latter were exposed for 5 hr/day for 3 days. Male hamsters were affected, but less so than females. Ozone concentration and time relationships were investigated in female mice. Concentrations from 196 to 9800 μg O₃/m³ (0.1 to 5 ppm) increased PEN-induced S.T. However, as the concentration was decreased, an increasing number of daily 3-hr exposures were needed to cause an effect. Once the maximal effect was observed, further daily exposures resulted in a dissipation or a disappearance of the effect. Also, recovery occurred within 24 hr after exposure ceased. Other experiments were performed in which mice received a continuous exposure to a C × T (concentration × time) of 5, ranging from 196 μg/m³ (0.1 ppm) × 50 hr to 1960 μg/m³ (1 ppm) × 5 hr. For most of the concentrations, the magnitudes of the O₃ effects were roughly equivalent. These data are interpreted as a systemic effect of O₃ on mechanisms of the termination of action of pentobarbital.     

Tracheal and bronchoalveolar permeability changes in rats inhaling oxidant atmospheres during rest or exercise

Permeability of tracheal and bronchoalveolar airways of rats was measured and used to examine the effects of inhaled oxidant-containing atmospheres. The atmospheres studied were (a) ozone (O3) at 0.6 ppm (1.2 mg/m3) or 0.8 ppm (1.6 mg/m3); (b) nitrogen dioxide (NO2) at 6 ppm (11.3 mg/m3) or 12 ppm (22.6 mg/m3); (c) O3 + NO2 at 0.6 ppm (1.2 mg/m3) and 2.5 ppm (4.7 mg/m3), respectively; and (d) a 7-component particle and gas mixture (complex atmosphere) representing urban air pollution in a photochemical environment. The rats were exposed for 2 h. The effects of exercise during exposure were evaluated by exposing additional groups in an enclosed treadmill. Exposure of resting rats to 0.8 ppm O3 increased tracheal permeability to DTPA and bronchoalveolar permeability to diethylenetriamine pentaacetate (DTPA) and bovine serum albumin (BSA) at 1 h after the exposure. Bronchoalveolar, but not tracheal, permeability remained elevated at 24 h after the exposure. Exercise during exposure to O3 increased permeability to both tracers in the tracheal and the bronchoalveolar zones, and prolonged the duration of increased permeability in the tracheal zone from 1 h to 24 h, and in the bronchoalveolar zone from 24 h to 48 h. Permeability in the tracheal and bronchoalveolar zones of rats exposed at rest to 6 or 12 ppm NO2 did not differ from controls. However, rats exposed during exercise to 12 ppm NO2 for 2 h developed a significant increase in tracheal and bronchoalveolar permeability to DTPA and BSA at 1 h, but not at 24 or 48 h, after exposure. Exposure at rest to 0.6 ppm O3 plus 2.5 ppm NO2 significantly increased bronchoalveolar permeability at 1 and 24 h after exposure, although exposure at rest to 0.6 ppm O3 alone increased bronchoalveolar permeability only at 1 h after exposure. Exposure to O3 + NO2 during exercise led to significantly greater permeability to DTPA than did exercising exposure to O3 alone. Resting rats exposed to a complex gas/aerosol atmosphere composed of the above O3 and NO2 concentrations, plus 5 ppm (13.1 mg/m3) sulfur dioxide (SO2) and an aerosol of insoluble colloidal Fe2O3 with an aerosol of manganese, ferric, and ammonium salts, demonstrated increased permeability at 1 and 24 h after exposure. Nitric acid vapor was formed in both the O3 + NO2 atmosphere and the complex gas/aerosol atmosphere.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effect of chronic DDT exposure on pentobarbital tolerance and intolerance in the rat

