[The pharmacological correction of the antioxidant status and of the immunological reactivity of the body during air and immersion cooling]

Beta-carotene, essential, and the heteropolysaccharide of chamomile racemes reduce the manifestation of the antioxidant status and immunological reactivity caused by air and immersion (water) cooling. The effect of the drugs is mediated by various fractions of the erythrocytes.

Superoxide dismutase activity and the effect of N-methyl-D-aspartate antagonists on lipid peroxidation in the early phase of cold injury

Free radicals, lipid peroxidation and excitatory amino acids have been implicated in the secondary mechanisms of traumatic brain injury. We used the cold injury model in rats to assess the endogenous activity of the protective enzyme superoxide dismutase (SOD) and the lipid peroxidation level in the contused tissue at an early phase of injury. Furthermore, we treated the rats with two different N-methyl-D-aspartate receptor antagonists, namely MK-801 and CPP, and evaluated their effect on lipid peroxidation in the contused tissue. Rats were divided into four groups: sham, control, treatment 1 and treatment 2 groups (n= 16 for each group). Thirty and 60 min after craniectomy or injury, tissue samples were removed. SOD activity didn't change in this period. However, lipid peroxidation in terms of malondialdehyde (MDA) amount showed a significant increase at 60 min. Fifteen minutes after injury, MK-801 (1 mg/kg), CPP (10 mg/kg) or saline (1 ml) were applied intraperitoneally in treatment 1, treatment 2 and the control groups. Treatment with MK-801 attenuated MDA levels, whereas treatment with CPP did not. The protective effect of MK-801 achieved statistical significance. These results demonstrate that SOD activity does not change in the early period of cold injury. Moreover, these results show that lipid peroxidation increases after 60 min of cold injury, and treatment with MK-801 15 min after injury can prevent this elevation.

Effects of ibuprofen on the physiology and survival of hypothermic sepsis. Ibuprofen in Sepsis Study Group

OBJECTIVES

The objective was to compare the clinical and physiologic characteristics of febrile septic patients with hypothermic septic patients; and to examine plasma levels of cytokines tumor necrosis factor alpha (TNF-alpha and interleukin 6 (IL-6) and the lipid mediators thromboxane B2 (TxB2) and prostacyclin in hypothermic septic patients in comparison with febrile patients. Most importantly, we wanted to report the effect of ibuprofen treatment on vital signs, organ failure, and mortality in hypothermic sepsis.

SETTING

The study was performed in the intensive care units (ICUs) of seven clinical centers in the United States and Canada.

PATIENTS

Four hundred fifty-five patients admitted to the ICU who met defined criteria for severe sepsis and were suspected of having a serious infection.

INTERVENTION

Ibuprofen at a dose of 10 mg/kg (maximum 800 mg) was administered intravenously over 30 to 60 mins every 6 hrs for eight doses vs. placebo (glycine buffer vehicle).

MEASUREMENTS AND MAIN RESULTS

Forty-four (10%) septic patients met criteria for hypothermia and 409 were febrile. The mortality rate was significantly higher in hypothermic patients, 70% vs. 35% for febrile patients. At study entry, urinary metabolites of TxB2, prostacyclin, and serum levels of TNF-alpha and IL-6 were significantly elevated in hypothermic patients compared with febrile patients. In hypothermic patients treated with ibuprofen, there was a trend toward an increased number of days free of major organ system failures and a significant reduction in the 30-day mortality rate from 90% (18/20 placebo-treated patients) to 54% (13/24 ibuprofen-treated patients).

CONCLUSIONS

Hypothermic sepsis has an incidence of approximately 10% and an untreated mortality twice that of severe sepsis presenting with fever. When compared with febrile patients, the hypothermic group has an amplified response with respect to cytokines TNF-alpha and IL-6 and lipid mediators TxB2 and prostacyclin. Treatment with ibuprofen may decrease mortality in this select group of septic patients.

