Acute Effects of Ozone on Heart Rate and Body Temperature in the Unanesthetized, Unrestrained Rat Maintained at Different Ambient Temperatures

Does ozone inhalation cause adverse metabolic effects in humans? A systematic review

We utilized a practical, transparent approach for systematically reviewing a chemical-specific evidence base. This approach was used for a case study of ozone inhalation exposure and adverse metabolic effects (overweight/obesity, Type 1 diabetes [T1D], Type 2 diabetes [T2D], and metabolic syndrome). We followed the basic principles of systematic review. Studies were defined as "Suitable" or "Supplemental." The evidence for Suitable studies was characterized as strong or weak. An overall causality judgment for each outcome was then determined as either causal, suggestive, insufficient, or not likely. Fifteen epidemiologic and 33 toxicologic studies were Suitable for evidence synthesis. The strength of the human evidence was weak for all outcomes. The toxicologic evidence was weak for all outcomes except two: body weight, and impaired glucose tolerance/homeostasis and fasting/baseline hyperglycemia. The combined epidemiologic and toxicologic evidence was categorized as weak for overweight/obesity, T1D, and metabolic syndrome,. The association between ozone exposure and T2D was determined to be insufficient or suggestive. The streamlined approach described in this paper is transparent and focuses on key elements. As systematic review guidelines are becoming increasingly complex, it is worth exploring the extent to which related health outcomes should be combined or kept distinct, and the merits of focusing on critical elements to select studies suitable for causal inference. We recommend that systematic review results be used to target discussions around specific research needs for advancing causal determinations.

Acute ozone exposure can cause cardiotoxicity: Mitochondria play an important role in mediating myocardial apoptosis

OBJECTIVE

To clarify the cardiotoxicity induced by acute exposure to different concentrations of ozone in both gender rats and explore the underlying mechanisms.

METHODS

A total of 240 rats were randomly sorted into 6 groups with equal numbers of male and female rats in each group. The rats were subjected to ozone inhalation at concentrations of 0, 0.12, 0.5, 1.0, 2.0 and 4.0 ppm, respectively, for 6 h. After ozone exposure, function indicators, myocardial injury indexes and risk factors of cardiovascular disease in blood were assayed.

RESULTS

High ozone exposure resulted in sustained ventricular tachycardia in male and female rats. Myocardial apoptosis in male rats started from 1.0 ppm ozone, and that in female rats started from 2.0 ppm ozone (p < 0.05). Caspase-9 increased significantly from 0.12 ppm ozone (p < 0.01) in both gender rats, while caspase-3 was initially activated at 0.5 ppm ozone. From 1.0 ppm ozone, mitochondrial cristae and myofilaments dissolved. The ratio of Bcl-2/Bax decreased significantly from 0.12 ppm and MRCC-IV decreased significantly from 2.0 ppm by ozone.

CONCLUSION

Acute ozone exposure can cause paroxysmal ventricular tachycardia in rats. Moreover, the changes of inflammatory factors in the heart tissues of female and male rats after ozone exposure were greater than those of oxidative stress. This study reported for the first time that 6 h ozone exposure does not cause acute cardiomyocyte necrosis, but promotes cardiomyocyte apoptosis in a mitochondrial-dependent manner. Ozone could regulate caspases-3 dependent cardiomyocyte apoptosis by affecting the balance between caspase-9 and XIAP.

Episodic ozone exposure in adult and senescent Brown Norway rats: acute and delayed effect on heart rate, core temperature and motor activity

Setting exposure standards for environmental pollutants may consider the aged as a susceptible population but the few published studies assessing susceptibility of the aged to air pollutants are inconsistent. Episodic ozone (O₃) is more reflective of potential exposures occurring in human populations and could be more harmful to the aged. This study used radiotelemetry to monitor heart rate (HR), core temperature (T(c)) and motor activity (MA) in adult (9-12 months) and senescent (20-24 months) male, Brown Norway rats exposed to episodic O₃ (6 h/day of 1 ppm O₃ for 2 consecutive days/week for 13 weeks). Acute O₃ initially led to marked drops in HR and T(c). As exposures progressed each week, there was diminution in the hypothermic and bradycardic effects of O₃. Senescent rats were less affected than adults. Acute responses were exacerbated on the second day of O₃ exposure with adults exhibiting greater sensitivity. During recovery following 2 d of O₃, adult and senescent rats exhibited an elevated T(c) and HR during the day but not at night, an effect that persisted for at least 48 h after O₃ exposure. MA was elevated in adults but not senescent rats during recovery from O₃. Overall, acute effects of O₃, including reductions in HR and T(c), were attenuated in senescent rats. Autonomic responses during recovery, included an elevation in T(c) with a pattern akin to that of a fever and rise in HR that were independent of age. An attenuated inflammatory response to O₃ in senescent rats may explain the relatively heightened physiological response to O₃ in younger rats.

