Pamela J. Rowsey

Tolerance to the hypothermic and hyperthermic effects of chlorpyrifos

Hypothermia is a commonly reported thermoregulatory response in rodents acutely exposed to organophosphates (OP); however, our laboratory has recently found a delayed hyperthermic response following the initial hypothermia when exposed to the OP, chlorpyrifos. It is well known that rodents display tolerance to OP-induced hypothermia but little is known about tolerance to OP-induced hyperthermia. Twenty female rats of the Long-Evans strain were made tolerant to chlorpyrifos by administering 0 or 10 mg/g chlorpyrifos by gavage daily for four days. Core temperature (T[c]) and motor activity (MA) were monitored continuously by telemetry. Twenty-four hours after the fourth 10 mg/kg injection, the animals were administered a challenge dose of 25 mg/kg chlorpyrifos or corn oil while the telemetry data were monitored for the next 72 h. Non-tolerant rats displayed an initial hypothermic response with reduced MA followed by a delayed increase in T(c) 24 h after exposure. The tolerant animals displayed a blunted hypothermic response with virtually no change in MA, but a delayed increase in T(c) similar to that of non-tolerant animals. The hyperthermic response of the non-tolerant animals persisted for two days, whereas the tolerant animals recovered by the second day. The data indicate that tolerance to the hypothermic and hyperthermic effects of chlorpyrifos involve separate neurochemical pathways.

Are circulating cytokines interleukin-6 and tumor necrosis factor α involved in chlorpyrifos-induced fever?

Oral exposure to chlorpyrifos (CHP) in the rat results in an initial hypothermic response followed by a delayed fever. Fever from infection is mediated by the release of cytokines, including interleukin-6 (IL-6) and tumor necrosis factor (TNF alpha). This study determined if the CHP-induced fever involves cytokine-mediated mechanisms similar to that of infectious fevers. Long-Evans rats were gavaged with the corn oil vehicle or CHP (10-50 mg/kg). The rats were euthanized and blood collected at various times that corresponded with the hypothermic and febrile effects of CHP. Plasma IL-6, TNF alpha, cholinesterase activity (ChE), total iron, unsaturated iron binding capacity (UIBC), and zinc were measured. ChE activity was reduced by approximately 50% 4 h after CHP. There was no effect of CHP on IL-6 when measured during the period of CHP-induced hypothermia or fever. TNF alpha levels nearly doubled in female rats 48 h after 25 mg/kg CHP. The changes in plasma cytokine levels following CHP were relatively small when compared to > 1000-fold increase in IL-6 and > 10-fold rise in TNF alpha following lipopolysaccharide (E. coli; 50 microg/kg; i.p.)-induced fever. This does not preclude a role of cytokines in CHP-induced fever. Nonetheless, the data suggest that the delayed fever from CHP is unique, involving mechanisms other than TNF alpha and IL-6 release into the circulation characteristic of infectious fevers.

Tumor necrosis factor is involved in chlorpyrifos--induced changes in core temperature in the female rat.

Chlorpyrifos (CHP), an OP-based pesticide, induces hypothermia in the rat followed by a fever that persists for several days. The cytokine, tumor necrosis factor-alpha (TNF), is induced by lipopolysaccharide (LPS) and released during fever and has both pyrogenic and cryogenic (i.e. antipyretic) properties. Administering antibodies to TNF (anti-TNF) is known to disrupt fever from infection. Thus, the purpose of this study was to examine whether anti-TNF also disrupts CHP-induced changes in body temperature of the female Long-Evans rat. A positive effect would suggest a role of TNF in the etiology of OP toxicity. In study one, rats were given either saline or anti-TNF (50,000 units, i.p.). Three hours later, animals were given corn oil (CO) or 25 mg/kg CHP by oral gavage in the morning. In study two, rats were given anti-TNF followed by CO or 10 mg/kg CHP in the afternoon. Core temperature and motor activity were monitored continuously by telemetry. In study one, anti-TNF (50,000 units) had no effect on the hypothermic response to 25 mg/kg CHP. However, anti-TNF treated animals maintained higher fevers 3 days (48-96 h post-injection) after CHP treatment. In study two, anti-TNF attenuated the hypothermic response induced by 10 mg/kg CHP but had no effect on the magnitude of the delayed fever. Overall, 25 mg/kg CHP elicited a longer period of hypothermia and delayed fever compared to 10 mg/kg CHP. Anti-TNF pretreatment attenuated the hypothermic response at the lower CHP dose and exacerbated the fever at the higher CHP dose. Anti-TNF also attenuated the hypothermic effect of high doses of LPS and exacerbated LPS-induced fever. These data indicate that endogenously produced TNF is involved in the etiology of CHP mediated hypothermia and fever.

