The effect of SB-236057-A, a selective 5-HT1B receptor inverse agonist, on in vivo extracellular 5-HT levels in the freely-moving guinea-pig

5-HT1B autoreceptors are involved in the control of extracellular 5-HT levels from both the terminal and cell body regions of serotonergic neurones. In this study we report on the effect of a selective and potent 5-HT1B receptor inverse agonist, SB-236057-A (1'-ethyl-5-(2'-methyl-4'-(5-methyl- 1,3,4-oxadiazolyl-2-yl)biphenyl-4-carbonyl)-2,3,6,7-tetrahydros piro [furo[2,3-f]indole-3,4' -piperidine] hydrochloride), on extracellular 5-HT levels in the cortex and dentate gyrus of the freely-moving guinea-pig, using the technique of in vivo microdialysis. SB-236057-A had ca. 23% bioavailability following oral drug administration. In vivo hypothermia pharmacodynamic assays demonstrated it was brain penetrant with a duration of action in excess of 18 h. SB-236057-A (0.75 mg/kg p.o.) increased extracellular 5-HT levels in the dentate gyrus to a maximum of 167+/-7% of basal but had no effect in the frontal cortex. However, a small increase in cortical 5-HT levels (117+11% of basal) was evident at 2.5 mg/kg p.o. In addition, SB-236057-A (0.75 mg/kg and 2.5 mg/kg p.o.) antagonised the sumatriptan-induced inhibition of extracellular 5-HT levels in the guinea-pig frontal cortex. These differences were attributed to MRN-innervated regions (e.g. dentate gyrus) being more responsive to 5-HT1B receptor-mediated negative feedback than DRN-innervated regions (e.g. frontal cortex). In the dentate gyrus, the increase in 5-HT release induced by SB-236057-A (0.75 mg/kg p.o.) was comparable to that after 14 days of paroxetine (10 mg/kg p.o.) administration, reaching a maximum of 183+/-13% of basal. These data suggest that acute 5-HT1B receptor blockade, by virtue of increased 5-HT release in the dentate gyrus, may provide a rapidly acting antidepressant.

Opposing interplay between Neuropeptide FF and nitric oxide in antinociception and hypothermia

This study examined the ability of the anti-opioid Neuropeptide FF (NPFF) to modify the endogenous activity of nitric oxide (NO). Antinociceptive and hypothermic effects of 1DMe (D.Tyr-Leu-(n.Me)Phe-Gln-Pro-Gln-Arg-Phe-NH(2)), an NPFF agonist, and of L-NAME (N(omega)nitro-L-arginine methyl ester), an inhibitor of nitric oxide synthase, were investigated in mice. Intraperitoneal (i.p.) injection of L-NAME induced, in the hot plate test, a dose-dependent antinociception not reversed by naloxone, an opioid antagonist, but inhibited by L-Arg, the NO synthesis precursor. Intracerebroventricular (i.c.v.) injections of 1DMe inhibit the antinociceptive activity of L-NAME in a dose-dependent manner. On the contrary, L-NAME markedly potentiated hypothermia induced by 1DMe injected in the third ventricle. These data show that Neuropeptide FF receptors exert a dual effect on endogenous NO functions and could modulate pain transmission independently of opioids.

The influence of gender and menstrual phase on thermosensitivity during cold water immersion

BACKGROUND

This investigation evaluated the influence of gender and phase of menstrual cycle [follicular (FOL: days 2-6) and luteal (LUT: days 19-24) phases] on thermosensitivity and metabolic heat production (HP) during cold water immersion (20 degrees C) in 10 females (22.4 +/- 2.8 yr) and 16 males (22.4 +/- 2.9 yr).

METHODS

Following a 20-min baseline period (BASE), subjects were immersed until esophageal temperature (Tes) reached 36.5 degrees C or for a maximum pre-occlusion (Pre-OCC) time of 40 min. An arm and thigh cuff were then inflated to 180 and 220 mmHg, respectively, for 10 min (OCC). Following release of the inflated cuffs (Post-OCC), the slope (beta) of the relationship between the decrease in Tes and the increase in HP was used to quantify thermosensitivity.

RESULTS

ANOVA revealed no significant difference in thermosensitivity between phases of the menstrual cycle or between men and women (FOL = -2.76, LUT = -3.05, Males = -3.24 W x kg(-1) x degrees C(-1)). A significant (p < 0.05) main effect for gender for HP, and a significant (p < 0.05) main effect for menstrual phase for mean skin temperature (Tsk) were observed.

CONCLUSIONS

These data suggest, despite gender differences in HP, that the thermosensitivity of HP during cold water immersion is similar between males and females and is not influenced by menstrual cycle phase. Therefore, these data indicate that when faced with a cold challenge, women respond similarly to men in both phases of their menstrual cycle.