Anoxia-induced dopamine release from rat striatal slices: involvement of reverse transport mechanism

Incubation of rat striatal slices in the absence of oxygen (anoxia), glucose (aglycemia), or oxygen plus glucose (ischemia) caused significant increases in dopamine (DA) release. Whereas anoxia decreased extracellular 3,4-dihydroxyphenylacetic acid levels by 50%, aglycemia doubled it, and ischemia returned this aglycemia-induced enhancement to its control level. Although nomifensine, a DA uptake blocker, completely protected the slices against anoxia-induced DA depletion, aglycemia- and ischemia-induced increases were not altered. Moreover, hypothermia differentially affected DA release stimulated by anoxia, aglycemia, and ischemia. Involvement of glutamate in DA release induced by each experimental condition was tested by using MK-801 and also by comparing the glutamate-induced DA release with that during anoxia, aglycemia, or ischemia. MK-801 decreased the anoxia-induced DA depletion in a dose-dependent manner. This treatment, however, showed a partial protection in aglycemic conditions but failed to improve ischemia-induced DA depletion. Like anoxia, DA release induced by exogenous glutamate was also sensitive to nomifensine and hypothermia. These results indicate that anoxia enhances DA release by a mechanism involving both the reversed DA transporter and endogenous glutamate. Partial or complete lack of effect of nomifensine, hypothermia, or MK-801 in the absence of glucose or oxygen plus glucose also suggests that experimental conditions, such as the degree of anoxia/ischemia, may alter the mechanism(s) involved in DA depletion.

Implications for atypical antioxidative properties of manganese in iron-induced brain lipid peroxidation and copper-dependent low density lipoprotein conjugation

Our group recently observed that manganese prevents oxidative brain injury in the iron-induced parkinsonian animal model. It has also been suggested that manganese retards while copper promotes the development of atherosclerosis. In this report, we provide further evidence to support a controversial notion that manganese is an atypical antioxidant. Among transition metals, Cu2+ and Fe2+ (0.1 to 125 microM), but not Mn2+, converted hydrogen peroxide to reactive hydroxyl radicals via the Fenton reaction at pH 7.4. Iron's pro-oxidative rate is relatively slow, but it is accelerated further by ascorbate (50 microM) in 37 degrees C Dulbecco's phosphate buffered saline. Moreover, Mn2+ (0-80 microM) concentration dependently retarded diene conjugation of human low density lipoproteins stimulated by 5 microM Cu2+. This new result is consistent with our recent finding that Mn2+ (0 to 20 microM) does not initiate brain lipid peroxidation while it inhibits iron-induced peroxidation of polyunsaturated fatty acids. These unexpected manganese results are somewhat at odds with a prominent theory that manganese is a prooxidative transition metal. Furthermore, iron and copper induced free radical generation and lipid peroxidation are suppressed by lowering the incubation temperature; this suggests that hypothermia may decrease the oxidative stress and damage in vivo. In conclusion, normal dietary intake of manganese may protect cells and neurons from oxidant stress through the inhibition of propagation of lipid peroxidation caused by hydroxyl radicals generated by pro-oxidative transition metals such as iron and copper. Potential therapeutical uses of manganese, manganese SOD mimetics and hypothermia for protecting brain neurons and vascular endothelial cells against oxidative stress and damage have been successfully demonstrated in both animal models and clinical trials.

Cerebral blood flow does not mediate the effect of brain temperature on recovery of extracellular potassium ion activity after transient focal ischemia in the rat

Temperature plays an important role in determining outcome following both global and focal brain ischemia. After focal ischemia, the degree of infarction decreases with mild hypothermia and increases with mild hyperthermia. In this study, brain extracellular potassium ion activity and local cerebral blood flow were measured in cerebral cortex during 60 min of middle cerebral artery occlusion and 60 min of re-perfusion. Brain temperature was maintained at 32-34 degrees C (mild hypothermia), 35.5-36.5 degrees C (normothermia), or 37.5-38.5 degrees C (mild hyperthermia) throughout ischemia and re-perfusion. In normothermic animals and to a greater degree in hyperthermic animals, extracellular potassium ion activity showed delayed secondary elevation above pre-ischemia values within 40-60 min after re-perfusion. No secondary elevation of extracellular potassium ion activity was observed in hypothermic animals. There was no difference in cortical blood flow among groups with varying brain temperature, indicating that delayed deterioration of brain potassium ion homeostasis was not caused by temperature dependent alteration of cerebral blood flow. The data suggest that loss of potassium ion homeostasis during re-perfusion after focal cerebral ischemia is caused by cellular rather than vascular dysfunction and may reflect secondary inhibition of energy metabolism.

