Effect of Ozone on the Activities of Reactive Oxygen Scavenging Enzymes in Rbc of Ozone Exposed Japanese Charr (Salvelinus Leucomaenis)

The effect of ozone exposure on the activities of reactive oxygen scavenging enzymes (SOD?, catalase, GSH-Px) in RBC of Japanese charr (Salvelinus leucomaenis) was examined. Ozone (0, 0.4 and 0.7 ppm as initial concentrations) was exposed to Japanese charr for 30 min, which definitely caused serious membrane damage to RBC of fish. Ozone exposure at 0.4 and 0.7 ppm decreased activities of both catalase and GSH-Px by 80 to 57+ of the control. On the other hand, the activities of SOD remained unaffected even by 0.7 ppm ozone exposure. A hypothesis on the RBC membrane damage and participation of SOD and heme-iron was proposed.     

Effect of ozone exposure on the compositions of gill and erythrocyte membrane lipids and proteins of Japanese charr (Salvelinus leucomaenis)

• 1.1. Compositions of lipids and proteins of erythrocytes (RBC) and gills from Japanese charr (Salvelinus leucomaenis) which were exposed to 0.4 and 0.7 ppm ozone for 30 min were compared with those of the control.
• 2.2. On exposure to ozone, both RBC and gill membrane phospholipid content, especially phosphatidylethanolamine (PE), dropped.
• 3.3. The decrease of PE was brought about by the decrease of docosahexaenoic acid content which comprised the major component of PE.
• 4.4. RBC membrane protein with 215 and 225 kDa, which is equivalent to cytoskeletal protein, selectively disappeared on exposure to ozone.

     

Mechanism of oxidative damage to fish red blood cells by ozone

The present study was conducted to elucidate the adverse effects of ozone exposure on rainbow trout (Oncorhynchus mykiss) red blood cells (RBCs). We evaluated whether hemoglobin (Hb) or Hb-derived free iron could participate in the RBC damage using an in vitro ozone exposure system. Ozone exposure induced hemolysis, formation of methemoglobin, and RBC membrane lipid peroxidation. This RBC damage was not suppressed by the addition of a specific iron chelator (deferoxamine mesilate) to the medium but was suppressed by carbon monoxide (CO) treatment before ozone exposure. Generation of hydrogen peroxide (H2O2) in RBC was observed upon ozone exposure but was significantly suppressed by CO treatment before ozone exposure. Thus the Hb status (i.e., Hb redox condition) and H2O2 generation in RBC should play important roles in mediating RBC damage by ozone exposure. In other words, neither ozone nor its derivative directly attacked from the outside of the cell, but ozone that penetrated through the membrane derived the reactive oxygen species from Hb inside of the cell.     

Ozone alleviates ischemia/reperfusion injury by inhibiting mitochondrion‐mediated apoptosis pathway in SH‐SY5Y cells

Cerebral ischemia/reperfusion (I/R) injuries are common and often cause severe complications. Ozone has been applied for protecting I/R injury in animal models of several organs including cerebra, but the detailed mechanism remains unclear. 3‐(4,5‐Dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT) assay and lactate dehydrogenase measurement were used to determine the influence of ozone on cell activity and damage of SH‐SY5Y cells. Some redox items such as catalase (CAT), malondialdehyde (MDA), glutathione peroxidase (GSH‐Px), and superoxide dismutase (SOD) were measured by enzyme‐linked immunosorbent assay. The mitochondrial membrane potential (ΔΨ_m) was determined by JC‐1 assay. Cytochrome‐c (cyt‐c) level in the cytoplasm and mitochondrion was measured by western blotting. Apoptosis was determined by flow cytometry, and some apoptosis‐related molecules were detected by quantitative real‐time polymerase chain reaction and western blotting. Ozone alleviated oxidative damage by increasing GSH‐Px, SOD, CAT, and decreasing MDA. Ozone decreased mitochondrial damage caused by I/R injury and inhibited the release of cyt‐c from mitochondrion to cytoplasm in SH‐SY5Y cells. The cell apoptosis caused by I/R was inhibited by ozone, and ozone could decrease apoptosis by increasing the ratio of Bcl‐2/Bax and inhibiting caspase signaling pathway in SH‐SY5Y cells. Ozone has the ability of maintaining redox homeostasis, decreasing mitochondrion damage, and inhibiting neurocytes apoptosis induced by I/R. Therefore, ozone may be a promising protective strategy against cerebral I/R injury.     

