Contribution of hypothermia and CB1 receptor activation to protective effects of TAK-937, a cannabinoid receptor agonist, in rat transient MCAO model

Background

Cannabinoid (CB) receptor agonists are expected to alleviate ischemic brain damage by modulating neurotransmission and neuroinflammatory responses via CB₁ and CB₂ receptors, respectively. In a previous study, TAK-937, a novel potent and selective CB₁ and CB₂ receptor agonist, was shown to exert significant cerebroprotective effects accompanied by hypothermia after transient middle cerebral artery occlusion (MCAO) in rats. Sustained hypothermia itself induces significant neuroprotective effects. In the present studies, we examined the relative contribution of hypothermia and CB₁ receptor activation to the cerebroprotective effects of TAK-937.

Methodology/Principal Findings

Using a multichannel brain temperature controlling system we developed, the brain temperature of freely moving rats was telemetrically monitored and maintained between 37 and 38°C during intravenous infusion of TAK-937 (100 µg/kg/h) or vehicle for 24 h after 2 h MCAO. AM251, a selective CB₁ receptor antagonist, was administered intraperitoneally at 30 mg/kg 30 min before starting intravenous infusion of TAK-937 (100 µg/kg/h) for 24 h. Rats were sacrificed and their brains were isolated 26 h after MCAO in both experiments. When the hypothermic effect of TAK-937 was completely reversed by a brain temperature controlling system, the infarct-reducing effect of TAK-937 was attenuated in part, but remained significant. On the other hand, concomitant AM251 treatment with TAK-937 completely abolished the hypothermic and infarct-reducing effects of TAK-937.

Conclusions/Significance

We conclude that the cerebroprotective effects of TAK-937 were at least in part mediated by induction of hypothermia, and mainly mediated by CB₁ receptor activation.

β-arrestin2 regulates cannabinoid CB1 receptor signaling and adaptation in a central nervous system region-dependent manner

BACKGROUND

Cannabinoid CB(1) receptors (CB(1)Rs) mediate the effects of ▵(9)-tetrahydrocannabinol (THC), the psychoactive component in marijuana. Repeated THC administration produces tolerance and dependence, which limit therapeutic development. Moreover, THC produces motor and psychoactive side effects. β-arrestin2 mediates receptor desensitization, internalization, and signaling, but its role in these CB(1)R effects and receptor regulation is unclear.

METHODS

CB(1)R signaling and behaviors (antinociception, hypothermia, catalepsy) were assessed in β-arrestin2-knockout (βarr2-KO) and wild-type mice after THC administration. Cannabinoid-stimulated [(35)S]GTPγS and [(3)H]ligand autoradiography were assessed by statistical parametric mapping and region-of-interest analysis.

RESULTS

β-arrestin2 deletion increased CB(1)R-mediated G-protein activity in subregions of the cortex but did not affect CB(1)R binding, in vehicle-treated mice. βarr2-KO mice exhibited enhanced acute THC-mediated antinociception and hypothermia, with no difference in catalepsy. After repeated THC administration, βarr2-KO mice showed reduced CB(1)R desensitization and/or downregulation in cerebellum, caudal periaqueductal gray, and spinal cord and attenuated tolerance to THC-mediated antinociception. In contrast, greater desensitization was found in hypothalamus, cortex, globus pallidus, and substantia nigra of βarr2-KO compared with wild-type mice. Enhanced tolerance to THC-induced catalepsy was observed in βarr2-KO mice.

CONCLUSIONS

β-arrestin2 regulation of CB(1)R signaling following acute and repeated THC administration was region-specific, and results suggest that multiple, overlapping mechanisms regulate CB(1)Rs. The observations that βarr2-KO mice display enhanced antinociceptive responses to acute THC and decreased tolerance to the antinociceptive effects of the drug, yet enhanced tolerance to catalepsy, suggest that development of cannabinoid drugs that minimize CB(1)R interactions with β-arrestin2 might produce improved cannabinoid analgesics with reduced motor suppression.