Psychological stress and arterial stiffness in Korean Americans

OBJECTIVE Arterial stiffness is identified as a causative factor for hypertension. The purpose of this study was to explore the relationship between psychological stress and arterial stiffness in Korean Americans. METHODS A convenience sample of 102 Korean Americans (aged 21-60 years, 60% women) was recruited from North Carolina. Psychological stress was measured by the Perceived Stress Scale, the Social, Attitudinal, Familiar, and Environmental (SAFE) Acculturative Stress Scale, and the Spielbergers State-Trait Anxiety Inventory. Arterial stiffness was measured by carotid-femoral pulse wave velocity (cfPWV) using the SphygmoCor system (AtCor Medical, Australia). RESULTS This study shows that the emotional stress response, measured by anxiety, significantly predicted arterial stiffness (β=.25, p=.008), independently of such confounding factors as age, mean arterial pressure (MAP), gender, body mass index, smoking, education, and income. Anxiety was neither related to age (r=.12, p=.212) nor MAP (r=.14, p=.151). Additionally, this sample of Korean Americans had higher levels of psychological stress when compared to previous findings from studies of other racial/ethnic groups in the U.S. CONCLUSION Findings demonstrate that anxiety is a significant and independent determinant of arterial stiffness. Given that anxiety was not related to MAP, these findings suggest that arterial stiffness may be a pathway to explain the connection between anxiety and hypertension risk. Studies that scrutinize the relationship between anxiety and arterial stiffness are an important next step for future research. Further studies are also recommended to explore cultural factors and individual characteristics that may affect anxiety in Korean Americans.

Effects of exercise conditioning on thermoregulatory responses to repeated administration of chlorpyrifos

Little is known about the effects of physical activity (i.e., exercise training) on susceptibility to environmental toxicants. Chlorpyrifos (CHP), an organophosphate (OP) insecticide, affects thermoregulation, causing an acute period of hypothermia followed by a delayed fever. Since exercise conditioning alters the thermoregulatory responses of rodents, this study examined whether exercise training would alter the thermoregulatory response to repeated CHP administration in the female Sprague-Dawley rat. Core temperature (T(c)) and motor activity (MA) were monitored by radiotelemetry in rats housed at an ambient temperature (T(a)) of 22 degrees C. The rats either were provided with continuous access to running wheels (exercise group) or were housed in standard cages without wheels (sedentary group). The exercise group rats ran predominantly at night with an average of 7.6 km/24h. After 8 weeks the rats in both groups were gavaged daily with corn oil or 10mg/kg CHP (dissolved in corn oil) for 4 days. CHP induced an immediate hypothermic response followed by a delayed fever throughout the next day in the sedentary group rats after the first three doses of CHP. The exercise group rats showed no hypothermia after the first dose of CHP. However, they became hypothermic after the second and third doses of CHP. The exercise group rats developed a smaller daytime fever after each dose of CHP compared to the sedentary group rats. Overall, exercise training attenuated the hypothermic and febrile effects of repeated CHP. Thus, the data suggest that a sedentary lifestyle may increase the sensitivity to OP insecticides. Exercise training was also associated with a more rapid recovery of plasma cholinesterase activity.

A peripheral mechanism of fever: differential sensitivity to the antipyretic action of methyl scopolamine.

The organophosphate pesticide (OP) chlorpyrifos leads to an acute period of hypothermia followed by a delayed fever in the rat. Methyl scopolamine, a peripheral muscarinic antagonist, is thought to have little effect on body temperature of the rat because it does not cross the blood brain barrier. However, administration of methyl scopolamine (1 mg/kg, i.p.) during the period of chlorpyrifos-induced fever results in a rapid recovery of core temperature. This indicates a peripheral cholinergic pathway is operative in the febrile response to chlorpyrifos and possibly other modes of fever. In this study, we evaluated the possible antipyretic role of methyl scopolamine (i.p.) to a variety of stimuli that lead to fever-like responses in the rat: stress-induced (handling and cage switch), chlorpyrifos-induced (15 mg/kg, p.o.), nocturnal-induced, and lipopolysaccharide (LPS)-induced fever (50 microg/kg, i.p.). Methyl scopolamine led to marked reversal in the elevated core temperature caused by handling, cage switch, and during the nocturnal phase. It is of interest to note that all these elevations of core body temperature are prostaglandin mediated and are blocked with the antipyretic drug, sodium salicylate. However, LPS-induced fever, also a prostaglandin dependent fever, was unaffected by methyl scopolamine. Methyl scopolamine also lowered baseline core temperature when administered during the afternoon, but not during the morning in unstressed animals. It is proposed that a peripheral cholinergic pathway, possibly mediated through afferent vagal pathways, is operative in controlling core temperature during fevers associated with stress, nocturnal phase, and a pesticide. During recovery from exposure to a LPS, the fever appears to be mediated independently of peripheral cholinergic activation.