Role of adenosine in the hypoxia-induced hypothermia of toads

The concept that hypoxia elicits a drop in body temperature (T(b)) in a wide variety of animals is not new, but the mechanisms remain unclear. We tested the hypothesis that adenosine mediates hypoxia-induced hypothermia in toads. Measurements of selected T(b) were performed using a thermal gradient. Animals were injected (into the lymph sac or intracerebroventricularly) with aminophylline (an adenosine receptor antagonist) followed by an 11-h period of hypoxia (7% O(2)) or normoxia exposure. Control animals received saline injections. Hypoxia elicited a drop in T(b) from 24.8 +/- 0.3 to 19. 5 +/- 1.1 degrees C (P < 0.05). Systemically applied aminophylline (25 mg/kg) did not change T(b) during normoxia, indicating that adenosine does not alter normal thermoregulatory function. However, aminophylline (25 mg/kg) significantly blunted hypoxia-induced hypothermia (P < 0.05). To assess the role of central thermoregulatory mechanisms, a smaller dose of aminophylline (0.25 mg/kg), which did not alter hypoxia-induced hypothermia systemically, was injected into the fourth cerebral ventricle. Intracerebroventricular injection of aminophylline (0.25 mg/kg) caused no significant change in T(b) under normoxia, but it abolished hypoxia-induced hypothermia. The present data indicate that adenosine is a central and possibly peripheral mediator of hypoxia-induced hypothermia.

Hypothermia, coagulopathy, and acidosis

The management of patients requiring a damage control approach taxes the abilities of the best equipped trauma center. These patients present with severe metabolic abnormalities, most notably characterized by a deadly triad of hypothermia, coagulopathy, and acidosis. Using volumetric, oxymetric pulmonary artery catheters, hypothermia and any ongoing cardiovascular abnormalities can be identified quickly and treatment can be monitored. External, forced air rewarming is a valuable technique in treating the patient with hypothermia, as are more invasive modalities, including body cavity lavage. Although there is no shotgun approach to blood component transfusion therapy, the coagulopathy shown by these patients has a time course that is more rapid than stat laboratories can presently keep up with. Given the fulminant nature of this coagulopathy, the authors feel justified in empirically initiating platelet and plasma or cryoprecipitate transfusion on identification of visible coagulopathy. The willingness of trauma surgeons to push the envelope in treating these most severely afflicted patients has allowed patients who once would have certainly died to lead meaningful lives.

Neurotoxicity after hypoxia/during ischemia due to glutamate with/without free radicals as revealed by dynamic changes in glucose metabolism

Fresh rat brain slices were incubated with [18F]2-fluoro-2-deoxy-D-glucose ([18F]FDG) in oxygenated Krebs-Ringer solution at 36 degrees C, and serial two-dimensional time-resolved images of [18F]FDG uptake in the slices were obtained on imaging plates. The fractional rate constant of [18F]FDG (proportional to the cerebral glucose metabolic rate) from pre-loading of ischemia (O(2) and glucose deprivation)/hypoxia (O(2) deprivation) to the reperfused/reoxygenated post-loading phase was quantitatively evaluated by applying the Gjedde-Patlak graphical method to the image data. Against ischemia an N-methyl-D-aspartate antagonist and hypothermia, but not a free radical scavenger, showed a protective effect when administered during ischemia, whereas no such effect was achieved with any of the above agents when administered after reperfusion. Against hypoxia, there was no protective effect with any of the above agents when administered during hypoxia, although an effect was noted with each when administered after reoxygenation. Excitatory amino acids during ischemia loading were found to be the main factor in the neuronal damage associated with ischemia, while in hypoxia, excitatory amino acids working in tandem with free radicals immediately after reoxygenation were implicated.

Anesthetics and mild hypothermia similarly prevent hippocampal neuron death in an in vitro model of cerebral ischemia

BACKGROUND

General anesthetics reduce neuron loss following focal cerebral ischemia in rodents. The relative efficacy of this action among different anesthetics clinically used for neuroprotection is uncertain. In addition, it remains unclear how anesthetics compare to neuroprotection afforded by mild hypothermia. This study was performed to evaluate the comparative effects of isoflurane, sodium pentothal, and mild hypothermia in a hippocampal slice model of cerebral ischemia and to determine if the mechanism of neuroprotection of isoflurane involves inhibition of glutamate excitotoxicity.

METHODS

Survival and morphology of CA1, CA3, and dentate gyrus neurons in rat hippocampal slices were examined after 10 or 20 min of combined oxygen-glucose deprivation (in vitro ischemia) followed by a 5-h recovery period.