Effects of adrenalectomy on 8-OH-DPAT induced hypothermia in mice

Complex interactions exist between the hypothalamic-pituitary-adrenal (HPA) axis and the serotonergic system, and it has been suggested that these interactions may be fundamental to the pathophysiology and treatment of depressive illnesses. It has previously been found that chronic administration of corticosterone leads to adrenal suppression and an attenuation of somatodendritic 5-HT1A receptor function. Adrenalectomy (ADX) has been shown to cause an increase in postsynaptic 5-HT1A receptor numbers and possibly function. However, other reports have suggested that ADX does not alter somatodendritic 5-HT1A receptor mRNA or binding, though little is known of the effect of ADX on the function of somatodendritic 5-HT1A receptors. This study investigated the effect of markedly reducing corticosterone levels by ADX on 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT)-induced hypothermia in mice, an in vivo model of somatodendritic 5-HT1A receptor function. The degree of 8-OH-DPAT-induced hypothermia did not differ between control, sham, and ADX animals 14 days post operatively. Although repeated administration of corticosterone attenuates somatodendritic 5-HT1A receptor function, these data demonstrate that lowering of corticosteroid levels by ADX have no effect. This suggests that the effects of repeated corticosterone administration is not mediated by a secondary adrenal suppression. The difference in the effects of ADX on somatodendritic as opposed to postsynaptic 5-HT1A receptors may reflect the differential expression of corticosteroid receptor subtypes at postsynaptic and somatodendritic sites.

Measurements of mitochondrial K+ fluxes in whole rat hearts using 87Rb-NMR

The rubidium efflux from hypothermic rat hearts perfused by the Langendorff method at 20 degreesC was studied. At this temperature 87Rb-NMR efflux experiments showed the existence of two 87Rb pools: cytoplasmic and mitochondrial. Rat heart mitochondria showed a very slow exchange of mitochondrial Rb+ for cytoplasmic K+. After washout of cytosolic Rb+, mitochondria kept a stable Rb+ level for >30 min. Rb+ efflux from mitochondria was stimulated with 0.1 mM 2, 4-dinitrophenol (DNP), by sarcolemmal permeabilization and concomitant cellular energy depletion by saponin (0.01 mg/ml for 4 min) in the presence of a perfusate mimicking intracellular conditions, or by ATP-sensitive K (KATP) channel openers. DNP, a mitochondrial uncoupler, caused the onset of mitochondrial Rb+ exchange; however, the washout was not complete (80 vs. 56% in control). Energy deprivation by saponin, which permeabilizes the sarcolemma, resulted in a rapid and complete Rb+ efflux. The mitochondrial Rb+ efflux rate constant (k) decreased in the presence of glibenclamide, a KATP channel inhibitor (5 microM; k = 0.204 +/- 0.065 min-1; n = 8), or in the presence of ATP plus phosphocreatine (1.0 and 5.0 mM, respectively; k = 0.134 +/- 0.021 min-1; n = 4) in the saponin experiments (saponin only; k = 0.321 +/- 0.079 min-1; n = 3), indicating the inhibition of mitochondrial KATP channels. Thus hypothermia in combination with 87Rb-NMR allowed the probing of the mitochondrial K+ pool in whole hearts without mitochondrial isolation.

Influence of Bretschneider's cardioplegia on norepinephrine release from isolated perfused guinea-pig hearts