[Neuroprotective and cardioprotective effects of hypothermic preconditioning]

The literature data testify the there is an early and delayed hypothermic preconditioning of brain. Neuroprotective effect of early hypothermic preconditioning is a result of activation of adenosine A1 receptors, KATP-channels. Ras protein and predetermined by a decrease in the synthesis of NO*. The infarct-sparing effect of delayed hypothermic preconditioning of brain is depended upon protein synthesis de novo. The presented data demonstrate that hypothermic preconditioning prevents cardiomyocyte necrosis in response to ischemia-reperfusion, improves pump function of the heart during reperfusion period, exerts an antiarrhythmic effect. The hypothermic preconditioning exerts more pronounced cardioprotective effect than ischemic preconditioning. The protective impact of hypothermic preconditioning is depended upon activation of protein kinase C, AMP-activated protein kinase (AMPK) and inhibition of MPT pore. The reactive oxygen species are triggers and mediators of hypothermic preconditioning of heart.

[Effect of total hypothermia on the fatty acid composition of blood phospholipids of rats and sousliks and light irradiation on chemical processes in lipid extract]

Effect of hypothermia on the fatty acid composition of rat and souslik blood phospholipids is studied. Different reaction of these animals to cooling is revealed: in rats no changes were observed in the fatty acid composition of blood phospholipids, whereas in the hibernating there were significant changes in the content of individual fatty acids (FA). The content of monoenic acids in sousliks decreased almost by 50%, while the content of saturated acid (C18) and of polyenic acids C18 : 2omega6 and C20 : 4omega6 rose significantly. Such changes seem to be the mechanism that promotes maintenance of the organism viability under conditions of a decreased level of metabolism, heart rhythm, and body temperature and is evolutionarily acquired. At the same time, the observed changes in the content of individual FA do not lead to sharp changes in such integrative parameters as the total non-saturation of phospholipids, which determines liquid properties of chylomicrons and other lipolipoprotein transport particles of the souslik blood. There are studied absorption spectra of blood lipid extracts of rats and sousliks under effect of light as well as effect of light upon the FA composition of lipid extracts of these animals. The FA composition of lipid extracts has been established to remain practically constant, whereas the character of changes of spectra under action of light indicates the presence in the extracts of oxidation-reduction reactions. The obtained data allow suggesting that in the lipid extract there occurs cooperation both of the phospholipid molecules themselves and of them with other organic molecules, which makes it possible for fatty acids to participate in processes of transport both of electrons and of protons. This novel role of FA as a participant of the electron transfer might probably be extrapolated to chemical reactions (processes) occurring inside the membrane.

The role of adenosine receptor and caveolae-mediated endocytosis in oligonucleotide-mediated gene transfer

We previously reported the preparation and characterization of ternary nanoparticles with the negative surface charge, which comprises histidine-conjugated polyallylamine (PAA-HIS)/DNA core complex and a single-stranded oligonucleotide outer layer, to transfect various cell lines. As a continued effort, here the investigations on the endocytotic mechanisms involved in the uptake of the oligonucleotide-coated PAA-HIS/DNA complexes are reported. Interestingly, these complexes showed enhanced transfection efficiency only when deoxyadenosine-containing oligonucleotides were deposited on the PAA-HIS/DNA complex surface. The addition of uncomplexed oligonucleotide, free adenosine and adenosine receptor antagonist significantly inhibited the transfection efficiency of oligonucleotide-coated PAA-HIS/DNA complexes. These results indicated that the oligonucleotide-coated PAA-HIS/DNA complexes could specifically recognize adenosine receptors on the cell surface and were taken up by adenosine receptor-mediated process. Uptake and transfection experiments with various endocytic inhibitors suggested that, after receptor/ligand binding, oligonucleotide-coated PAA-HIS/DNA/complexes were mainly internalized via caveolae-mediated pathway to result in effective intracellular processing for gene expression. In conclusion, both adenosine receptor and caveolae-mediated endocytosis play important roles in oligonucleotide-mediated gene transfer.