RESULTS

10 or 20 min in vitro ischemia at 37 degrees C killed 35-40% of neurons in CA1 (P < 0.001), 6% in CA3 (not significant) and 18% in dentate (P < 0.05). Isoflurane (0.7 and 2.0%, approximately 0.45 and 1.5 minimum alveolar concentration), pentothal (50 microm, approximately 1 minimum alveolar concentration equivalent) and mild hypothermia (34 degrees C) all reduced CA1 cell loss and morphologic damage to similar degrees in 10- and 20-min periods of ischemia (P < 0.001). The noncompetitive N-methyl-D-aspartate antagonist MK-801 prevented cell damage, showing that N-methyl-D-aspartate receptor activation is an important mechanism of injury in this model. Glutamate (1 mm) produced cell loss similar to in vitro ischemia. Isoflurane (2%) prevented cell damage from glutamate exposure.

CONCLUSIONS

In hippocampal slices, neuron death from simulated ischemia was predominately due to activation of glutamate receptors. Isoflurane, sodium pentothal, an N-methyl-D-aspartate receptor antagonist, and mild hypothermia prevented cell death to similar degrees. For isoflurane, the mechanism appears to involve attenuation of glutamate excitotoxicity.

Reduced metabolic rate accompanies the hemorrhage-induced hypothermia in conscious rats

The mechanism for the hemorrhage-induced drop in body temperature is unknown. This study determined the alterations in cutaneous heat exchange and metabolic heat production caused by a moderate hemorrhage in conscious rats. Chronically instrumented rats were subjected to a 16 ml/kg hemorrhage, followed by a 4-h recovery period, while monitoring body core temperature and cutaneous temperature. Cutaneous heat transfer was disrupted by housing the animals at an elevated (28 degrees C) ambient temperature. A separate group of experiments measured the change in oxygen consumption in the post-hemorrhage period. Moderate hemorrhage caused a drop in body core temperature which stabilized at 0.7+/-0.3 degrees C below control in the second hour following hemorrhage. Disruption of cutaneous heat exchange by reducing the thermal gradient did not diminish the hemorrhage-induced hypothermia. Hemorrhage caused a significant decline of oxygen consumption (-0. 21+/-0.05 ml O(2)/g per h). This 16% drop in resting oxygen consumption was prevented by immediately retransfusing the aspirated blood back into the rat. These data indicate that a decrease in metabolic heat production mediates the drop in body core temperature caused by moderate hemorrhage in conscious rats.

Effect of mild hypothermia on cerebral oxygen uptake during gradual cerebral perfusion pressure decrease in piglets

OBJECTIVE

To study the effect of mild hypothermia on cerebral oxygen metabolism and brain function in piglets during reduced cerebral blood flow because of gradual reduction of the effective cerebral perfusion pressure (CPP).

DESIGN

Comparison of two randomized treatment groups: normothermic group (NT; n = 7) and hypothermic group (HT; n = 7).

SETTING

Work was conducted in the research laboratory of the Institute for Pathophysiology, Friedrich Schiller University, Jena, Germany.

SUBJECTS

Fourteen piglets (14 days old) of mixed German domestic breed.

INTERVENTION

Animals were anesthetized and mechanically ventilated. An epidural balloon was gradually inflated to increase intracranial pressure to 25 mm Hg, 35 mm Hg, and 45 mm Hg every 30 mins at adjusted mean arterial blood pressures. After determination of baseline CPP (NT, 79+/-14 mm Hg; HT, 84+/-9 mm Hg), CPP was reduced to approximately 70%, 50%, and 30% of baseline (NT, 38.1+/-0.5 degrees C; HT, 31.7+/-0.5 degrees C).

MEASUREMENTS AND MAIN RESULTS

Every 25 mins after the gradual CPP reductions. Mild hypothermia induced a reduction of the cerebral metabolic rate of oxygen (CMRO2) to 50%+/-15% of baseline values (baseline values, 352+/-99 micromol x 100 g(-1) x min(-1)) (p < .05). Moreover, the electrocorticogram was altered to a pattern of reduced delta activity (p < .05) but unchanged higher frequency activity. The cerebral oxygen balance in HT animals remained improved until CPP reduction to 50%, indicated by a reduced cerebral arteriovenous difference of oxygen but elevated brain tissue Po2 (p < .05). Further CPP reduction gave rise to a strong CMRO2 reduction (NT, 19+/-21%; HT, 15+/-15%; p < .05). However, the high-frequency band of electrocorticogram was less reduced in hypothermic animals (p < .05).

CONCLUSIONS

Mild whole body hypothermia improves cerebral oxygen balance by reduction of brain energy demand in juvenile piglets. The improvement of brain oxygen availability continues during a mild to moderate CPP decrease. A loss of the difference in CMRO2 between the hypothermic and normothermic piglets together with the fact that brain electrical activity was less suppressed under hypothermia during severe cerebral blood flow reduction indicates that hypothermic protection may involve some other mechanisms than reduction of brain oxidative metabolism.