Central and peripheral changes in catecholamine biosynthesis and turnover in rats after a short period of ozone exposure

We investigated in rat the effects of ozone exposure (0.7 ppm) for 5 h on the catecholamine biosynthesis and turnover in sympathetic efferents and various brain areas. For this purpose, the activity of tyrosine hydroxylase, the rate-limiting enzyme in catecholamine biosynthesis, was assessed in superior cervical ganglia and in two major noradrenergic cell groups, A2 and A6 (locus coeruleus). Tyrosine hydroxylase activity was estimated in vivo by measuring the accumulation of l-dihydroxyphenylalanine after pharmacological blockade of L-aromatic acid decarboxylases by NSD-1015 (100 mg/kg i.p.). The catecholamine turnover rate was measured after inhibition of tyrosine hydroxylase by alpha-methyl-para-tyrosine (AMPT, 250 mg/kg, i.p., 2.5 h) in peripheral sympathetic target organ (heart and lungs) as well as in some brain catecholamine terminal areas (cerebral cortex, hypothalamus and striatum). Ozone caused differential effects according to the structure. Catecholamine biosynthesis was stimulated in superior cervical ganglia (+44%, P < 0.05) and caudal A2 subset (+126%, P < 0.01), whereas catecholamine turnover was increased in heart (+183%, P < 0.01) and cortex (+22%, P < 0.05). On the other hand, catecholamine turnover was inhibited in lungs (-53%, P < 0.05) and striatum (-24%, P < 0.05). A brief exposure to ozone, at a concentration chosen to mimic pollution level encountered in urban areas, can modulate catecholamine biosynthesis and utilization rate in the sympathetic and central neurones.

Cardiac and thermoregulatory responses to inhaled pollutants in healthy and compromised rodents: modulation via interaction with environmental factors

Rodents often demonstrate a profound depression in physiological function following acute exposure to toxic xenobiotic agents. This effect, termed the hypothermic response, is primarily characterized by significant decreases in core temperature and heart rate and is generally accompanied by similar deficits in other important functional parameters. This response appears to be remarkably consistent across a wide variety of toxic agents and exposure regimens; however, the magnitude and duration of the induced effects may be modulated by changes in dose, animal mass, and environmental conditions. While the initiating stimulus and underlying mechanism(s) remains elusive, this response may represent an inherent reflexive pattern that is unique to the rodent and serves to attenuate the induced toxicity. Given that rodents are the primary animal species used in toxicological studies, it is important to consider this hypothermic response and its modulatory factors when interpreting the results of such studies and extrapolating those results to man.

Overview of testing methods used in inhalation toxicity: from facts to artifacts

For smaller rodent species, homogenous in size and growth, small head or nose-only chambers are commonly used up to subchronic exposure durations, whereas larger whole-body exposure chambers are used for long-term exposures or exposure paradigms exceeding the normal working day. The advantages and disadvantages of each different technique have already been identified and published in detail. It is often believed best that whole-body inhalation chambers simulate potential human exposure to environmental chemicals or pesticides and this serves as a justification for preferring this mode of exposure. However, real-life exposure conditions of humans cannot be readily duplicated. A comparable mode of exposure may be employed rather than duplicating both the exposure regimens and atmospheres similar to those present in real-world settings. Especially in inhalation studies with complex mixtures, in which atmosphere generation is difficult to control, non-homogenous exposure atmospheres and artifacts are more likely to occur in larger whole-body chambers than in the smaller nose-only inhalation chambers. Inhalation studies with complex mixtures not only face all the challenges of traditional inhalation toxicity testing, but also they are frequently subject to artifacts not readily detected. Thus, a disproportionation of volatile and particulate constituents might occur in inhalation chambers depend on selected technical features, i.e., whether a dynamic or (quasi)static mode of exposure is chosen. Inappropriate timing of the sampling of biological specimens may lead to the underestimation of effects, especially in whole-body exposed animals.