Expressions of heat shock and metallothionein genes in the heart of common carp (Cyprinus carpio): effects of temperature shock and heavy metal exposure

Heat shock proteins (HSPs) and metallothioneins (MTs) play important roles in protection against environmental stressors. The present study analyzes and compares the regulation of heat shock ( hsp70, hsc70-1 and hsp90alpha ) and metallothionein (MT-1 and MT-2) genes in the heart of common carp, in response to elevated temperature, cold shock and exposure to several heavy metal ions (As 3+ , Cd 2+ and Cu 2+ ), in whole-animal experiments. Among these metals, arsenate proved to be the most potent inducer of the examined stress genes; the hsp90alpha and MT-1 mRNA levels were elevated 11- and 10-fold, respectively, after a 24-h exposure. In contrast, Cd 2+ at 10 mg/L had no impact on the expression of hsp90alpha , and the MT genes also proved to be rather insensitive to Cd 2+ treatment in the heart: only a 2-2.5-fold induction was observed in response to 10 mg/L Cd 2+ . Heat shock resulted in a transient induction of hsp70 (19-fold) and hsp90alpha (15-fold), while elevated temperature had no effect on the expression of the MTs. Direct cold shock induced hsp70 expression (14-fold), while the hsp90alpha (26-fold) and MT-2 (2-fold) expressions peaked after the recovery period following a direct cold shock. The five stress genes examined in this study exhibited a unique, tissue-specific basal expression pattern and a characteristic sensitivity to metal treatments and temperature shocks.

1H-MRSI pattern perturbation in a mouse glioma: the effects of acute hyperglycemia and moderate hypothermia

MR spectroscopic Imaging (MRSI), with PRESS localization, is used here to monitor the effects of acute hyperglycemia in the spectral pattern of 11 mice bearing GL261 gliomas at normothermia (36.5-37.5 degrees C) and at hypothermia (28.5-29.5 degrees C). These in vivo studies were complemented by ex vivo high resolution magic angle spinning (HR-MAS) analysis of GL261 tumor samples from 6 animals sacrificed by focused microwave irradiation, and blood glucose measurements in 12 control mice. Apparent glucose levels, monitored by in vivo MRSI in brain tumors during acute hyperglycemia, rose to an average of 1.6-fold during hypothermia (p < 0.05), while no significant changes were detected at normothermia, or in control experiments performed at euglycemia, or in normal/peritumoral brain regions. Ex vivo analysis of glioma-bearing mouse brains at hypothermia revealed higher glucose increases in distinct regions during the acute hyperglycemic challenge (up to 6.6-fold at the tumor center), in agreement with maximal in vivo blood glucose changes (5-fold). Phantom studies on taurine plus glucose containing solutions explained the differences between in vivo and ex vivo measurements. Our results also indicate brain tumor heterogeneity in the four animal tumors investigated in response to a defined metabolic challenge.

FGF21 is dispensable for hypothermia induced by fasting in mice

BACKGROUND

Fibroblast growth factor 21 (FGF21) is a key metabolic regulator that is induced by peroxisome proliferator-activated receptor alpha (PPARalpha) activation in response to fasting. We recently reported that bezafibrate, a pan-agonist of PPARs, decreases body temperature late at night through hypothalamic neuropeptide Y (NPY) activation and others have shown that mice overexpressing FGF21 are prone to torpor.

OBJECTIVES

We examined whether FGF21 is essential for fasting-induced hypothermia using FGF21 knockout (KO) mice.

RESULTS

Acute fasting decreased body temperature late at night accompanied by the induction of hepatic FGF21 and hypothalamic NPY expression in wild-type mice. A deficiency of FGF21 affected neither fasting-induced hypothermia nor hypothalamic NPY induction. Fasting enhanced locomotor activity in both genotypes. On the other hand, a deficiency of FGF21 significantly attenuated chronic hypothermia and hypoactivity induced by a ketogenic diet (KD).

CONCLUSIONS

Our findings suggest that FGF21 is not essential for the hypothermia that is associated with the early stages of fasting, although it might be involved in the adaptive response of body temperature to chronic starvation.

c-Fos expression in the supraoptic nucleus is the most intense during different durations of restraint water-immersion stress in the rat

Restraint water-immersion stress (RWIS) can induce anxiety, hypothermia, and severe vagally-mediated gastric dysfunction. The present work explored the effects of different durations of RWIS on neuronal activities of the forebrain by c-Fos expression in conscious rats exposed to RWIS for 0, 30, 60, 120, or 180 min. The peak of c-Fos induction was distinct for different forebrain regions. The most intense c-Fos induction was always observed in the supraoptic nucleus (SON), and then in the hypothalamic paraventricular nucleus (PVN), posterior cortical amygdaloid nucleus (PCoA), central amygdaloid nucleus (CeA), and medial prefrontal cortex (mPFC). Moreover, body temperature was reduced to the lowest degree after 60 min of RWIS, and the gastric lesions tended to gradually worsen with the prolonging of RWIS duration. These data strongly suggest that these nuclei participate in the organismal response to RWIS to different degrees, and may be involved in the hypothermia and gastric lesions induced by RWIS.

