Increased synthesis of nitric oxide in rat brain cortex due to halogenated volatile anesthetics confirmed by EPR spectroscopy

Comparison of serum dynamic thiol/disulphide homeostasis and nitric oxide levels of total intravenous vs inhaled anaesthesia in endoscopic transsphenoidal pituitary surgery

BACKGROUND

Transsphenoidal pituitary surgery (TPS) is traditionally performed under general anaesthesia. This study aimed to compare the effects of total intravenous anaesthesia (TIVA) or sevoflurane, an inhalation anaesthetic, on thiol-disulphide homeostasis in patients undergoing endoscopic endonasal TPS.

METHODS

In this study, 84 patients scheduled for TPS were randomly categorised into two groups: propofol (n = 42, the TIVA group) or sevoflurane (n = 42, the SEVO group). Blood samples were taken before induction of general anaesthesia and at the 30 minutes of postoperation. Serum native thiol and total thiol levels were detected, and the number of dynamic disulphide bonds and related ratios were calculated from these values. Serum nitric oxide (NO) levels were measured using a chemiluminescence method.

RESULTS

Although native thiol levels in TIVA postoperation group were markedly increased (P < .05), total thiol levels in SEVO postoperation group were significantly decreased (P < .01). Disulphide levels were declined in both groups (P < .05 for TIVA and P = .001 for SEVO groups). Disulphide/native thiol (P < .05 for both groups) and disulphide/total thiol ratios (P < .05 for TIVA and P < .01 for SEVO groups) were depressed in postoperation groups. We found a marked elevation in native thiol/total thiol ratio in both groups (P < .05 for TIVA and P < .01 for SEVO groups). There was significant augmentation in serum NO levels in the SEVO postoperation group (P < .05).

CONCLUSION

These results are the first to show that both TIVA and sevoflurane showed similar antioxidant effect with reduced disulphide levels, but sevoflurane may offer more robust oxidative stress protection and augmented NO production than TIVA during TPS. However, the clinical effect is needed to further investigate.

Role of Endothelial Nitric Oxide Synthase in Isoflurane Conditioning-Induced Neurovascular Protection in Subarachnoid Hemorrhage

Background

Delayed cerebral ischemia remains a common and profound risk factor for poor outcome after subarachnoid hemorrhage (SAH). The aim of our current study is to define the role of endothelial nitric oxide synthase (eNOS) in isoflurane conditioning‐induced neurovascular protection after SAH.

Methods and Results

Ten‐ to 14‐week‐old male wild‐type mice (C57BL/6) as controls and eNOS knockout male mice (strain # 002684) were obtained for the study. Animals underwent either sham surgery, SAH surgery, or SAH with isoflurane conditioning. Anesthetic post conditioning was performed with isoflurane 2% for 1 hour, 1 hour after SAH. Normothermia was maintained with the homeothermic blanket. In a separate cohort, nitric oxide synthase was inhibited by a pan nitric oxide synthase inhibitor, L‐nitroarginine methyl ester. Vasospasm measurement was assessed 72 hours after SAH and neurological function was assessed daily. Isoflurane‐induced changes in the eNOS protein expression were measured. eNOS protein expression was significantly increased by isoflurane conditioning in naïve mice as well as mice subjected to SAH. Vasospasm of the middle cerebral artery and neurological deficits were evident following SAH versus sham surgery, both in wild‐type mice and eNOS knockout mice. Isoflurane conditioning attenuated vasospasm and neurological deficits in wild‐type mice. This delayed cerebral ischemia protection was lost in L‐nitroarginine methyl ester ‐administered mice and eNOS knockout mice.

Conclusions

Our data indicate isoflurane conditioning provides robust protection against SAH‐induced vasospasm and neurological deficits, and that this delayed cerebral ischemia protection is critically mediated via isoflurane‐induced augmentation of eNOS.