Antioxidant defenses and biochemical changes in pacu (Piaractus mesopotamicus) in response to single and combined copper and hypoxia exposure

The effect of combined-factors (hypoxia+copper) on the biochemical parameters and antioxidant defenses were studied in the neotropical fish Piaractus mesopotamicus. Fish were exposed for 48 h to 0.4 mg Cu(2+) L(-1) (0.4Cu), hypoxia=50 mm Hg (Hpx), and 0.4 mg Cu(2) L(-1)+hypoxia=50 mm Hg (0.4CuHpx). The exposure to 0.4Cu increased the reactive oxygen species (ROS) in the liver, accompanied by increases in superoxide dismutase (SOD) and decreases in catalase (CAT) activity, showing the influence of copper in this protection. The exposure to Hpx decreased the activity of glutathione peroxidase (GSH-Px) and CAT. Exposure to a combined-factor caused an increase in the ROS production followed by an increase in SOD and a decrease in GSH-Px and CAT. At 0.4Cu, fish presented a reduction in CAT, while in Hpx decreases in SOD, CAT and GSH-Px were observed in red muscles. Single-factors were insufficient to cause ROS production. In combined-factors, increased ROS formation and decreased SOD, CAT and GSH-Px were observed. RBC increased in all groups, but only under combined-factors was there an increase in hemoglobin. Copper plasma concentration increased in groups exposed to copper. Na(+)/K(+)-ATPase activity in gills decreased in 0.4Cu and 0.4CuHpx, and increased in Hpx. Metallothionein concentration in gills increased under combined-factors. Combined-factors caused significant disturbances in the antioxidant defenses and biochemical parameters than single-factors.     

Effects of chromium supplementation on food energy utilization and the trace-element composition in the liver and heart of glucose-exposed young mice

Essentiality of selenium (Se) for Japanese quail,Coturnix coturnix japonica, was confirmed using a formulated semipurified low-Se diet (basal) (0.05 ppm). Selenium-deficiency symptoms appeared in quails on this diet within 15 d, which corresponded to low levels of hemolysate glutathione peroxidase (GSH-Px) activity. Selenium administration at 0.05 and 2.0 ppm levels resulted in an increase of hemolysate GSH-Px activity by 64 and 116%, respectively, in both short- and long-term experiments. Growth over a 2-mo period increased the hemolysate GSH-Px activity by 120% at each level of dietary Se. A differential response was exhibited by hepatic mitochondrial and soluble GSH-Px activity to Se supplementation, the former increasing progressively with increments of Se at 0.05, 2.0, and 4.0 ppm by 45, 70 and 150%, respectively. The soluble GSH-Px activities of tissues, such as liver, kidney, and testis, and RBC membrane-bound activity remained unchanged in long-term studies at different levels of Se. Replenishment of Se to quails maintained on low-Se diets reflected no change in RBC membrane-bound and liver-soluble GSH-Px activities, although the activity in hemolysate increased consistently with Se. The GSH-Px activity in hemolysate was restored to the levels comparable to those of long-term studies only at Se administration at the 2.0-ppm level. The differential response of mitochondrial and soluble GSH-Px activities to Se and other related observations on mitochondrial functions suggest an additional role for Se in mitochondrial membrane processes and glutathione-related metabolic regulations.     

Ozone inhibits endothelial cell cyclooxygenase activity through formation of hydrogen peroxide

We have previously demonstrated that a 2H exposure of cultured pulmonary endothelial cells to ozone (0.0-1.0 ppm) in-vitro resulted in a concentration-dependent reduction of endothelial prostacyclin production (90% decrease at the 1.0 ppm level). Ozone-exposed endothelial cells, incubated with 20 uM arachidonate, also demonstrated a significant inhibition of prostacyclin synthesis. To further examine the mechanisms of the inhibition of prostacyclin synthesis, bovine pulmonary endothelial cells were exposed to 1.0 ppm ozone for 2H. A significant decrease in prostacyclin synthesis was found within 5 min of exposure (77 +/- 36% of air-exposed control values, p less than 0.05). Endothelial prostacyclin synthesis returned to baseline levels by 12H after ozone exposure, a time point which was similar to the recovery time of unexposed endothelium treated with 0.5 uM acetylsalicylic acid. Incubation of endothelial cells, previously exposed to 1.0 ppm ozone for 2 hours, with 4 uM PGH2 resulted in restoration of essentially normal prostacyclin synthesis. When endothelial cells were co-incubated with catalase (5 U/ml) during ozone exposure, no inhibition of prostacyclin synthesis was observed. Co-incubation with either heat-inactivated catalase or superoxide dismutase (10 U/ml) did not affect the ozone-induced inhibition of prostacyclin synthesis. These data suggest that H2O2 is a major toxic species produced in endothelial cells during ozone exposure and responsible for the inhibition of endothelial cyclooxygenase activity.     

