Specific Alternation Of Rhythm In Temperature Research Articles

Stress enhances gait disturbance induced by lumbar disc degeneration in rat.

Although psychological factors are assumed to be the primary cause of stress-related back pain, there have been no studies of the relationships between stress and low back pain in an animal model. The purpose of this study was to examine the influence of specific alternation of rhythm in temperature (SART) stress on gait abnormality using the CatWalk method in a rat model of low back pain caused by lumbar facetectomy. Sixty rats were divided into three groups: the control, sham and experimental groups. Each group was then divided into non-SART stress and SART stress subgroups. We evaluated the behavioral changes 7weeks postoperatively using the von Frey test and the CatWalk method. Threshold values for the hind paw in the SART stress subgroups were significantly lower than those in the non-SART stress subgroups. In the experimental group, significant changes by CatWalk in step cycle, stand time and average speed were observed under non-SART stress conditions, but SART stress resulted in additional significant changes in not only these parameters, but in other parameters including the duty cycle and swing time, compared with those in the control and sham groups. The demonstration by CatWalk analysis may indicate that SART stress enhanced gait disturbance. In this animal model, we demonstrated for the first time that stress may be a factor involved in worsening of low back pain.

ストレスにより惹起される心身症の病態モデル : SART(Specific Alternation of Rhythm in Temperature)ストレス動物の症状と病態

ストレスにより惹起される心身症の病態モデル : SART(Specific Alternation of Rhythm in Temperature)ストレス動物の症状と病態

Repeated Cold Stress Enhances the Acute Restraint Stress-Induced Hyperthermia in Mice.

The rodents exposed to repeated cold stress according to a specific schedule, known as specific alternation of rhythm in temperature (SART), exhibit autonomic imbalance, and is now used as an experimental model of fibromyalgia. To explore the susceptibility of SART-stressed animals to novel acute stress, we tested whether exposure of mice to SART stress for 1 week alters the extent of acute restraint stress-induced hyperthermia. Mice were subjected to 7-d SART stress sessions; i.e., the mice were alternately exposed to 24 and 4°C at 1-h intervals during the daytime (09:00-16:00) and kept at 4°C overnight (16:00-09:00). SART-stressed and unstressed mice were exposed to acute restraint stress for 20-60 min, during which rectal temperature was monitored. Serum corticosterone levels were measured before and after 60-min exposure to restraint stress. SART stress itself did not alter the body temperature or serum corticosterone levels in mice. Acute restraint stress increased the body temperature and serum corticosterone levels, both responses being greater in SART-stressed mice than unstressed mice. The enhanced hyperthermic responses to acute restraint stress in SART-stressed mice were significantly attenuated by SR59230A, a β3 adrenoceptor antagonist, but unaffected by diazepam, an anxiolytic, mifepristone, a glucocorticoid receptor antagonist, or indomethacin, a cyclooxygenase inhibitor. These results suggest that SART stress enhances the susceptibility of mice to acute restraint stress, characterized by increased hyperthermia and corticosterone secretion, and that the increased hyperthermic responses to acute stress might involve accelerated activation of sympathetic β3 adrenoceptors, known to regulate non-shivering thermogenesis in the brown adipose tissue.

Neurotropin® inhibits calpain activity upregulated by specific alternation of rhythm in temperature in the mesencephalon of rats