Relationship between local cerebral blood flow and metabolism during mild and moderate hypothermia in rats

BACKGROUND

Hypothermia may interfere with the relationship between cerebral blood flow (CBF) and metabolism. Because this conclusion was based on the analysis of global values, the question remains whether hypothermic CBF/metabolism uncoupling exists on a local cerebral level. This study investigated the effects of hypothermic anesthesia on local cerebral blood flow (LCBF) and local cerebral glucose utilization (LCGU).

METHODS

Thirty-six rats were anesthetized with isoflurane (1 minimum alveolar concentration) and artificially ventilated to maintain normal arterial carbon dioxide partial pressure (pH-stat). Pericranial temperature was maintained as normothermic (37.5 degrees C, n = 12) or was reduced to 35 degrees C (n = 12) or 32 degrees C (n = 12). Pericranial temperature was maintained constant for 60 min until LCBF or LCGU were measured by autoradiography. Twelve conscious rats served as normothermic controls.

RESULTS

Compared with conscious animals, mean CBF remained unchanged during normothermic anesthesia. Mean CBF significantly increased during mild hypothermia but was unchanged during moderate hypothermia. During normothermic anesthesia, mean CGU was 45% lower than in conscious controls (P < 0.05). No further CGU reduction was found during mild hypothermia, whereas CGU further decreased during moderate hypothermia (48%; P < 0.05). Local analysis showed a linear LCBF/LCGU relationship in conscious (r = 0.94) and anesthetized (r = 0.94) normothermic animals, as well as in both hypothermic groups (35 degrees C: r = 0.92; 32 degrees C: r = 0.95; P < 0.05). The LCBF-to-LCGU ratio increased from 1.4 (conscious controls) to 2.4 (normothermic isoflurane) and 3.6 ml/micromol (mild and moderate hypothermia, P < 0.05).

CONCLUSIONS

Decrease of mean CGU at unchanged or increased mean CBF during hypothermic anesthesia may not indicate uncoupling. Local analysis shows a maintained linear relationship that is reset to a higher CBF/CGU ratio.

Temperature-dependent pharmacokinetics and pharmacodynamics of vecuronium

BACKGROUND

The authors evaluated the influence of temperature on the pharmacokinetics and pharmacodynamics of vecuronium because mild core hypothermia doubles its duration of action.

METHODS

Anesthesia was induced with alfentanil and propofol and maintained with nitrous oxide and isoflurane in 12 healthy volunteers. Train-of-four stimuli were applied to the ulnar nerve, and the mechanical response of the adductor pollicis was measured. Volunteers were actively cooled or warmed until their distal esophageal temperatures were in one of four ranges: < 35.0 degrees C, 35.0-35.9 degrees C, 36.0-36.9 degrees C, and > or = 37.0 degrees C. With temperature stabilized, vecuronium was infused at 5 microg x kg(-1) x min(-1) until the first response of each train-of-four had decreased by 70%. Arterial blood (for vecuronium analysis) was sampled at intervals until the first response recovered to at least 90% of its prevecuronium level. Vecuronium, 20 microg x kg(-1) x min(-1), was then infused for 10 min, and arterial blood was sampled at intervals for up to 7 h. Population-based nonlinear mixed-effects modeling was used to examine the effect of physical characteristics and core temperature on vecuronium pharmacokinetics and pharmacodynamics.

RESULTS

Decreasing core temperature over 38.0-34.0 degrees C decreases the plasma clearance of vecuronium (11.3% per degrees C), decreases the rate constant for drug equilibration between plasma and effect site (0.023 min(-1) per degrees C), and increases the slope of the concentration-response relationship (0.43 per degrees C).

CONCLUSIONS

Our results show that reduced clearance and rate of effect site equilibration explain the increased duration of action of vecuronium with reducing core temperature. Tissue sensitivity to vecuronium is not influenced by core temperature.

Effects of mild hypothermia on the cortical release of excitatory amino acids and nitric oxide synthesis following hypoxia