Age-related changes in antioxidant enzyme activities and lipid peroxidation in lungs of control and sulfur dioxide exposed rats

Antioxidant defenses within the lung are pivotal in preventing damage from oxidative toxicants. There have also been several reports with conflicting results on the antioxidant system during aging. In this study, we attempted to investigate age-related alterations in both antioxidant enzyme activities and thiobarbituric acid-reactive substances (TBARS), a product of lipid peroxidation, in the whole lung of control and sulfur dioxide (SO₂) exposed rats of different age groups (3-, 12-, and 24-months-old). Swiss-Albino Male rats were exposed to 10 ppm SO₂ 1 hr/day, 7 days/week for 6 weeks. The antioxidant enzymes examined include Cu,Zn-superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px) and glutathione S-transferase (GST). A mixed pattern of age-associated alterations in antioxidant activities was observed. SOD, GSH-Px and GST activities were increased with age, but CAT activity was decreased. Lung SOD, GSH-Px and GST activities were also increased in response to SO₂. The level of TBARS was increased with age. SO₂ exposure stimulated lipid peroxide formation in the lung as indicated by an increase in the level of TBARS. These findings suggest that both aging and SO₂ exposure may impose an oxidative stress to the body. We conclude that the increase in the activities of the antioxidant enzymes of the lung during aging, could be interpreted as a positive feedback mechanism in response to rising lipid peroxidation.     

Age-related changes in antioxidant enzyme activities and lipid peroxidation in lungs of control and sulfur dioxide exposed rats

Antioxidant defenses within the lung are pivotal in preventing damage from oxidative toxicants. There have also been several reports with conflicting results on the antioxidant system during aging. In this study, we attempted to investigate age-related alterations in both antioxidant enzyme activities and thiobarbituric acid-reactive substances (TBARS), a product of lipid peroxidation, in the whole lung of control and sulfur dioxide (SO₂) exposed rats of different age groups (3-, 12-, and 24-months-old). Swiss-Albino Male rats were exposed to 10 ppm SO₂ 1 hr/day, 7 days/week for 6 weeks. The antioxidant enzymes examined include Cu,Zn-superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px) and glutathione S-transferase (GST). A mixed pattern of age-associated alterations in antioxidant activities was observed. SOD, GSH-Px and GST activities were increased with age, but CAT activity was decreased. Lung SOD, GSH-Px and GST activities were also increased in response to SO₂. The level of TBARS was increased with age. SO₂ exposure stimulated lipid peroxide formation in the lung as indicated by an increase in the level of TBARS. These findings suggest that both aging and SO₂ exposure may impose an oxidative stress to the body. We conclude that the increase in the activities of the antioxidant enzymes of the lung during aging, could be interpreted as a positive feedback mechanism in response to rising lipid peroxidation.     

Influence of Catalase and Superoxide Dismutase on Ozone Inactivation of Listeria monocytogenes

The effects of ozone at 0.25, 0.40, and 1.00 ppm on Listeria monocytogenes were evaluated in distilled water and phosphate-buffered saline. Differences in sensitivity to ozone were found to exist among the six strains examined. Greater cell death was found following exposure at lower temperatures. Early stationary-phase cells were less sensitive to ozone than mid-exponential- and late stationary-phase cells. Ozonation at 1.00 ppm of cabbage inoculated with L. monocytogenes effectively inactivated all cells after 5 min. The abilities of in vivo catalase and superoxide dismutase to protect the cells from ozone were also examined. Three listerial test strains were inactivated rapidly upon exposure to ozone. Both catalase and superoxide dismutase were found to protect listerial cells from ozone attack, with superoxide dismutase being more important than catalase in this protection.     