Cold assessment criteria and prediction of cooling risk in humans: the Russian perspective

Protection of humans working in open areas during a cold period is of great importance. Cold influences human heat state, health and functional capacity. The assessment criteria for optimal permissible heat state during work time and maximum permissible heat state demanding regulation of cold exposure time are described. They form the basis for estimation and forecast of cold risk. Classification of cooling risk is made on the basis of factors such as mean skin temperature, heat deficit, strain of thermo regulative reactions, thermal sensation, and occupational conditions. Cooling risk is also dependent on human factors such as metabolic rate and clothing thermal insulation and ambient conditions such as air temperature, wind velocity, and exposure time. For evaluation of the cooling risk a regression equation is presented for determination of the integral index of cooling conditions (IICC). On basis of the IICC value, presented in a nomogram it is possible to predict the probability of cooling risk of various rates. In consideration of the shifting climate conditions of Russia, requirements for thermal insulation of protective clothing for four major climate regions of the country are presented.

[Ishemic-reperfusion syndrome prophylaxis in general hypothermia in experiment]

The influence of general supercooling on rats were studied. The action of corvitin and pentoxiphillin on the prooxidant-antioxidant homeostasis for conditions of general supercooling were analysed. On the based of investigations results analysis of lipids peroxide oxidation indexes and antioxidant protection system in animals it were established, that corvitin in difference of pentoxiphillin give more significant protectory effect in conditions of ishemic-reperfusion syndrome.

Hypothermia exerts negative inotropy in human atrial preparations: in vitro-comparison to rabbit myocardium

AIM

We investigated the effect of mild hypothermia on the contractility and calcium response of atrial and ventricular myocardium.

METHODS

Human atrial tissue was excised during cannulation process from patients undergoing elective open heart surgery following informed consent. Trabeculae were carefully dissected and compared to rabbit atrial and ventricular trabeculae. All probes were electrically stimulated while clamped to a force transducer and suspended in buffer media. Developed force, time to peak tension and time to 50% of relaxation were measured during mild hypothermia (37-31 degrees C). SR Ca++-content was studied by rapid cooling contractures, Ca++-responsiveness by a stepwise increase of extracellular calcium concentration to 10 mM.

RESULTS

Hypothermia decreased twitch tension and SR Ca++-content in human atrial myocardium but increased contractility and SR Ca++-content in rabbit atrial and rabbit ventricular myocardium. Cooling induced a lengthening of contraction and relaxation times in all preparations. In all preparations the positive inotropic response to calcium was diminished at 34 degrees C and almost abolished at 31 degrees C.

CONCLUSIONS

In contrast to rabbit ventricular and atrial myocardium, human atrial myocardium showed a negative inotropic effect when exposed to hypothermia. This alteration could be secondary to a declined SR-Ca++ storage and decreased atrial calcium sensitivity. Calcium dependent inotropy is suppressed at temperatures below 34 degrees C.

[Morphologic characteristic of lipid-containing and lipid-producing structures of human integument under normal conditions and in death caused by freezing]

This investigation was aimed at the study of lipid-containing and lipid-producing structures of human integument under normal conditions and in death caused by freezing. The skin of interscapular and epigastral areas was studied in 105 cadavers of individuals of both sexes aged 19-83 years, who died as a result of freezing. In the control group, the skin of 10 cadavers of people killed in the car accidents and those who died by the reasons, not associated with the effect of cold, was studied. Paraffin sections were stained with hematoxylin and eosin. To demonstrate lipids, unfixed cryostat sections were stained with sudan III. The following structures are producing the skin lipids: fat cells of adipose tissue, which is localized not only in subcutaneous fat tissue (hypodermis), but forms the pads, that surround the vascular networks, secretory portions of the gland, hair follicles; keratinocytes, producing lipids as a result of terminal differentiation; a sebaceous glands containing cells (sebocytes) which transform into the sebum as a result of holocrine secretion. The lipids produced by this structures are localized either in situ or are transported to the epidermal surface. Lipid-containing structures of the skin are stratum corneum and a superficial lipid film, which is formed from the secretion of the sebaceous glands--sebum. In people who died as a result of general cooling, the content and distribution of lipids in the skin are significantly changed. In the adipose tissue, the adipocyte dimensions and number is decreased, cells without lipids are found. The thickness of the superficial lipid film was decreased as compared to that in the control group; in some areas it could be absent. In the orifices of hair follicles significant amounts of lipids are deposited.

