Isoflurane-induced cerebral hyperemia is partially mediated by nitric oxide and epoxyeicosatrienoic acids in mice in vivo

BACKGROUND: Despite intense investigation, the mechanism of isoflurane-induced cerebral hyperemia is unclear. The current study was designed to determine the contributions of neuronal nitric oxide synthase, prostaglandins, and epoxyeicosatrienoic acids to isoflurane-induced cerebral hyperemia. METHODS: Regional cerebral cortical blood flow was measured with laser Doppler flowmetry during stepwise increases of isoflurane from 0.0 to 1.2, 1.8, and 2.4 vol% end-tidal concentration in alpha-chloralose-urethane-anesthetized, C57BL/6 mice before and 45 min after administration of the neuronal nitric oxide synthase inhibitor 7-nitroindazole (7-NI, 40 mg/kg, intraperitoneal), the cyclooxygenase inhibitor indomethacin (INDO, 10 mg/kg, intravenous), and the cytochrome P450 epoxygenase inhibitor N-methylsulfonyl-6-(2-proparglyoxyphenyl)hexanoic acid (PPOH, 20 mg/kg, intravenous). RESULTS: Isoflurane increased regional cerebral cortical blood flow by 9 +/- 3, 46 +/- 21, and 101 +/- 26% (SD) at 1.2, 1.8, and 2.4 vol%, respectively. The increases in regional cerebral cortical blood flow were significantly (*P < 0.05) smaller after 7-NI (5 +/- 6, 29 +/- 19*, 68 +/- 15%*) or PPOH (4 +/- 8, 27 +/- 17*, 67 +/- 30%*), but not after administration of INDO (4 +/- 4, 33 +/- 18 [NS], 107 +/- 35% [NS]). The effect of combined treatment with 7-NI, PPOH, and INDO was not additive and was equal to that of either 7-NI or PPOH alone (5 +/- 5, 30 +/- 12*, 76 +/- 24%*). Chronic treatment of mice for 5 days with 7-NI (2 x 40 mg/kg, intraperitoneal) produced similar decreases in regional cerebral cortical blood flow as those seen with acute administration. Neither PPOH nor INDO conferred a significant additional block of the hyperemia in these animals. CONCLUSIONS: Nitric oxide and epoxyeicosatrienoic acids contribute to isoflurane-induced hyperemia. However, only approximately one third of the cerebral hyperemic response to isoflurane is mediated by autacoids. The remaining part of this response appears to be mediated by a direct action of isoflurane on smooth muscle by some yet-unknown mechanism.     

Isoflurane-induced Cerebral Hyperemia Is Partially Mediated by Nitric Oxide and Epoxyeicosatrienoic Acids in Mice In Vivo

Background: Despite intense investigation, the mechanism of isoflurane-induced cerebral hyperemia is unclear. The current study was designed to determine the contributions of neuronal nitric oxide synthase, prostaglandins, and epoxyeicosatrienoic acids to isoflurane-induced cerebral hyperemia.

Methods: Regional cerebral cortical blood flow was measured with laser Doppler flowmetry during stepwise increases of isoflurane from 0.0 to 1.2, 1.8, and 2.4 vol% end-tidal concentration in [alpha]-chloralose-urethane-anesthetized, C57BL/6 mice before and 45 min after administration of the neuronal nitric oxide synthase inhibitor 7-nitroindazole (7-NI, 40 mg/kg, intraperitoneal), the cyclooxygenase inhibitor indomethacin (INDO, 10 mg/kg, intravenous), and the cytochrome P450 epoxygenase inhibitor N-methylsulfonyl-6-(2-proparglyoxyphenyl)hexanoic acid (PPOH, 20 mg/kg, intravenous).

Results: Isoflurane increased regional cerebral cortical blood flow by 9 +/- 3, 46 +/- 21, and 101 +/- 26% (SD) at 1.2, 1.8, and 2.4 vol%, respectively. The increases in regional cerebral cortical blood flow were significantly (*P < 0.05) smaller after 7-NI (5 +/- 6, 29 +/- 19*, 68 +/- 15%*) or PPOH (4 +/- 8, 27 +/- 17*, 67 +/- 30%*), but not after administration of INDO (4 +/- 4, 33 +/- 18 [NS], 107 +/- 35% [NS]). The effect of combined treatment with 7-NI, PPOH, and INDO was not additive and was equal to that of either 7-NI or PPOH alone (5 +/- 5, 30 +/- 12*, 76 +/- 24%*). Chronic treatment of mice for 5 days with 7-NI (2 x 40 mg/kg, intraperitoneal) produced similar decreases in regional cerebral cortical blood flow as those seen with acute administration. Neither PPOH nor INDO conferred a significant additional block of the hyperemia in these animals.     