It was the aim of the present study to investigate the influence of Bretschneider's cardioplegia on norepinephrine (NE) release [determined by high pressure liquid chromatography (HPLC) and electrochemical detection] in isolated perfused guinea-pig hearts. The following resulted were noted. (1) Calcium-dependent exocytotic NE release evoked by electrical field stimulation (12 Hz, 1 min) was completely suppressed after only 3 min of normothermic (37.5 degrees C) Bretschneider's cardioplegia. (2) Stop-flow ischemia is associated with a substantial calcium-independent, non-exocytotic NE release, which is regarded as a sodium-dependent carrier-mediated process. Accordingly, it is inhibited by blockers of the sodium/proton-exchanger (e.g. amiloride) and the neuronal uptake1-carrier (e.g. desipramine). Compared with stop-flow ischemia alone, cardioplegia with 3 min of Bretschneider's histidine-tryptophan-ketoglutarate (HTK)-solution preceding stop-flow enhanced NE release at all stop-flow durations (10-90 min) investigated (e.g. after 30 min of normothermic Bretschneider's cardioplegia: 1070+/-41 pmol/g, n = 45, v stop-flow alone: 764+/-48 pmol/g, n = 27, P<0.05). The NE concentrations determined in the cardiac effluent upon reperfusion followed a typical first order kinetic indicating that the transmitter release had already occurred during stop-flow. Hypothermia reduced NE release in a temperature-dependent manner down to intramyocardial temperatures of 2 7.5 degrees C. NE release evoked by Bretschneider's cardioplegia still exceeded that induced by stop-flow ischemia alone by up to 60%. The NE release evoked by Bretschneider's cardioplegia and stop-flow ischemia was calcium-independent. However, it was significantly reduced by desipramine and amiloride, but both agents had a more pronounced inhibitory effect on NE release evoked by stop-flow ischemia alone. (3) This difference may be due to an intrinsic effect of Bretschneider's HTK-solution, as continuous administration of normothermic Bretschneider's HTK-solution induced a substantial NE release which was neither calcium-dependent nor inhibited by blockade of either uptake1 or sodium/proton-exchange. It is concluded that Bretschneider's cardioplegia is not neuroprotective, as it even augments the stop-flow ischemia-induced nonexocytotic NE release.

Cold stress increases lipolysis, FFA Ra and TG/FFA cycling in humans

BACKGROUND

To characterize the important changes in the selection and mobilization of metabolic fuel during cold stress, six males rested for 3 h at 29 degrees C and at 5 degrees C dressed only in shorts while 2H5 glycerol, 1-13C palmitate and 6,6 2H2 glucose were continuously infused for 3 h in each condition to determine their rate of turnover (Ra).

METHODS

Metabolic rate (M) as well as rates of carbohydrate (CHOox) and lipid oxidation (FATox) were assessed by indirect calorimetry whereas all isotopic enrichments were determined by mass spectrometry.

RESULTS

Cold exposure decreased rectal and mean skin temperatures and increased M, FATox and CHOox compared with the same test at thermal neutrality (p<0.05). As expected, cold increased plasma glucose Ra and plasma FFA Ra (from 4.58+/-0.19 to 14.69+/-1.07 micromol kg(-1) x min(-1); p < 0.05). However, in absolute terms, plasma FFA Ra in the cold remained more than twice greater than FATox (FATox only increased up to 6.9 +/-0.85 micromol kg(-1) x min(-1)), suggesting an enhanced non-oxidative disposal of fatty acids (i.e., TG/FFA cycling) to account for all FFA Ra. Indeed, cold increased extracellular TG/FFA recycling rate (2.23+/-0.40 vs 7.77+/-1.19 micromol kg(-1) x min(-1); p<0.05) whereas intracellular cycling was unaffected.

CONCLUSION

Even though lipolysis and FFA Ra are greatly increased by cold stress in humans, the present results demonstrate that only about half the rate of FFA Ra is ultimately oxidized, suggesting that under the present cold conditions: 1) non-oxidative FFA disposal or TG/FFA cycling is significantly enhanced; 2) white adipose tissue-derived fatty acids could easily account for most of FATox. The results further emphasize the importance of the TG/FFA cycle in amplifying the ability of stored TG to react quickly to major changes in energy expenditure induced by a sustained cold stress.

Mitochondrial permeability transition during hypothermic to normothermic reperfusion in rat liver demonstrated by the protective effect of cyclosporin A

The purpose of this study was to test the hypothesis that mitochondrial permeability transition might be implicated in mitochondrial and intact organ dysfunctions associated with damage induced by reperfusion after cold ischaemia. Energetic metabolism was assessed continuously by 31P-NMR on a model system of isolated perfused rat liver; mitochondria were extracted from the livers and studied by using top-down control analysis. During the temperature transition from hypothermic to normothermic perfusion (from 4 to 37 degrees C) the ATP content of the perfused organ fell rapidly, and top-down metabolic control analysis of damaged mitochondria revealed a specific control pattern characterized by a dysfunction of the phosphorylation subsystem leading to a decreased response to cellular ATP demand. Both dysfunctions were fully prevented by cyclosporin A, a specific inhibitor of the mitochondrial transition pore (MTP). These results strongly suggest the involvement of the opening of MTP in vivo during the transition to normothermia on rat liver mitochondrial function and organ energetics.