Model-based evaluation of the microhemodynamic effects of PEGylated HBOC molecules in the rat brain cortex: a laser speckle imaging study

Hemoglobin-based oxygen carriers (HBOCs) were developed with the aim of substituting transfusions in emergency events. However, they exhibit adverse events, such as nitric oxide (NO) scavenging, vasoactivity, enhanced platelet aggregation, presently hampering their clinical application. The impact of two prototypical PEGylated HBOCs, Euro-PEG-Hb and PEG-HbO₂, endowed by different oxygen affinities and hydrodynamic volumes, was assessed on the cerebrocortical parenchymal microhemodynamics, and extravasation through the blood-brain-barrier (BBB) by laser speckle contrast imaging (LSCI) method and near-infrared (NIR) imaging, respectively. By evaluating voxel-wise cerebrocortical red blood cell velocity, non-invasively for its mean kernel-wise value ( v ¯ RBC ), and model-derived kernel-wise predictions for microregional tissue hematocrit, ^TH_t, and fractional change in hematocrit-corrected vascular resistance, R', as measures of potential adverse effects (enhanced platelet aggregation and vasoactivity, respectively) we found i) no significant difference between tested HBOCs in the systemic and microregional parameters, and in the relative spatial dispersion of ^TH_t, and R' as additional measures of HBOC-related adverse effects, and ii) no extravasation through BBB by Euro-PEG-Hb. We conclude that Euro-PEG-Hb does not exhibit adverse effects in the brain microcirculation that could be directly attributed to NO scavenging.

Sensitivity to Sevoflurane anesthesia is decreased in mice with a congenital deletion of Guanylyl Cyclase-1 alpha

BACKGROUND

Volatile anesthetics increase levels of the neurotransmitter nitric oxide (NO) and the secondary messenger molecule cyclic guanosine monophosphate (cGMP) in the brain. NO activates the enzyme guanylyl cyclase (GC) to produce cGMP. We hypothesized that the NO-GC-cGMP pathway contributes to anesthesia-induced unconsciousness.

METHODS

Sevoflurane-induced loss and return of righting reflex (LORR and RORR, respectively) were studied in wild-type mice (WT) and in mice congenitally deficient in the GC-1α subunit (GC-1^-/- mice). Spatial distributions of GC-1α and the GC-2α subunit in the brain were visualized by in situ hybridization. Brain cGMP levels were measured in WT and GC-1^-/- mice after inhaling oxygen with or without 1.2% sevoflurane for 20 min.

RESULTS

Higher concentrations of sevoflurane were required to induce LORR in GC-1^-/- mice than in WT mice (1.5 ± 0.1 vs. 1.1 ± 0.2%, respectively, n = 14 and 14, P < 0.0001). Similarly, RORR occurred at higher concentrations of sevoflurane in GC-1^-/- mice than in WT mice (1.0 ± 0.1 vs. 0.8 ± 0.1%, respectively, n = 14 and 14, P < 0.0001). Abundant GC-1α and GC-2α mRNA expression was detected in the cerebral cortex, medial habenula, hippocampus, and cerebellum. Inhaling 1.2% sevoflurane for 20 min increased cGMP levels in the brains of WT mice from 2.6 ± 2.0 to 5.5 ± 3.7 pmol/mg protein (n = 13 and 10, respectively, P = 0.0355) but not in GC-1^-/- mice.

CONCLUSION

Congenital deficiency of GC-1α abolished the ability of sevoflurane anesthesia to increase cGMP levels in the whole brain, and increased the concentration of sevoflurane required to induce LORR. Impaired NO-cGMP signaling raises the threshold for producing sevoflurane-induced unconsciousness in mice.

A simple functional carbon nanotube fiber for in vivo monitoring of NO in a rat brain following cerebral ischemia

A simple ratiometric electrochemical biosensor for NO monitoring in rat brain following cerebral ischemia was developed based on a carbon nanotube fiber modified with hemin.

Impact of anesthesia on pathophysiology and mortality following subarachnoid hemorrhage in rats

BACKGROUND

Anesthesia is indispensable for in vivo research but has the intrinsic potential to alter study results. The aim of the current study was to investigate the impact of three common anesthesia protocols on physiological parameters and outcome following the most common experimental model for subarachnoid hemorrhage (SAH), endovascular perforation.

METHODS

Sprague-Dawley rats (n = 38) were randomly assigned to (1) chloral hydrate, (2) isoflurane or (3) midazolam/medetomidine/fentanyl (MMF) anesthesia. Arterial blood gases, intracranial pressure (ICP), mean arterial blood pressure (MAP), cerebral perfusion pressure (CPP), and regional cerebral blood flow (rCBF) were monitored before and for 3 hours after SAH. Brain water content, mortality and rate of secondary bleeding were also evaluated.