Correlation of regional cerebral blood flow (rCBF) with EEG changes during isoflurane anesthesia for carotid endarterectomy: critical rCBF

A prospective evaluation of regional cerebral blood flow (rCBF) (ipsilateral middle cerebral artery distribution) was determined using a 133Xe clearance technique in 31 ASA P.S. II-III patients anesthetized with isoflurane-50% N2O in O2 for carotid endarterectomy. Each patient was monitored with 16-channel EEG throughout anesthesia and surgery. Critical rCBF was defined as that flow below which EEG signs of ischemia occurred. Critical rCBF (T1/2 method of analysis) was less than 10 ml X 100 g-1 X min-1 (mean +/- SE 5.9 +/- 1.2) in the six patients in whom transient EEG changes occurred at the time of temporary surgical carotid artery occlusion. No EEG changes occurred with occlusion in the other 25 patients; mean (+/- SE) occlusion rCBF in this group was 18.9 +/- 1.3 ml X 100 g-1 X min-1 (P less than 0.001). Preocclusion flows were not significantly different in the two groups. Critical rCBF during isoflurane anesthesia was less than that previously determined during halothane anesthesia (18-20 ml X 100 g-1 X min-1), and is compatible with the effects of isoflurane on CMRO2 and CBF.     

Regional cerebral blood flow and response to carbon dioxide during controlled hypotension with isoflurane anesthesia in the rat

Regional (frontal, parietal, occipital, cortical, and basal ganglia) cerebral blood flow (rCBF) was examined at 1.5 and 3.5 MAC inspired isoflurane/O2 anesthesia in the rat using the radioactive microsphere technique to determine the effects of controlled hypotension with deep isoflurane anesthesia on rCBF and the response of rCBF to changes in PaCO2 when mean blood pressure (BP) was decreased to levels below the lower limit of the autoregulatory threshold. Four groups of six rats were studied with rCBF 1 determined at 1.5 MAC (mean BP 80-90 mm Hg) followed by two rCBF determinations at 3.5 MAC (mean BP 46-48 mm Hg). For CBF 1 the regional CO2 response was a 3.1-3.9% increase in rCBF/mm Hg increase in CO2. Regional cerebral blood flow (ml/g/min) ranged from 0.64 +/- 0.05-0.83 +/- 0.15 at PaCO2 of 19 mm Hg to 1.34 +/- 0.11-1.80 +/- 0.33 at PaCO2 of 41 mm Hg to 2.61 +/- 0.26-3.72 +/- 0.37 at PaCO2 of 59 mm Hg (mean +/- SEM). With controlled hypotension (CBF 2) rCBF was unchanged during normocarbia, increased 100% during hypocarbia, P less than 0.01 vs CBF 1 and decreased 30% during hypercarbia, P less than 0.01 vs CBF 1. For rCBF 3 measurements, the BP and inspired concentration of isoflurane were kept constant, while PaCO2 was increased in two and decreased in two of the four groups. Within-group comparisons between rCBF 2 and rCBF 3 results demonstrated loss of CO2 responsiveness of the rat cerebrovasculature in every region during controlled hypotension to below the autoregulatory threshold at 3.5 MAC isoflurane/O2 anesthesia.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mice with gene disruption of both endothelial and neuronal nitric oxide synthase exhibit insulin resistance

Studies from our laboratory using acute pharmacologic blockade of nitric oxide synthase (NOS) activity have suggested that nitric oxide (NO) has an important role in regulating carbohydrate metabolism. We now report on insulin sensitivity in mice with targeted disruptions in endothelial NOS (eNOS) and neuronal NOS (nNOS) genes compared with their wild-type (WT) counterparts. Mice underwent hyperinsulinemic-euglycemic clamp studies after a 24-h fast, during an insulin infusion of 20 mU x kg(-1) x min(-1). Glucose levels were measured at baseline and every 10 min during the clamp. Insulin levels were measured at baseline and at the end of the clamp study. Glucose infusion rates (GIRs) during the last 30 min of the clamp study were in a steady state. Tritiated glucose infusion was used to measure rates of endogenous glucose output (EGO) both at baseline and during steady-state euglycemia. Glucose disposal rates (GDRs) were computed from the GIR and EGO. Fasting and steady-state glucose and insulin levels were comparable in the 3 groups of mice. No differences in fasting EGO were noted between the groups. GIR was significantly reduced (37%, P = 0.001) in the eNOS knockout (KO) mice compared with the WT mice, with values for the nNOS mice being intermediate. EGO was completely suppressed in the nNOS and WT mice during insulin infusion, but not in the eNOS mice. Even so, the eNOS mice displayed significantly reduced whole-body GDRs compared with those of the WT mice (82.67+/-10.77 vs. 103.67+/-3.47 mg x kg(-1) x min(-1), P = 0.03). eNOS KO mice are insulin resistant at the level of the liver and peripheral tissues, whereas the nNOS KO mice are insulin resistant only in the latter. These data indicate that NO plays a role in modulating insulin sensitivity and carbohydrate metabolism and that the eNOS isoform may play a dominant role relative to nNOS.     

