Sham Stress Research Articles

Role of Spinal Microglia in Visceral Hyperalgesia and NK1R Up-Regulation in a Rat Model of Chronic Stress (Gastroenterology 2009;136:1339-1348)

Chronic psychological stress is associated with visceral hyperalgesia. Microglia in the central nervous system are a type of nonneuronal cells and play a key role in the initiation or maintenance of hyperalgesia and allodynia, as demonstrated in animal models of chronic pain caused by peripheral inflammation or nerve injury.1 However, the mechanisms of microglia activation and the downstream pathways leading to amplification of the nociceptive signaling are only partially understood. Activated microglia produce and release a range of proinflammatory mediators, such as cytokines (IL-1, IL-6, tumor necrosis factor α), chemokines, nitric oxide, and prostaglandins, all of which can act on afferent nerve terminals and spinal sensory neurons and increase neuronal excitability.2 The authors wanted to identify the role of spinal microglia in the development of visceral hyperalgesia from chronic stress in a rat model. In the study, the authors used adult male Wistar rats with or without water avoidance (WA) stress. Rats were placed on a block (8×8×10 cm) affixed to the center of a Plexiglas cage (25×25×45 cm) filled with fresh water at room temperature (25℃) to within 1 cm of the top of the block (WA) or kept empty (sham WA) for a period of one hour daily for 10 consecutive days.3 The rats had a surgically implanted chronic intrathecal (IT) catheter and an osmotic mini-pump. The rats then had a Teflon-coated electrode inserted into the external oblique musculature for electromyographic (EMG) recording.4 One group of rats was exposed to chronic WA stress or sham WA for 10 days and were sacrificed on day 11. Samples of lumbar spinal cord (L6S1) were collected and processed for immunohistochemically for P-p38, the microglia marker OX42, or the neuronal marker NeuN. Also, other groups of rats were exposed to WA stress or sham stress for 10 days and given daily injections of minocycline, the mitogen-activated protein kinase (MAPK) p38 inhibitor SB203580, or vehicle (0.9% saline) via osmotic pump connected to an IT catheter. Phosphorylation levels of the kinase p38 (P-p38), the microglia marker OX42, NK1R, and IκBα were assessed by immunoblotting and/or immunostaining of spinal samples. The authors also performed EMG recordings and baseline recordings of the visceromotor response (VMR) to colorectal distention (CRD) before beginning the treatment (day 0) and then again 24 hours after the last WA or sham WA sessions (day 11). The effects of the microglia-activating factor fractalkine were assessed on the visceral sensitivity in control nonstressed rats exposed to minocycline or vehicle. The immunohistochemistry for the activation marker of microglia, P-p38, revealed greater P-p38 staining in the spinal dorsal horn from WA stressed rats compared with controls. The immunoreactivity for P-p38 colocalized with OX42-positive cells (microglia) from WA stressed rats. Western blotting also demonstrated increased levels of P-p38 in WA stressed rats compared with controls. This increase was inhibited by treatment with IT minocycline or with IT SB203580. Western blotting showed increased expression of NK1R in WA stressed rats compared with controls. Stress-induced increased NK1R expression was completely blocked by minocycline but not SB203580. WA stress induced decreased IκBα expression, and this decrease was partially blocked by minocycline and SB203580. WA stress induced hyperalgesia in stressed rats treated with vehicle. WA induced visceral hyperalgesia was blocked by daily treatment with IT injection of minocycline or SB203580. Fractalkine injection-induced hyperalgesia was blocked by minocycline.

Effects of cannabinoid 1 receptor on regulation of visceral sensitivity in rats with acute restraint stress