Hypothermia augments NF-kappaB activity and the production of IL-12 and IFN-gamma

BACKGROUND

The differentiation of Th1 and Th2 is strictly regulated by humoral and cellular factors. The imbalance between Th1 and Th2 is considered to be the pathogenesis of allergic and autoimmune disorders. It is important to elucidate the effect of environmental factors, such as temperature, on the expression of cytokines of Th1 and Th2.

METHODS

We investigated the expression of IFN-gamma, IL-4, IL-5, IL-10 and IL-12 from LPS- or PHA-stimulated PBMCs at 30 degrees C or 37 degrees C using ELISA and Real-time PCR. We measured the change of NF-kappaB activity at 30 degrees C or 37 degrees C with LPS stimulation using the reporter gene assay.

RESULTS

IFN-gamma production from LPS-stimulated PBMCs at 30 degrees C was up-regulated compared with 37 degrees C. IL-5 and IL-10 production from PHA-stimulated PBMCs at 30 degrees C were down-regulated compared with 37 degrees C. This augmented IFN-gamma production was caused by the up-regulation of IL-12 production from CD14+ blood monocytes. Both IL-12 mRNA and IL12 protein at 30 degrees C were up-regulated compared with 37 degrees C. NF-kappaB, the key molecule for the expression of IL-12, was also augmented at 30 degrees C compared with 37 degrees C.

CONCLUSIONS

Hypothermia up-regulated the expression of IL-12 and IFN-gamma due to the augmented NF-kappaB activity. It is suggested that hypothermia modifies the pattern of cytokine gene expression.

Identification and characterization of two mtf-1 genes in common carp

The Metal-responsive Transcription Factor (MTF-1) serves as an essential regulator of Zn(2+) homeostasis via the activation of metallothionein gene expression. Only a single mtf-1 gene has been identified in any organism investigated previously. We report here the first evidence of the existence of two genes encoding MTF-1 proteins (mtf-1.1 and mtf-1.2). The expression patterns were followed in the liver, kidney, muscle, brain and heart by means of Northern hybridization and reverse transcription coupled polymerase chain reactions (RT-PCR). mtf-1.1 mRNA was detected in all tissues examined, with the highest level in the brain, and the lowest in the kidney and the liver. mtf-1.2 expression was detected exclusively in the brain. Cold shock and Cd(2+) exposure influence the gene expression at the transcriptional level, in a stress-specific manner.

[Functioning of tyrosine protein kinases and phosphatases in gastric mucosa cells under conditions of oxidative and nitrosative stress in gastric lesions]

Acute cold stress caused lesions of gastric mucosa as a result of its attack by active oxygen and nitrogen compounds. The tissue regeneration is regulated by a cascade of tyrosine protein kinases. Gastric ulceration leads to a decrease in activity of tyrosine protein kinases and phosphatases, following by fall in phosphotyrosine content in proteins of plasma membranes of gastric mucosa cells. No changes in superoxide dismutase activity, slight increase in catalase activity, inhibition of glutathione peroxydase, significant increase in OH* content and decrease in zinc level were observed in the gastric mucosa cells of stressed rats. That increased oxidative damage can lead to inactivation of protein tyrosine phosphatases. Nitric oxide synthase activity was three times higher in gastric mucosa cells after the cold stress. That can promote nitrosylation of tyrosine residues. During following days nitric oxide synthase activity remains high. Superoxide dismutase is activated on the 4 and 5th day after the stress. Catalase activity normalizes after second day. Tyrosine protein kinase activity increases in membranes with maximum on the 4th day, and remains inhibited in cytosole. Tyrosine protein phosphatases keep inhibited as well. Gluthatione peroxydase activity and zinc level decreased on the 5th day. Obtained results can be the evidence of violations in signal transduction through protein tyrosine kinase cascades, due to the reduction in tyrosine phosphorylation, as a result of increase in the content of active oxygen and nitrogen species.