Effect of isoflurane-induced hypotension on cerebral autoregulation in the anesthetized pig

The influence of isoflurane-induced hypotension on regional cerebral blood flow (rCBF) and cerebrovascular autoregulation was evaluated in 11 normocapnic pigs during anesthesia comprising fentanyl and nitrous oxide in oxygen. rCBF was determined as sagittal sinus outflow and recorded continuously by an electromagnetic technique. Regional cerebral metabolic rate for oxygen (rCMRO2) was calculated as rCBF multiplied by the arteriosagittal sinus oxygen content difference. Cerebral autoregulation was evaluated by two formal tests; blood pressure increase by infusion of angiotensin and blood pressure decrease by caval block. Light hypotension [mean arterial blood pressure (MABP) 94 +/- 3 mm Hg] and moderate hypotension (MABP 56 +/- 1 mm Hg) were achieved with the inspired concentrations of 1.7 +/- 0.2 and 2.7 +/- 0.2% isoflurane, respectively. rCBF was measured and the tests were performed before, during, and after isoflurane administration. Isoflurane produced no significant change in rCBF at either level of hypotension. At moderate hypotension the rCMRO2 was decreased by 40 +/- 6%. At both levels of hypotension, isoflurane produced a dose-dependent impairment of the auto-regulatory response to the angiotensin test as well as to the caval block. After hypotension, the autoregulatory response to increased blood pressure was restored within 15-25 min and to decreased blood pressures within 25-50 min.     

Inhibition of neuronal nitric oxide synthase reduces isoflurane MAC and motor activity even in nNOS knockout mice

Background. The glutamate–nitric oxide–cyclic GMPpathway has been identified as a potential target for volatileanaesthetic agents as acute inhibition of nitric oxide synthase(NOS) reduces the minimum alveolar concentration (MAC) in mostanimal studies. However, mice deficient in the type I NOS isoform(nNOS) are reported to have a similar MAC for isoflurane andare not affected by non-isoform specific inhibitors. Methods. We determined whether the nNOS specific inhibitor,7-nitroindazole (7-NI), had an effect on isoflurane MAC andrighting reflex (RRF) and investigated spontaneous motor activityin an open-field study in wild-type (WT) and knockout (KO) mice. Results. 7-NI reduced isoflurane MAC and RRF in both WT andKO animals (all P<0.04). 7-NI profoundly reduced spontaneousmotor activity in both the WT and KO animals in the open-fieldstudy as indicated by a reduction in the number of line crossingsand rearings in both WT and KO mice (both P<0.001). Conclusion. We conclude that isoform specific inhibition ofnNOS reduces MAC and spontaneous motor activity even in nNOSKO animals. Our results indicate that the NMDA receptor–nitricoxide–cyclic GMP pathway remains a credible target inmodulating the effects of isoflurane.     

Subanesthetic concentration of sevoflurane increases regional cerebral blood flow more, but regional cerebral blood volume less, than subanesthetic concentration of isoflurane in human volunteers.

Both sevoflurane and isoflurane are used in moderate concentrations in neuroanesthesia practice. The limiting factors for using higher concentrations of inhalational anesthetics in patients undergoing neurosurgery are the agents' effects on cerebral blood flow (CBF) and cerebral blood volume (CBV). In particular, an increase in CBV, which is a key determinant of intracranial pressure, may add to the neurosurgical patient's perioperative risk. To compare the effects of a subanesthetic concentration (0.4 minimum alveolar concentration) of sevoflurane or isoflurane on regional CBF (rCBF), regional CBV (rCBV) and regional mean transit time (rMTT), contrast-enhanced magnetic resonance imaging perfusion measurements were made in spontaneously breathing human volunteers. Absolute changes in rCBF, regional CBV, and rMTT during administration of either drug in regions of interest outlined bilaterally in white and grey matter were nonparametrically (Mann-Whitney test) analyzed. Sevoflurane increased rCBF in practically all regions (absolute change, 4.44 +/- 2.87 to 61.54 +/- 2.39 mL/100g per minute) more than isoflurane did (absolute change, 12.91 +/- 2.52 to 52.67 +/- 3.32 mL/100g per minute), which decreased frontal, parietal, and white matter rCBF (absolute change, -1.12 +/- 0.59 to -14.69 +/- 3.03 mL/100g per minute). Regional CBV was higher in most regions during isoflurane administration (absolute change, 0.75 +/- 0.03 to 4.92 +/- 0.16 mL/100g) than during sevoflurane administration (absolute change, 0.05 +/- 0.14 to 3.57 +/- 0.14 mL/100g). Regional mean transit time was decreased by sevoflurane (absolute change, -0.18 +/- 0.05 to -0.60 +/- 0.04 s) but increased by isoflurane (absolute change, 0.19 +/- 0.03 to 0.69 +/- 0.04 s). In summary, regional CBV was significantly lower during sevoflurane than during isoflurane administration, although sevoflurane increased rCBF more than isoflurane, which even decreased rCBF in some regions. For sevoflurane and, even more pronouncedly, for isoflurane, the observed changes in cerebral hemodynamics cannot be explained by vasodilatation alone.     