Objective To investigate the effects of cannabinoid 1 receptor (CB1R) on regulating visceral sensitivity in rats with acute partial restraint stress. Methods Thirty Sprague-Dawley rats were divided into blank control (sham stress), acute stress and CB1R groups with 10 each. The frequency of discharge of electromyogram (EMG) was recorded at the 1st, 2nd, 5th and 8th day to evaluate the visceral sensitivity to colorectal distension (CRD) in rats. The expression of the CB1R mRNA was determined by means of RT-PCR at day 8. Results There was no significant difference in baseline discharge frequency among three groups at the 1st day. But the discharge frequencies corresponding to CRD at 40,60,80 mm Hg at the 2nd day were significantly lower in CB1R group [(22.37±1.49)/min, (42.24±3.03)/min and (69.09±5.54)/min, respectively] than in acute stress group [(39.71±1.84)/min, (84.45±8.85)/min and (112.56±11.66)/min, respectively, P<0.05)]. The discharge frequencies corresponding to CRD at 40, 60,80 mm Hg in acute stress group [(104.12±6.77)/min, (158.07±18.68)/min, (193.58±25.69)/min,respectively] showed a significant elevation at the 5th day in comparison with blank control group[(36.33±5.42)/min, (74.07±8.25)/min, (102.94±7.95)/min, respectively, P<0.05] or CB1R group [(74.66±6.44)/min,(140.10±4.68)/min and (160.39±5.60)/min,respectively, P<0.05]. However, at the 8th day after stress, there was no significant difference in discharge frequency among three groups. The expressions of CB1R mRNA in ileocecal junction, proximal colonic and distal colonic tissues were significantly higher in acute stress group (2.53±0.52, 2.29±0.42, 2.54±0.29 respectively) than in blank control group(0.56±0.15, 0. 73±0.12, 0.82±0.09, respectively, P<0.05). There was no effect of CB1R agonist on CB1R mRNA expression in rats. Conclusion The visceral sensitivity in rats induced by stress can trigger the accommodation of endogenous cannabinoid system that plays an important role in modulation of visceral sensitivity. Key words: Receptors, cannabinoid; Stress disorders, traumatic, acute; Hyperalgesia

Role of Spinal Microglia in Visceral Hyperalgesia and NK1R Up-Regulation in a Rat Model of Chronic Stress

Chronic psychological stress is associated with visceral hyperalgesia and increased expression of spinal NK1 receptors (NK1Rs). We aimed to identify the role of spinal microglia in this process. Male Wistar rats were exposed to water avoidance (WA) or sham stress 1 hour each day for 10 days and given daily injections of minocycline, the p38 inhibitor SB203580, or saline. Phosphorylation levels of the kinase p38 (P-p38), the microglia marker OX42, NK1R, and IkappaBalpha were assessed by immunoblotting and/or immunostaining of spinal samples collected at day 11. The visceromotor response to colorectal distention at baseline and following WA were also assayed in rats given injections of minocycline, SB203580, or vehicle. The effects of fractalkine were assessed on the visceromotor response in rats exposed to minocycline or vehicle. P-p38 protein levels and immunoreactivity were increased in stressed rats and colocalized with OX42-positive cells and neurons in the dorsal horn. This increase was reversed by minocycline or SB203580 exposure. Stress-induced increased NK1R expression was blocked by minocycline but not SB203580. WA-induced decreased IkappaBalpha expression was blocked by minocycline and SB203580. WA-induced hyperalgesia was blocked by minocycline and SB203580 intrathecally. Fractalkine-induced hyperalgesia was blocked by minocycline. This is the first demonstration that stress-induced activation of spinal microglia has a key role in visceral hyperalgesia and associated spinal NK1R up-regulation.

Corticotropin-releasing factor type 1 receptors mediate the visceral hyperalgesia induced by repeated psychological stress in rats

Visceral hypersensitivity has been implicated as an important pathophysiological mechanism in functional gastrointestinal disorders. In this study, we investigated whether the sustained visceral hyperalgesia induced by repeated psychological stress in rats involves the activation of CRF(1) signaling system using two different antagonists. Male Wistar rats were exposed to 10 consecutive days of water avoidance stress (WAS) or sham stress for 1 h/day, and the visceromotor response to phasic colorectal distension (CRD) was assessed before and after the stress period. Animals were injected subcutaneously with the brain penetrant CRF(1) antagonist, CP-154,526, acutely (30 min before the final CRD) or chronically (via osmotic minipump implanted subcutaneously, during stress) or with the peripherally restricted, nonselective CRF(1) and CRF(2) antagonist, astressin, chronically (15 min before each stress session). Repeated WAS induced visceral hypersensitivity to CRD at 40 and 60 mmHg. CP-154,526 injected acutely significantly reduced stress-induced visceral hyperalgesia at 40 mmHg but not at 60 mmHg. Chronic subcutaneous delivery of astressin reduced the stress-induced visceral hyperalgesia to baseline at all distension pressures. Interestingly, chronically administered CP-154,526 eliminated hyperalgesia and produced responses below baseline at 40 mmHg and 60 mmHg, indicating a hypoalgesic effect of the compound. These data support a major role for CRF(1) in both the development and maintenance of visceral hyperalgesia induced by repeated stress and indicate a possible role of peripheral CRF receptors in such mechanisms.