RESULTS

Under baseline conditions isoflurane anesthesia resulted in deterioration of respiratory parameters (arterial pCO2 and pO2) and increased brain water content. After SAH, isoflurane and chloral hydrate were associated with reduced MAP, incomplete recovery of post-hemorrhagic rCBF (23 ± 13% and 87 ± 18% of baseline, respectively) and a high anesthesia-related mortality (17 and 50%, respectively). Anesthesia with MMF provided stable hemodynamics (MAP between 100-110 mmHg), high post-hemorrhagic rCBF values, and a high rate of re-bleedings (> 50%), a phenomenon often observed after SAH in humans.

CONCLUSION

Based on these findings we recommend anesthesia with MMF for the endovascular perforation model of SAH.

Do inhalational anesthetics cause cognitive dysfunction?

Increasing evidence indicates that inhalational anesthetics may cause or increase the risk of developing postoperative cognitive dysfunction (POCD), especially in the elderly population. POCD may exist as a transient or long-term complication of surgery and anesthesia and is associated with reduced quality of life. There remains great discrepancy between clinical studies investigating the prevalence of POCD and inhalational anesthetics as many fail to show an association. However, numerous animal studies have suggested that inhalational anesthetics may alter cognitive function via amyloid β accumulation, modified neurotransmission, synaptic changes and dysregulated calcium homeostasis. Other factors such as neuroinflammation and pro-inflammatory cytokines may also play a role. This paper reviews the role of inhalational anesthetics in the etiology and underlying mechanisms that result in POCD.

NO-dependent protective effect of VEGF against excitotoxicity on layer VI of the developing cerebral cortex

In industrialized countries, cerebral palsy affects 2.5‰ of preterm and term infants. At a neurochemical level, the massive release of glutamate constitutes a major process leading to excitotoxicity and neonatal brain lesions. Previous studies, conducted in the laboratory, revealed that, in (δ/δ)VEGF(A) transgenic mice, glutamate-induced brain lesions are exacerbated suggesting that VEGF(A) could play a protective action against excitotoxicity. Using a model of cultured cortical brain slices, the aim of the study was to characterize the central effects of VEGF against glutamate-induced excitotoxicity in neonates. Exposure of brain slices to glutamate induced a strong increase of necrotic cell death in the deep cortical layer VI and a decrease of apoptotic death in superficial layers II-IV. When administered alone, a 6-h treatment with VEGF(A) had no effect on both apoptotic and necrotic deaths. In contrast, VEGF(A) abolished the glutamate-induced necrosis observed in layer VI. While MEK and PI3-K inhibitors had no effect on the protective action of VEGF(A), L-NAME, a pan inhibitor of NOS, abrogated the effect of VEGF(A) and exacerbated the excitotoxic action of glutamate. Calcimetry experiments performed on brain slices revealed that VEGF(A) reduced the massive calcium influx induced by glutamate in layer VI and this effect was blocked by L-NAME. Neuroprotective effect of VEGF(A) was also blocked by LNIO and NPLA, two inhibitors of constitutive NOS, while AGH, an iNOS inhibitor, had no effect. Nitrite measurements, electron paramagnetic resonance spectroscopy and immunohistochemistry indicated that glutamate was a potent inducer of NO production via activation of nNOS in the cortical layer VI. In vivo administration of nNOS siRNA promoted excitotoxicity and mimicked the effects of L-NAME, LNIO and NPLA. A short-term glutamate treatment increased nNOS Ser1412 phosphorylation, while a long-term exposure inhibited nNOS/NR2B protein-protein interactions. Altogether, these findings indicate that, in deep cortical layers of mice neonates, glutamate stimulates nNOS activity. Contrasting with mature brain, NO production induced by high concentrations of glutamate is neuroprotective and is required for the anti-necrotic effect of VEGF(A).