PI3K/Akt在深低温低流量脑保护中的作用

目的 观察PI3K/Akt在深低温低流量(DHLF)脑保护中的作用并探讨其机制.方法 Akt1+/-小鼠与野生型(WT)小鼠各48只分别随机并平均的分为假手术组与手术组.手术组在深低温下钳闭颈总动脉120 min并重新开放,模拟DHLF过程.各组脑血流经激光多普勒血流仪监测.经TUNEL和Western blot检测各组脑细胞凋亡及Akt下游bcl-2与bax的改变.结果 阻断颈总动脉后,小鼠脑血流量减少86%以上.野生型手术组死亡率在再灌注24h后约为15%,72h死亡率达到20%,而Akt1+/-小鼠死亡率增加,24h后约为25%,72 h达到40%(P<0.05).Akt1+/-脑细胞凋亡数量增多(P<0.01),Western blot显示Akt下游bcl-2与bax表达增强.结论 抑制Akt1后小鼠脑损害程度加重,PI3K/Akt通过抑制线粒体凋亡通路发挥作用.     

Effects of sevoflurane and isoflurane on systemic vascular resistance: use of cardiopulmonary bypass as a study model

We have examined the dose-related effects of sevoflurane and isoflurane on systemic vascular resistance (SVR) during cardiopulmonary bypass (CPB) in patients undergoing elective coronary artery surgery. Fifty- two patients were allocated randomly to one of six groups to receive 1.0, 2.0 or 3.0 vol% (inspiratory) sevoflurane or 0.6, 1.2 or 1.8 vol% isoflurane, or to a control group. During hypothermic (32-33 degrees C) non-pulsatile CPB, systemic vascular resistance index (SVRI) was recorded before administration of volatile anaesthetics and every 5 min for 20 min. Sevoflurane and isoflurane concentrations were measured next to the gas inlet port and at the gas outlet port of the oxygenator. Wash-in of sevoflurane occurred more rapidly than that of isoflurane, reaching a relatively steady state for both agents from the 10th to the 20th min. There was no significant change in SVRI in patients receiving 1.0 and 2.0 vol% sevoflurane, and 0.6 and 1.2 vol% isoflurane, compared with baseline values. However, 3 vol% sevoflurane decreased SVRI at 10, 15 and 20 min, and 1.8 vol% isoflurane decreased SVRI significantly at 15 and 20 min, whereas SVRI increased at 15 and 20 min in the control group. Thus during CPB, sevoflurane had similar vasodilator effects on SVRI as isoflurane.      

Feedback control of glomerular vascular tone in neuronal nitric oxide synthase knockout mice.

For further elucidation of the role of neuronal nitric oxide synthase (nNOS) in macula densa (MD) cells, experiments were performed in anesthetized nNOS knockout mice (nNOS -/-). At comparable levels of arterial BP, renal blood flow was not significantly different between nNOS +/+ and nNOS -/- (1.7 +/- 0.2 versus 1.4 +/- 0.1 ml/min), and autoregulation of renal blood flow was maintained to a pressure level of approximately 85 mmHg in both groups of mice (n = 6 in each group). The fall in proximal tubular stop-flow pressure in response to an increase in loop of Henle perfusion rate from 0 to 30 nl/min was comparable in nNOS +/+ and -/- mice (40.7 +/- 1.6 to 32 +/- 2 mmHg versus 40.6 +/- 1.6 to 31.6 +/- 2 mmHg; not significant; n = 13 versus 18 nephrons). Luminal application of the nonselective NOS inhibitor nitro-L-arginine (10(-3) and 10(-2) M) enhanced the perfusion-dependent fall in stop-flow pressure in nNOS +/+ (7 +/- 1 to 13 +/- 2 mmHg; P < 0.05) but not in nNOS -/- (7 +/- 1 to 8 +/- 1 mmHg; not significant) mice. nNOS -/- mice exhibited a lower nephron filtration rate, compared with nNOS +/+, during free-flow collections from early distal tubules (influence of MD intact, 7 +/- 0.7 versus 10.9 +/- 1 nl/min; P = 0.002) but not from late proximal tubule (influence of MD minimized, 10.1 +/- 1 versus 11.7 +/- 1 nl/min; not significant; n = 16 nephrons). Distal Cl concentration and fractional absorption of fluid or chloride up to the early distal tubule was not different between nNOS -/- and +/+ mice. The data indicate that nNOS in MD tonically attenuates the GFR-lowering influence of ambient luminal NaCl, which may serve to increase the fluid and electrolyte load to the distal tubule, consistent with a role of MD nNOS in tubuloglomerular feedback resetting.     