Chronic psychological stress enhances nociceptive processing in the urinary bladder in high-anxiety rats

This study sought to determine whether acute and/or chronic psychological stress produce changes in urinary bladder nociception. Female Sprague–Dawley (SD; low/moderate anxiety) or Wistar–Kyoto (WK; high-anxiety) rats were exposed to either an acute (1 day) or a chronic (10 days) water avoidance stress paradigm or a sham stress paradigm. Paw withdrawal thresholds to mechanical and thermal stimuli and fecal pellet output, were quantified at baseline and after the final stress or sham stress exposure. Rats were then sedated, and visceromotor responses (VMRs) to urinary bladder distension (UBD) were recorded. While acute stress exposure did not significantly alter bladder nociceptive responses in either strain of rats, WK rats exposed to a chronic stress paradigm exhibited enhanced responses to UBD. These high-anxiety rats also exhibited somatic analgesia following acute, but not chronic, stress. Furthermore, WK rats had greater fecal pellet output than SD rats when stressed. Significant stress-induced changes in nociceptive responses to mechanical stimuli were observed in SD rats. That chronic psychological stress significantly enhanced bladder nociceptive responses only in high-anxiety rats provides further support for a critical role of genetics, stress and anxiety as exacerbating factors in painful urogenital disorders such as interstitial cystitis (IC).

Acute psychological stress raises plasma ghrelin in the rat

Ghrelin is produced by the A-like cells of the stomach and mobilized by food deprivation. It was reported recently that acute psychological stress increases ghrelin gene expression in rat oxyntic mucosa. The aim of this study was to examine the effect of such stress on circulating ghrelin levels. To this end, we measured plasma ghrelin in Wistar Kyoto (WKY) rats (a high-anxiety strain) and Sprague–Dawley (SPD) rats (a low-anxiety strain), exposed to water avoidance stress for 60 min. Blood was collected before and after the stress. Acute stress increased the plasma ACTH concentration ∼5-fold ( p < 0.01) in both strains of rats, while plasma ghrelin increased by 85% ( p < 0.01) in the SPD rats and by 40% ( p < 0.001) in the WKY rats. Ghrelin levels after acute stress were higher ( p < 0.05) in the SPD rats than in the WKY rats. Sham stress did not affect plasma ghrelin. We conclude that acute psychological stress mobilizes ghrelin and that the SPD rats respond with a higher plasma ghrelin concentration than the WKY rats.

Chronic Psychological Stress in Rats Induces Intestinal Sensitization to Luminal Antigens

There is increasing evidence that stress plays a role in the pathophysiology of chronic intestinal disorders, but the mechanisms remain unclear. Previous studies in rats have revealed that stress decreases gut barrier function and allows excessive uptake of luminal material. Here, we investigated whether chronic psychological stress acts to induce sensitization of intestinal tissues to oral antigens. Rats were subjected to 1 hour per day of water avoidance stress or sham stress daily for 10 days, and horseradish peroxidase (HRP) was delivered by gavage on day 5. Studies to determine sensitization were conducted on day 20. All stressed rats developed HRP-specific IgE antibodies, antigen-induced intestinal secretion, and increased numbers of inflammatory cells in gut mucosa. Luminal HRP was absorbed more readily by enterocytes of stressed animals. In addition, stressed rats had increased expression of interleukin-4 and decreased expression of interferon-gamma in gut mucosa, a cytokine profile that is typical of allergic conditions. Treatment of stressed rats with an antagonist to corticotropin-releasing hormone (previously shown to inhibit stress-enhanced gut permeability) eliminated the manifestations of intestinal hypersensitivity. Our results indicate that the presence of oral antigen during chronic psychological stress alters the immune response (to sensitization rather than oral tolerance) and causes subsequent antigen-induced gut pathophysiology.