Ozone inhibits endothelial cell cyclooxygenase activity through formation of hydrogen peroxide

We have previously demonstrated that a 2H exposure of cultured pulmonary endothelial cells to ozone (0.0–1.0 ppm) resulted in a concentration-dependent reduction of endothelial prostacyclin production (90% decrease at the 1.0 ppm level). Ozone-exposed endothelial cells, incubated with 20 uM arachidonate, also demonstrated a significant inhibition of prostacyclin synthesis. To further examine the mechanisms of the inhibition of prostacyclin synthesis, bovine pulmonary endothelial cells were exposedto 1.0 ppm ozone for 2H. A significant decease in protacyclin synthesis was found within 5 min of exposure (77 ± 36% of air-exposed control values, p < 0.05). Endothelial prostacyclin synthesis returned to baseline levels by 12H after ozone exposure, a time point which was similar to the recovery time of unexposed endothelium treated with 0.5 uM acetylsalicylic acid. Incubation of endothelial cells, previously exposed to 1.0 ppm ozone for 2 hours, with 4 uM PGH₂ resulted in restoration of essentially normal prostacyclin synthesis. When endothelial cells were co-incubated with catalase (5U/ml) during ozone exposure, no inhibition of prostacycline synthesis was observed. Co-incubation with either heat-inactivated catalase or superoxide dismutase (10U/ml) did not affect the ozone-induced inhibition of prostacycline synthesis. These data suggest that H₂O₂ is a major toxic species produced in endothelial cells during ozone exposure and responsible for the inhibiton of endothelial cyclooxygenase activity.     

A Historical Overview of the Ozone Exposure Problem

Ozone can be found in essentially all locations in the troposphere. Too much exposure of vegetation and humans to this potent oxidizing gas can prove toxic. Reports of human toxicity to ozone first appeared in the 1800's from accidental occupational exposures when ozone was first discovered. Ozone was recognized as damaging field vegetation with a report of altered leaf morphology in grapes in the 1950s. Ozone is the major oxidant component in photochemical smog, and is produced by reactions of volatile organic compounds and oxides of nitrogen with sunlight present. Soon after the inception of the U.S. Environmental Protection Agency (US EPA), the Agency set a general “oxidants” standard (which included ozone) in 1971. A primary standard was created to protect human health and a secondary standard to protect against agricultural losses, ecological damage, and other losses. Ozone concentrations have decreased steadily over the last two decades in some areas of the U.S., but have increased in other areas. Several aspects of ozone exposure need further characterization, including better determination of rural concentrations and the relationship of outdoor to indoor concentrations. Ozone is one of the six criteria air pollutants requiring a formal reexamination of the new findings of effects on health and vegetation on a periodic basis, a process that leads to the publication of an US EPA criteria document. As a result of further study concerning ozone effects, significant changes were made to pollution standards in 1979 and 1997. This toxicant has remained a major air pollutant of concern in the U.S. despite regulation and intense study over several decades.     

Ozone inhibits prostacyclin synthesis in pulmonary endothelium

The effects of ozone on lung arachidonate metabolism in-vitro were studied in cultured bovine pulmonary endothelial cells exposed for 2 hours to ozone in concentrations up to 1.0 ppm. A concentration-dependent decrease in prostacyclin synthesis was found (90% decrease at the highest ozone level of 1.0 ppm). The inhibition of prostacyclin synthesis was not due to a decreased release of arachidonic acid from membrane lipids. We also examined the hypoxic pulmonary vasoconstrictive response to 10% oxygen inhalation in anesthetized dogs in-vivo after exposure to 1.0 ppm ozone for 1 hour. Pulmonary vascular resistance was significantly increased after ozone exposure, similar to the findings in dogs given indomethacin (15 mg/kg). The percentage change in the hypoxic pulmonary pressor response was similar between the ozone exposure and indomethacin-treated groups, although due to the variance of the pulmonary vascular resistance values during hypoxia the results did not reach statistical significance. These results suggest that ozone inhalation affects pulmonary endothelial arachidonate metabolism in-vivo as well as in-vitro.     

The effect of paraquat on the peroxide metabolism enzymes in erythrocytes of freshwater fish species

The toxic effects of 10 ppm paraquat in vivo on the enzymes superoxide dismutase (SOD), catalase (C), peroxidase (P), glutathione peroxidase (GSH-Px) and on lipid peroxidation (LP) were estimated in erythrocytes of the carp, the tench and the crucian carp. Paraquat caused activity enhancement of the peroxide metabolism enzymes and increase of the lipid peroxidation in the carp and the crucian carp. The enzyme activities and lipid peroxidation were dependent on the species and on the length of the exposure to paraquat.     