Barbiturate tolerance and intolerance were studied in female albino rats. Three consecutive daily ip doses of pentobarbital (30 mg/kg) were shown to produce a significant tolerance in naive rats, with sleeping times significantly shortened on both day 2 (to 65% of control) and day 3 (to 53%). This tolerance was correlated with a significant increase in the in vitro rate of hepatic microsomal pentobarbital metabolism (235% at day 3). On day 23 (after 20 days of barbiturate abstinence) the animals exhibited an intolerance (sleeping time 126%) not associated with any change in hepatic enzyme activity. All parameters returned to control values by day 43. These results suggest that the intolerance is nonhepatogenic and likely related to enhanced CNS sensitivity. In parallel studies, chronic dietary exposure to DDT (p,p-DDT 13.1 ppm; o,p-DDT 5.3 ppm) caused increased liver enzyme activity which did not prevent the appearance of tolerance by day 3 (sleeping time 72%; barbiturate metabolism 139%) but did prevent the appearance of day 23 intolerance. The hepatic induction produced by DDT appears to offset any CNS sensitivity associated with delayed barbiturate intolerance.     

Effect of ozone on drug-induced sleeping time in mice pretreated with mixed-function oxidase inducers and inhibitors

Prior studies have shown that ozone (O₃) increases pentobarbital (PEN)-induced sleeping time (S.T.) in female mice, rats, and hamsters. To investigate some potential mechanisms producing these effects, we measured zoxazolamine-induced paralysis time and thiopental- and hexobarbital-induced S.T., all of which were prolonged significantly in mice following a 5-hr exposure to 1960 μg O₃/m³ (1 ppm). To probe the effect of O₃ exposure on the drug metabolism microsomal monooxygenase system, CD-1 mice were pretreated with mixed-function oxidase inducers [PEN, phenobarbital, pregnenolone-16α-carbonitrile, and β-naphthoflavone (BNF)] or inhibitors (SKF 525A and piperonyl butoxide) prior to a 5-hr exposure to 1960 μg O₃/m³ (1 ppm). In CD-1 mice, pretreatment with PEN caused no effects on PEN-induced S.T. For all other compounds, the PEN-induced S.T. of CD-1 mice was significantly decreased, irrespective of whether the animals were exposed to air or O₃. Ozone exposure significantly increased PEN-induced S.T. equivalently in the vehicle- and inducer-pretreated animals. Similar studies were conducted in DBA and C57BL mice pretreated with BNF. DBA mice responded similarly to CD-1 mice. However, with C57BL mice, O₃ significantly increased PEN-induced S.T. in the vehicle, but not in the BNF group. When CD-1 mice were pretreated with inhibitors, a generally increased magnitude of the O₃ effect was observed with increasing doses of inhibitor. These data suggest that O₃ exposure may affect several aspects of drug metabolism and distribution.     

Synergistic interaction of ozone and respirable aerosols on rat lungs. III. Ozone and sulfuric acid aerosol

Previously we have demonstrated that a synergistic interaction, as evaluated by several biochemical, toxicological, and morphological responses of the lung, results from exposure of rats to ozone (O3) in conjunction with moderate concentrations of acidic, but not neutral, aerosols. To extend these studies, groups of rats were continuously exposed to either O3 or sulfuric acid aerosol alone, or to combinations of these pollutants. Pulmonary responses from these rats were measured by assay, after exposures for 6 hr to 7 days, of total lavageable protein content, total lung tissue protein content after 5, 7, or 9 days of exposure, or apparent collagen synthesis rates from lung tissue after 7 days of exposure. While the lavageable protein content from rats exposed for 3 days to 0.1 or 1.0 mg/m3 of sulfuric acid aerosol alone was not different from control values, significant elevations from control values were observed from groups exposed to 0.12, 0.20, or 0.64 ppm of O3. Synergy was demonstrated by this assay upon exposure of rats to 0.20 ppm of O3 in conjunction with 0.1, 0.5, or 1.0 mg/m3 of sulfuric acid aerosol. Similarly, the tissue protein content from rats exposed to 0.1 or 1.0 mg/m3 of sulfuric acid aerosol alone was indistinguishable from control values. Significant elevations from control values were observed by this assay from groups of rats exposed to 0.64 or 0.20 ppm of O3, and a synergistic interaction was demonstrated between 0.64 ppm of O3 and 1.0 mg/m3 of sulfuric acid aerosol. Furthermore, synergy was observed by quantification of increased total lung protein between 0.20 ppm of O3 + 40 micrograms/m3 and higher concentrations of sulfuric acid aerosol. Values of the lung collagen synthesis rate from rats exposed to 0.1, but not 1.0, 0.5, or 0.04 mg/m3 of sulfuric acid aerosol were significantly higher than values from lungs of control animals. Significant elevations from control values were also observed by this assay from groups of rats exposed to 0.64 or 0.20 ppm of O3. A synergistic interaction was demonstrated by the collagen synthesis rate assay between groups of rats exposed to 0.64 ppm of O3 + 0.20 mg/m3 and higher concentrations of sulfuric acid aerosol or between groups exposed to 0.20 ppm of O3 + 40 micrograms/m3 and higher concentrations of sulfuric acid aerosol. These results demonstrate synergy between O3 and sulfuric acid aerosol upon exposure to concentrations of each pollutant at or near peak hourly ambient levels in polluted urban atmospheres.     