Modulation of Stress- and Inflammation induced Visceral Hypersensitivity by peripheral Neurokinin 1 Receptors

Aims: Altered processing of visceral afferent information is believed to play a key role for the manifestation of symptoms in patients with functional gastrointestinal disorders. While it is well recognized that initiating events such as mucosal inflammation and stress precipitate the onset of symptoms the underlying mechanisms are poorly understood. Tachykinins and their receptors are known to modulate gastrointestinal function including motility, visceral sensitivity and inflammation. Aims: We aimed to study (1) the effect of mucosal inflammation, (2) a repeated standardized stressor and (3) the role of Neurokinin 1 receptors (NK1R) on visceral sensory function. Methods: In randomized order a total of 30 rats underwent intracolonic instillation of Trinitrobenzenesulphonic acid (TNB) or saline while additional 30 rats underwent seven days (1h/day) repetitive water avoidance stress (WAS) or Sham stress. Colorectal distensions (CRD) were performed with a barostat device (3min/40mmHg) and the visceromotor response (VMR) to CRD was quantified as abdominal electromyographic muscle activity (EMG). Measurements were performed 28 days after treatment initiation. After a baseline measurement (3x phasic 40mmHg CRD) either placebo or an NK1R antagonist (Sendide 5nmol) were administered intraperitoneally and a total of four CRD's 2, 5, 10 and 15 min after drug injection were performed. Results: Compared to controls (767±104μV), either TNB (908±144μV) and WAS (885±87μV) significantly (p<0.05) enhanced the VMR to CRD. The NK1R antagonist caused a significant decrease of VMR compared to baseline level in all study groups. The analgesic effect was significantly more potent, with a maximum after 10 min, in TNB (–66.7±4.1%) or WAS (–73±7.2%) treated rats compared to controls (–42.7±6.1). NK1R expression was significantly elevated in TNB (+33.2±4.5%) and WAS (+28.7±3.1%) treated rats compared to controls without any significant difference between those two treatment groups. Conclusions: Either stress or an acute mucosal inflammation have profound effects on visceral sensory function and peripheral NK1R function. The enhanced responsiveness to an NK1R antagonist in visceral hypersensitivity might be of therapeutic relevance

Repeated exposure to water avoidance stress in rats: a new model for sustained visceral hyperalgesia

Chronic stress plays an important role in the development and exacerbation of symptoms in functional gastrointestinal disorders. To better understand the mechanisms underlying this relationship, we aimed to characterize changes in visceral and somatic nociception, colonic motility, anxiety-related behavior, and mucosal immune activation in rats exposed to 10 days of chronic psychological stress. Male Wistar rats were submitted daily to either 1-h water avoidance (WA) stress or sham WA for 10 consecutive days. The visceromotor response to colorectal distension, thermal somatic nociception, and behavioral responses to an open field test were measured at baseline and after chronic WA. Fecal pellets were counted after each WA stress or sham WA session as a measure of stress-induced colonic motility. Colonic samples were collected from both groups and evaluated for structural changes and neutrophil infiltration, mast cell number by immunohistochemistry, and cytokine expression by quantitative RT-PCR. Rats exposed to chronic WA (but not sham stress) developed persistent visceral hyperalgesia, whereas only transient changes in somatic nociception were observed. Chronically stressed rats also exhibited anxiety-like behaviors, enhanced fecal pellet excretion, and small but significant increases in the mast cell numbers and the expression of IL-1beta and IFN-gamma. Visceral hyperalgesia following chronic stress persisted for at least a month. Chronic psychological stress in rats results in a robust and long-lasting alteration of visceral, but not somatic nociception. Visceral hyperalgesia is associated with other behavioral manifestations of stress sensitization but was only associated with minor colonic immune activation arguing against a primary role of mucosal immune activation in the maintenance of this phenomenon.

Behavioral models of binge-type eating

Purpose: To describe and evaluate behavioral models of binge-type eating. Data identification: Studies were identified using Medline and hand searches of bibliographies of identified articles. Study selection: Isomorphic studies were selected that were judged to have some measure of construct validity. Data extraction: Face and construct validity were assessed, as well as simplicity and cost of use. Results of data synthesis: Several different models of binge-type eating exist, each with different strengths of validity and use. These include models using sham feeding, restriction/refeeding cycles and/or stress, limited access (LA) to optional foods, and eating induced by operant schedules of behavior. Conclusions: We concur with Harry Harlow, who was quoted by Gerry Smith as saying: “You'd be crazy to use animal models, but you'd also be crazy not to use them.”

