Hirotsugu Okamoto

Production of 20-HETE and Its Role in Autoregulation of Cerebral Blood Flow

In the brain, pressure-induced myogenic constriction of cerebral arteriolar muscle contributes to autoregulation of cerebral blood flow (CBF). This study examined the role of 20-HETE in autoregulation of CBF in anesthetized rats. The expression of P-450 4A protein and mRNA was localized in isolated cerebral arteriolar muscle of rat by immunocytochemistry and in situ hybridization. The results of reverse transcriptase-polymerase chain reaction studies revealed that rat cerebral microvessels express cytochrome P-450 4A1, 4A2, 4A3, and 4A8 isoforms, some of which catalyze the formation of 20-HETE from arachidonic acid. Cerebral arterial microsomes incubated with [(14)C]arachidonic acid produced 20-HETE. An elevation in transmural pressure from 20 to 140 mm Hg increased 20-HETE concentration by 6-fold in cerebral arteries as measured by gas chromatography/mass spectrometry. In vivo, inhibition of vascular 20-HETE formation with N-methylsulfonyl-12, 12-dibromododec-11-enamide (DDMS), or its vasoconstrictor actions using 15-HETE or 20-hydroxyeicosa-6(Z),15(Z)-dienoic acid (20-HEDE), attenuated autoregulation of CBF to elevations of arterial pressure. In vitro application of DDMS, 15-HETE, or 20-HEDE eliminated pressure-induced constriction of rat middle cerebral arteries, and 20-HEDE and 15-HETE blocked the vasoconstriction action of 20-HETE. Taken together, these data suggest an important role for 20-HETE in the autoregulation of CBF.

Role of Inducible Nitric Oxide Synthase and Cyclooxygenase-2 in Endotoxin-Induced Cerebral Hyperemia

BACKGROUND AND PURPOSE Bacterial lipopolysaccharide (LPS), an endotoxin, has been reported to induce the expression of inducible isoforms of both nitric oxide synthase (iNOS) and cyclooxygenase (COX-2) in various cell types. LPS is also known to dilate systemic vasculature, including cerebral vessels. This study aimed to determine to what extent LPS induces iNOS and COX-2 expression in the brain and whether NO and/or cyclooxygenase metabolites derived from iNOS and/or COX-2 contribute to the LPS-induced cerebral hyperemia. METHODS Regional cerebral blood flow (rCBF) was measured by laser-Doppler flowmetry in halothane-anesthetized, artificially ventilated rats for 4 hours after intracerebroventricular administration of LPS. RESULTS LPS at doses of 0.01 mg/kg to 1 mg/kg caused dose-dependent, progressive increases in rCBF at 1 to 4 hours after administration. The increase in rCBF was attenuated by systemic administration of the selective iNOS inhibitor aminoguanidine (100 mg/kg IP) or the selective COX-2 inhibitor NS-398 (5 mg/kg IP), and it was abolished by preventing induction of these isoforms with dexamethasone (4 mg/kg IP). LPS significantly increased iNOS and COX-2 mRNA, iNOS protein, and iNOS and cyclooxygenase enzyme activity. The increases in iNOS and cyclooxygenase enzyme activity were eliminated by aminoguanidine and NS-398, respectively. Dexamethasone also prevented the increase in iNOS and cyclooxygenase activity. CONCLUSIONS These results indicate that induction of iNOS and COX-2 expression and the increased production of NO and vasodilator prostanoids in the brain contribute to the elevation in CBF after intracerebroventricular administration of LPS.

Neuronal system-dependent facilitation of tumor angiogenesis and tumor growth by calcitonin gene-related peptide

A neuropeptide, calcitonin gene-related peptide (CGRP), is widely distributed in neuronal systems and exhibits numerous biological activities. Using CGRP-knockout mice (CGRP−/−), we examined whether or not endogenous CGRP facilitates angiogenesis indispensable to tumor growth. CGRP increased tube formation by endothelial cells in vitro and enhanced sponge-induced angiogenesis in vivo. Tumor growth and tumor-associated angiogenesis in CGRP−/− implanted with Lewis lung carcinoma (LLC) cells were significantly reduced compared with those in wild-type (WT) mice. A CGRP antagonist, CGRP8-37 or denervation of sciatic nerves (L1–5) suppressed LLC growth in the sites of denervation compared with vehicle infusion or sham operation. CGRP precursor mRNA levels in the dorsal root ganglion in LLC-bearing WT were increased compared with those in non-LLC-bearing mice. This increase was abolished by denervation. The expression of VEGF in tumor stroma was down-regulated in CGRP−/−. These results indicate that endogenous CGRP facilitates tumor-associated angiogenesis and tumor growth and suggest that relevant CGRP may be derived from neuronal systems including primary sensory neurons and may become a therapeutic target for cancers.