Discovery and anticonvulsant activity of the potent metabolic inhibitor 4-amino-N-(2,6-dimethylphenyl)-3,5-dimethylbenzamide

Compound 2 [4-amino-N-(2,6-dimethylphenyl)benzamide] is an effective anticonvulsant in several animal models. For example, following oral administration to mice, it antagonized maximal electroshock (MES) induced seizures with an ED50 of 1.7 mg/kg. During drug disposition studies with 2, we found that it was rapidly metabolized by N-acetylation. Thirty minutes after oral administration of 1.7 mg/kg of 2 to mice, plasma concentrations of parent drug and the N-acetyl metabolite 5 were 1.09 and 0.41 microgram/mL, respectively. Six hours postadministration the concentrations were 0.23 and 0.22 microgram/mL, respectively. In order to sterically preclude or diminish the rate of metabolic N-acetylation, we synthesized analogues of 2 possessing either one (3) or two (4) methyl groups ortho to the 4-amino substituent. Both compounds antagonized MES-induced seizures after administration to mice; oral ED50 values for 3 and 4 were 3.5 and 5.6 mg/kg, respectively. Compound 3 was rapidly metabolized by N-acetylation. However, 4 provided exceptionally high and long-lived plasma concentrations of parent drug; no N-acetyl metabolite could be detected. While 2 and 3 had no pharmacologically relevant effects on hexobarbital-induced sleeping time in mice, 4 was a potent, dose-dependent potentiator of sleeping time. Oral administration of 375 micrograms/kg led to a 61% increase in sleeping time relative to control values. Thus, 4 represents one of the most potent potentiators of hexobarbital-induced sleeping time described to date.     

Chronic maternal methanol inhalation in nonhuman primates (Macaca fascicularis): exposure and toxicokinetics prior to and during pregnancy

Toxicokinetic studies were conducted following daily inhalation exposure to methanol vapor prior to and throughout pregnancy in adult female Macaca fascicularis monkeys. They were part of a larger study to investigate the effects of chronic methanol exposure on maternal reproductive performance and early offspring effects. In a two-cohort study design, 48 females (24/cohort) were assigned to parallel exposure groups at 0 (control), 200, 600, or 1800 ppm methanol vapor for approximately 2.5 h/day, 7 days/week throughout breeding and pregnancy. Blood methanol at 30 min postexposure was monitored biweekly. The time course for the clearance of blood MeOH concentrations following exposure was characterized on four occasions: twice during the prebreeding period and during mid- and late pregnancy. Average blood methanol concentrations at 30 min postexposure were 5, 11, and 35 microg/ml across all four toxicokinetic studies in the 200, 600 and 1800 ppm groups, respectively. Blood concentrations in the 200 ppm group were barely above basal (preexposure) blood methanol concentrations or those observed in the control group (approximately 3 microg/ml). Nonlinear elimination kinetics were observed in most of the 1800 ppm group females. There was a decrease in elimination half-life (7-20%) and an increase in clearance (30%) after 3-months of daily MeOH exposure compared to the initial exposure. There were no statistically significant changes in the first-order blood methanol half-life or clearance during pregnancy, but the mean distribution volume per kilogram body weight decreased by 22% and 17% in the 600 and 1800 ppm groups. Plasma formate levels did not differ between the methanol and control exposure groups. Plasma formate and serum folate concentrations increased slightly over the course of this study in both the exposed and control groups but these increases were not related to methanol exposure.     