Effects of Lycopene, Indole-3-Carbinol, and Luteolin on Nitric Oxide Production and iNOS Expression are Organ-Specific in Rats

Natural compounds are known to modify NO content in tissues; however, the biological activity of polyphenol-rich food often does not correspond to the effects of individual polyphenols on NO synthase activity. The aim of this study was to see how natural compounds luteolin, indole-3-carbinol, and lycopene modify NO production in rat tissues and change the expression of the iNOS gene and protein. Indole-3-carbinol produced multiple effects on the NO level; it significantly decreased NO concentration in blood, lungs, and skeletal muscles and increased it in the liver. Indole-3-carbinol enhanced lipopolyssaccharide (LPS)-induced NO production in all rat organs. It decreased iNOS gene expression in the brain cortex of animals that did not receive LPS and up-regulated it in the LPS-treated animals. Lycopene increased the iNOS gene transcription rate in the brain cortex of LPS-treated animals. Luteolin did not modify NO production in any organ of LPS-untreated rats, nor did it affect gene expression in the liver. In the brain it slightly decreased iNOS gene expression. Luteolin decreased NO production in the blood of LPS-treated animals and the number of iNOS-positive cells in these animals. Our results suggest that changes in tissue NO levels caused by natural compounds cannot be predicted from their effect on NOS expression or activity obtained in model systems. This stresses the importance of direct measurements of NO and NOS expression in animal tissues.

Sevoflurane-induced post-conditioning has no beneficial effects on neuroprotection after incomplete cerebral ischemia in rats

BACKGROUND

The aim of this study was to investigate whether sevoflurane-induced post-conditioning has a neuroprotective effect against incomplete cerebral ischemia in rats.

METHODS

After cerebral ischemia by right common carotid artery occlusion in combination with hemorrhagic hypotension (35 mmHg) for 30 min, 1.0 minimum alveolar concentration of sevoflurane was administered for 15 min (Post-C 15, n=8), 30 min (Post-C 30, n=8), or 60 min (Post-C 60, n=8) in rats. Sevoflurane was not administered in control (n=8) and sham control rats (n=8). Neurologic evaluations were performed at 24, 48, and 72 h after ischemia. Degrees of neuronal damage in ischemic hippocampal CA1 and the cortex were assessed by counting eosinophilic neurons, and detection of DNA fragmentation was performed by terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) staining.

RESULTS

Neurologic deficit scores in the Post-C 60 group were higher than in the control group at 48 and 72 h post-ischemia (P<0.05). No differences were observed in the percentages of eosinophilic neurons among the control (CA1: 37.3 +/- 25.4, cortex: 26.0 +/- 8.9), Post-C 15 (CA1: 54.0 +/- 21.4, cortex: 30.8 +/- 19.9), or Post-C 30 (CA1: 68.4 +/- 17.5, cortex: 38.0 +/- 11.0) groups in ischemic CA1 and cortices. However, in the Post-C 60 group, the percentages of eosinophilic neurons were higher than in the control group in CA1 and cortices (P<0.05). The percentages of TUNEL-positive cell were similar in the control group and the post-conditioned groups.

CONCLUSION

These findings show that sevoflurane administration after ischemia does not provide neuroprotection in rats subjected to incomplete cerebral ischemia.

Postconditioning with isoflurane reduced ischemia-induced brain injury in rats

BACKGROUND

Preexposure of brain to isoflurane, a commonly used anesthetic, induces ischemic tolerance. This phenomenon is called isoflurane preconditioning. However, it is not known whether isoflurane application after ischemia provides neuroprotection.

METHODS

Corticostriatal slices (400 microm) freshly prepared from adult male Sprague-Dawley rats were subjected to a 15-min oxygen-glucose deprivation (OGD; to simulate ischemia in vitro). Isoflurane was applied after OGD. Brain slices were harvested 2 h after OGD for measuring 2,3,5-triphenyltetrazolium chloride (TTC) conversion to quantify cell injury. Adult male Sprague-Dawley rats were also subjected to middle cerebral arterial occlusion for 90 min and then treated with or without 2% isoflurane for 60 min started at the onset of reperfusion. The infarct volumes, neurologic deficit scores, and performance on rotarod were evaluated at 24 h after the onset of reperfusion.

RESULTS

Isoflurane applied immediately after the 15-min OGD for 30 min dose-dependently reversed the OGD-induced decrease of TTC conversion. The TTC conversion was 34 +/- 16% and 58 +/- 28% of the control, respectively, for OGD alone and OGD plus 2% isoflurane (P < 0.05, n = 12). Application of 2% isoflurane for 30 min started at 10 min after the OGD also reduced the OGD-decreased TTC conversion. The presence of 0.3 microm glibenclamide, a general adenosine 5'-triphosphate-sensitive potassium channel blocker, or 500 microm 5-hydroxydecanoic acid, a mitochondrial adenosine 5'-triphosphate-sensitive potassium channel blocker, during the application of 2% isoflurane abolished the isoflurane preservation of TTC conversion. Application of isoflurane during reperfusion also improved neurologic outcome after brain ischemia.