Role of neuronal nitric oxide synthase in the macula densa.

BACKGROUND: There is evidence that macula densa nitric oxide (NO) inhibits tubuloglomerular feedback (TGF). However, TGF response is not altered in mice deficient in neuronal nitric oxide synthase (nNOS) (-/-). Furthermore, nNOS expression in the macula densa is inversely related to salt intake, yet micropuncture studies have shown that NOS inhibition potentiates TGF in rats on high sodium intake but not in rats on a low-salt diet. These inconsistencies may be due to confounding systemic factors, such as changes in circulating renin. To further clarify the role of macula densa nNOS in TGF response, independent of systemic factors, we tested the hypothesis that (1) TGF response is inversely related to sodium intake, and (2) during low sodium intake, NO produced by macula densa nNOS tonically controls the basal diameter of the afferent arteriole (Af-Art). METHODS: Af-Arts and attached macula densas were simultaneously microperfused in vitro. TGF response was determined by measuring Af-Art diameter before and after increasing NaCl in the macula densa perfusate. TGF response was studied in wild-type (+/+) and nNOS knockout mice (-/-), as well as in juxtaglomerular apparatuses (JGAs) from rabbits fed a low-, normal-, or high-NaCl diet. RESULTS: TGF responses were similar in nNOS +/+ and -/- mice. However, in nNOS +/+ mice, 7-nitroindazole (7-NI) perfused into the macula densa significantly potentiated the TGF response (P = 0.001), while in nNOS -/- mice, this potentiation was absent. In rabbits on three different sodium diets, TGF responses were similar and were potentiated equally by 7-NI. However, in JGAs from rabbits on a low-NaCl diet, adding 7-NI to the macula densa while perfusing it with low-NaCl fluid caused Af-Art vasoconstriction, decreasing the diameter by 14% (from 21.7 +/- 1.3 to 18.6 +/- 1.5 microm; P < 0.001). This effect was not observed in JGAs from rabbits fed a normal- (19.0 +/- 0.5 vs. 19.3 +/- 0.8 microm after 7-NI) or high-NaCl diet (18.6 +/- 0.7 vs. 18.4 +/- 0.7 microm). CONCLUSIONS: First, in this in vitro preparation, chronic changes in macula densa nNOS do not play a major role in the regulation of TGF. Compensatory mechanisms may develop during chronic alteration of nNOS that keep TGF relatively constant. Second, nNOS regulates TGF response acutely. Third, the results obtained in the +/+ and -/- mice also confirm that the effect of 7-NI is due to inhibition of macula densa nNOS. Finally, during low sodium intake (without induction of TGF), the regulation of basal Af-Art resistance by macula densa nNOS suggests that NO in the macula densa helps maintain renal blood flow during the high renin secretion caused by low sodium intake.     

Attenuation of oxidative injury after induction of experimental intracerebral hemorrhage in heme oxygenase-2 knockout mice

OBJECT: Experimental evidence suggests that hemoglobin degradation products contribute to cellular injury after intracerebal hemorrhage (ICH). Hemoglobin breakdown is catalyzed in part by the heme oxygenase (HO) enzymes. In the present study, the authors tested the hypothesis that HO-2 gene deletion is cytoprotective in an experimental ICH model. METHODS: After anesthesia was induced with isoflurane, 3- to 6-month-old HO-2 knockout and wild-type mice were stereotactically injected with 15 microl autologous blood and a group of control mice were injected with an equal volume of sterile saline. Striatal protein and lipid oxidation were quantified 72 hours later using carbonyl and malondialdehyde assays. Cell viability was determined by performing a 3(4,5-dimethylthiazol-2-yl)2,5-diphenyltetrazolium bromide (MTT) assay. Following blood injection, the investigators found a 3.4-fold increase in protein carbonylation compared with that in the contralateral striatum in wild-type mice; in knockout mice, the investigators found a twofold increase. The mean malondialdehyde concentration in injected striata was increased twofold in wild-type mice at this time, compared with 1.5-fold in knockout mice. Cell viability, as determined by MTT reduction, was reduced in injected striata to 38 +/- 4% of that in the contralateral striata in wild-type mice, compared with 66 +/- 5% in HO-2 knockout mice. Baseline striatal HO-1 protein expression was similar in wild-type and HO-2 knockout mice, but was induced more rapidly in the former after blood injection. CONCLUSIONS: Deletion of HO-2 attenuates oxidative cell injury after whole-blood injection into the mouse striatum. Therapies that specifically target HO-2 may improve outcome after ICH.     