Neuropeptide FF receptors antagonist, RF9, attenuates opioid-evoked hypothermia in mice

The present study used the endpoint of hypothermia to investigate opioid and neuropeptide FF (NPFF) interactions in conscious animals. Both opioid and NPFF systems played important roles in thermoregulation, which suggested a link between opioid receptors and NPFF receptors in the production of hypothermia. Therefore, we designed a study to investigate the relationship between opioid and NPFF in control of thermoregulation in mice. The selective NPFF receptors antagonist RF9 (30nmol) injected into the third ventricle failed to induce significant effect, but it completely antagonized the hypothermia of NPFF (45 nmol) after cerebral administration in mice. In addition, RF9 (30 nmol) co-injected i.c.v. in the third ventricle reduced the hypothermia induced by morphine (5nmol,) or nociceptin/orphanin FQ (N/OFQ) (2 nmol). Neither the classical opioid receptors antagonist naloxone (10 nmol) nor NOP receptor antagonist [Nphe(1)]NC(1-13)NH(2) (7.5 nmol) reduced the hypothermia induced by the central injection of NPFF at dose of 45 nmol. Co-injected with a low dose of NPFF (5 nmol), the hypothermia of morphine (5 nmol) or N/OFQ (2 nmol) was not modified. These results suggest that NPFF receptors activation is required for opioid to produce hypothermia. In contrast, NPFF-induced hypothermia is mainly mediated by its own receptors, independent of opioid receptors in the mouse brain. This interaction, quantitated in the present study, is the first evidence that NPFF receptors mediate opioid-induced hypothermia in conscious animals.

Systemic administration of [6]-gingerol, a pungent constituent of ginger, induces hypothermia in rats via an inhibitory effect on metabolic rate

We investigated the effects of systemic administrations of ginger (Zingiber officinale Roscoe, Zingiberaceae) or its pungent constituent, [6]-gingerol, on resting body temperature in rats. Rats given ginger-containing rat chow for 5 days showed no changes in their day-night cycle of body temperature or physical activity. However, a single intraperitoneal (i.p.) injection of [6]-gingerol (2.5 or 25 mg/kg) induced a rapid, marked drop in body temperature in a dose-related manner, with no change in physical activity. A significant decrease in metabolic rate was observed immediately after an i.p. injection of [6]-gingerol (25 mg/kg), although heat-loss responses underwent no alteration (versus vehicle). These results suggest that in rats: (a) a decrease in metabolic rate is responsible for the [6]-gingerol-induced hypothermia, and (b) [6]-gingerol modulates or interferes with the mechanisms underlying body temperature regulation, while other bioactive constituents of ginger may counteract the hypothermic effect of [6]-gingerol.

Antioxidative and metabolic responses to extended cold exposure in rats

In this work, we investigated whether extended cold exposure increases oxidative damage and susceptibility to oxidants of rat liver, heart, kidney and lung which are metabolically active tissues. Moreover in this study the effect of cold stress on some of the lipid metabolic mediators were studied in rat experimental model. Male albino Sprague-Dawley rats were randomly divided into two groups: The control group (n=12) and the cold-stress group (n=12). Tissue superoxide dismutase (SOD), catalase (CAT), glutathion S-transferase (GST) and glutathion reductase (GR) activities and glutathion (GSH) were measured using standard protocols. The biochemical analyses for total lipid, cholesterol, trigliceride, HDL, VLDL and LDL were done on autoanalyzer. In cold-stress groups SOD activity was decreased in the lung whereas it increased in the heart and kidney. CAT activity was significantly decreased (except liver) in all the tissues in treated rats. GST activity of cold-induced rats increased in liver and heart while decreased in the lung. GR activity was significantly decreased (except in liver) in all the tissues in cold-stressed rats. GSH level was significantly increased in the heart but decreased in the lung of animals exposed to cold when compared to controls. It was found that among the groups trigliceride, total lipid, HDL and VLDL parameters varied significantly but cholesterol and LDL had no significant variance. In this study, we found that exposure of extended (48 h) cold (8 degrees C) caused changes both in the antioxidant defense system (as tissue and enzyme specific) and serum lipoprotein profiles in rats.

