Background: Diesel exhaust (DE), which is emitted from on- and off-road sources, is a complex mixture of toxic gaseous and particulate components that leads to triggered adverse cardiovascular effects such as arrhythmias.Objective: We hypothesized that increased risk of triggered arrhythmias 1 day after DE exposure is mediated by airway sensory nerves bearing transient receptor potential (TRP) channels [e.g., transient receptor potential cation channel, member A1 (TRPA1)] that, when activated by noxious chemicals, can cause a centrally mediated autonomic imbalance and heightened risk of arrhythmia.Methods: Spontaneously hypertensive rats implanted with radiotelemeters were whole-body exposed to either 500 μg/m3 (high) or 150 μg/m3 (low) whole DE (wDE) or filtered DE (fDE), or to filtered air (controls), for 4 hr. Arrhythmogenesis was assessed 24 hr later by continuous intravenous infusion of aconitine, an arrhythmogenic drug, while heart rate (HR) and electrocardiogram (ECG) were monitored.Results: Rats exposed to wDE or fDE had slightly higher HRs and increased low-frequency:high-frequency ratios (sympathetic modulation) than did controls; ECG showed prolonged ventricular depolarization and shortened repolarization periods. Rats exposed to wDE developed arrhythmia at lower doses of aconitine than did controls; the dose was even lower in rats exposed to fDE. Pretreatment of low wDE–exposed rats with a TRPA1 antagonist or sympathetic blockade prevented the heightened sensitivity to arrhythmia.Conclusions: These findings suggest that a single exposure to DE increases the sensitivity of the heart to triggered arrhythmias. The gaseous components appear to play an important role in the proarrhythmic response, which may be mediated by activation of TRPA1, and subsequent sympathetic modulation. As such, toxic inhalants may partly exhibit their toxicity by lowering the threshold for secondary triggers, complicating assessment of their risk.
Extensive research has lead to a growing appreciation that the heart is acutely sensitive to a broad array of toxicants via multiple routes of exposure. These agents are as diverse as the antineoplastic drug doxorubicin and environmental agents including ambient air pollution. Adverse effects in the heart often manifest as a change in the electrocardiogram (ECG). The ECG has long been used in the clinic to assess human cardiovascular health. Surface electrocardiographic recordings (i.e., those made from the skin) in humans often help to detect abnormal myocardial impulse formation, conduction, cardiac rhythm disturbances, and altered autonomic regulation of the heart. In toxicology, the ECG provides a collection of end points that may be used to assess both the quality and magnitude of cardiac toxicity. Increasingly over the last two decades, the cardiotoxicity of agents have been characterized using small rodent electrocardiography. Additionally, tremendous insight into possible mechanisms of action of known human cardiotoxicants has been gained. Rat and mouse models offer a number of advantages relative to larger animals including lower cost, less variability, the availability of transgenic models, and a plethora of research tools. Modern day advances in small rodent electrocardiography have enabled assessments in conscious unrestrained animals and improved ECG interpretation. Thus, the incorporation of small rodent electrocardiographic assessments into toxicology studies may facilitate the screening of cardiotoxic potential and the elucidation of mechanisms of action. This review will discuss the utility of the small rodent ECG, various methodologies used to derive ECG data in rats and mice, and various applications in toxicology.
Background:Epidemiological studies suggest that increased ozone exposure during gestation may compromise fetal growth. In particular, the implantation stage of pregnancy is considered a key window of susceptibility for this outcome.Objectives:The main goals of this study were to investigate the effects of short-term ozone inhalation during implantation on fetal growth outcomes and to explore the potential for alterations in uterine arterial flow as a contributing mechanism.Methods:Pregnant Long-Evans rats were exposed to filtered air, 0.4 ppm ozone, or 0.8 ppm ozone for 4 h/d during implantation, on gestation days (GD) 5 and 6. Tail cuff blood pressure and uterine artery Doppler ultrasound were measured on GD 15, 19, and 21. To assess whether peri-implantation ozone exposure resulted in sustained pulmonary or systemic health effects, bronchoalveolar lavage fluid, serum metabolic and inflammatory end points, and kidney histopathology were evaluated in dams at GD 21. Growth parameters assessed in GD 21 offspring included fetal weight, length, and body composition.Results:Measures of maternal uterine arterial flow, including resistance index and mean velocity, indicated that resistance increased between GD 15 and GD 21 in 0.8 ppm dams but decreased in controls, although absolute values were similar in both groups on GD 21. Ozone-exposed dams also had lower serum glucose and higher free fatty acid concentrations than controls on GD 21. On GD 21, both male and female offspring had lower body weight than controls, and pooled subsets of 3 male and 3 female fetuses from litters exposed to 0.8 ppm ozone had lower lean mass and fat mass than pooled control offspring.Conclusions:Findings from our experimental model suggest that the offspring of dams exposed to ozone during implantation had reduced growth compared with controls, possibly as a consequence of ozone-induced vascular dysfunction. https://doi.org/10.1289/EHP2019
The body responds to environmental stressors by triggering autonomic reflexes in the pulmonary receptors, baroreceptors, and chemoreceptors to maintain homeostasis. Numerous studies have shown that exposure to various gases and airborne particles can alter the functional outcome of these reflexes, particularly with respect to the cardiovascular system. Modulation of autonomic neural input to the heart and vasculature following direct activation of sensory nerves in the respiratory system, elicitation of oxidative stress and inflammation, or through other mechanisms is one of the primary ways that exposure to air pollution affects normal cardiovascular function. Any homeostatic process that utilizes the autonomic nervous system to regulate organ function might be affected. Thus, air pollution and other inhaled environmental irritants have the potential to alter both local airway function and baro-and chemoreflex responses, which modulate autonomic control of blood pressure and detect concentrations of key gases in the body. While each of these reflex pathways causes distinct responses, the systems are heavily integrated and communicate through overlapping regions of the brainstem to cause global effects. This short review summarizes the function of major pulmonary sensory receptors, baroreceptors, and carotid body chemoreceptors and discusses the impacts of air pollution exposure on these systems.
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