The role of endothelial nitric oxide synthase in the cerebral hemodynamics after controlled cortical impact injury in mice

Traumatic brain injury causes a reduction in cerebral blood flow, which may cause additional damage to the brain. The purpose of this study was to examine the role of nitric oxide produced by endothelial nitric oxide synthase (eNOS) in these vascular effects of trauma. To accomplish this, cerebral hemodynamics were monitored in mice deficient in eNOS and wild-type control mice that underwent lateral controlled cortical impact injury followed by administration of either L-arginine, 300 mg/kg, or saline at 5 min after the impact injury. The eNOS deficient mice had a greater reduction in laser Doppler flow (LDF) in the contused brain tissue at the impact site after injury, despite maintaining a higher blood pressure. L-Arginine administration increased LDF post-injury only in the wild-type mice. L-Arginine administration also resulted in a reduction in contusion volume, from 2.4 +/- 1.5 to 1.1 +/- 1.2 mm(3) in wild-type mice. Contusion volume in the eNOS deficient mice was not significantly altered by L-arginine administration. These differences in cerebral hemodynamics between the eNOS-deficient and the wild-type mice suggest an important role for nitric oxide produced by eNOS in the preservation of cerebral blood flow in contused brain following traumatic injury, and in the improvement in cerebral blood flow with L-arginine administration.     

Phenylephrine increases regional cerebral blood flow following hemorrhage during isoflurane-oxygen anesthesia

Using the radioactive microsphere technique regional cerebral blood flow (rCBF) and total CBF (tCBF) were examined in rats at three time periods: baseline (CBF1) during 1.5 MAC inspired isoflurane-oxygen anesthesia, CBF2; during 1.5 MAC inspired isoflurane anesthesia combined with hypotension induced by hemorrhage and CBF3; during isoflurane and hemorrhage plus phenylephrine infused to restore mean arterial pressure (MAP) to baseline. For CBF1 MAP was 89 +/- 3 mmHg (mean +/- SEM, n = 9) with PaCO2 44 +/- 1 mmHg. For CBF2 following graded hemorrhage MAP was 48 +/- 2 mmHg and PaCO2 43 +/- 1 mmHg. For CBF3 MAP was 93 +/- 2 and PaCO2 45 +/- 1 mmHg, following infusion of phenylephrine (PE) at 13.9 +/- 4.0 micrograms.kg-1.min-1. Total CBF1 was 1.84 +/- 0.18 ml.g-1.min-1, tCBF2 1.32 +/- 0.09 ml.g-1.min-1 (P less than 0.05 vs. tCBF1) and tCBF3 2.60 +/- 0.18 (P less than 0.05 vs. tCBF1 and 2). For tCBF3 hemoglobin concentration had decreased 23% from 14.2 +/- 0.2 g.100 ml-1 to 11.0 +/- 0.5 g.100 ml-1 (P less than 0.05). Regional CBF decreased significantly in seven of 12 regions examined from CBF1 to CBF2 and was significantly higher in all regions for CBF3. For CBF1-3 infratentorial blood flows (cerebellar and brain stem) were significantly higher than flows to the supratentorial structures (cerebral cortical and basal ganglia). During isoflurane anesthesia, phenylephrine infused to support MAP following hemorrhagic hypotension effectively maintains rCBF and tCBF. There is no indication that phenylephrine infused to increase MAP following hemorrhage results in cerebral vasoconstriction in rats anesthetized with isoflurane.     

Biphasic Effects of Isoflurane on the Cardiac Action Potential: An Ionic Basis for Anesthetic-induced Changes in Cardiac Electrophysiology

Background: The mechanism underlying isoflurane modulation of cardiac electrophysiology is not well understood. In the present study, the authors investigated the effects of isoflurane on the cardiac action potential (AP) characteristics. The results were correlated to modulation of the L-type calcium (ICa,L), the delayed-rectifier potassium (IKdr), and the inward-rectifier potassium (IKir) currents.

Methods: Single ventricular myocytes were enzymatically isolated from guinea pig hearts. The current clamp and whole cell voltage clamp configurations of the patch clamp technique were used to monitor the cardiac AP and ionic currents, respectively. A dynamic AP voltage protocol that mimicked changes in membrane potential during an AP was used to monitor the ICa,L, IKdr, and IKir.