Continuous venovenous rewarming: results from a juvenile animal model

OBJECTIVE

To compare a standard and an experimental method of rewarming in 5-wk-old goats with induced moderate hypothermia.

DESIGN

Hypothermia was induced in ten juvenile Nubian goats. Five goats were randomly assigned to be rewarmed using standard techniques, and five were assigned to the experimental rewarming technique of a modified continuous venovenous hemofiltration circuit.

SETTING

Animal research facility, Greenville Hospital System/Clemson University Biomedical Cooperative, Clemson, S.C.

SUBJECTS

Ten 5-wk-old goats.

INTERVENTIONS

Hypothermia to a body temperature of 29.4 degrees C was induced in the goats. Each of the control group of five goats was rewarmed using standard methods. Each of the experimental group of five goats was rewarmed using a modified continuous venovenous hemofiltration circuit.

MEASUREMENTS AND MAIN RESULTS

At 2 hrs, the median temperature increase in the experimental group was 6.5 degrees C, compared with an increase of only 1.5 degrees C in the control group (p=.02). The mean increase in core body temperature over time (from baseline to 150 mins) was also significantly greater in the experimental group (p=.006).

CONCLUSIONS

The use of a modified continuous venovenous hemofiltration circuit for rewarming in a juvenile goat model after induction of moderate hypothermia is more effective than are standard methods.

Effects of hypothermic hypoxia on anaerobic energy metabolism in isolated anuran livers

Many lower vertebrates (reptilian and amphibian species) are capable of surviving natural episodes of hypoxia and hypothermia. It is by specific metabolic adaptations that anurans are able to tolerate prolonged exposure to harsh environmental stresses. In this study, it was hypothesized that livers from an aquatic frog would possess an inherent metabolic ability to sustain high levels of ATP in an isolated organ system, providing insight into a metabolic system that is well-adapted for low temperature in vitro organ storage. Frogs of the species, R. pipiens were acclimated at 20 degrees C and at 5 degrees C. Livers were preserved using a clinical preservation solution after flushing. Livers from 20 degrees C-acclimated frogs were stored at 20 degrees C and 5 degrees C and livers from 5 degrees C-acclimated frogs were stored at 5 degrees C. The results indicated that hepatic adenylate status was maintained for 96 h during 5 degrees C storage, but not longer than 4-10 h during 20 degrees C storage. In livers from 5 degrees C-acclimated animals subjected to 5 degrees C storage, ATP was maintained at 100% throughout the 96-h period. Warm acclimation (20 degrees C) and 20 degrees C storage resulted in poorer maintenance of ATP; energy charge values dropped to 0.50 within 2 h and by 24 h, only 24% of control ATP remained. Lactate levels remained less than 25 mumol/g dry weight in all 5 degrees C-stored livers; 20 degrees C-stored livers exhibited greater accumulation of this anaerobic endproduct (lactate reached 45-50 mumol/g by 10 h). The data imply that hepatic adenylate status is largely dependent on exposure to hypothermic hypoxia and although small amounts of ATP were accounted for by anaerobic glycolysis, there must have been either a substantial reduction in cellular energy-utilization or an efficient use of low oxygen tensions.

Does capsaicin affect physiologic and thermal responses of males during immersion in 22 degrees C?

BACKGROUND

Capsaicin alters thermoregulation in adult rats by producing a dose-dependent fall in body temperature and metabolism. The present investigation examined the thermal and metabolic responses in males who were fed capsaicin (CAP: 2 mg.kg(-1) body weight) vs. a placebo (PL: a maltodextrin capsule) prior to immersion in cold water.

METHODS

Seven Caucasian males aged 20-28 yr were immersed in 22 degrees C twice (PL vs. CAP), for 120 min. The following were examined: metabolism (M; W.m(-2)), rectal temperature (Tre; degrees C), mean skin temperature (Tsk; degrees C), tissue insulation (I; degrees C.m(-2).W(-1) and proportion of energy derived from carbohydrate (%CHO).