Sulfuric acid-layered ultrafine particles potentiate ozone-induced airway injury

Urban air pollution in the United States is composed of a complex mixture of particles and gases. Among the most prominent products of the atmospheric pollutants are sulfur oxides and ozone. In this report, we use two exposure protocols to examine the interaction between exposure to these two pollutants. In the first exposure regimen, guinea pigs were exposed to sulfuric acid (pure sulfuric acid mist or sulfuric acid layered on ZnO) for 1 h. Each exposure is followed 2 h later by another exposure to 0.15 ppm ozone for 1 h. Pulmonary function parameters were measured immediately after the ozone exposure. In guinea pigs that were exposed to 300 micrograms/m3 pure sulfuric acid mist, subsequent exposure to 0.15 ppm ozone did not produce additional change in pulmonary functions. In guinea pigs that were exposed to 84 micrograms/m3 sulfuric acid layered on ZnO, subsequent exposure to 0.15 ppm ozone produced more than additive alterations in vital capacity and diffusing capacity. In the second exposure regimen, guinea pigs were exposed to 24 micrograms/m3 sulfuric acid layered on ZnO for 3 h/d for 5 d. On d 8 and 9, animals received two additional daily 3-h exposures to 24 micrograms/m3 sulfuric acid layered on ZnO, and pulmonary functions were measured at the end of the daily exposure. Greater reductions in lung volumes and diffusing capacity were observed in animals on d 9 than would be observed in animals that received no additional exposure. In the third exposure regimen, guinea pigs were exposed to 24 micrograms/m3 sulfuric acid layered on ZnO for 3 h/d for 5 d. On d 9, animals were exposed to 0.15 ppm ozone for 1 h and pulmonary functions were measured at the end of the ozone exposure. Ozone exposure on d 9 induced reductions in lung volumes and diffusing capacity that were not observed in animals receiving exposures to either ozone or sulfuric acid layered ZnO alone. We conclude that single or multiple exposure to sulfuric acid-layered ZnO sensitizes guinea pigs to subsequent sulfuric acid or ozone exposure.     

EFFECTS OF REPEATED EXPOSURES OF GERIATRIC RATS TO OZONE AND PARTICLE-CONTAINING ATMOSPHERES: AN ANALYSIS OF BRONCHOALVEOLAR LAVAG E AND PLASMA PROTEINS