AimsNeurotropin® (NTP), an analgesic for chronic pain, has antihyperalgesic effects in specific alternation of rhythm in temperature (SART)-stressed rats. Previous studies have shown that SART stress induces hyperalgesia, as well as post-translational modification of proteins (including substrates for calpain, a calcium-dependent cysteine protease) in the mesencephalon of rats. To better understand the mechanism of action of NTP, we investigated whether SART stress activates calpain in the mesencephalon of rats and whether NTP inhibits this activation. Main methodsWistar rats were exposed to SART stress for 5days. NTP (200NU/kg/day) was administered intraperitoneally every day from the onset of SART stress. The mechanical pain threshold was measured using the Randall-Selitto test on the 6th day. Thereafter, the rat mesencephalon was immediately collected and calpain activity was examined using western blot analysis with a calpain cleavage site-specific antibody. Key findingsSART stress induced hyperalgesia and increased the calpain activity in the mesencephalon of rats. In contrast, NTP treatment attenuated the hyperalgesia and prevented the increase in calpain activity in the mesencephalon of SART-stressed rats. Interestingly, a negative correlation was identified between calpain activity and mechanical pain threshold in SART-stressed rats treated with or without NTP. Furthermore, NTP inhibited calpain activity on mammalian uncoordinated-18 in rat mesencephalon homogenate and Ac-LLY-AFC as substrates in an in vitro cell-free system. SignificanceOur data demonstrate that NTP treatment prevents SART stress-induced calpain activation in the mesencephalon of rats and suggests that NTP-mediated antihyperalgesia is associated with an inhibition of calpain activity in the mesencephalon.

Impaired diffuse noxious inhibitory controls in specific alternation of rhythm in temperature-stressed rats

Fibromyalgia is characterized by chronic widespread musculoskeletal pain. A hypofunction in descending pain inhibitory systems is considered to be involved in the chronic pain of fibromyalgia. We examined functional changes in descending pain inhibitory systems in rats with specific alternation of rhythm in temperature (SART) stress, by measuring the strength of diffuse noxious inhibitory controls (DNIC). Hindpaw withdrawal thresholds to mechanical von Frey filament or fiber-specific electrical stimuli by the Neurometer system were used to measure the pain response. To induce DNIC, capsaicin was injected into the intraplantar of the forepaw. SART-stressed rats were established by exposure to repeated cold stress for 4 days. In the control rats, heterotopic intraplantar capsaicin injection increased withdrawal threshold, indicative of analgesia by DNIC. The strength of DNIC was reduced by naloxone (μ-opioid receptor antagonist, intraperitoneally and intracerebroventricularly), yohimbine (α2-adrenoceptor antagonist, intrathecally), and WAY-100635 (5-HT1A receptor antagonist, intrathecally) in the von Frey test. In SART-stressed rats, capsaicin injection did not increase withdrawal threshold in the von Frey test, indicating deficits in DNIC. In the Neurometer test, deficient DNIC in SART-stressed rats were observed only for Aδ- and C-fibers, but not Aβ-fibers stimulation. Analgesic effect of intracerebroventricular morphine was markedly reduced in SART-stressed rats compared with the control rats. Taken together, in SART-stressed rats, capsaicin-induced DNIC were deficient, and a hypofunction of opioid-mediated central pain modulation system may cause the DNIC deficit.

Specific Alternation of Rhythm in Temperature (SART) Stress-Induced Irritable Bowel Syndrome-Like Changes in Mice and Effects of Drugs

Stress is closely associated with the manifestation and progress of irritable bowel syndrome (IBS). For the purpose of establishing experimentally the relationship between IBS and stress, the transportation capacity of the small intestine in specific alternation of rhythm in temperature (SART)-stressed animals was studied using charcoal transportation method. The charcoal suspension was administered orally into the stomach of fasting mice. Mice were sacrificed after a certain time and %charcoal transit (%CT) of the small intestine was measured. The %CTs in SART-stressed mice were greater than those in unstressed or continuously cold-stressed mice. This increase in %CT remained for 1 week after discontinuation of SART stress loading. Cholinergic blockers decreased %CTs in SART-stressed mice. Increases in %CT by a cholinesterase inhibitor were less in SART-stressed mice than in unstressed mice. Increases of %CT in SART-stressed mice were suppressed by Neurotropine. These results suggested that the parasympathetic hypertonicity, not just cold, played a role in the increases in the transportation capacity in SART-stressed mice and that these animals can be a useful tool for elucidation of the mechanism of IBS.

