William P. Watkinson

Effects of 3,4-methylenedioxymethamphetamine on autonomic thermoregulatory responses of the rat ☆ ☆☆

3,4-Methylenedioxymethamphetamine (MDMA), a substituted amphetamine analogue which stimulates serotonin release in the CNS, has been shown to induce near lethal elevations in core temperature in the rat. To characterize the effects of MDMA on temperature regulation, we measured metabolic rate (MR), evaporative water loss (EWL), motor activity (MA), and colonic temperature (Tc) in male, Long-Evans rats at 60 min following 30 mg/kg (SC) MDMA or saline at ambient temperature (Ta) of 10, 20 and 30 degrees C. MDMA caused an elevation in MR at Tas of 20 and 30 degrees C but had no effect at 10 degrees C. At a Ta of 30 degrees C, MR of the MDMA group was double that of the saline group. EWL was elevated by MDMA, an effect which was potentiated with increasing Ta. MDMA also elicited an increase in MA at all three Tas. MDMA led to a 3.2 degrees C increase in Tc at 30 degrees C, no change in Tc at 20 degrees C, and a 2.0 degrees C decrease in Tc at 10 degrees C. A second study found that treatment with 20 mg/kg MDMA failed to elicit an increase in blood flow to the tail in spite of a hyperthermic core temperature of 41.4 degrees C. Preliminary studies using radiotelemetry methodology suggested that MDMA lethality is preceded by precipitous elevations in heart rate and core temperature. The data suggest that, at relatively warm Tas. MDMA-induced stimulation of serotonergic pathways causes an elevation in MR and peripheral vasoconstriction, thus producing life-threatening elevations in Tc.(ABSTRACT TRUNCATED AT 250 WORDS)

Temperature regulation in laboratory mammals following acute toxic insult

The purpose of this paper is to provide a concise review of the effects of acute chemical toxicity on thermoregulation in mammals, with particular emphasis on the effects of xenobiotic compounds in laboratory rodents. It has been shown that acute administration of compounds such as nickel, cadmium, lead, and some pesticides causes a reduction in the body temperature of mice when tested at normal room temperatures. When provided with the option of selecting their preferred ambient temperature, the toxic-treated animals generally select cool temperatures which augment the hypothermic effect of the toxic compounds. It would appear that many of the xenobiotic compounds have central as well as peripheral effects on the control of body temperature. That is, the hypothermic animals select cool temperatures, a condition indicative of a centrally mediated decrease in the set-point. This decrease in set-point, or regulated hypothermia, may be beneficial to survival since the lethality of most xenobiotic compounds increases with rising body temperature. The observation that acute doses of various compounds leads to behaviorally and autonomically mediated changes in body temperature may have significant implications for the measurement of other biological effects of these chemical agents (e.g., CNS dysfunction, bradycardia, immunosuppression).

Cardiac and thermoregulatory effects of instilled particulate matter-associated transition metals in healthy and cardiopulmonary-compromised rats