Inhalation of ozone (O3) and airborne particles less than 10 m (PM-10) in mass median aerodynamic diameter (MMAD) is associated with adverse health effects in sensitive human populations, and pulmonary injury in laboratory animals. In order to simulate environmental exposures of sensitive individuals, such as the elderly, geriatric rats were exposed to O and particulate mixtures. This pilot study determined whether the pul3 monary effects of higher O3 concentrations reported in earlier studies are also seen after repeated exposures to lower O3 concentration used in this study, whether the O3 effects are modified by PM-10 components, and whether plasma biomarkers can be developed as noninvasive tests of pulmonary injury. Male Fischer 344 rats, 22-24 mo old, were exposed 4 h/ day, 3 days/wk for 4 wk to (a) purified air, (b) O3 (0.2 ppm), (c) low-level mixture of carbon (C, 50 g/ m3) plus ammonium bisulfate (ABS, 70 g/m3) plus O3, and (d) high-level mixture of C (100 g/m3) plus ABS (140 g/m3) plus O3. Twenty-four hours after the last exposure, groups of rats were prepared for measurement of protein and albumin concentrations in bronchoalveolar lavage (BAL) as markers of airways permeability, and blood was drawn for analysis of plasma immunoreactive prolyl 4-hydroxylase and fibronectin. Exposures to O3 and O3 /particle mixtures did not produce a consistent, significant change in the BAL markers of permeability. Nonsignificant changes represented individual animal variations. On the other hand, a significant increase in plasma fibronectin was observed in the group exposed to O3, but not in the rats exposed to O3/particle combinations. Such an effect was not observed for plasma immunoreactive prolyl 4- hydroxylase. The inability of low-level O3 and O3/particle combinations to produce intra pulmonary effects suggests potential utility of plasma biomarkers for the evaluation of pulmonary toxicity. These results also suggest modification of O3 effects upon its combination with PM-10.     

Clearance of renin in unanesthetized rats: effects of chronic lead exposure

These experiments studied the influence of chronic lead exposure on the steady-state clearance of exogenous homologous renin in unanesthetized, unrestrained rats. Relative to time controls (TC), rats chronically exposed to 500 ppm lead in drinking water had significantly elevated basal plasma renin concentrations (PRC) (Pb = 12.0 +/- 1.6 ng/ml/hr, TC = 7.6 +/- 0.8). During the infusion of homologous renin sufficient to increase plasma renin approximately 10-fold, the clearance of renin was not different between the two groups (after 60-min infusion, Pb = 16.1 +/- 1.8 ml/kg/min, TC = 15.9 +/- 1.5). Rats exposed to 1000 ppm lead did not have higher PRCs than time controls (Pb = 10.9 +/- 2.2 TC = 9.2 +/- 1.8). The clearances of renin in these two groups were also not significantly different (Pb = 15.3 +/- 2.8 TC = 18.3 +/- 2.5). Renal renin concentrations were significantly elevated in the 500 ppm rats (Pb = 1426 +/- 110 micrograms/kidney, TC = 1065 +/- 118) consistent with an increased basal renin secretion, but were not elevated in the 1000-ppm rats. There were no significant differences in the clearances of sulfobromophthalein (BSP) between any of the groups. The renin infusion significantly reduced BSP clearance, but did not so equally in all groups. It is concluded that in unanesthetized, unrestrained rats the clearance of renin is not altered by chronic lead exposure of either 500 or 1000 ppm and that increased secretion of renin accounts for the elevated basal PRC observed in rats exposed to the lower dose of lead.     

Effect of ozone on diesel exhaust particle toxicity in rat lung

Ambient particulate matter (PM) concentrations have been associated with mortality and morbidity. Diesel exhaust particles (DEP) are present in ambient urban air PM. Coexisting with DEP (and PM) is ozone (O(3)), which has the potential to react with some components of DEP. Some reports have shown increased lung injury in rats coexposed to PM and O(3), but it is unclear whether this increased injury was due to direct interaction between the pollutants or via other mechanisms. To examine whether O(3) can directly react with and affect PM bioactivity, we exposed DEP to O(3) in a cell-free in vitro system and then examined the bioactivity of the resultant DEP in a rat model of lung injury. Standard Reference Material 2975 (diesel exhaust PM) was initially exposed to 0.1 ppm O(3) for 48 h and then instilled intratracheally in Sprague-Dawley rats. Rat lung inflammation and injury was examined 24 h after instillation by lung lavage. The DEP exposed to 0.1 ppm O(3) was more potent in increasing neutrophilia, lavage total protein, and LDH activity compared to unexposed DEP. The increased DEP activity induced by the O(3) exposure was not attributable to alteration by air that was also present during the O(3) exposure. Exposure of DEP to a higher O(3) concentration (1.0 ppm) led to a decreased bioactivity of the particles. In contrast, carbon black particles, low in organic content relative to DEP, did not exhibit an increase in any of the bioactivities examined after exposure to 0.1 ppm O(3). DEP incorporated O(3) (labeled with (18)O) in a linear fashion. These data suggest that ambient concentrations of O(3) can increase the biological potency of DEP. The ozonized DEP may play a role in the induction of lung responses by ambient PM.     