Studies concerning neurotransmitter release following cerebral hypoxia are scarce, and the effects of mild hypothermia on hypoxia-induced neurotransmitter release are unknown. The purpose of this study was to investigate changes in excitatory amino acid (EAA) concentrations and nitric oxide (NO) synthesis following cerebral hypoxia in rats, and the effects of mild hypothermia on both. Cerebral hypoxia (PaO2, 30-40 mm Hg) was induced in each rat for 60 min. Cerebral blood flow (CBF) was measured by laser-Doppler flowmetry, and the extracellular concentrations of EAAs and NO end-products (nitrite and nitrate) were measured by in vivo microdialysis in normothermic (37 degrees C) and hypothermic (32 degrees C) rats. In both groups, CBF showed modest increases during hypoxia and returned to baseline during reoxygenation. The EAA levels of the normothermic rats increased markedly after hypoxia induction and returned to baseline levels during reoxygenation. Hypothermia abolished these increases completely. The NO end-product levels under normothermic conditions declined slightly during hypoxia, and then increased transiently during reoxygenation. Hypothermia appeared to attenuate the NO end-product level and to delay the peak. When the relationship between glutamate and the NO end-products was examined on an individual-animal basis, glutamate release did not parallel NO synthesis. The results indicate that hypothermic neuroprotection during cerebral hypoxia may be attributable to the amelioration of damage by reduction of presynaptic EAA release. Although it is unclear from the present results alone whether endothelial NO synthase, neuronal NO synthase or both caused the elevation of the NO end-products during reoxygenation, it is possible that the attenuation and delay of the peak of the NO end-product level plays a role in protection from NO-induced neuronal damage.

Immersion of distal arms and legs in warm water (AVA rewarming) effectively rewarms mildly hypothermic humans

INTRODUCTION

Active rewarming of hypothermic victims for field use, and where transport to medical facilities is impossible, might be the only way to restore deep body temperature. In active rewarming in warm water, there has been a controversy concerning whether arms and legs should be immersed in the water or left out. Further, it has been suggested in the Royal Danish Navy treatment regime, that immersion of hands, forearms, feet, and lower legs alone might accomplish rapid rates of rewarming (AVA rewarming).

METHODS

On three occasions, six subjects (one female) were cooled in 8 degrees C water, to an esophageal temperature of 34.3+/-0.8 (+/-SD) degrees C. After cooling the subjects were warmed by shivering heat production alone, or by immersing the distal extremities (hands, forearms, feet and lower legs) in either 42 degrees C or 45 degrees C water.

RESULTS

The post cooling afterdrop in esophageal temperature was decreased by both 42 degrees C and 45 degrees C water immersion (0.4+/-0.2 degrees C) compared with the shivering alone procedure (0.6+/-0.4 degrees C; p < 0.05). The subsequent rate of rewarming was significantly greater with 45 degrees C water immersion (9.9+/-3.2 degrees C x h(-1)) than both 42 degrees C water immersion (6.1+/-1.2 degrees C x h(-1)) and shivering alone (3.4+/-1.5 degrees C x h(-1); p < 0.05).

CONCLUSION

The extremity rewarming procedure was experienced by the subjects as the most comfortable as the rapid rise in deep body temperature shortened the period of shivering. During the extremity rewarming procedures the rectal temperature lagged considerably behind the esophageal and aural canal (via indwelling thermocouple) temperatures. Thus large gradients may still exist between body compartments even though the heart is warmed.

Adenosine-triphosphate in trauma-related and elective hypothermia

BACKGROUND

In trauma patients, hypothermia is a frequent event. According to the literature, the majority of trauma patients are presenting a core temperature of less than 34 degrees C at admission. In contrast to the benefit of hypothermia in elective surgery, clinical experience with hypothermia in trauma patients has identified hypothermia to be one major cause of severe posttraumatic complications. It was hypothesized that this diverse effect of hypothermia is related to depletion of high-energy phosphates like adenosine triphosphate (ATP) in trauma patients. To verify this hypothesis, the relation of ATP plasma levels and hypothermia was examined in a clinical study.

METHODS

Three different groups of patients were under study. The first group (group A, normothermic control group) included patients (n = 15) undergoing elective surgery of the lower limb with a mean operation time of 113 minutes. The second study group (group B, hypothermic control) was composed of patients (n = 15) who were subjected to elective coronary artery bypass operation under hypothermia (31 degrees C for 48 minutes, mean total operation time being 205 minutes). The third study group (group C) included trauma patients (n = 23, mean Injury Severity Score [ISS] of 24.7). At the time of admission, 10 patients presented a core temperature more than or equal to 34 degrees C (group C1, mean ISS, 25.2; mean T(A), 34.5 degrees C), 13 patients presented a T(A) less than 34 degrees C (group C2, mean ISS, 26.0; mean T(A), 32.9 degrees C). In both groups of surgical patients, the ATP plasma level was measured preoperatively, at 2, 4, and 24 hours postoperatively. For trauma patients, this measurement was performed at admission and 24 hours later. Within the same schedule, body core temperature was recorded and the clinical course was documented as well.