Particulate matter air pollution has been associated with cardiopulmonary morbidity and mortality in many recent epidemiological studies. Previous toxicological research has demonstrated profound cardiac and thermoregulatory changes in rats following exposure to residual oil fly ash (ROFA), a combustion-derived particulate. The response to ROFA appeared biphasic, consisting of both immediate (0-6 h) and delayed (24-96 h) bradycardia and hypothermia. Other studies have demonstrated that much of the pulmonary toxicity of ROFA was caused by its constitutive transition metals, namely, Fe, Ni, and V. This study examined the contributions of these metals to the observed cardiac and thermoregulatory changes caused by ROFA in conscious, unrestrained rats. Prior to exposure, each animal was surgically implanted with a radiotelemetry device capable of continuously monitoring heart rate, electrocardiographic, and core temperature data. Individual metals were intratracheally instilled in healthy rats ( n = 4 per metal species) and in rats with monocrotaline (MCT; 60 mg/kg)-induced pulmonary hypertension ( n = 10 per metal species); combinations of metals were instilled in MCT-treated rats only ( n = 6 per combination of metal species). Metals were administered in doses equivalent to those found in the highest dose of ROFA used in previous studies, that is, 105 w g Fe 2 (SO 4 ) 3 , 263 w g NiSO 4 , and 245 w g VSO 4 . Healthy and MCT-treated rats demonstrated similar responses to metals. Fe caused little response, whereas V caused marked bradycardia, arrhythmogenesis, and hypothermia immediately following instillation and lasting ~6 h. Ni caused no immediate response, but induced a delayed bradycardia, arrhythmogenesis, and hypothermia that began ~24 h after instillation and lasted for several days. When instilled in combination, Ni appeared to exacerbate the immediate effects of V, whereas Fe attenuated them. These data suggest that the biphasic response to instilled ROFA may result from a summation of the temporally different effects of V and Ni.

Ambient particulate matter and respiratory and cardiovascular illness in adults: particle-borne transition metals and the heart-lung axis(,).

Epidemiological studies have consistently shown associations of exposure to ambient particulate matter (PM) with severe health effects, including mortality and hospitalization, in adults. From the standpoints of both relative risk and attributable risk, the public health burden of ambient PM exposure is potentially greatest in elderly adults with underlying cardiopulmonary illness. Recent experimental data suggest that PM-borne transition metals have toxicity that could be mechanistically relevant to PM-related epidemiological findings. These data may prove to be especially relevant in elderly adults with cardiopulmonary illness. At the same time, important uncertainties remain in the epidemiological and experimental databases, such that the true degree of correspondence between the two is not yet known. In our opinion, this combination of emerging experimental-epidemiological coherence and remaining uncertainty imparts high priority to further research into the health effects of PM-borne transition metals. This research should not be confined to the respiratory system. Rather, it should examine the entire heart-lung axis and should probably consider other body systems (e.g. the vascular system) as well. In this research, close interdisciplinary communication should be sustained and experimental and epidemiological approaches should be coordinated to the maximum feasible extent.

Heart rate variability in rodents: uses and caveats in toxicological studies

Heart rate variability (HRV) is a measure of cardiac pacing dynamics that has recently garnered a great deal of interest in environmental health studies. While the use of these measures has become popular, much uncertainty remains in the interpretation of results, both in terms of human and animal research. In humans, HRV endpoints, specifically chronic alterations in baseline HRV patterns, have been reasonably well characterized as prognostic indicators of adverse outcomes for a variety of diseases. However, such information is lacking for reversible HRV changes that may be induced by short-term exposures to environmental toxicants. Furthermore, there are minimal substantive data, either acute or chronic, regarding the pathological interpretation or prognostic value of toxicant-induced changes in HRV in rodents. The present report summarizes the physiological and clinical aspects of HRV, the methodological processes for obtaining these endpoints, and previous human and animal studies in the field of environmental health. Furthermore, we include a discussion of important caveats and recommendations for the interpretation of HRV data in animal research.

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 rats 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.

Effects of Instilled Combustion-Derived Particles in Spontaneously Hypertensive Rats. Part I: Cardiovascular Responses