RESULTS

For M, Tre, I, and Tsk there was no significant differences between treatments (PL vs. CAP) when the variables were pooled jointly over time. However, significant differences across time was detected for Tre (p = 0.0003), Tsk (p = 0.0147), and M (p = 0.0036). Values for %CHO demonstrate a main effect for treatment (p = 0.0210) suggesting the CAP (46.7-/+25.9%) treatment demonstrated a decreased reliance on carbohydrate utilization for energy provision as compared to the PL (75.0+/-21.9%) treatment. Additionally, the treatment x time interaction was significant (p = 0.0096) whereby, PL differed from CAP at 5 min only.

CONCLUSION

From these data it appears that while M, Tre, and Tsk differed across time, a CAP (which differentially affected percent of energy derived from carbohydrate) feeding did not differentially affect the thermal and metabolic responses of males during acute cold water immersion.

Effects of brain temperature on CBF thresholds for extracellular glutamate release and reuptake in the striatum in a rat model of graded global ischemia

We simultaneously measured extracellular glutamate ([Glu]e) elevation and local CBF using a real-time monitoring method and laser-Doppler flowmetry, respectively, in the rat striatum in a modified graded global ischemia model. Ischemic brain temperatures were kept at 32 degrees C, 37 degrees C and 39 degrees C. Three distinct types of intraischemic [Glu]e elevation, reflecting mild, moderate and massive glutamate release, were observed. Brain temperature plays an important role in determining CBF thresholds for each of the three types of [Glu]e elevation. CBF thresholds for [Glu]e elevations shifted to a lower level range as brain temperature was reduced. In mild or moderate ischemia, there is no exposure to sustained [Glu]e elevation, which is seen only in relatively severe ischemia characterized by biphasic [Glu]e elevation.

Hypothermia attenuates hyperglycolysis in the periphery of ischemic core in rat brain

Hypothermia has proven to be neuroprotective against ischemic brain injury. However, the exact mechanism has not yet been fully understood. In this study, we investigated the effects of hypothermia on cerebral glucose metabolism and blood flow in focal ischemic rats. Rats were divided into normothermic (37+/-0.5 degrees C) and hypothermic (30+/-0.5 degrees C) groups. Focal cerebral ischemia was induced by middle cerebral and ipsilateral common carotid arteries occlusion. Two hours after ischemia, autoradiographic studies of 2-deoxyglucose and iodoantipyrine were performed to measure local cerebral glucose utilization (LCGU) and cerebral blood flow. LCGU in the ischemic core was excessively reduced in both groups. However, a marked increase in LCGU was observed in the boundary zone of the ischemic core in normothermic rats. On the other hand, hyperglycolysis in the boundary zone of the ischemic core was suppressed in hypothermia. This attenuation of hyperglycolysis might be closely related to survival of the ischemic penumbra in hypothermia.

Repeated trimipramine induces dopamine D2/D3 and alpha1-adrenergic up-regulation

Trimipramine (TRI), which shows a clinical antidepressant activity, is chemically related to imipramine but does not inhibit the reuptake of noradrenaline and 5-hydroxytryptamine, nor does it induce beta-adrenergic down-regulation. The mechanism of its antidepressant activity is still unknown. The aim of the present study was to find out whether TRI given repeatedly was able to induce adaptive changes in the dopaminergic and alpha1-adrenergic systems, demonstrated by us previously for various antidepressants. TRI was given to male Wistar rats and male Albino Swiss mice perorally twice daily for 14 days. In the acute experiment TRI (given i.p.) does not antagonize the reserpine hypothermia in mice and does not potentiate the 5-hydroxytryptophan head twitches in rats. TRI given repeatedly to rats increases the locomotor hyperactivity induced by d-amphetamine, quinpirole and (+)-7-hydroxy-dipropyloaminotetralin (dopamine D2 and D3 effects). The stereotypies induced by d-amphetamine or apomorphine are not potentiated by TRI. It increases the behaviour stimulation evoked by phenylephrine (given intraventricularly) in rats, evaluated in the open field test as well as the aggressiveness evoked by clonidine in mice, both these effects being mediated by an alpha1-adrenergic receptor. It may be concluded that, like other tricyclic antidepressants studied previously, TRI given repeatedly increases the responsiveness of brain dopamine D2 and D3 (locomotor activity but not stereotypy) as well as alpha1-adrenergic receptors to their agonists. A question arises whether the reuptake inhibition is of any importance to the adaptive changes induced by repeated antidepressants, suggested to be responsible for the antidepressant activity.