Effects of Some .BETA.-Adrenoceptor Antagonists on Orthostatic Hypotension in Repeatedly Cold- (SART-) Stressed Rats

Rats stressed by specific alternation of rhythm in temperature (SART) show various symptoms of disautonomia, increased pulse rates, continuous hypotension, and severe orthostatic hypotension (OH) when they are subjected to postural change. The OH symptoms are improved by muscarinic M2-receptor blockers. In the present study, effects of beta-adrenoceptor blocking agents on OH in SART-stressed rats were investigated. Anesthetized rats were restrained on a board in the supine position, and direct blood pressure and ECG were measured automatically using Fluclet Jr.2. Postural change was performed by raising the rat's head up to a 60 degrees angle for 4 min. Unstressed rats treated with hexamethonium showed large decrease in blood pressure, small reflex from the bottom of pressure and decreased tachycardia reflex, whereas isoproterenol showed little changes. In SART-stressed rats, isoproterenol alleviated the decrease in blood pressure in postural change, brought large reflex from the bottom of pressure and increased tachycardia reflex, whereas hexamethonium had little changes. Propranolol and atenolol induced the similar changes as those seen by hexamethonium. ICI-118,551, a selective beta2-adrenoceptor antagonist showed large reflex from the bottom of pressure and increased tachycardia reflex in stressed rats, whereas little changes in unstressed rats. In conclusion, it was suggested that the hypotension in OH manifestation time of rats reflects the state of peripheral blood vessels, and beta1-adrenoceptors played a role in compensatory tachycardia reflex and beta2-adrenoceptors in blood pressure reflex. The circulatory regulation in SART-stressed rats seems to be poorly functioning in nervous reflex in postural changes.

Effects of AF-DX116 and Other Muscarinic Receptor Antagonists on Orthostatic Hypotension in Autonomic Imbalanced (SART-Stressed) Rats

SART (specific alternation of rhythm in temperature)-stressed rats are an animal model of autonomic imbalance created by exposing animals to repeated cold stress. The SART-stressed rats have been shown to easily develop orthostatic hypotension (OH). In this study, effects of AF-DX116, a selective M2 antagonist, and other muscarinic receptor antagonists on OH were investigated in SART-stressed and unstressed rats. Each anesthetized rat was canulated into the left common carotid artery, and blood pressure (BP) and heart rate were measured. Stimulation for postural change was initiated by head-up tilting. As the indices of OH, the maximum fall of BP, % reflex (recovery from maximum fall), and the area enclosed between the baseline and the recovery curve for BP (AUC) were used. Large AUC and small % reflex in SART-stressed rats were changed, becoming similar to those of the unstressed rats by AF-DX116 and methoctoramine. Atropine and methylatropine had similar effects to AF-DX116. However, the effects of methoctoramine, atropine, and methylatropine were less than that of AF-DX116. Pirenzepine was not effective. In conclusion, it was suggested in SART-stressed rats that OH was related to hyperactivity in the parasympathetic nerve and the M2 receptor played the major role in OH.

A Role for Corticotropin-Releasing Factor in Repeated Cold Stress-Induced Anxiety-Like Behavior during Forced Swimming and Elevated Plus-Maze Tests in Mice