The effects of styrene on lung cells in female mice and rats.

Styrene has been shown to cause an increase in the incidence of lung tumors in CD-1 mice following chronic exposure at 40 and 160 ppm, whereas no treatment-related increase in tumors in any organ was seen in rats chronically exposed to up to 1000 ppm styrene. So far most of the mechanistic studies have been performed with male animals. The aim of the present study was to further elucidate the target cell population in mouse lungs exposed to styrene, and to investigate possible differential in vivo effects (e.g., glutathione depletion, increased lipid peroxidation, and oxidative DNA damage). Groups of female CD-1 mice were exposed to styrene at concentrations of 0, 172 or 688 mg/m3 (0, 40 or 160 ppm) for 6 h per day on 1 day, 5 consecutive days or for 20 days during a 4 week period. Groups of female Crl:CD rats were exposed to styrene at concentrations of 0, 688 or 2150 mg/m3 (0, 160 or 500 ppm) for a single 6 h period or for 6 h per day on 5 consecutive days. No signs of lung toxicity were observed in rats. The cytology of cells in lung lavage fluid provided no signs of an inflammatory response in either rats or mice. In mice, both exposure levels caused decreased CC16 protein concentrations in lung lavage fluid after 1 and 5 exposures and in mouse blood serum throughout the study, suggesting that styrene may cause destruction of Clara cells in mice. Degenerative lesions in mouse Clara cells (vacuolar cell degeneration, cell necrosis) were revealed by electronmicroscopy. After 5 and 20 exposures of mice at 160 ppm, cellular crowding, expressed as an irregular epithelial lining and indicative of a very early hyperplasia was noted. Although a depletion of glutathione was noted in mouse lung homogenates after 20 exposures, there was no evidence of oxidative stress as indicated by unchanged concentrations of 8-OH-deoxyguanosine. Malondialdehyde, an indicator of lipid peroxidation, was slightly increased in mice after 1 exposure at 160 ppm only.     

Nasal allergy-like symptoms aggravated by ozone exposure in a concentration-dependent manner in guinea pigs

Our previous study revealed that exposure to 0.4 ppm ozone (O(3)) enhanced nasal allergy-like reactions in guinea pigs. In the present study, we investigated the concentration-dependency of the effects of exposure to O(3) on the aggravation of nasal allergy-like reactions induced by repeated nasal administration of antigen. Guinea pigs were exposed to filtered air or 0.1-0.6 ppm O(3) for 5 weeks. After each weekly administration of ovalbumin (OVA), sneezes and nasal secretions were measured. The number of eosinophils infiltrating the nasal septum and the titers of OVA-specific antibody were measured 24h after the last administration. Ozone increased sneezing and nasal secretion induced by OVA, nasal responsiveness to physical stimuli, and the number of infiltrating eosinophils in a concentration-dependent manner. The titer of anti-OVA-IgG was increased in animals exposed to 0.6 ppm O(3). Thus, exposure to O(3) aggravated nasal allergy-like symptoms concentration dependently. The aggravation was caused by induction of nasal hyperresponsiveness, the infiltration of eosinophils, and the increase in the production of anti-OVA-IgG. The estimated maximum likelihood estimation concentrations (MLECs) and bench mark concentrations (BMCs) of O(3) for these indices were in the range of 0.09-0.18 and 0.02-0.06 ppm, respectively.     