RESULTS

Elective limb surgery in normothermic patients resulted only in a transient decrease in ATP plasma levels (preoperative, 87.8 micromol/dL; 4 hours postoperative, 52.0 micromol/dL). At 24 hours, the ATP plasma level (62.6 +/- 10.0 micromol/dL) has increased toward baseline level. Elective hypothermia in patients subjected to coronary bypass also resulted only in a transient decrease in ATP plasma levels. During the operation period, including hypothermia, the ATP plasma level was comparable (50.4 micromol/dL) to group A and also returned back toward normal values at 24 hours (58.2 micromol/dL). All trauma patients revealed a significant low ATP plasma level at admission compared with both control groups. Looking at subdivided groups the most significant drop in ATP plasma level (28.5 micromol/dL) was noted in patients presenting an initial core temperature less than 34 degrees C and ISS more than 30. Even 24 hours later, the ATP level of this subgroup was significantly diminished, despite a rise up to 44.4 micromol/dL. In contrast, only a moderate drop in ATP plasma concentration (59.2 micromol/dL) was noted in the group of T(A) more than or equal to 34 degrees C and ISS less than 20. This group revealed almost normal values (68.3 micromol/dL) 24 hours after trauma. In addition to hypothermia, the metabolic state, reflected by the plasma lactate levels, significantly influenced the ATP plasma levels, as high lactate levels were paralleled by low ATP levels. Also, the overall outcome was related to injury severity and hypothermia.

CONCLUSION

Hypothermia in elective surgery, established by active cooling, preserves the ATP storage and maintains an aerobic metabolism, which both contribute to the beneficial effect of hypothermia in ischemia/reperfusion in cardiovascular surgery. However, in trauma patients hypothermia is caused by insufficient heat production due to utilization of ATP under anaerobic metabolic conditions. Low ATP plasma levels combined with hypothermia seem to be a predisposition for post-traumatic complications like organ failure.

Hypothermia and the trauma patient

Hypothermia has profound effects on every system in the body, causing an overall slowing of enzymatic reactions and reduced metabolic requirements. Hypothermic, acutely injured patients with multisystem trauma have adverse outcomes when compared with normothermic control patients. Trauma patients are inherently predisposed to hypothermia from a variety of intrinsic and iatrogenic causes. Coagulation and cardiac sequelae are the most pertinent physiological concerns. Hypothermia and coagulopathy often mandate a simplified approach to complex surgical problems. A modification of traditional classification systems of hypothermia, applicable to trauma patients is suggested. There are few controlled investigations, but clinical opinion strongly supports the active prevention of hypothermia in the acutely traumatized patient. Preventive measures are simple and inexpensive, but the active reversal of hypothermia in much more complicated, often invasive and controversial. The ideal method of rewarming is unclear but must be individualized to the patient and institution specific. An algorithm reflecting newer approaches to traumatic injury and technical advances in equipment and techniques is suggested. Conversely, hypothermia has selected clinical benefits when appropriately used in cases of trauma. Severe hypothermia has allowed remarkable survivals in the course of accidental circulatory arrest. The selective application of mild hypothermia in severe traumatic brain injury is an area with promise. Deliberate circulatory arrest with hypothermic cerebral protection has also been used for seemingly unrepairable injuries and is the focus of ongoing research.

Discordant responses of mitogen-activated protein kinases to anoxia and freezing exposures in hatchling turtles

The role of two vertebrate mitogen-activated protein kinases (MAPKs) in mediating responses to in vivo anoxia or freezing exposures was examined in four organs (liver, heart, kidney and brain) of hatchling red-eared turtles, Trachemys scripta elegans, which are naturally tolerant of these stresses. The extracellular signal-regulated kinases were not stress-activated except in brain of frozen turtles. The c-Jun NH2-terminal kinases (JNKs) were transiently activated by anoxia exposure in all four organs (after 1 h in brain or 5 h in other organs) but activity was suppressed during freezing except in brain which showed a transient activation of JNK after 1 h. Changes in the concentrations of the transcription factors, c-Fos and c-Myc, were also stress- and organ-specific. The patterns of MAPK activation in a stress-tolerant animal suggest the relative importance of these kinase pathways in cellular adaptation to oxygen deprivation or freezing and identify novel natural activators of MAPKs in vivo. The specificity of the signaling pathways is also emphasized here as the general whole-body stresses, anoxia and freezing, activated individual MAPKs in a tissue-, time-, and stress-dependent manner.