Critical analysis of potential body temperature confounders on neurochemical endpoints caused by direct dosing and maternal separation in neonatal mice: a study of bioallethrin and deltamethrin interactions with temperature on brain muscarinic receptors

The present investigation was conducted to understand better possible confounding factors caused by direct dosing of neonatal mice during the pre-weaning developmental period. By direct dosing, pups might encounter thermal challenges when temporarily removed from their 'natural habitat'. Typically, this leads to a cold environment and food deprivation (impaired lactation) and modulation of the toxic potency of the substance administered. Growth retardation as a consequence of such behavioural changes in pups makes it increasingly difficult to differentiate specific from non-specific mechanisms. Neonatal NMRI mice were dosed daily by gavage (0.7 mg kg(-1) body wt.) from postnatal day (PND) 10-16 with S-bioallethrin, deltamethrin or the vehicle. Then the pups, including their non-treated foster dams, were subjected temporarily for 6 h day to a hypo-, normo- or hyperthermic environment, which was followed by normal housing. The measured temperatures in the environmental chambers were ca. 21, 25 and 30 degrees C, respectively. Thus, temperatures in the hypo- and normothermic groups are comparable to the temperatures commonly present in testing laboratories, whereas the hyperthermic condition is that temperature typically present in the 'natural habitat' of pups. A deviation from the normal behaviour of both pups and dams was observed in the hypo- and normothermic groups. In these groups the rectal temperatures of pups were markedly decreased, especially in the early phase of the study (PND 10-12). Neonates that received either test substance displayed changes in body weights and brain weights at terminal sacrifice (PND 17) when subjected temporarily to a non-physiological environment. An enormous influence of environmental temperature on the density of muscarinic receptors in the crude synaptosomal fraction of the cerebral cortex was ascertained. In summary, these results demonstrate that the direct dosing of thermolabile neonatal mice by gavage is subject to significant artefacts that render the interpretation of findings from such studies difficult. It appears that if direct dosing of neonatal pups is mandated, and inhalation is a relevant route of exposure, the combined inhalation exposure of dams with their litters is an alternative procedure that does not cause disruption of the 'natural habitat' of pups. However, owing to their higher ventilation, under such conditions the pups may receive dosages at least double those of the dams.

Effects of ozone on evaporative water loss and thermoregulatory behavior of marine toads (Bufo marinus)

Ozone (O(3)) is a strong pulmonary irritant and causes a suite of respiratory tract inflammatory responses in humans and other mammals. In addition to lung injury, rodents exposed to O(3) exhibit a pronounced decrease in core body temperature at rest, which may offer a protective effect against O(3) damage. The effects of O(3) on other vertebrates have not been studied. Compared to individuals exposed to air (N=34), Bufo marinus toads exposed to O(3) (N=32) for 4 h lost 3.78 g body mass (adjusted mean from analysis of covariance, body mass mean+/-SD, 90.1+/-21.90 g). We tested the thermoregulatory responses of 22 toads in a thermal gradient 1, 24, and 48 h after 4-h exposure to air (N=11) or 0.8 ppm O(3) (N=11). Individual toad thermal preferences were also significantly repeatable across all trials (intraclass correlation=0.66, P <0.001). We did not observe a direct effect of O(3) exposure on the preferred body temperatures (PBT) of toads. However, O(3) exposure did have an indirect effect on selected temperatures. Ozone-exposed toads with higher evaporative water loss rates, in turn, also selected lower PBT, voluntary minimum, and voluntary maximum temperatures 24 h post-exposure. Ozone exposure may thus alter both water balance and thermal preferences in anuran amphibians.

Inhalation studies in laboratory animals--current concepts and alternatives

Highly standardized and controlled inhalation studies are required for hazard identification to make test results reproducible and comparable and to fulfill general regulatory requirements for the registration of new drugs, pesticides, or chemicals. Despite significant efforts, the results of inhalation studies have to be analyzed judiciously due to the great number of variables. These variables may be related to technical issues or to the specific features of the animal model. Although inhalation exposure of animals mimics human exposure best, ie, error-prone route-to-route extrapolations are not necessary, not all results obtained under such very rigorous test conditions may necessarily also occur under real-life exposure conditions. Attempts are often made to duplicate as closely as possible these real-life exposure conditions of humans in appropriate bioassays. However, this in turn might affect established baseline data, rendering the interpretation of new findings difficult. In addition, specific use patterns, eg, of inhalation pharmaceuticals or pesticide-containing consumer products, may impose test agent-specific constraints that challenge traditional approaches. Moreover, specific modes of action of the substance under investigation, the evaluation of specific endpoints, or the clarification of equivocal findings in common rodent species may require exposure paradigms or the use of animal species not commonly used in inhalation toxicology. However, particularly in inhalation toxicology, the choice of animal models for inhalation toxicity testing is usually based on guideline requirements and practical considerations, such as exposure technology, expediency, and previous experience rather than validity for use in human beings. Larger animal species, apart from the welfare aspects, may require larger inhalation chambers to accommodate the animals, but for technical reasons and the difficulty of generating homogeneous exposure atmospheres in such inhalation chambers, this may jeopardize the outcome of the study. Some of the many variables and possible artifacts likely to occur in animal inhalation studies are addressed in this paper.