Ozone increases the permeability of isolated pea chloroplasts

The effect of short-term exposure of chloroplasts isolated from the leaves of Pisum sativum to high concentrations of ozone was examined. The inhibitory effect of O₃ on endogenous photophosphorylation was apparently related to an increased permeability of the chloroplast limiting membranes induced by ozone exposure. A 5 min treatment with 50 ppm O₃ reduced the reflection coefficient of meso-erythritol from 0.84 to 0.58 and that of glycerol from 0.26 to 0.03. Such decreases in reflection coefficients indicate that ozone caused a marked increase in the permeability of the limiting membranes of the chloroplasts, which may result from an oxidation of membrane lipids. The decrease in the reflection coefficient of meso-erythritol was proportional both to ozone concentration (up to 30 ppm for 5 min of bubbling) and to time (up to 5 min at 30 ppm). Extrapolating these results to lower concentrations and longer times, ozone injury should be possible for a 2 hr exposure of plants to 0.3 ppm ozone, as is indeed the case.     

Ozone exposure alters tracheobronchial mucociliary function in humans

Mucociliary function is a primary defense mechanism of the tracheobronchial airways, and yet the response of this system to an inhalational hazard, such as ozone, is undefined in humans. Utilizing noninvasive techniques to measure deposition and retention of insoluble radiolabeled particles on airway mucous membranes, we studied the effect on mucus transport of 0.2 and 0.4 ppm ozone compared with filtered air (FA) in seven healthy males. During 2-h chamber exposures, subjects alternated between periods of rest and light exercise with hourly spirometric measurement of lung function. Mechanical and mucociliary function responses to ozone by lung airways appeared concentration dependent. Reduction in particle retention was significant (P less than 0.005) (i.e., transport of lung mucus was increased during exposure to 0.4 ppm ozone and was coincident with impaired lung function; e.g., forced vital capacity and midmaximal flow rate fell by 12 and 16%, respectively, and forced expiratory volume at 1 s by 5%, of preexposure values). Regional analysis indicated that mucus flow from distal airways into central bronchi was significantly increased (P less than 0.025) by 0.2 ppm ozone. This peripheral effect, however, was buffered by only a marginal influence of 0.2 ppm ozone on larger bronchi, such that the resultant mucus transport for all airways of the lung in aggregate differed only slightly from FA exposures. These data may reflect differences in regional diffusion of ozone along the respiratory tract, rather than tissue sensitivity. In conclusion, mucociliary function of humans is acutely stimulated by ozone and may result from fluid additions to the mucus layer from mucosal and submucosal secretory cells and/or alteration of epithelial permeability.     

Ozone enhancement of lower airway allergic inflammation is prevented by gamma-tocopherol

Ozone is a commonly encountered environmental oxidant which has been linked to asthma exacerbation in epidemiological studies. Ozone induces airway inflammation and enhances response to inhaled allergen. It has been suggested that antioxidant therapy may minimize the adverse effects of ozone in asthma. We have previously shown that the antioxidant gamma-tocopherol (gammaT), an isoform of vitamin E, also has anti-inflammatory effects. We employed a Brown Norway rat model of ozone-enhanced allergic responses to test the therapeutic effects of gammaT on O(3)-induced airway inflammation. Ovalbumin (OVA)-sensitized rats were intranasally challenged with 0 or 0.5% OVA on Days 1 and 2, and exposed to 0 or 1 ppm ozone (8 h/day) on Days 4 and 5. Rats were also given 0 or 100 mg/kg gammaT on Days 2 through 5. Pulmonary tissue and bronchoalveolar lavage fluid (BALF) were collected on Day 6. OVA challenge caused increased total cells (267% increase) and eosinophils (4000%) in BALF that was unaffected by ozone exposure. Morphometric evaluation of lung tissue revealed increases in intraepithelial mucosubstances (IM) (300%) and subepithelial eosinophils (400%) in main axial airways. Ozone exposure of allergic rats enhanced IM increases in proximal axial airways (200%), induced cys-leukotrienes, MCP-1, and IL-6 production in BALF, and upregulated expression of IL-5 and IL-13 mRNA. gammaT treatment had no effect on IM increases by allergen, but blocked enhancement by ozone. gammaT attenuated both OVA- or ozone-stimulated eosinophilic infiltration, and increases of BALF cys-leukotrienes, MCP-1, and IL-6, as well as IL-5 and IL-13 mRNA. These data demonstrate broad anti-inflammatory effects of a gammaT and suggest that it may be an effective therapy of allergic airway inflammation.     