SART (specific alternation of rhythm in temperature) stress is known to cause anxiety-like behavior in mice/rats in several anxiety-related behavioral tests. In the present study, we investigated possible roles for corticotropin-releasing factor (CRF) and glucocorticoids in SART stress-induced anxiety-like behavior in two different anxiety-related behavioral tests. In the forced swimming test, CRF, administered intracerebroventricular (i.c.v.) at 0.5-2 pmol/mouse, dose-dependently reduced immobility time in unstressed and SART-stressed mice. alpha-Helical CRF, a specific CRF receptor antagonist, administered i.c.v. at 0.1-1 nmol/mouse, dose-dependently increased immobility time in SART-stressed mice, but not in unstressed mice. In the elevated plus-maze test, CRF at 10-20 pmol/mouse significantly decreased the time spent in open arms in unstressed mice. CRF at a high dose tended to decrease this time in SART-stressed mice, but this decrease was not statistically significant. alpha-Helical CRF failed to modify the time in unstressed mice. In contrast, alpha-helical CRF at 0.38 and 0.75 nmol/mouse increased the time in SART-stressed mice. Both immobility time in the forced swimming test and time spent in open arms in the elevated plus-maze test in unstressed and SART-stressed mice were unaffected by adrenalectomy. These results suggest that CRF plays an important role in anxiety-like behavior caused by SART stress.

Anxiety-Like Behavior in Elevated Plus-Maze Tests in Repeatedly Cold-Stressed Mice

To clarify the relationship between SART (specific alternation of rhythm in temperature) stress (repeated cold stress) and anxiety, the effects of various types of stress on the behavior of mice were studied in elevated plus-maze tests and then the effects of anxiolytics were evaluated. The percentage of time spent in the open arms of the plus-maze apparatus decreased in mice subjected to SART stress without change in the total number of arm entries. No change was noted in mice subjected to other stresses, such as 1-h, 2-day and 5-day cold stress and 1-h, 15-h and 5 χ 15-h restraint stress. The reduction in the percentage of time spent in the open arms caused by SART stress was inhibited by single and repeated administrations of diazepam and alprazolam and by a single administration of buspirone, which have no influence on the percentage of time spent in the open arms in nonstressed mice, but not by flumazenil, WAY-100635 and chronic treatment with buspirone. The effects of diazepam and buspirone were antagonized by flumazenil and WAY-100635, respectively. The behavior of SART-stressed mice in the plus-maze would thus appear to arise from anxiety, to which benzodiazepine and serotonin receptors are related, but the diazepam binding inhibitor, an endogenous anxiogenic protein, is not. Thus SART-stressed animals may be useful for investigating the psychopharmacological and neuropharmacological basis of anxiety.

Blood Pressure and Heart Rate Are Increased by AF-DX 116, a Selective M2 Antagonist, in Autonomic Imbalanced and Hypotensive Rats Caused by Repeated Cold Stress

Rats exposed to SART (specific alternation of rhythm in temperature) stress, which are ideal animal models for vagotonia-type dysautonomia, show various changes in cardiac and circulatory systems. In this study, attention was directed to cholinergic function in the SART-stressed rat heart and the effects of AF-DX 116, a specific muscarinic M2 antagonist, on blood pressure and heart rate. The results were compared with those obtained for atropine and pirenzepine. In SART-stressed rats, systolic and diastolic blood pressures (SBP and DBP) were lower than in unstressed rats. Oral AF-DX 116 resulted in greater elevation of DBP than SBP in unstressed rats. In stressed rats, greater and more prolonged elevation of SBP than in unstressed rats was noted, particularly at higher doses. A dose-dependent SBP change in stressed rats, caused by intravenous AF-DX 116, was shifted upward in parallel with that in unstressed groups, unlike with oral administration. The positive chronotropic effect of this drug was smaller in stressed rats than in unstressed rats, in contrast to the pressor effect. SART-stressed rats may thus have an enhanced sympathetic tone in the heart, as well as changes in muscarinic M2 receptors at sympathetic nerve endings and at the heart muscle. The effects of AF-DX 116 on blood pressure and heart rate thus may arise from peripheral action and AF-DX 116 may be useful for treating hypotension related to autonomic imbalance of the vagotonia type.