Results: Isoflurane produced a concentration-dependent, biphasic effect on the AP duration (APD). At 0.6 mm (1.26 vol%), isoflurane significantly increased APD50 and APD90 by 50.0 +/- 7.6% and 48.9 +/- 7.2%, respectively (P < 0.05; n = 6). At 1.0 mm (2.09 vol%), isoflurane had no significant effect on APD (n = 6). In contrast, at 1.8 mm (3.77 vol%), isoflurane decreased APD50 and APD90 by 38.3 +/- 5.4% and 32.2 +/- 5.5%, respectively (P < 0.05; n = 7). The inhibitory effects of isoflurane on IKdr chord conductance were greater than those on ICa,L (P < 0.05; n = 6/group). Both ICa,L inactivation and IKdr activation kinetics were accelerated by isoflurane. Isoflurane had no significant effects on IKir chord conductance (n = 6).     

Isoflurane depresses electroencephalographic and medial thalamic responses to noxious stimulation via an indirect spinal action

Anesthetics such as isoflurane act in the spinal cord to suppress movement in response to noxious stimulation. Spinal anesthesia decreases hypnotic/sedative requirements, possibly by decreasing afferent transmission of stimuli. We hypothesized that isoflurane action in the spinal cord would similarly depress the ascending transmission of noxious input to the thalamus and cerebral cortex. In six isoflurane-anesthetized goats, we measured electroencephalographic (EEG) and thalamic single-unit responses to a clamp applied to the forelimb. Cranial bypass permitted differential isoflurane delivery to the torso and cranial circulations. When the cranial-torso isoflurane combination was 1.3% +/- 0.2%-1.0% +/- 0.4% the noxious stimulus did not evoke significant changes in the EEG or thalamic activity: 389 (153-544) to 581 (172-726) impulses/min, (median, 25th-75th percentile range, P: > 0.05). When the cranial-torso isoflurane combination was 1.3% +/- 0.2%-0.3% +/- 0.2%, noxious stimulation increased thalamic activity: 804 (366-1162) to 1124 (766-1865) impulses/min (P: < 0.05), and the EEG "desynchronized": total EEG power decreased from 25 +/- 20 microV(2) to 12 +/- 8 microV(2) (P: < 0.05). When the cranial-torso isoflurane was 1.7% +/- 0.1%-0.3% +/- 0.2%, the noxious stimulus did not significantly affect thalamic: 576 (187-738) to 1031 (340-1442) impulses/min (P: > 0.05), or EEG activity. The indirect torso effect of isoflurane on evoked EEG total power (12.6 +/- 2.7 microV(2)/vol%, mean +/- SE) was quantitatively similar to the direct cranial effect (17.7 +/- 3.0 microV(2)/vol%; P: > 0.05). These data suggest that isoflurane acts in the spinal cord to blunt the transmission of noxious inputs to the thalamus and cerebral cortex, and thus might indirectly contribute to anesthetic endpoints such as amnesia and unconsciousness. Implications: Isoflurane action in the spinal cord diminished the transmission of noxious input to the brain. Because memory and consciousness are likely dependent on the "arousal" state of the brain, this indirect action of isoflurane could contribute to anesthetic-induced amnesia and unconsciousness.     

Effect of low isoflurane concentrations on the ventilation-perfusion distribution in injured canine lungs

BACKGROUND: Rapid recovery and weaning from ventilatory support and cardiovascular stability are suggested advantages of isoflurane inhalation, in concentrations ranging from 0.1 to 0.6 vol%, for long-term sedation in mechanical ventilated patients. This study was designed to determine whether isoflurane in low concentrations impairs pulmonary gas exchange by increasing ventilation and perfusion (V(A)/Q) mismatch during lung injury. METHODS: Fourteen anesthetized dogs received in random order 0, 0.25, or 0.5 vol% end-tidal isoflurane before and after induction of lung injury with oleic acid. Gas exchange was assessed by blood gas analysis and by estimating the V(A)/Q distributions using the multiple inert gas elimination technique. RESULTS: Administration of oleic acid produced a lung injury with severe V(A)/Q mismatch and 38 +/- 4% intrapulmonary shunting of blood. During lung injury, isoflurane accounted for a dose-related increase in blood flow to shunt units from 38 +/- 4 to 42 +/- 3 (0.25 vol%) and 48 +/- 4% (0.5 vol%) (P < 0.05), dispersion pulmonary blood flow distribution from 0.94 +/- 0.07 to 1.01 +/- 0.09 (0.25 vol%) and 1.11 +/- 0.11% (0.5 vol%) (P < 0.05), and a decrease in perfusion of normal V(A)/Q units from 58 +/- 5 to 55 +/- 4 (0.25 vol%) and 50 +/- 4% (0.5 vol%) (P < 0.05) (mean +/- SE). Isoflurane decreased arterial oxygen partial pressure from 72 +/- 4 to 62 +/- 4 mmHg (0.25 vol%) and 56 +/- 4 mmHg (0.5 vol%) (P < 0.05) and oxygen delivery from 573 +/- 21 to 529 +/- 19 ml. kg. min (0.25 vol%) and 505 +/- 22 ml. kg. min (0.5 vol%) (P < 0.05). Gas exchange, perfusion of shunt and normal V(A)/Q units, and pulmonary blood flow distribution was similar in absence of lung injury with and without isoflurane. Isoflurane 0.5 vol% lowered cardiac output during all conditions (P < 0.05). CONCLUSIONS Inhalation of low concentrations of isoflurane contributed to increased V(A)/Q mismatch and decreased systemic blood flow and oxygen delivery in mechanically ventilated animals with injured lungs.     