Chronic stress induces mast cell–dependent bacterial adherence and initiates mucosal inflammation in rat intestine

Background & Aims: Chronic psychological stress is an important factor in relapses of intestinal disorders, but it remains unclear if stress can induce primary gut inflammation in a previously healthy host. Methods: Mast cell-deficient (Ws/Ws) rats and wild-type control (+/+) rats were submitted to water avoidance stress or sham stress (1 h/day) for 10 consecutive days, as a model of ongoing life stress. Results: Both rat groups had similar systemic responses to stress, as assessed by changes in weight, corticosterone levels, and defecation. In +/+ rats, chronic stress induced barrier dysfunction in the ileum and colon (increased macromolecular permeability and depletion of mucus) and ultrastructural changes in epithelial cells (enlarged mitochondria and presence of autophagosomes) associated with bacterial adhesion and penetration into enterocytes. Moreover, hyperplasia and activation of mast cells, infiltration of neutrophils and mononuclear cells, and increased myeloperoxidase (MPO) activity were documented in the mucosa. In intestine of Ws/Ws rats, epithelial function and morphology were unchanged by chronic stress, bacterial-epithelial cell interaction was not demonstrated, and there was no evidence of inflammatory cell infiltration. Conclusions: These findings suggest that chronic psychological stress can be an initiating factor in intestinal inflammation by impairing mucosal defenses against luminal bacteria and highlight the importance of mast cells in this process.GASTROENTEROLOGY 2002;123:1099-1108

Neonatal maternal separation predisposes adult rats to colonic barrier dysfunction in response to mild stress.

Intestinal dysfunction is related to stress and early life events, but the mechanisms are largely unknown. Our aim was to determine whether early trauma predisposes adult rats to intestinal mucosal dysfunction in response to stress. Neonatal Sprague-Dawley rats were individually separated from their mothers for 3 h/day at 4-21 days of age. Between days 80 and 90, separated and control rats were subjected to mild acute stress (30-min water avoidance) or sham stress. Mucosal barrier function and ion transport were assessed in colonic tissues mounted in Ussing chambers. Mild stress increased short-circuit current, conductance, and transepithelial transport of macromolecules in separated rats, while having minimal effects in controls. Pretreatment of the separated rats with a corticotropin-releasing hormone (CRH) antagonist, the peptide alpha-helical CRH(9-41) injected intraperitoneally 20 min before stress, abolished the stress-induced mucosal changes. Our results indicate that neonatal trauma can induce phenotypic changes in adulthood, including enhanced vulnerability of the gut mucosa to stress via mechanisms involving peripherally located CRH receptors.

Role of mast cells in chronic stress induced colonic epithelial barrier dysfunction in the rat

BACKGROUND AND AIMSStress may be an important factor in exacerbating inflammatory bowel disease but the underlying mechanism is unclear. Defective epithelial barrier function may allow uptake of luminal antigens that...

Chronic stress impairs rat growth and jejunal epithelial barrier function: role of mast cells.

We examined the impact of chronic stress on rat growth rate and intestinal epithelial physiology and the role of mast cells in these responses. Mast cell-deficient (Ws/Ws) rats and +/+ littermate controls were submitted to water avoidance stress or sham stress, 1 h/day, for 5 days. Seven hours after the last sham or stress session, jejunal segments were mounted in Ussing chambers, in which secretion and permeability were measured. Body weight (as a growth index) and food intake were determined daily. Stress increased baseline jejunal epithelial ion secretion (indicated by short-circuit current), ionic permeability (conductance), and macromolecular permeability (horseradish peroxidase flux) in +/+ rats, but not in Ws/Ws rats, compared with nonstressed controls. Stress induced weight loss and reduced food intake similarly in the groups. In +/+ rats, these parameters remained altered 24-72 h after the cessation of stress. Modulation of stress-induced mucosal mast cell activation may help in the management of certain intestinal conditions involving epithelial pathophysiology.

Role of tachykinin NK2 receptors in normal and altered rectal sensitivity in rats.