Stress-induced anxiety and endogenous anxiogenic substances

Anxiety observed in animals subjected to stress was stated in relation to anxiety level and biological backgrounds of animals, changes in neurotransmitters and causal stressors. 1. Anxiety is thought to be a negative emotion caused by many kinds of stress such as restraint stress, SART (specific alternation of rhythm in temperature) stress (a repeated cold stress caused by environmental temperature), social stress, etc. 2. Emotional behavior in those stressed animals were attenuated by anxiolytics like diazepam, a benzodiazepine receptor agonist and buspirone, a serotonin (5-HT) 1A agonist. 3. Stressed rats had changed brain levels of a variety of neurotransmitters such as corticotropin-releasing factor (CRF), noradrenaline, 5-HT, dopamine, acetylcholine, histamine, cholecystokinin, etc. The percentage of time spent on the open arms of an elevated plus-maze apparatus decreased in those stressed animals. Abnormal elevated plus-maze behaviors were attenuated by diazepam, buspiron and a CRF antagonist. 4. Anxiety level differs according to the coping strategy of the recipients. Rats of different strain, sex, aging and/or family display different behaviors in elevated plus-maze. 5. Stress-induced anxiety-related behaviors were observed when levels of some neurotransmitters became unbalanced. Thus modulators of unbalanced brain substances are thought to have anxiolytic properties.

Effect of the lipid peroxide reaction caused by repeated cold stress on cisplatin-induced nephrotoxicity.

The peroxide reaction in mouse kidney was examined in order to determine the relationship between the lipid peroxide reaction caused by SART (specific alternation of rhythm in temperature) stress and that caused by drug administration. After exerting SART stress for one wk on 6-wk-old male ddY mice (stress group), the peroxide reaction generated by the administration of a single dose of cis-diamminedichloroplatinum (cisplatin: CDDP, 10 mg/kg, i.p.) into SART-stressed mice (stress + CDDP group) was compared with the reaction of CDDP-administered nonstressed mice (CDDP group), saline-administered nonstressed mice (saline group), and saline-administered SART-stressed mice (stress + saline group). Lipid peroxidation in the kidneys was significantly higher in the stress group upon cessation of stress exertion than in the normal group. However, no significant difference in the lipid peroxide level after administration of CDDP was observed between the CDDP groups. The renal glutathione levels were significantly different between the CDDP groups and the saline administered groups. These results indicate that the peroxide reaction is generated in the kidneys by stress, but stress has no effect on the peroxide damage caused by CDDP administration. However, the contribution of stress to renal function impairment requires further evaluation.

Cross tolerance to environmental stress and endotoxin

Mild DIC-like phenomena develop in rodents exposed to environmental stress, induced by prolonged fluctuation in ambient temperature, known as SART (specific alternation of rhythm in temperature) stress, the symptoms being essentially similar to those produced by endotoxin. The aim of the present study was to investigate whether common mechanisms are involved in the stress-induced DIC-like phenomena and endotoxaemia. The mortality in mice after intraperitoneal injection with endotoxin at 8.3, 16.7 and 33.3 mg kg increased in a dose-dependent manner. In the mice exposed to stress for 7 days, the death rate following endotoxin at 8.3 mg kg was markedly lower than that in unstressed mice, although no difference was detected between the two groups following endotoxin at 16.7 and 33.3 mg kg . Conversely, repeated administration of endotoxin at a low dose, 0.5 mg kg , during exposure to stress for 7 days inhibited the stress-induced thrombocytopenia and hypofibrinogenemia. These findings indicate the development of cross tolerance to prolonged environmental stress and endotoxin, implying involvement of a common mechanism.