Impact of the hypothermic response in inhalation toxicology studies

Previous studies from this laboratory showed that the decreases in Tco and associated functional parameters often observed in rodents following exposure to xenobiotic agents are capable of modulating the subsequent toxic response and that the magnitude of this induced hypothermic response may itself be modified by a number of experimental conditions. A moderate hypothermic response, characterized by a temperature drop of approximately 2 degrees C, appears to afford the optimal protection. Studies in which exposures occur through inhalation of harmful gases or particles present a special set of problems. In such studies, the dose of the toxic agent to which the animal is exposed is a function of the concentration of the agent in the atmosphere and the minute ventilation of the animal. Although ambient concentrations is generally held constant in laboratory studies, minute ventilation varies directly with metabolism, and both of these parameters may change significantly across experimental conditions. Thus, at low Tas, metabolism and minute ventilation are relatively high and uptake of inhalable toxic agents is increased. However, the development of the hypothermic response during the exposure entails a directly correlated reduction in these parameters and, presumably, in dose. For the most part, inhalation toxicological studies are conducted using resting animals or exercising humans. Animals are sometimes concurrently exposed to CO2 to simulate the increased ventilation of exercise and more closely mimic human studies. The experimental protocols employed in the above inhalation studies permitted examination of (1) the impact of species, size, handling stress, and changes in Ta on both the induced hypothermic response and the concomitant pulmonary toxicity; (2) the additive impact of exercise stress on O3 toxicity; and (3) the toxicity of ambient-derived particulate matter in normal rats and in rats with preexisting pulmonary inflammation. The results of these studies demonstrate that the magnitude of the induced hypothermic response is directly proportional to the uptake of the toxic agent by the lung and inversely proportional to the mass of the animal and the ambient temperature at which the exposure is conducted. The hypothermic response is sensitive to a number of experimental stresses including handling and changes in cage conditions. Exercise attenuates the hypothermic response, whereas CO2-stimulated increases in ventilation employed as an exercise surrogate may potentiate the response. Toxic exposures conducted in animals with lung disease or compromised pulmonary function may induce a severe hypothermic response while comparable exposures in normal animals produce only mild or moderate responses. In general, the development of the hypothermic response in the presence of ambient pollutants serves to decrease the minute ventilation of the animal and therefore limits the uptake and dose of the airborne toxicant. The results of these inhalation studies support our previous conclusions concerning the impact of the hypothermic response on toxicity and emphasize the need to monitor and incorporate these changes in functional parameters into analyses of toxicological data. Furthermore, because humans do not demonstrate a robust hypothermic response following exposure to toxic agents, extrapolation of the results obtained from animal studies and comparisons with data from human studies are considerably more complicated.

Ozone toxicity in the rat. III. Effect of changes in ambient temperature on pulmonary parameters

Pulmonary toxicity of ozone (O3) was examined in adult male Fischer 344 rats exposed to 0.5 parts/million O3 for either 6 or 23 h/day over 5 days while maintained at an ambient temperature (Ta) of either 10, 22, or 34 degrees C. Toxicity was evaluated by using changes in lung volumes and the concentrations of constituents of bronchoalveolar lavage fluid that signal lung injury and/or inflammation. Results indicated that toxicity increased as Ta decreased. Exposures conducted at 10 degrees C were associated with the greatest decreases in body weight and total lung capacity and the greatest increases in lavageable protein, lysozyme, alkaline phosphatase activity, and percent neutrophils. O3 effects not modified by Ta included increases in residual volume and lavageable potassium, glucose, urea, and ascorbic acid with exposure at 34 degrees C. Most effects were attenuated during the 5 exposure days and/or returned to normal levels after 7 air recovery days, regardless of prior O3 exposure or Ta. It is possible that Ta-induced changes in metabolic rate may have altered ventilation and, therefore, the O3 doses among rats exposed at the three different Ta levels.