Inhalation anesthetics induce apoptosis in normal peripheral lymphocytes in vitro.

BACKGROUND: The authors hypothesized that perioperative lymphocytopenia is partially caused by apoptosis of lymphocytes induced by inhalation anesthetics. Therefore, they evaluated whether sevoflurane and isoflurane induce apoptosis of normal peripheral lymphocytes. METHODS: Normal peripheral blood mononuclear cells were exposed to sevoflurane and isoflurane, and the percentages of apoptotic lymphocytes was measured by Annexin V-fluorescein isothiocyanate-7-amino actinomycin D flow cytometry after 24 h of exposure (0.5, 1.0, and 1.5 mm) and after 6, 12, and 24 h of exposure (1.5 mm). The percentages of lymphocytes with caspase 3-like activity were also measured after 24 h of exposure (1.5 mm). RESULTS: The percentages of apoptotic lymhocytes were increased in a dose-dependent manner (controls: 5.1 +/- 1.4%; sevoflurane: 7.3 +/- 1.3% [0.5 mm], 9.1 +/- 1.5% [1.0 mm], 12.6 +/- 2.1% [1.5 mm]; isoflurane: 7.5 +/- 1.6% [0.5 mm], 10.5 +/- 1.5% [1.0 mm], 16.3 +/- 2.7% [1.5 mm]) after 24 h of exposure and in a time-dependent manner (controls: 1.2 +/- 0.4% [6 h], 3.4 +/- 0.7% [12 h], 5.6 +/- 1.2% [24 h]; sevoflurane: 1.8 +/- 0.4% [6 h], 6.4 +/- 1.2% [12 h], 11.3 +/- 2.2% [24 h]; isoflurane: 2.6 +/- 0.5% [6 h], 8.8 +/- 1.5% [12 h],16.0 +/- 1.9% [24 h]) at the concentration of 1.5 mm. The percentages of lymphocytes with caspase 3-like activity were increased (controls: 10.0 +/- 1.1%; sevoflurane: 13.8 +/- 1.2%; isoflurane: 17.0 +/- 1.3%). CONCLUSIONS: Both sevoflurane and isoflurane induced apoptosis in peripheral lymphocytes in dose-dependent and time-dependent manners in vitro.     

Comparative Pharmacodynamic Modeling of the Electroencephalography-slowing Effect of Isoflurane, Sevoflurane, and Desflurane

Background: The most common measure to compare potencies of volatile anesthetics is minimum alveolar concentration (MAC), although this value describes only a single point on a quantal concentration-response curve and most likely reflects more the effects on the spinal cord rather than on the brain. To obtain more complete concentration-response curves for the cerebral effects of isoflurane, sevoflurane, and desflurane, the authors used the spectral edge frequency at the 95th percentile of the power spectrum (SEF95) as a measure of cerebral effect.

Methods: Thirty-nine patients were randomized to isoflurane, sevoflurane, or desflurane groups. After induction with propofol, intubation, and a waiting period, end-tidal anesthetic concentrations were randomly varied between 0.6 and 1.3 MAC, and the EEG was recorded continuously. Population pharmacodynamic modeling was performed using the software package NONMEM.

Results: The population mean EC50 values of the final model for SEF (95) suppression were 0.66 +/- 0.08 (+/- SE of estimate) vol% for isoflurane, 1.18 +/- 0.10 vol% for sevoflurane, and 3.48 +/- 0.66 vol% for desflurane. The slopes of the concentration-response curves were not significantly different; the common value was [Greek small letter lambda] = 0.86 +/- 0.06. The Ke0 value was significantly higher for desflurane (0.61 +/- 0.11 min-1), whereas separate values for isoflurane and sevoflurane yielded no better fit than the common value of 0.29 +/- 0.04 min (-1). When concentration data were converted into fractions of the respective MAC values, no significant difference of the C50 values for the three anesthetic agents was found.