Effects of Repeated Cold Stress on Feeding, Avoidance Behavior, and Pain-Related Nerve Fiber Activity

The specific alternation of rhythm in temperature (SART), which is defined as rapid and frequent changes in the environmental temperature several times within the course of a day, produces abnormalities in behavior such as hyperphagia and in sensory sensation such as hyperalgesia. As the first step toward understanding the mechanisms of these abnormalities, we studied the effects of SART stress on ingestive behavior. During the light and dark phases, the animals’ food intake increased, but their body weight gain decreased. In addition, diurnal variation in body weight also decreased. Next, we examined the behavioral and electrophysiological effects of SART stress on avoidance behavior by studying the rat’s avoidance of a noxious stimulus in the form of a footshock. The rats demonstrated hyperreactivity; the delay in escaping the footshock was decreased by SART stress. The excitability of C-fiber activity, which responds to mechanical and thermal stimuli to a single saphenous nerve, was not changed by SART stress. This suggests that the hyperreactivity in footshock avoidance and the hyperalgesia in pain response induced by SART stress are based on excessive emotionality.

Attenuation by prolonged nitric oxide synthase inhibition of the enhancement of fibrinolysis caused by environmental stress in the rat.

1. Nitric oxide (NO) suppresses platelet aggregation and plasminogen activator inhibitor (PAI) release from platelets, playing physiological and/or pathological roles in the haemostatic system. We investigated the effect of NG-nitro-L-arginine methyl ester (L-NAME), an NO synthase inhibitor, on the disseminated intravascular coagulation (DIC)-like phenomena in rats under environmental stress, induced by prolonged fluctuation in air temperature, known as SART (specific alternation of rhythm in temperature) stress. 2. Exposure of rats to SART stress for 7 days caused mild DIC-like symptoms such as thrombocytopenia, hypofibrinogenemia, decreased factor VIII: coagulant activity and shortened euglobulin clot lysis time (ECLT). The enhanced fibrinolysis was accompanied by a marked decrease in the activity of plasma PAI. 3. L-NAME, but not its D-enantiomer, when administered orally at 0.3-10 mg kg-1, twice a day for 7-day exposure to stress, inhibited the stress-induced decrease in fibrinogen levels in a dose-dependent manner, whereas it failed to alter platelet count, factor VIII:coagulant activity and plasma protein levels in stressed rats. All these parameters in unstressed rats were resistant to L-NAME at 10 mg kg-1. 4. Repeated treatment with 10 mg kg-1 of L-NAME blocked the shortening of ECLT and the decrease in PAI activity following stress exposure, although it was without effect in unstressed rats. 5. The inhibitory effects of L-NAME at 10 mg kg-1 on the stress-induced alterations in fibrinogen levels and in ECLT were significantly reduced by coadministered L-arginine at 1000 mg kg-1. 6. These findings demonstrate that repeated administration of L-NAME attenuates the enhanced fibrinolysis, without aggravating thrombocytopenia, in SART-stressed rats. Endogenous NO appears to contribute to the stress-induced development of fibrinolysis by suppressing, plasma PAI activity, most probably as a result of inhibition of the PAI release from platelets.

Mechanism of hyperalgesia in sart stressed (repeated cold stress) rats and effects of drugs

The decrease in nociceptive threshold has been demonstrated in rats exposed to 24 C and cold environment (-3 C) for alternate one hour periods from 10:00-17:00 hours and then kept with cold temperature from 17:00-10:00 hours in the following morning for several days. This model is referred to as the SART (Specific Alternation of Rhythm in Temperature) stress. In the present study, to verify the mechanisms underlying such hyperalgssia, antinociceptive effects of various neuroactive drugs were investigated with the intrathecal injections. The analgesic effects of intrathecal serotonin (5-HT, 30 and 100 nmol/rat), 1-(m-chlorophenyl)-biguanlde hydrochlorlde (mCPBG,10-10Omol/rat, a 5-HT3 agonist) and clonldine (30nmoVrat, an 0~ agonist) in SART stressed rats were significantly greater than in normal rats. (±)-8-hydroxy-2-(di-n-propylamino) tetralin hydrochloride (DPAT, a 5-HT~A agonist) and CGS12066B (a 5-HT,B agonist) produced hyperalgesic action in normal rats. An intrathecal a-methyl 5-HT (a 5-HT2 agonist), phenylephrine (an o¢, agonist), isoproteranol (a I~ agonist) and dopamine had no influence on the nociceptive threshold in both normal and SART stressed rats. On the other hand, the analgesic effects of intrathecal morphine and [D-Ala =, MetS] enkephalinamide (an opioidergic I~ agonist) or [D-Pen~,S]-enkephalin (a ~ agonist) were same degree between SART stressed and normal rats. These results suggest that SART stressed rat exhibit the hyperalgesis resulting from the decreased activltiss of descending monoaminergic pain inhibitory systems, probably mediated by either 5-HT~ serotonergic or o~ noradrenergic receptors in the spinal dorsal horn.