Thermoregulatory effects of chlorpyrifos in the rat: long-term changes in cholinergic and noradrenergic sensitivity

Subcutaneous injection of a sublethal dose of chlorpyrifos (CHLP), an organophosphate (OP) pesticide, causes long-term inhibition in cholinesterase activity (ChE) of brain, blood, and other tissues. Such prolonged inhibition in ChE should lead to marked behavioral and autonomic thermoregulatory patterns, especially in terms of altered noradrenergic and cholinergic sensitivity. To evaluate the behavioral and autonomic effects of long-term ChE inhibition, Long-Evans rats were implanted with radiotelemetry transmitters that continuously monitored core temperature (Tc), heart rate (HR), and motor activity (MA). These parameters were monitored for 7 days following a single injection of peanut oil (vehicle control) or 280 mg/kg CHLP. CHLP led to a significant reduction in Tc during the first night after treatment but had no other effects on Tc. CHLP also resulted in a significant elevation in HR which lasted for approximately 72 h. Motor activity was unaffected by CHLP. Cholinergic and noradrenergic drug sensitivity was assessed between 7 and 25 days after CHLP. CHLP-treated rats were more sensitive to norepinephrine as based on a greater hyperthermic response. MA of CHLP-treated rats was more sensitive to scopolamine. On the other hand, the hypothermic effects of oxotremorine (0.4 mg/kg) were nearly abolished by CHLP treatment, indicating tolerance to cholinergic stimulation. The tachycardic effects of methyscopolamine were also greater in the CHLP group. Overall, the acute effects of CHLP are unusual compared to other OP's in that there is no hypothermic response, an attenuated nocturnal elevation in Tc and a prolonged elevation in HR.(ABSTRACT TRUNCATED AT 250 WORDS)

Caveats regarding the use of the laboratory rat as a model for acute toxicological studies: modulation of the toxic response via physiological and behavioral mechanisms

The rodent, specifically the laboratory rat, is the primary experimental animal used in toxicology testing. Despite its popularity, recent studies from our laboratory and others raise a number of questions concerning the rat's appropriateness as an animal model for toxicological studies. While there may be additional areas in which the rat and other small rodents fail to adequately mimic the human response to xenobiotic agents, this article will focus on the area of temperature regulation. Thus, this article will review the thermoregulatory response of the laboratory rat following acute exposure to toxic agents and examine the impact of this response on the extrapolation of toxicological data from experimental animals to humans. In general, the rat responds to acute intoxication by lowering its core temperature via both physiological and behavioral mechanisms, thereby attenuating the induced toxicity. Similar responses have not been reported in humans.

Acute and delayed effects of diisopropyl fluorophosphate on body temperature, heart rate, and motor activity in the awake, unrestrained rat

Acute exposure to diisopropyl fluorophosphate (DFP) causes irreversible inhibition of acetylcholinesterase activity, leading to various behavioral and autonomic sequelae including hypothermia, reduced motor activity, and other neurological dysfunctions. To characterize the acute response and recovery of autonomic and behavioral processes to DFP exposure, rats of the Long-Evans strain were implanted with radiotransmitters that allowed the monitoring of core temperature, heart rate, and motor activity in unrestrained animals 24 h/d. These parameters were monitored for 96 h following subcutaneous injection of DFP at a dose of 0, 0.1, or 1.0 mg/kg. Rats given 0 and 0.1 mg/kg DFP displayed an increase in core temperature and motor activity during the first 24 h postinjection. The 1.0 mg/kg group showed a typical hypothermic response for the first 24 h following DFP administration. Core temperature decreased a maximum of 1.9 degrees C by 5 h after DFP and then started to recover, reaching control levels by 17 h after DFP treatment. Motor activity was also depressed during the first 24-h period in the 1.0 mg/kg group. Heart rate was initially elevated above basal levels in all treatment groups for several hours after treatment, but the 1.0 mg/kg group showed a decrease in heart rate at the time when core temperature began its recovery from hypothermia. Core temperature was the only parameter significantly affected by DFP during the 24-96 h recovery phase. The 0.1 and 1.0 mg/kg groups showed a significant elevation in core temperature for the 3 d after DFP administration. The elevation in core temperature during the recovery from DFP treatment may represent an important facet of the acute cholinergic neurotoxicity of organophosphate compounds.