Epidemiological studies have reported statistically significant associations between the levels of ambient particulate matter (PM) and the incidence of morbidity and mortality, particularly among persons with cardiopulmonary disease. While similar effects have been demonstrated in animals, the mechanism(s) by which these effects are mediated are unresolved. To further investigate this phenomenon, the cardiovascular and thermoregulatory effects of an oil combustion-derived PM (HP-12) were examined in spontaneously hypertensive (SH) rats. The particle used in this study had considerably fewer water-soluble metals than the residual oil fly ash (ROFA) particles widely used in previous animal toxicity studies, with Zn and Ni constituting the primary water-leachable elements in HP-12. Rats were surgically implanted with radiotelemeters capable of continuously monitoring electrocardiogram (ECG), heart rate (HR), systemic arterial blood pressure (BP), and core temperature (Tco). Animals were divided into four dose groups and were administered one of four doses of HP-12 suspended in saline vehicle (0.00, 0.83, 3.33, 8.33 mg/kg; control, low, mid, and high dose, respectively) via intratracheal instillation (IT). Telemetered rats were monitored continuously for up to 7 days post-IT, and were sacrificed 4 or 7 days post-IT. Exposures to mid- and high-dose HP-12 induced large decreases in HR (↓30–120 bpm), BP (↓20–30 mmHg), and Tco (↓1.2–2.6°C). The decreases in HR and BP were most pronounced at night and did not return to pre-IT values until 72 and 48 h after dosing, respectively. ECG abnormalities (rhythm disturbances, bundle branch block) were observed primarily in the high-dose group. This study demonstrates substantial dose-related deficits in cardiac function in SH rats after IT exposure to a low-metal content, combustion-derived particle.

LUNG INJURY FROM INTRATRACHEAL AND INHALATION EXPOSURES TO RESIDUAL OIL FLY ASH IN A RAT MODEL OF MONOCROTALINE-INDUCED PULMONARY HYPERTENSION

A rat model of monocrotaline (MCT)-induced pulmonary injury/hypertension has been recently used in particulate matter (PM) health effects studies, however, results have been equivocal. Neither the mechanism by which mortality occurs in this model nor the variation in response due to differences in PM exposure protocols (i.e., a bolus dose delivered intratracheally versus a similar cumulative dose inhaled over three days) have been fully investigated. Sprague Dawley rats (SD, 60 d old; 250-300 g) were injected with either saline (healthy) or MCT, 60 mg/kg, i.p. (to induce pulmonary injury/hypertension). Ten days later they were exposed to residual oil fly ash (ROFA), either intratracheally (IT; saline, 0.83 or 3.33 mg/kg) or by nose-only inhalation (15 mg/m3 x 6 h/d x 3 d). Lung histology, pulmonary cytokine gene expression (0 and 18 h postinhalation), and bronchoalveolar lavage fluid (BALF) markers of injury were analyzed (24 and 96 h post-IT; or 18 h post-inhalation). Data comparisons examined three primary aspects, 1) ROFA IT versus inhalation effects in healthy rats; 2) pulmonary injury caused by MCT; and 3) exacerbation of ROFA effects in MCT rats. In the first aspect, pulmonary histological lesions following ROFA inhalation in healthy rats were characterized by edema, inflammatory cell infiltration, and thickening of alveolar walls. Increases in BALF markers of lung injury and inflammation were apparent in ROFA-IT or nose-only exposed healthy rats. Increased IL-6, and MIP-2 expression were also apparent in healthy rats following ROFA inhalation. In regards to the second aspect, MCT rats exposed to saline or air showed perivascular inflammatory cell infiltrates, increased presence of large macrophages, and alveolar thickening. Consistently, BALF protein, and inflammatory markers (macrophage and neutrophil counts) were elevated indicating pulmonary injury. In regards to the third aspect, 58% of MCT rats exposed to ROFA IT died within 96 h regardless of the dose. No mortality was observed using the inhalation protocol. ROFA inhalation in MCT rats caused exacerbation of lung lesions such as increased edema, alveolar wall thickening, and inflammatory cell infiltration. This exacerbation was also evident in terms of additive or more than additive increases in BALF neutrophils, macrophages and eosinophils. IL-6 but not MIP-2 expression was more than additive in MCT rats, and persisted over 18 h following ROFA. IL-10 and cellular fibronectin expression was only increased in MCT rats exposed to ROFA. In summary, only the bolus IT ROFA caused mortality in the rat model of lung injury/hypertension. Exacerbation of histological lesions and cytokine mRNA expression were most reflective of increased ROFA susceptibility in this model.