Irritable bowel syndrome is characterized by visceral hyperalgesia commonly associated with stress and inflammatory processes. We investigated the role of tachykinin NK2 receptors in the ability of trinitrobenzenesulphonic acid (TNBS) and stress to enhance the sensitivity of the rat rectum to distension using a selective tachykinin NK2 receptor antagonist (MEN 11420). Rats were fitted with electrodes implanted in the striated muscles of the abdomen. Rectal distension (RD) was performed with a balloon inflated by steps of 0.4 ml from 0 to 1.6 ml. Five groups were submitted to RD performed 3 days before and after intrarectal instillation of TNBS. Fifteen minutes before RD, rats were treated with saline or MEN 11420 (5 - 100 microg kg(-1) i.v.). Two other groups, submitted to 2 h restraint or sham stress sessions were randomly treated i.v. with saline or MEN 11420 (10 - 200 microg kg(-1)) prior to RD applied 20 min later. The basal response to RD was characterized by a significant increase in the number of abdominal contractions. This response occurred with a threshold volume of 0.8 ml and was dose-dependently reduced by MEN 11420 (5 - 100 microg kg(-1) i.v.). Rectal inflammation lowered the volume of distension producing abdominal contractions to 0.4 ml (allodynia). This effect was either reduced or suppressed by MEN 11420. A similar allodynia was observed after a stress session and this effect was reduced (49%) or suppressed by MEN 11420 at 200 and 100 microg kg(-1), respectively. Tachykinin NK2 receptors are involved in rectal hypersensitivity associated with inflammation and stress. British Journal of Pharmacology (2000) 129, 193 - 199

Effect of an auditory stress on peritoneal and alveolar cells in C57 BL/6J mice of advanced age.

The aim of this study was to analyse the effects of auditory stress on peritoneal and alveolar macrophages in C57 BL/6J mice of advanced age, and to compare the results to those obtained in old mice submitted to a sham stress, and to those observed in young mice submitted to the same auditory stress. We used a chemiluminescence assay to measure the production of free oxygen radicals (FOR) by macrophages. Eight 22 month-old mice were exposed to a sound stress of 110 dB for three consecutive nights; nine were submitted to a sham stress. The results were compared to those obtained in young (8 week-old) mice, 21 submitted to noise stress, and 17 controls. The corticosterone level was not increased after stress in any group. FOR production in old mice was significantly higher than that in young mice. Stress did not induce significant changes in FOR production by alveolar cells in young mice; however, the FOR production by alveolar cells was significantly higher in the stressed group than in the control group of old mice. These results show that noise stress is associated with modifications of macrophage functions that are influenced by cell localization, the behaviour of alveolar and peritoneal macrophages of old mice being clearly different in our experimental model.

Alteration in the production of free oxygen radicals and proinflammatory cytokines by peritoneal and alveolar macrophages in old mice and immunomodulatory effect of RU 41740 administration: Part I: Effect of short and repetitive noise stress

The aim of this study was to analyze the effects of stress on natural immunity in old mice, and the potential of an immunomodulating drug to correct stress-induced immune abnormalities. We analyzed both the alveolar (ALM) and peritoneal macrophage (PerM) oxidative responses and cytokine productions of TNF-α and IL-1α, in old mice after exposure to 3 days of noise stress, with and without treatment with RU 41740, an immunomodulating compound. Production of Free Oxygen Radicals (FOR) by ALM and PerM macrophages was evaluated using a luminol-dependent chemiluminescence method at the basal state and after stimulation. Serum corticosterone was also measured. Three groups of 22–24 month-old C57BL/6 mice were studied. Seven mice were treated with RU 41740 (10 mg kg−1) every day for 5 days and then exposed to sound stress (110 dB, 1000 Hz, for 3 nights). Ten mice were treated with saline, then submitted to a sham stress. Eight animals received neither treatment nor stress. There was no difference in corticosterone level between the three groups and between these groups and a control group nonstressed, noncannulated. After stimulation by fMetLeuPhe, production of FOR by ALM and PerM significantly increased after stress and returned to normal values after RU 41740 treatment (p<0.001). The cytokine levels (TNF-α and IL-1α) decreased after stress and returned to normal levels after RU 41740 treatment. This study shows that, in aged mice, auditory stress is associated with modifications of macrophage functions which are different, depending on their localization and on the function under study. It confirms the immunomodulatory capacities of RU 41740 that was shown to counteract these effects of stress in elderly animals.