Renal ischemia-induced increase in vascular permeability is limited by hypothermia

The purpose of the present work was to evaluate the kallikrein-kinin system and effects of hypothermia during renal ischemia and reperfusion. Male C57BL/KSJmdb mice were subjected to 20 or 60 min ischemia for different periods of reperfusion. Our results demonstrate that short periods of ischemia followed by reperfusion did not cause significant alterations in kallikrein activity, Evans Blue (EB) extravasation, prokallikreins, myeloperoxidase activity or plasma creatinine concentration. Edema was evident at 1 h reperfusion in the treated mice, but returned to basal values after 24 h reperfusion. Kallikrein activities and EB extravasation showed a significant increase in 60 min ischemic mice. Myeloperoxidase activity in the kidney of the mice confirmed net infiltration in the group with 60 min ischemia and 24 h reperfusion. The generation of kinins and activation of matrix degrading enzymes by tissue kallikrein, liberated from both renal and infiltrated leukocytes, could be responsible at least in part for the damage observed in the kidney of mice subject to 60 min ischemia and reperfusion. The hypothermia significantly reduced the inflammatory process in the 60 min ischemic mice, and did prevent an increase in vascular permeability. Nevertheless, the tissue edema was not shown to change between normothermic and hypothermic ischemic mice.

The time-course of DNA fragmentation in the choroid plexus and the CA1 region following transient global ischemia in the rat brain. The effect of intra-ischemic hypothermia

The time-course of DNA fragmentation in the CA1 region of the hippocampus and the choroid plexus was studied following induction of transient forebrain ischemia under lethal normothermic (37 degrees C), or sublethal hypothermic (33 degrees C) conditions. Oligonucleosomal- and high-molecular-weight DNA fragmentation were analysed by conventional agarose gel electrophoresis and pulsed-field gel electrophoresis, respectively. DNA breaks were visualized by the terminal deoxynucleotidyl transferase-mediated biotin-deoxyuridinetriphosphate nick-end labeling method. At 48 h of recovery following normothermic ischemia, in situ labeling of DNA breaks were widespread in medial CA1 and high-molecular-weight DNA cleavage was seen. In contrast, at the same time-point in lateral CA1, many pyknotic but few cells displaying in situ labeling of DNA breaks were observed. Major oligonucleosomal DNA fragmentation was not seen until 72 h of recovery. Following hypothermic ischemia, DNA fragmentation was absent in CA1. DNA fragmentation was seen in the choroid plexus at 24 h of recovery following normothermic ischemia, which was diminished by 48 h of recovery. In conclusion, oligonucleosomal and high-molecular-weight DNA fragmentation at 10-50 kilobase pairs, occur in CA1 after morphological signs, and acidophilia signifying neurodegeneration appear. DNA fragmentation and cell death in the choroid plexus precede neuronal death in CA1 and may play a causative role.

[Changes of serum biochemical parameters during hypothermia and hypoxia in rats]

OBJECTIVE

To study the effects of hypothermia and hypoxia on serum biochemical parameters. Method Acute hypobaric hypoxia experiment in cold environment was carried out in 48 healthy Wistar rats to observe changes of hepatic, cardiac and renal functions.

RESULT

Hepatic, cardiac and renal functions changed non-prominently after acute hypoxia exposure under cold condition. Under hypoxic exposure of the same degree, serum lactic dehydrogenase(LDH), alanine transaminase(ALT), blood urea nitrogen (BUN) and creatinine (Cr) increased more significantly at 10 degrees C than those at 20 degrees C (P < 0.01) while creatine kinase (CK) decreased significantly at 10 degrees C than that at 20 degrees C.

CONCLUSION

After acute hypoxia in cold environment, the changes in cardiac function did not simply equal to the changes by cold environment plus changes by acute hypoxia.

Hypothermia ameliorates ischemic brain damage and suppresses the release of extracellular amino acids in both normo- and hyperglycemic subjects

It has previously been shown that hypothermia markedly reduces cellular release of the excitatory amino acid glutamate and ameliorates ischemic damage. Based on extensive data showing that preischemic hyperglycemia exaggerates brain damage due to transient forebrain ischemia we posed the question whether glutamate release during ischemia in hyperglycemic rats is attenuated or prevented by induced hypothermia, and if such attenuation/prevention correlates with amelioration of the characteristic brain damage observed in hyperglycemic subjects. The experiments were performed in rats subjected to a 15-min period of forebrain ischemia, plasma glucose concentration being maintained at approximately 5 mM (control) or approximately 20 mM (hyperglycemia) prior to ischemia. Extracellular amino acid concentrations were measured by HPLC techniques on microdialysis samples which were collected from left dorsal hippocampus and right neocortex, and tissue damage was assessed by histopathology. Hypothermia (30 degrees C), which was induced 45 min prior to ischemia, reduced the neuronal damage not only in the ischemia-vulnerable regions but also in the normally ischemia-resistant areas that are recruited in the damage process in hyperglycemic subjects. The extracellular glutamate concentration was markedly increased in response to the ischemic insult in normothermic-normoglycemic animals. The concentration of glutamate was further increased in normothermic-hyperglycemic animals. Hypothermia inhibited the rise in glutamate concentrations, as well as in the concentrations of other excitatory and inhibitory amino acids. It is discussed whether hypothermia reduces the hyperglycemia-mediated damage by inhibiting extracellular glutamate release during an ischemic transient.