CONCLUSIONS

The results suggest that isoflurane administrated after OGD or brain ischemia provides neuroprotection. Mitochondrial adenosine 5'-triphosphate-sensitive potassium channels may be involved in this protection.

Paradoxical effects of two oximes on nitric oxide production by purified NO synthases, in cell culture and in animals

We have studied the impact of two novel compounds TO-85 (2,6-di-(alpha-aziridino-alpha-hydroxyiminomethyl)pyridine and TO-133 (bis-(diaziridinoglyoximato)copper), designed as NO donors, on nitrite production by cell cultures, NO production in rat tissues and their ability to inhibit purified NO synthases (NOS). Both substances induced considerable increase of nitrite production in cell cultures. When NO production was assayed in rat organs by means of ESR using Fe(DETC) as a spin trap the anticipated NO-increasing activity of TO-85 was observed only in kidneys; the NO level increasing almost 10-fold. Treatment of rats with TO-133, decreased the NO concentration in brain cortex, cerebellum and liver. When the drugs were administered to animals with high level of iNOS expression induced by LPS, TO-85 did not significantly modify the LPS-induced NO production; administration of TO-133 caused a significant decrease of NO production in blood, brain cortex and cerebellum. Only high concentrations of TO-85 were capable of inhibiting iNOS (IC50=7 mM), the substance inhibited eNOS at lower concentrations (IC50=250 microM). Inhibitory activities of TO-85 on nNOS were dependent on BH4 concentrations, suggesting eventual competition of TO-85 with BH4 when the substance interacts with nNOS. TO-133 reduced eNOS activity with IC50=200 microM, nNOS activity with IC50=200 microM, iNOS activity was not much affected by this substance. Thus, the two tested compounds manifest opposite effects on NO production by purified enzymes and in cell culture. The pattern of the NO synthesis modification in a living animal appears to be even more complex. Our results stress the importance of direct measurements of NO in the tissues using the ESR method.

The beta-adrenoceptor antagonist propranolol counteracts anti-inflammatory effects of isoflurane in rat endotoxemia

BACKGROUND

Recent studies suggest that volatile anaesthetics have anti-inflammatory and preconditioning properties and that beta-adrenoceptors are involved in the signalling pathways for these effects. Concurrently, the blockade of beta-adrenoceptors has been shown to augment the release of inflammatory mediators in response to pro-inflammatory stimuli. We therefore aimed to investigate whether the beta-adrenoceptor antagonist propranolol might modulate the anti-inflammatory effects of isoflurane on the systemic and pulmonary release of pro-inflammatory cytokines in endotoxemic rats.

METHODS

Forty anaesthetized and ventilated Sprague-Dawley rats were randomly treated as follows. Lipopolysaccharide (LPS) only (n = 8), endotoxemia with LPS [5 mg/kg, intravenously (i.v.)]. LPS-isoflurane (n = 8): endotoxemia and continuous inhalation of 1 minimum alveolar concentration (MAC) of isoflurane. LPS-isoflurane-propranolol (n = 8): administration of propranolol (3 mg/kg) before continuous inhalation of isoflurane and induction of endotoxemia. LPS-propranolol (n = 8): administration of propranolol (3 mg/kg) before endotoxemia without inhalation of isoflurane. Sham (n = 8): control-group only with surgical preparation. After 4 h of endotoxemia, levels of tumour necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta) and interleukin-10 (IL-10) in plasma and bronchoalveolar fluid (BALF) were analysed. Release of nitric oxide (NO) and amount of inducible nitric oxide synthase (iNOS) protein in alveolar macrophages was measured by Griess assay or determined by Western Blotting, respectively.

RESULTS

Inhalation of isoflurane reduced the release of TNF-alpha (P < 0.05) and IL-1beta (P < 0.05) in plasma and IL-1beta (P < 0.05) in BALF. Co-administration of propranolol significantly inhibited these effects. During inhalation of isoflurane, the increased release of NO and iNOS protein from alveolar macrophages was also completely inhibited by propranolol.

CONCLUSION

Our results indicate for the first time, that blockade of beta-adrenoceptors counteracts the anti-inflammatory effects of isoflurane in endotoxemic rats.