The Physiological Response of Phyllostachys edulis under the Elevated Atmospheric Ozone

In order to provide theoretical evidences for bamboo cultivation under the background of climate change, the method of open top chambers (OTCs) was employed to approach the effects of elevated ozone on photosynthetic pigments content, lipid peroxidation and anti oxidation enzymes in the leaves of Phyllostachys edulis. The result indicated that with the increasing of ozone concentration, the content of the chlorophyll, carotenoid and SOD activity decreased, while the content of souble protein, relative electrical conductivity, contents of MDA, O2- and the activity of POD increased.Correlation analyses showed that there was significant negative correlation between O2- content and SOD activity as well as photosynthetic pigment,whereas significant positive correlation between O2- and relative electeical conductivity, MDA, POD as well as soluble protein. It was summarried that, on one hand, long time exposure to high ozone concentration exposure, accelerated the aging of leaves, intensified the damage to membrane lipid, and destroyed the structure of cell membrane and the function of anti oxidation system as well. It affected the regular growth of P.edulis. This research was conducted to provide theoretical evidence for bamboo cultivation during this time of possible climate change.     

Ozone therapy on rats submitted to subtotal nephrectomy: role of antioxidant system

Chronic renal failure (CRF) represents a world health problem. Ozone increases the endogenous antioxidant defense system, preserving the cell redox state. The aim of this study is to evaluate the effect of ozone/oxygen mixture in the renal function, morphology, and biochemical parameters, in an experimental model of CRF (subtotal nephrectomy). Ozone/oxygen mixture was applied daily, by rectal insufflation (0.5 mg/kg) for 15 sessions after the nephrectomy. Renal function was evaluated, as well as different biochemical parameters, at the beginning and at the end of the study (10 weeks). Renal plasmatic flow (RPF), glomerular filtration rate (GFR), the urine excretion index, and the sodium and potassium excretions (as a measurement of tubular function) in the ozone group were similar to those in Sham group. Nevertheless, nephrectomized rats without ozone (positive control group) showed the lowest RPF, GFR, and urine excretion figures, as well as tubular function. Animals treated with ozone showed systolic arterial pressure (SAP) figures lower than those in the positive control group, but higher values compared to Sham group. Serum creatinine values and protein excretion in 24 hours in the ozone group were decreased compared with nephrectomized rats, but were still higher than normal values. Histological study demonstrated that animals treated with ozone showed less number of lesions in comparison with nephrectomized rats. Thiobarbituric acid reactive substances were significantly increased in nephrectomized and ozone-treated nephrectomized rats in comparison with Sham group. In the positive control group, superoxide dismutase (SOD) and catalase (CAT) showed the lowest figures in comparison with the other groups. However, ozone/oxygen mixture induced a significant stimulation in the enzymatic activity of CAT, SOD, and glutathione peroxidase, as well as reduced glutathione in relation with Sham and positive control groups. In this animal model of CRF, ozone rectal administrations produced a delay in the advance of the disease, protecting the kidneys against vascular, hemorheological, and oxidative mechanisms. This behavior suggests ozone therapy has a protective effect on renal tissue by downregulation of the oxidative stress shown in CRF.     

Respiratory and behavioral effects of ozone on a lizard and a frog

Ozone at concentrations found in urban air pollution is known to have significant physiological effects on humans and other mammals. Exposure of the lizard, Sceloporus occidentalis, to 0.6 ppm ozone for 4 h at 25 degrees C induced 1.6 degrees C of behavioral hypothermia immediately following exposure, but selected body temperature recovered to control 35.3 degrees C the next day. Lizards exposed at 35 degrees C to 0.6 ppm ozone for 4 h selected body temperatures 1.9 degrees C below controls after exposure, and the behavioral hypothermic response persisted and increased to 3.3 degrees C the following day. Four-hour exposures of the frog, Pseudacris cadaverina, to 0.2 to 0.8 ppm ozone resulted in concentration-dependent alterations of respiration including depression of lung ventilation and oxygen consumption and the adoption of a low profile posture that reduced the exposed body surface. Ozone levels in wilderness habitats downwind of urban sources can potentially have stressful physiological effects on wildlife. Defensive physiological and behavioral reactions to ozone exposure may interfere with routine activities, and oxidant air pollution may be in part responsible for observed wildlife population declines.