Global birth hypoxia increases the neonatal testosterone surge in the rat

BACKGROUND/AIMS

Global birth hypoxia in rats has been shown to produce long-term changes in central nervous system functions, known to be influenced by neonatal testosterone secretion. Birth hypoxia alters levels of several circulating hormones, but it is unknown if it affects neonatal testosterone.

METHODS

Using a rat model of acute global hypoxia during cesarean section (C-section) birth, this study tested whether birth hypoxia affects neonatal testosterone. We then evaluated whether the observed hypoxia-induced changes in neonatal testosterone may be mediated via N-methyl-D-aspartate (NMDA) receptor activation and/or altered luteinizing hormone (LH), adrenocorticotropic hormone (ACTH) or corticosterone levels. Longer-term effects of birth hypoxia on testosterone-related function were also assessed.

RESULTS

Rats born by C-section + 15 min of anoxia had significantly higher plasma testosterone at 2 and 3 h after birth compared to controls born either vaginally or by C-section. Administration of an NMDA receptor antagonist at birth increased neonatal testosterone in both anoxic pups and controls. Pups exposed to birth anoxia under hypothermic conditions also showed increased neonatal testosterone. Circulating LH, follicle-stimulating hormone and corticosterone in neonates, and testosterone at adulthood were unaffected by birth hypoxia. However, plasma ACTH was significantly increased in anoxic neonates at 2 h after birth. Birth condition had no effect on anogenital distance or juvenile play behavior.

CONCLUSION

It is concluded that birth hypoxia augments plasma testosterone during the critical period of the neonatal testosterone surge, by a mechanism that is independent of NMDA-mediated LH secretion, but may involve increased circulating ACTH.

Vascular endothelial growth factor protein expression in a renal ablation rabbit model under prolonged warm and cold ischemia

BACKGROUND/AIMS

To establish a potential correlation between renal and systemic production of vascular endothelial growth factor (VEGF) protein after prolonged ischemia in a renal ablation model under normothermic and hypothermic conditions.

METHODS

38 uninephrectomized New Zealand rabbits were divided into 5 groups. The rabbits of each group underwent partial nephrectomy under 90 and 60 min of warm and 90 and 120 min of cold ischemia, except for the sham group (S), which served as control. Serum creatinine (SCr) and blood-urea-nitrogen (BUN) levels were assessed. On the 15th postoperative day (POD), the animals were euthanized and the remaining kidneys were evaluated. VEGF immunohistochemistry and serum Western blot analysis were performed.

RESULTS

In comparison to the control group, groups 60W, 90C and 120C showed 1.6-, 1.14- and 1.75-fold decreases, respectively, while the production of VEGF was significantly declined by 7.4-fold in group 90W (p < 0.05). Immunohistochemistry revealed prominent VEGF staining in the above-mentioned three groups, while in group 90W staining was negative. Serum biochemistry and microscopic evaluation verified the same differentiation.

CONCLUSION

Renal and serum VEGF seem to have an analogous expression under conditions of prolonged ischemia. VEGF is overexpressed in hypothermic conditions compared to warm ischemia exceeding 60 min. Hypothermia can be more advantageous in a procedure applying prolonged ischemia.

Change in pharmacokinetics of model compounds with different elimination processes in rats during hypothermia