Detrimental effects of halothane narcosis on damage after endothelin-1-induced MCAO

The influence of anaesthesia in experimental stroke research is controversial. We addressed this problem using the model of endothelin-1-induced occlusion of the middle cerebral artery (eMCAO). This model provided the opportunity to compare the infarct volumes of rats which were under halothane anaesthesia during eMCAO induction with the lesions of rats which were without anaesthesia during eMCAO. All animals were implanted with guide cannulae which allowed the induction of ischaemia in freely moving animals. For comparison, one group of animals was exposed to halothane during the induction of ischaemia. Seven days after eMCAO, the average infarct volume of halothane-anaesthetised rats was significantly larger than the lesion in freely moving animals. This difference was mainly due to increased cortical damage, whereas the striatum was much less influenced. The cortical infarct volume 21 days after induction of eMCAO under anaesthesia was significantly reduced compared to the infarct volume 7 days after eMCAO under anaesthesia. Our results indicate that halothane anaesthesia during eMCAO can cause a transient cortical increase in ischaemic infarct volume. The influence of volatile anaesthetics on ischaemic pathophysiology should be taken into consideration when preclinically testing potential neuroprotective drugs for clinical applications.

A Description of the Preterm Fetal Sheep Systemic and Central Responses to Maternal General Anesthesia

BACKGROUND

The second trimester is recommended as the optimal time to conduct a surgical procedure on pregnant patients, even though the fetal responses to anesthesia at this age are not known. Here we assessed the responses of preterm fetal sheep to a standard anesthetic regimen of midazolam, thiopental, and isoflurane.

METHODS

Variables were monitored in previously instrumented preterm pregnant sheep before, during, and after 4 h of general anesthesia. Isoflurane produced moderate fetal hypotension and bradycardia, whereas extubation was accompanied by increases in fetal heart rate and mean arterial blood pressure.

RESULTS

We observed an initial increase in fetal Sao2 followed by a gradual decline to baseline. Within the fetal brain, oxygenated hemoglobin changed by <10% (nonsignificant) and deoxygenated hemoglobin and total hemoglobin varied by <5%. Overall, although O2 levels within the preterm fetal brain were not independently enhanced by isoflurane (as occurs in the older fetus and in the adult), they did remain constant even as fetal mean arterial pressure decreased by more than 20%. By extension, we failed to identify changes in cerebral oxygenation that could be construed as injurious.

CONCLUSION

Any adverse preterm fetal response to maternal surgery should not be attributed solely to the actions of general anesthesia upon the fetus.

Beta-MSH inhibits brain inflammation via MC(3)/(4) receptors and impaired NF-kappaB signaling

The anti-inflammatory effects of melanocortin peptides have been demonstrated in different inflammation models. This is the first report describing the molecular mechanisms for the beta-MSH-induced suppression of bacterial lipopolisaccharide (LPS)-caused brain inflammation. We found that beta-MSH suppresses LPS-induced nuclear translocation of the transcription factor NF-kappaB, and inhibits the expression of inducible nitric oxide synthase, and the following nitric oxide overproduction in the brain, in vivo. Moreover, administering the preferentially MC(4) receptor selective antagonist HS014 blocked completely these effects, suggesting a tentative MC(4) receptor mediated mechanism of action for the beta-MSH. However, as HS014 shows quite low selectivity vis-à-vis the MC(3) receptor, a role for the MC(3) receptor cannot be excluded. In conclusion, our results show that beta-MSH is capable of inhibiting brain inflammation via activation of melanocortin receptors, of the subtypes 4 and/or 3.

Sevoflurane Impairs Cerebral Blood Flow Autoregulation in Rats: Reversal by Nonselective Nitric Oxide Synthase Inhibition