Alveolar epithelial cell injuries by subchronic exposure to low concentrations of ozone correlate with cumulative exposure

Electron microscopy morphometry has been used to study the effects of cumulative exposure of low levels of inhaled O3 on lung proximal alveolar tissue. Six-week-old Fisher 344 rats were exposed to O3 in two different subchronic low-level exposure patterns. The first was a 12 hr/day exposure for 6 weeks and included two O3 concentrations, 0.12 and 0.25 ppm. The second consisted of an exposure profile having a background level of 0.06 ppm with an exposure peak 5 days each week that went from 0.12 to 0.25 ppm and back to 0.12 ppm over a 9-hr period. Rats given the second exposure pattern were exposed for either 3 or 13 weeks. Changes in the volumes of alveolar epithelium were found to be consistent and reproducible markers for cell injury and/or response. Results from the first study indicated that the relative volume of the type I epithelium increased 13 and 23% over the control value (p less than 0.05) following exposures for 6 weeks to 0.12 and 0.25 ppm, respectively. The magnitude of the increases were clearly concentration related. Similarly, when a fixed exposure concentration was employed the relative volume of type I epithelium was found to increase in proportion to the exposure time. In the second exposure, increases of 9 and 33% in relative volume of type I epithelium were found respectively after 3 and 13 weeks of exposure. If the total exposure determined by the product of O3 concentration (including background) and exposure time is plotted against the relative volume of type I epithelium from both the 0.12 ppm (60.5 ppm-hr) and 0.25 ppm (126 ppm-hr) exposures and the 3-week (45.3 ppm-hrs) and 13-week (196.2 ppm-hr) exposures, a linear relationship between increases in type I cell volume and the concentration X time product is observed. The coefficient of correlation (r2) for the linear regression of the animal means is 0.72. Changes in the volume of Type II epithelial cell also correlate with the concentration X time product (r2 = 0.66). This suggests that epithelial cell reactions to low-level subchronic exposure of O3 are directly related to the cumulative oxidant concentration. The pattern of exposure did not appear to affect the resulting degree of injury. Furthermore, a low level of background exposure may contribute to the epithelial cell injuries.     

Sanjoinine A isolated from Zizyphi Spinosi Semen augments pentobarbital-induced sleeping behaviors through the modification of GABA-ergic systems

Zizyphi Spinosi Semen (ZSS) has been widely used for the treatment of insomnia in oriental countries. This experiment was performed to investigate whether sanjoinine A, one of major alkaloid compounds of ZSS, has hypnotic effects and/or enhances pentobarbital-induced sleeping behaviors through the gamma-aminobutyric acid (GABA)-ergic systems. Sanjoinine A itself did not induce sleeping at the higher dose used in this experiment. However, sanjoinine A prolonged sleeping time and reduced the sleeping latency induced by pentobarbital in a dose-dependent manner similar to muscimol, a GABA(A) receptor agonist. Sanjoinine A also increased sleeping rate and sleeping time when administered combined with pentobarbital at a sub-hypnotic dosage and showed synergistic effects with muscimol in potentiating sleeping onset and enhancing sleeping time induced by pentobarbital. In addition, both sanjoinine A and pentobarbital increased chloride influx in primary cultured cerebellar granule cells. Sanjoinine A also showed similar effects with muscimol in potentiating chloride influx inducing effects of low dose pentobarbital. Sanjoinine A decreased GABA(A) receptor alpha-subunit expression and increased gamma-subunit expression, and had no effects on the abundance of beta-subunits in primary cultured cerebellar granule cells, showing different subunit expression from pentobarbital. In addition, we found that sanjoinine A also enhanced expression of glutamic acid decarboxylase (GAD), but pentobarbital did not. In conclusion, sanjoinine A itself does not induce sleeping, but it augments pentobarbital-induced sleeping behaviors through the modification of GABA-ergic systems.     