We compared the pharmacokinetics of model compounds with different elimination processes between hypothermic and normothermic rats, to obtain basic information concerning drug therapy during hypothermia. Male Wistar rats were anesthetized with sodium pentobarbital and kept at temperatures of 37 degrees C (normothermic group) by heat lamp, and 32 degrees C or 28 degrees C (hypothermic group) by external cooling. We chose phenolsulfonphthalein (PSP), indocyanine green (ICG) and fluorescein isothiocyanate (FITC)-dextran (FD-4, Mw 4400) as model compounds to determine changes in clearance pathways during hypothermia therapy. The plasma concentrations of PSP as biliary, urinary and metabolic elimination type were increased significantly in the hypothermic group (32 degrees C, 28 degrees C) after i.v. administration at a dose of 1 mg, compared to the normothermic group (37 degrees C). Each PSP clearance (bile, urine and metabolites) in the hypothermic group was decreased, suggesting an influence of hypothermia on the active elimination process. The decreasing tendency was marked at a temperature of 28 degrees C. Moreover, the plasma concentrations of ICG as the biliary excretion type after i.v. administration to the hypothermic rats at a dose of 1 mg were higher with more than 50% decrease in the total body clearance compared to normothermic rats. On the other hand, there was almost no difference in the i.v. pharmacokinetics of FD-4 as the urinary excretion type between 37 degrees C and 32 degrees C. However, renal clearance of FD-4 was significantly decreased at a temperature of 28 degrees C. Accordingly, the change in pharmacokinetics of a drug in the hypothermic group could differ with the elimination processes.

Hyperglycemia and lipopolysaccharide decrease depression effect of interleukin 8 production by hypothermia: an experimental study with endothelial cells

OBJECTIVE

This study assessed whether hyperglycemia and lipopolysaccharide (LPS) decrease the depression effect of interleukin (IL) 8 production by hypothermia in endothelial cells.

DESIGN AND SETTING

Laboratory study in a university laboratory.

SUBJECTS

Human umbilical vein endothelial cells (HUVECs).

INTERVENTIONS

HUVECs were cultivated in various concentrations of glucose (5.5 or 16.5mM = 100 or 300mg/dl) with or without LPS stimulation for 5, 12, or 24h at either 30 degrees or 37 degrees C.

RESULTS

After culturing, IL-8 mRNA expressions and IL-8 levels were measured. At 37 degrees C, hyperglycemia significantly increased basal IL-8 mRNA at 12h and basal IL-8 at 24h. At 37 degrees C hyperglycemia significantly increased LPS-stimulated IL-8 mRNA at 12h and LPS-stimulated IL-8 at 12 and 24h. At 30 degrees C basal IL-8mRNA, basal IL-8, and LPS-stimulated IL-8 were significantly decreased by hypothermia, but these hypothermic effects were not observed in LPS-stimulated IL-8 mRNA. Furthermore even at 30 degrees C hyperglycemia significantly increased LPS-stimulated IL-8 mRNA at all time points and LPS stimulated IL-8 at 24h.

CONCLUSIONS

Hypothermia (30 degrees C) decreases the production of IL-8 in HUVECs but does not decrease the expression of IL-8 mRNA. When hypothermia is followed by hyperglycemia and LPS stimulation, such a combination may expose the patients to a high risk of secondary tissue damage during therapeutic hypothermia.

Evaluation of two cold thermoregulatory models for prediction of core temperature during exercise in cold water

Cold thermoregulatory models (CTM) have primarily been developed to predict core temperature (T(core)) responses during sedentary immersion. Few studies have examined their efficacy to predict T(core) during exercise cold exposure. The purpose of this study was to compare observed T(core) responses during exercise in cold water with the predicted T(core) from a three-cylinder (3-CTM) and a six-cylinder (6-CTM) model, adjusted to include heat production from exercise. A matrix of two metabolic rates (0.44 and 0.88 m/s walking), two water temperatures (10 and 15 degrees C), and two immersion depths (chest and waist) were used to elicit different rates of T(core) changes. Root mean square deviation (RMSD) and nonparametric Bland-Altman tests were used to test for acceptable model predictions. Using the RMSD criterion, the 3-CTM did not fit the observed data in any trial, whereas the 6-CTM fit the data (RMSD less than standard deviation) in four of eight trials. In general, the 3-CTM predicted a rapid decline in core temperature followed by a plateau. For the 6-CTM, the predicted T(core) appeared relatively tight during the early part of immersion, but was much lower during the latter portions of immersion, accounting for the nonagreement between RMSD and SD values. The 6-CTM was rerun with no adjustment for exercise metabolism, and core temperature and heat loss predictions were tighter. In summary, this study demonstrated that both thermoregulatory models designed for sedentary cold exposure, currently, cannot be extended for use during partial immersion exercise in cold water. Algorithms need to be developed to better predict heat loss during exercise in cold water.