In this study, we investigated the effects of 1.0 and 2.0 minimum alveolar anesthetic concentration (MAC) sevoflurane on cerebral blood flow (CBF) autoregulation before and after nonselective inhibition of nitric oxide (NO) synthase in rats. Rats were randomly assigned as follows: Group 1 (n = 8): 1.0 MAC sevoflurane; Groups 2 and 3 (n = 8 per group): 2.0 MAC sevoflurane. Assessment of autoregulation within a mean arterial blood pressure range of 140-60 mm Hg was performed by graded hemorrhage before and after administration of l-arginine methyl ester (l-NAME, 30 mg/kg IV, Groups 1 and 2) or during hypocapnia (Group 3). In 10 additional animals, brain tissue NO(2)(-) concentrations were measured at 1.0 and 2.0 MAC sevoflurane. CBF autoregulation was maintained with 1.0 MAC sevoflurane (Group 1) regardless of NO synthase status indicating that CBF autoregulation might not be related to NO availability. Sevoflurane dose-dependently increased brain tissue NO(2)(-) and impaired CBF autoregulation. Administration of l-NAME (Group 2) but not hypocapnia (Group 3) restored CBF autoregulation. This suggests that sevoflurane impairs the autoregulatory capacity secondary to an increase of the perivascular NO availability and questions the importance of basal cerebrovascular tone in terms of vasodilatory capacity during hypotensive challenges.

IMPLICATIONS

The present study suggests that the volatile anesthetic sevoflurane dose-dependently impairs cerebrovascular autoregulation by mechanisms secondary to increase of perivascular nitric oxide availability.

Endothelium- and nitric oxide-dependent vasorelaxing activities of gamma-butyrobetaine esters: possible link to the antiischemic activities of mildronate

Mildronate [3-(2,2,2-trimethylhydrazine) propionate (THP)] is an antiischemic drug acting mainly via inhibition of fatty acid beta-oxidation. Some effects of the drug cannot be explained by the latter mechanism. We tested the eventual nitric oxide (NO) dependence of the mildronate action. Mildronate, gamma-butyrobetaine (GBB) and GBB methyl ester induced transient increases in nitric oxide (NO) concentrations in rat blood and myocardium. In vitro, these compounds neither modified the activities of purified neuronal and endothelial recombinant nitric oxide synthases (NOSs) nor were able to interact with their active site. GBB induced vasodilatation at high concentrations only (EC50 = 5 x 10(-5) M) while mildronate alone displayed no vasodilating effect although it enhanced the GBB vasodilating activity. GBB methyl and ethyl esters were found more potent vasodilators (EC50 = 2.5 x 10(-6) M). Pretreatment of aortic rings with NOS inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME) abolished vasodilating effects of the compounds. A hypothesis explaining NO and endothelium-dependent effects of mildronate and its analogues is proposed.

Investigations on the pharmacology of the cardioprotective guanidine ME10092

The guanidine compound ME10092 (1-(3,4-dimethoxy-2-chlorobenzylideneamino)-guanidine), which possesses a strong cardioprotective effect to ischemia-reperfusion, was assessed for different pharmacological actions that may underlie its cardioprotective effect. In the living rat ME10092 decreased the blood pressure and heart rate in a dose-dependent manner. We found ME10092 to bind to alpha 1- and alpha 2-adrenoreceptors with moderate affinity (Ki values 1-4 microM), and to block adrenaline-elicited contractile responses in isolated guinea pig aortas. Our results indicate that ME10092 possesses a certain anti-oxidant profile. Thus, in a competitive manner and with low affinity it inhibited the bovine milk xanthine oxidase enzyme, as well as NAD(P)H oxidase driven oxyradical formation in membrane fractions isolated from the rat brain. By using electron paramagnetic resonance we here show that, after its systemic administration, ME10092 modulates the nitric oxide (NO) content in several tissues of the rat in a time-dependent manner. However, in vitro ME10092 inhibited the activities of nitric oxide synthases nNOS and eNOS, but not that of iNOS. Our data give evidence that the cardioprotective effect of ME10092 could be mediated through pharmacological mechanisms that include some modulation of NO production, as well as possible inhibition of radical formation during ischemia-reperfusion.

Putative role of nitric oxide synthase isoforms in the changes of nitric oxide concentration in rat brain cortex and cerebellum following sevoflurane and isoflurane anaesthesia