Nasopharyngeal removal of ozone in rabbits and guinea pigs

In estimating pollutant concentrations responsible for observed pulmonary effects, nasopharyngeal removal of the pollutant plays an important role. The nasopharyngeal removal of ozone (O3) in anesthetized male guinea pigs and male and female rabbits was determined by drawing O3 through the isolated upper airways at a constant flow rate which approximated the animal's respiratory minute volume. The tracheal O3 concentration in rabbits and guinea pigs was markedly similar and was linearly related to the chamber concentration of O3 over a range of 196--3920 micrograms/m3 (0.1--2.0 ppm O3). Regression analyses showed that O3 removal in the nasopharyngeal region is approximately 50% in both species. Both rabbit sexes responded similarly over the concentration range studied. Exposures of guinea pigs to O3 concentrations between 3920 and 5880 micrograms/m3 (2.0 and 3.0 ppm) showed that, at these higher concentrations, relatively more O3 is removed by the upper airways.     

Changes in the levels of polyunsaturated fatty acids in the lung and lecithin cholesterol acyl transferase activity in plasma of monkeys exposed to ambient levels of ozone

A group of 8 sub-adult bonnet monkeys (Macaca radiata) was exposed to 0.15 ppm ozone (O3) and another group of 8 to 0.3 ppm O3, 8 h/day, for 90 days. Four monkeys in the control group breathed filtered air during this period. Polyunsaturated fatty acids (PUFA) comprised about 22% of total fatty acids in the lungs of controls. The PUFA level decreased to about 90% and 6% in monkeys exposed to 0.15 ppm and 0.3 ppm O3, respectively. Lecithin cholesterol acyl transferase (LCAT) activity in the plasma of monkeys exposed to 0.15 ppm O3 was similar to that in the controls. However, the LCAT activity of plasma was significantly increased by the exposure of monkeys to 0.3 ppm O3.     

Alterations in urethan-induced adenoma formation in mice exposed to selenium and nickel

Female Swiss mice were exposed to sodium selenite (3 micrograms/ml selenium content) and nickelous chloride (100 micrograms/ml nickel content) in the drinking water on alternate days for 15 weeks. After 3 weeks of metal exposure, the mice were administered urethan (1.5 mg/g) intraperitoneally. Pulmonary adenoma formation was evaluated 12 weeks later. Selenium exposure did not alter the tumor incidence (P = 0.059) or the tumour size (P = 0.98). Nickel exposure did not affect the tumour incidence (P = 0.25), but increased the average tumour size (P = 0.0025). Combined selenium and nickel exposure resulted in significant interactions associated with tumour size (P = 0.00075) and tumour number (P = 0.045). Urethan-induced sleeping times were reduced by selenium exposure (P = 0.0049), but were unaffected by nickel exposure (P = 0.99). Combined metal exposure did not influence urethan-induced sleeping times (P = 0.48).     

Uptake and disposition of inhaled methanol vapor in humans.

Methanol is a widely used solvent and a potential fuel for motor vehicles. Human kinetic data of methanol are sparse. As a basis for biological exposure monitoring and risk assessment, we studied the inhalation toxicokinetics of methanol vapor in four female and four male human volunteers during light physical exercise (50 W) in an exposure chamber. The relative uptake of methanol was about 50% (range 47-53%). Methanol in blood increased from a background level of about 20 to 116 and 244 microM after 2 h exposure at 0, 100 ppm (131 mg/m3) and 200 ppm (262 mg/m3), respectively. Saliva showed substantially higher levels than blood immediately after exposure. This difference disappeared in a few minutes; thereafter the concentrations and time courses in blood, urine, and saliva were similar, with half times of 1.4, 1.7, and 1.3 h, respectively. The postexposure decrease of methanol in exhaled air was faster, with a half time of 0.8 h. The methanol concentrations were approximately twice as high in all four types of biological samples at 200 compared to 100 ppm. No increase in urinary formic acid was seen in exposed subjects. Our study indicates non-saturated, dose-proportional kinetics of methanol up to 200 ppm for 2 h. No gender differences were detected. Similar, parallel patterns were seen with regard to the methanol time courses in blood, urine, and saliva, whereas the concentration in exhaled air decreased markedly faster. Thus, apart from blood and urine, saliva also seems suitable for biomonitoring of methanol exposure.