Effects of mild hypothermia on the release of regional glutamate and glycine during extended transient focal cerebral ischemia in rats

The present study is to determine the effect of mild hypothermia (MHT) on the release of glutamate and glycine in rats subjected to middle cerebral artery occlusion and reperfusion. The relationship between amino acid efflux and brain infarct volume was compared in different periods during MHT. Reversible middle cerebral artery occlusion was performed in Sprague-Dawley rats using a suture model. The rats were divided into four groups including (1) MHT during ischemia (MHTi), (2) MHT during reperfusion (MHTr), (3) MHT during ischemia and reperfusion (MHTi + r), and (4) a normothermic group (NT). Extracellular concentrations of glutamate and glycine in the cortex and striatum were monitored using in vivo microdialysis and analyzed using high-performance liquid chromatography. Morphometric measurements for infarct volume were performed using 2,3,5-triphenyltetrazolium chloride staining. The increase of glutamate and glycine in the ischemic cortex of the MHTi and MHTi + r rats during ischemic and reperfusion periods was significantly less than that of the NT rats (p < 0.05). However, there was no statistical difference among these groups in the peak of glutamate and glycine release in the striatum. Infarct volume paralleled the release of glutamate and glycine. The protective effect of MHTi and MHTi + r in reducing ischemia and reperfusion brain injury may be due to the attenuation of both glutamate and glycine release during ischemia and reperfusion.

Neuromodulators and hypoxic hypothermia in the rat

This study was designed to assess if opioids or adenosine are involved in the hypometabolism induced by hypoxia in the rat. Accordingly, antagonists such as naloxone (NLX) for opioids or theophylline (THEO) for adenosine were injected into conscious adult rats acutely exposed to either ambient hypoxia (AHx, FIO2: 12%) at ambient temperatures of 26 or 9 degrees C, or to CO hypoxia (COHx, FICO = 0.05%) at an ambient temperature (Ta) of 9 degrees C. Oxygen consumption, ventilation, colonic temperature and shivering were recorded. The results show that with NLX, the degree of hypoxic hypometabolism was reduced with AHx at 26 degrees C and slightly decreased with COHx at 9 degrees C. With THEO, hypoxic hypometabolism was slightly reduced with AHx and COHx at 9 degrees C. The ventilatory response to AHx and COHx was not consistently affected by either NLX or THEO. It is concluded that adenosine and opioids play a minor role, in mediating AHx or COHx hypothermia, especially during cold exposure.

Metabolic changes during recovery in normothermic versus hypothermic patients undergoing surgery and receiving general anesthesia and epidural local anesthetic agents

BACKGROUND

Mild hypothermia is accompanied by metabolic changes. Epidural local anesthetic agents attenuate the surgical stress response, but it is not known whether they modulate thermal stress.

METHODS

Thirty patients undergoing colorectal surgery, performed by one surgical team, received epidural 0.5% bupivacaine to achieve T3-S5 sensory block. They were then assigned randomly to two groups of 15 patients each. The control or unwarmed group was left to cool during surgery, whereas active warming was used in the warmed group. General anesthesia was induced by thiopentone, vecuronium, fentanyl, nitrous oxide in oxygen, and enflurane. At the end of surgery, both groups received epidural 0.25% bupivacaine to maintain a T5-L3 sensory block. Aural canal (core) and skin surface (15 sites) temperatures; oxygen consumption; pain visual analogue score; and concentrations of epinephrine, norepinephrine, glucose, cortisol, lactate, and free fatty acids in plasma were measured before epidural blockade, 30 min after epidural blockade, at the end of surgery, and for 4 h after surgery. Patients and those measuring the outcomes were unaware of group allocation.

RESULTS

Core and mean skin temperatures decreased significantly in the control group (P < 0.001) but not in the warmed group. Catecholamine concentrations in plasma decreased significantly after epidural block, and although concentration of epinephrine in plasma increased from baseline sharply in the control group at the end of surgery (P = 0.004), it decreased in the warmed group (P = 0.007). During recovery, there was no difference between the two groups for norepinephrine concentrations in plasma, body weight-adjusted oxygen consumption, pain visual analogue score, and metabolites.

CONCLUSIONS

The postoperative metabolic changes obtained with epidural block were similar except for an attenuated concentration of epinephrine in normothermic patients compared with those who were mildly hypothermic.