We have previously observed an increase in nitric oxide (NO) content in rat brain cortex following halothane, sevoflurane or isoflurane anaesthesia. This study was undertaken in order to determine whether isoform-specific nitric oxide synthase (NOS) inhibitors and inducers could modify these increases in NO contents. Rats were subjected to isoflurane and sevoflurane anaesthesia with concomitant administration of neuronal nitric oxide synthase (nNOS) inhibitor 7-Nitro-indazole (7-NI), inducible nitric oxide synthase (iNOS) inhibitor 2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine (AMT) or lipopolysaccharide. NO concentration in different organs was measured by electron paramagnetic resonance (EPR) spectroscopy. 7-NI significantly decreased NO concentration in cerebellum but not in brain cortex, whereas AMT decreased NO in all the organs studied. Anaesthesia significantly increased NO concentration in brain cortex and decreased that in cerebellum. AMT abolished the NO increase in brain cortex. Anaesthesia enhanced the drastic increase in NO concentration in brain cortex after intraventricular lipopolysaccharide administration. Isoflurane was found to inhibit recombinant nNOS and iNOS activities at high concentrations (EC50=20 mM). Our data suggest a putative role for iNOS in the increase in NO levels produced by isoflurane and sevoflurane, whereas nNOS activity is probably inhibited during anaesthesia.

Electron spin resonance spectroscopy reveals alpha-phenyl-N-tert-butylnitrone spin-traps free radicals in rat striatum and prevents haloperidol-induced vacuous chewing movements in the rat model of human tardive dyskinesia

The typical antipsychotic drug haloperidol causes vacuous chewing movements (VCM) in rats, which are representative of early-Parkinsonian symptoms or later-onset extrapyramidal side effects of tardive dyskinesia (TD) in humans. Haloperidol (HP) has been hypothesized to potentiate increases in oxidative stress or free radical-mediated levels of toxic metabolites in rat striatum while simultaneous upregulating dopamine (DA)-D2 receptors leading to presumed DA supersensitivity. Alpha(alpha)-Phenyl-N-tert-butylnitrone (PBN) is an antioxidant used to combat oxidative stress and measure increases in PBN spin-adduct activity. Thus, the aim of this study was to investigate whether VCMs are related to upregulation of DA-D2 receptors or to increased levels of free radicals produced during oxidative stress, and whether PBN had any protective effects. Rats received daily chronic (28 day) i.p. injections of saline, haloperidol (2 mg/kg), PBN (150 mg/kg), or haloperidol + PBN. The VCM model was used to measure extrapyramidal side effects of drug treatments. Electron spin resonance (ESR) spectroscopy was performed to compare concentrations of free radical species in rats receiving injections of HP + PBN. To examine the upregulation of DA-D2 receptors, binding assays were carried out to assess the increase in DA-D(2) receptor numbers with respect to VCMs following treatment of rats injected with HP, PBN, and HP + PBN. Results of these experiments show that HP-induced VCMs in rats results from increases in oxidative cellular events and may not be related to increases in striatal DA-D(2) receptors.

Coupling of changes in cerebral blood flow with neural activity: what must initially dip must come back up

Activation flow coupling, increases in neuronal activity leading to changes in cerebral blood flow (CBF), is the basis of many neuroimaging methods. An early rise in deoxygenation, the "initial dip," occurs before changes in CBF and cerebral blood volume (CBV) and may provide a better spatial localizer of early neuronal activity compared with subsequent increases in CBF. Imaging modality, anesthetic, degree of oxygenation, and species can influence the magnitude of this initial dip. The observed initial dip may reflect a depletion of mitochondrial oxygen (O(2)) buffers caused by increased neuronal activity. Changes in CBF mediated by nitric oxide (NO) or other metabolites and not caused by a lack of O(2) or energy depletion most likely lead to an increased delivery of capillary O(2) in an attempt to maintain intracellular O(2) buffers.

β- and γ-melanocortins inhibit lipopolysaccharide induced nitric oxide production in mice brain

The pro-opiomelanocortin-derived peptide alpha-melanocyte stimulating hormone (alpha-MSH) mediates many diverse physiological actions, including anti-inflammatory and immunomodulatory effects. However, little is known about the physiological roles of the other melanocortins, beta- and gamma-MSH. Here, we investigated the effects of melanocortin peptides in an in vivo neuroinflammation model. Six hours following intracisternal (i.c.) administration of 10 microg lipopolysaccharide (LPS) to mice a five-fold increase in the nitric oxide (NO) level was seen in the animals' brains, when detected by electron paramagnetic resonance (EPR). All tested melanocortins, alpha-, beta-, gamma1- and gamma2-MSH (0.001-10 nmol/mouse i.c.), dose dependently reduced the LPS induced increases in brain NO, with an order of effectiveness: beta-MSH > or = gamma1-MSH=gamma2-MSH>alpha-MSH. Our results suggest specialized functions of beta- and gamma-MSH melanocortins in inflammatory signal modulation in the brain.