Auditory stress induces changes in membrane functions of mouse peritoneal macrophages.

Stressful events induce responses in the endocrine and immune systems. The authors analysed the influence of repetitive noise stress on peritoneal macrophage oxidative and phagocytic responses. Plasma corticosterone levels were also measured. Different groups of 6- to 8-week-old C57BL/6 male mice were exposed for 1 night (n = 14) and 3 nights (n = 21) to a sound stress of 110 dB in an audiogenic stress chamber. Control animals were submitted to a sham stress for 1 night (n = 13) and 3 nights (n = 17). A marked decrease was observed in the phagocytic response to yeast (P = 3 x 10(-4)) while a mild increase in the oxidative response stimulated by opsonized zymosan was noted only after the 3 night stress (P = 0.02). Corticosterone levels of control and stressed mice did not differ. These results indicate that the stress resulting from repetitive noise causes modifications in peritoneal macrophage activity, and that these changes are dependent on the duration of stress. These functional alterations seem more complex than a simple general suppression or activation.

The Protective Effect of Heat Stress Against Reperfusion Arrhythmias in the Rat

Heat stress provides protection against mechanical dysfunction and myocardial necrosis after prolonged ischemia. We have investigated whether this protection extends to reperfusion arrhythmias occurring after a short (non-lethal) ischemic insult. Anaesthetized open chest rats were subjected to a 5-min occlusion of the left coronary artery. The incidence and duration of reperfusion arrhythmias and the duration of sinus rhythm were assessed in the first 5 min of reperfusion. Prior heat stress led to a reduction in the incidence (100-63%, P ⩽ 0.05) and duration (66.2 ± 15.8 to 9.4 ± 2.9s, P ⩽ 0.05) of ventricular tachycardia and a non-significant reduction in the incidence (76-50%) and duration (74.3 ± 23.4 to 42.9 ± 24.4s, P = 0.09) of ventricular fibrillation. This resulted in a significant increase in the duration of sinus rhythm (142.1 ± 27.6 to 216.7 ± 24.8s, P ⩽ 0.05) and reduction in arrhythmia score ( P ⩽ 0.05) in heat stressed rats compared with controls. This protection against reperfusion arrhythmias was associated with a two-fold increase in endogenous catalase activity and expression of the inducible heat stress protein HSP 70. Inhibition of catalase with pre-administered 3-amino triazole resulted in a paradoxical protection in both sham and heat stress hearts. We conclude that heat stress leads to protection against reperfusion arrhythmias; however, we have been unable to resolve whether the changes in catalase activity of HSP expression are the mediators of the demonstrated cardioprotection.

Attenuation by Heat Stress of a Submaximal Calcium Paradox in the Rabbit Heart

Heat stress limits the injury associated with myocardial ischaemia and reperfusion, an effect previously attributed to enhanced endogenous anti-oxidant activity. We examined the influence of heat stress on the calcium paradox, and injury in which oxidant stress in not thought to play a major role. Twenty-four hours following sham or true heat stress, rabbits were re-anaesthetized and hearts either removed for stress protein analysis (n = 8), or Langendorff-perfused (n = 20) and subjected to a calcium paradox. Ten minutes following calcium repletion (Ca2+ = 1.3 mM), left ventricular developed pressure was better preserved in heat stress vs control hearts (38.3 ± 5.0 vs 18.8 ± 4.1 mmHg, respectively, P = 0.003) whilst contracture, measured by left ventricular enddiastolic pressure, was diminished (21.6 ± 4.7 vs 39.9 ± 5.2 mmHg, respectively, P = 0.02). Creatine phosphokinase release at 1 min was less in heat stress vs control hearts (10.6 ± 8.6 vs 86.4 ± 33.7 U/min/g, respectively, P = 0.01). The myocardial content of the 72 kDa stress protein was elevated eight-fold in heat stress vs control hearts (2.8 ± 0.02 vs 0.4 ± 0.1 U, respectively, P = 0.01), This study suggest that some portion of the stress protein response represents a form of cardiac adaptation capable of limiting myocyte injury independent of anti-oxidant mechanisms.