Possible involvement of oxygen-derived free radicals in abnormal hemostasis induced by SART stress (repeated cold stress) in laboratory animals

Abnormal hemostatic profiles indicating hemorrhagic tendency have been reported in rodents exposed to prolonged fluctuation in ambient temperature, known as SART (specific alternation of rhythm in temperature)-stressed animals. In this study, investigation was made of possible involvement of oxygen-derived free radicals in the development of stress-induced hemostatic alteration. SART-stressed rats and mice exhibited marked decrease in platelet count, fibrinogen level and factor VIII:C activity. Superoxide dismutase, when administered s.c. twice a day to mice for 7 days of stress exposure, inhibited the above alterations. Catalase given in the same manner, had essentially the same effect, though to a lesser extent. Allopurinol administered orally once daily during stress reduced stress-induced thrombocytopenia, but caused considerable increase in fibrinogen and factor VIII:C activity in stressed and unstressed mice. Lipid peroxide significantly increased in the heart but not in the plasma following stress exposure in rats and mice. Active oxygens would thus appear to be, at least partially, involved in the development of abnormal hemostasis induced by SART stress.

Characterization of platelet hypofunctions in rats under SART stress (repeated cold stress)

Platelet hypoaggregability has been reported in rats exposed to a chronic form of environmental stress induced by long-lasting fluctuation in air temperature, known as SART (specific alternation of rhythm in temperature) stress. This study examines functional characteristics of platelets from stressed rats in more detail. Exposure to stress reduced aggregation and ATP release in platelets stimulated with collagen, as determined using platelet-rich plasma (PRP). The resting levels of ATP but not ADP in platelets from stressed rats were lower than those from unstressed ones. Collagen-induced release and resting level of serotonin also decreased in platelets from stressed rats. In contrast, stress failed to cause hypoaggregability of washed platelets. Circulating platelet aggregates were detected in stressed rats. From these data, SART stress appears to cause intravascular activation of platelets in spite of in vitro hypofunctions. Alteration in plasma milieu may be associated with stress-induced platelet hypofunctions in PRP.

Platelet hypoaggregability in rats exposed to SART stress (repeated cold stress)

A prolongation of bleeding time accompanied by thrombocytopenia and abnormalities in coagulation-fibrinolysis systems has been observed in laboratory animals exposed to a chronic form of environmental stress induced by severe fluctuations of air temperature, known as SART (specific alternation of rhythm in temperature) stress. In order to clarify the hemostatic profile under SART stress in more detail, the present study examined platelet aggregability in vitro as well as in vivo in stressed rats. During exposure to stress, thrombocytopenia developed from day 5, and remained up to at least day 14. In vitro aggregation of platelets stimulated by ADP or collagen was markedly decreased in stressed rats, compared with unstressed rats. Furthermore, stressed rats exhibited in vivo hypoaggregability of platelets, as estimated by the magnitude of the drop in circulating platelet counts following intravenous injection of ADP and collagen. Protein and cholesterol content in platelets remained constant after stress exposure. These results indicate that SART-stressed rats exhibit platelet dysfunctions in addition to thrombocytopenia. Considering the previous findings, the hemostatic system under SART stress appears to show a general tendency toward hemorrhage.