Cardiac and Thermoregulatory Toxicity of Residual Oil Fly Ash in Cardiopulmonary-Compromised Rats

Recent epidemiological studies have reported a positive association between levels of ambient particulate matter (PM) and daily morbidity and mortality due to respiratory or cardiovascular causes; however, toxicological evidence supporting these findings is limited. The present study compared cardiac and thermoregulatory responses to intratracheal instillations of residual oil fly ash (ROFA) in normal and cardiopulmonary-compromised male Sprague-Dawley rats. Animals (n = 64) were implanted with radiotelemetry transmitters capable of continuously monitoring heart rate, core body temperature, and electrocardiographic waveforms. Comparisons of ROFA toxicity were conducted between (1) healthy rats and rats with cardiopulmonary stress or disease, including (2) rats exposed to an ambient temperature of 10° C, (3) rats preexposed to ozone to induce pulmonary inflammation, and (4) rats pretreated with monocrotaline (MCT) to induce pulmonary hypertension and vasculitis. Animals from each regimen were instilled with 1 of 4 doses of ROFA (0, 0.25, 1.0, 2.5 mg), and telemetry data were acquired for 96 h following ROFA instillation. Dose-related hypothermia and bradycardia were observed in healthy animals following exposure to ROFA; the magnitude and duration of these responses were potentiated in all compromised models. Delayed hypothermic and bradycardic responses occurred in healthy animals receiving 2.5 mg ROFA up to 48 h following instillation. These delayed responses were exacerbated in the MCT-and 10°C-exposure models, but attenuated in the 03-preexposed group. Additional observed effects of ROFA included induction of cardiac arrhythmias and increased mortality. These results demonstrate a distinct cardiac component to ROFA toxicity that agrees with epidemiological findings of PM-related excess cardiovascular mortality. Furthermore, the dose-related hypothermia and bradycardia observed in rodents from this study may confound the interpretation of results from similar air pollution toxicology studies.

Particulate matter inhalation exacerbates cardiopulmonary injury in a rat model of isoproterenol-induced cardiomyopathy.

Ambient particulate matter (PM) exposure is linked to cardiovascular events and death, especially among individuals with heart disease. A model of toxic cardiomyopathy was developed in Spontaneously Hypertensive Heart Failure (SHHF) rats to explore potential mechanisms. Rats were infused with isoproterenol (ISO; 2.5 mg/kg/day subcutaneous [sc]), a β-adrenergic agonist, for 28 days and subsequently exposed to PM by inhalation. ISO induced tachycardia and hypotension throughout treatment followed by postinfusion decrements in heart rate, contractility, and blood pressures (systolic, diastolic, pulse), and fibrotic cardiomyopathy. Changes in heart rate and heart rate variability (HRV) 17 days after ISO cessation indicated parasympathetic dominance with concomitantly altered ventilation. Rats were subsequently exposed to filtered air or Harvard Particle 12 (HP12) (12 mg/m3)—a metal-rich oil combustion-derived PM—at 18 and 19 days (4 h/day) after ISO infusion via nose-only inhalation to determine if cardio-impaired rats were more responsive to the effects of PM exposure. Inhalation of PM among ISO-pretreated rats significantly increased pulmonary lactate dehydrogenase, serum high-density lipoprotein (HDL) cholesterol, and heart-to-body mass ratio. PM exposure increased the number of ISO-pretreated rats that experienced bradyarrhythmic events, which occurred concomitantly with acute alterations of HRV. PM, however, did not significantly affect mean HRV in the ISO- or saline-pretreated groups. In summary, subchronic ISO treatment elicited some pathophysiologic and histopathological features of heart failure, including cardiomyopathy. The enhanced sensitivity to PM exposure in SHHF rats with ISO-accelerated cardiomyopathy suggests that this model may be useful for elucidating the mechanisms by which PM exposure exacerbates heart disease.