Delayed febrile effects of chlorpyrifos: is there cross-tolerance to bacterial lipopolysaccharide? ☆

Oral chlorpyrifos (CHP) induces hypothermia followed by a fever that persists for several days in the rat. To understand the neuro-immune mechanisms of CHP-induced fever, we compared the tolerance and cross-tolerance between CHP and the fever elicited by lipopolysaccharide (LPS) (Escherichia coli). Female rats were administered the corn oil (CO) vehicle or CHP (10 mg/kg; p.o.) daily for 4 days while core temperature (Tc) and motor activity (MA) were monitored by telemetry. There was a reduction in Tc followed by an elevation the next day after each CHP treatment. The day after the last CHP treatment, rats were administered saline or 50 microg/kg LPS (i.p.). CHP-treated rats had a smaller LPS fever that was attributed to their elevated baseline Tc. In another study, rats were dosed with saline or LPS daily for three days. By the time of the third LPS injection there was no febrile response, indicating tolerance to LPS. Rats were then dosed with CO or CHP (10 mg/kg) 24 h after the third LPS treatment. LPS-tolerant rats displayed an accentuated hypothermic and febrile response to CHP. Plasma cholinesterase activity was unaffected by repeated LPS treatment, suggesting that the metabolism of CHP in the liver was unaffected by LPS. Overall, the neural-immune mechanisms for LPS fever is distinct from that of CHP in view of marked difference in mechanisms of tolerance.

Serum biomarkers of aging in the Brown Norway rat.

Serum biomarkers to identify susceptibility to disease in aged humans are well researched. On the other hand, our understanding of biomarkers in animal models of aging is limited. Hence, we applied a commercially available panel of 58 serum analytes to screen for possible biomarkers of aging in 4, 12, and 24 month old Brown Norway rats. We found that serum levels of 5 of the 58 analytes were significantly affected by age: C-reactive protein (CRP), myoglobin, macrophage derived chemokine-2 (MDC), fibroblast growth factor-basic, and vascular cell adhesion molecule-1. Among these analytes, CRP was the only one that increased with aging. The variability of CRP and MDC-2 was relatively low compared to the other analytes of the panel. It is concluded that CRP and possibly MDC-2 are candidates for biomarkers of aging in the BN rat.

Temperature Regulation in Experimental Mammals and Humans Exposed to Organophosphate and Carbamate Agents

Publisher Summary The chapter reviews the effects of anti-ChE agents on the thermoregulatory system of mammals and humans, including studies on the central nervous system. The regulation of body temperature is an ideal benchmark to study the toxicity of the anti-ChE insecticides in experimental mammals and humans. The inhibition in acetylcholinesterase (AChE) activity, and subsequent stimulation of cholinergic pathways in the central and peripheral nervous systems is a key mechanism responsible for driving changes in body temperature and activation of thermoregulatory effectors. Body size and ambient temperature are perhaps the most critical factors governing the thermoregulatory effects of these toxicants. Small mammals undergo a marked increase in heat loss and become hypothermic when exposed to anti-ChEs. Small mammals exposed to these agents lower their body temperature by selective activation of heat loss thermoeffectors. This hypothermic response is often protective and increases the likelihood of surviving the toxic insult. Large mammals such as humans are unable to take advantage of this hypothermic response, and it is not clear whether a fever from these toxicants will affect the health effects of these agents. It appears that exercise and/or heat stress will exacerbate the toxic effects of anti-ChE insecticides and nerve gas agents. The redistribution of blood to the skin combined with sweating will increase the cutaneous absorption of OP agents that are applied to the skin. The increase in pulmonary ventilation during exercise combined with higher tissue temperature is bound to increase the intake and toxicity of airborne anti-ChE agents.