Metabolic response to neonatal surgery

The energy and protein metabolism of newborn infants differs from that of older individuals. Although energy expenditure and protein turnover are higher in newborn infants than in adults, the metabolic response to surgery in neonates has not been fully characterized. Preliminary studies indicate that metabolic response to operative stress is different in infants and adults: infants have an increased metabolic rate postoperatively for only 6 to 12 hours and do not have increased protein catabolism. More studies are needed in "stressed" newborn infants to further characterize substrate use and the metabolism of single organs.

Enhanced thermogenesis in rats by a composite Indian herbal preparation-I and its mechanism of action

OBJECTIVE

A composite Indian herbal preparation-I (CIHP-I) containing ingredients derived from 7 different plants and asphalt was tested for its adaptogenic activity and its mechanism of action was investigated.

DESIGN

CIHP-I was tested using the cold-hypoxia-restraint (C-H-R) animal model in which the restrained rats were exposed to 5 degrees C at 428 mm Hg atmospheric pressure. Rectal temperature (Trec) of the rats was continuously monitored during the exposure and the recovery periods. The time for fall of Trec to 23 degrees C and its recovery to 37 degrees C were used as indices of endurance and the adaptogenic activity. Carbohydrate and lipid parameters were investigated to find out the nature of fuel being used during thermogenesis.

RESULTS

After 12 weeks of administration of an oral dose of 7.5 mg/kg(-1)/day(-1), CIHP-I was found to possess significant adaptogenic activity. CIHP-I helped improve resistance to C-H-R induced hypothermia (Trec 23 degrees C) in animals by increased mobilization of free fatty acids (FFA) from adipose tissue. Blood glucose and muscle glycogen levels were maintained. CIHP-I treatment restricted the release of creatine phosphokinase (CPK) into the circulation during C-H-R exposure.

CONCLUSIONS

The results suggested that CIHP-I is a strong adaptogen. It improved cold resistance during C-H-R exposure and enhanced recovery from hypothermia. The energy-dependent cell membrane permeability was maintained. Stored lipids were mobilised and possibly used for thermogenesis in preference to carbohydrates.

Hypothermic stress leads to activation of Ras-Erk signaling

The small GTPase Ras is converted to the active, GTP-bound state during exposure of vertebrate cells to hypothermic stress. This activation occurs more rapidly than can be accounted for by spontaneous nucleotide exchange. Ras-guanyl nucleotide exchange factors and Ras GTPase-activating proteins have significant activity at 0 degrees C in vitro, leading to the hypothesis that normal Ras regulators influence the relative amounts of Ras-GTP and Ras-GDP at low temperatures in vivo. When hypothermic cells are warmed to 37 degrees C, the Raf-Mek-Erk protein kinase cascade is activated. After prolonged hypothermic stress, followed by warming to physiologic temperature, cultured fibroblasts assume a rounded morphology, detach from the substratum, and die. All of these biologic responses are attenuated by pharmacologic inhibition of Mek. Previously, it had been found that low temperature blocks acute growth factor signaling to Erk. In the present study, we found that this block occurs at the level of Raf activation. Temperature regulation of Ras signaling could help animal cells respond appropriately to hypothermic stress, and Ras-Erk signaling can be manipulated to improve the survival of cells in cold storage.

Improved high altitude hypoxic tolerance and amelioration of anorexia and hypophagia in rats on oral glutamate supplementation

BACKGROUND

The objective of this study is to evaluate the efficacy of oral glutamic acid supplementation in promoting hypoxic tolerance.

METHODS

The experiments were conducted in albino rats by exposing them to three levels of hypoxia in a simulated environment for varying periods of time. The parameters studied include: gasping time at 35,000 ft (10,668 m), food and water intake, and heart to body weight (b.w.) ratio at 25,000 ft (7620 m), tolerance to composite stress at 15,000 ft (4572 m) and biodistribution of glutamate (glu).

RESULTS

Supplementation of Glu (27 mg x kg(-1) b.w.) as glutamic acid dissolved in normal saline resulted in 4.8 times enhanced hypoxic tolerance (time taken for appearance of first gasp), 23% body weight gain and 24% increase in food consumption over control during hypoxia. When animals were subjected to composite stress of cold, hypoxia and restraint (CHR), the Glu fed animals showed higher resistance to fall in rectal temperature than the control group. Hypoxia significantly enhanced heart to body weight ratio compared with control, and Glu supplementation reduced and brought it down to that of control.

CONCLUSION

The study reveals that Glu in optimal doses may be a conditionally essential amino acid resulting in enhanced tolerance to hypoxia and cold.