General anesthesia for patients with Brugada syndrome. A report of six cases.

PurposeTo review six cases of Brugada syndrome presenting for insertion of a cardioverter-defibrillator under general anesthesia.Clinical featuresAll patients had a history of syncope, ST segment elevation in the right precordial lead of the electrocardiogram (ECG) which became prominent after a pilsicainide challenge test. Routine monitors, right precordial lead of the ECG and an external defibrillator were installed prior to anesthesia. We administered propofol/midazolam for induction, and propofol/sevoflurane combined with fentanyl for maintenance of anesthesia. Atropine and ephedrine were administered to decrease vagal tone. No ECG change or arrhythmia was observed perioperatively. After the successful implantation of the defibrillator, all patients were discharged without any adverse event.ConclusionBy avoiding agents or conditions that may exacerbate Brugada syndrome during anesthesia, we were able to manage the patients uneventfully for implantation of a cardioverter-defibrillator.ObjectifPasser en revue six cas de syndrome de Brugada admis pour l’insertion d’un défibrillateur à synchronisation automatique sous anesthésie générale.éléments cliniquesLes patients avaient des antécédents de syncope, d’élévation du segment ST dans la dérivation précordiale droite de l’électrocardiogramme (ECG) qui est devenu proéminent après le test de provocation à la pilsicaïnide. Les moniteurs réguliers, la dérivation précordiale droite de l’ECG et un défibrillateur externe ont été installés avant l’anesthésie. Un mélange de propofol/midazolam a été administré pour l’induction de l’anesthésie et de propofol/sévoflurane combiné à du fentanyl pour son maintien. De l’atropine et de l’éphédrine ont permis de diminuer le tonus vagal. Aucune modification de l’ECG, ni arythmie périopératoires n’ont été observées. Après l’implantation réussie du défibrillateur, tous les patients ont pu quitter l’hôpital sans complication.ConclusionEn évitant les médicaments ou les conditions qui pourraient exacerber le syndrome de Brugada pendant l’anesthésie, nous avons pu procéder sans incident à l’implantation d’un défibrillateur à synchronisation automatique.

Changes in end-tidal carbon dioxide tension following sodium bicarbonate administration: Correlation with cardiac output and haemoglobin concentration

An intravenous administration of sodium bicarbonate (NaHCO3) forms excess CO2, resulting in an immediate increase in end‐tidal carbon dioxide tension (PetCO2). We hypothesized that the time until PetCO2 reached a maximum, and the magnitude of the increase in PetCO2 are influenced by cardiac output and haemoglobin concentration, respectively. To test this hypothesis, we examined changes in PetCO2 following an intravenous administration of NaHCO3, at different levels of cardiac output and haemoglobin concentration. We administered 0.2 mmol · kg−1 of 8.4% NaHCO3 into the vena cava in 15 anesthetized dogs under mechanical ventilation of 20 breaths per min. Cardiac output was increased by dopamine infusion, and decreased by blood withdrawal under halothane anaesthesia. Haemoglobin concentrations were changed by haemodilution with hydroxyethyl starch. When control measurements were taken, time‐max (the time until the increase in PetCO2 reached a maximum) was 4 ± 0.2 breaths‐time, and ΔCO2‐max (the magnitude of the increase in PetCO2) was 0.90 ± 0.04 kPa (6.6 ± 0.3 mmHg). Cardiac output was inversely correlated with time‐max (r = 0.94, P<0.0001), while it revealed a poor correlation with ΔCO2‐max. Haemoglobin concentration showed a significant correlation with ΔCO2‐max (r = 0.736, P<0.005), but not with time‐max. We concluded that the time course and the magnitude of changes in PetCO2 following intravenous administration of NaHCO3 reflect changes in cardiac output and haemoglobin concentration, respectively.

Amelioration of hyperalgesia by kinin receptor antagonists or kininogen deficiency in chronic constriction nerve injury in rats

Abstract:Objective: The present study was designed to examine the involvement of bradykinin in thermal and mechanical hyperalgesia induced by chronic constriction nerve injury (CCI) using B1 and B2 receptor antagonists and mutant kininogen-deficient rats. Methods: Sprague-Dawley (SD) rats and Brown Norway (B/N-) rats given CCI treatment on day 0, were used as a model of neuropathic pain. Either a kinin B1 antagonist des-Arg9-[Leu8]-bradykinin or the receptor B2 antagonist HOE-140 was constantly infused into the left jugular vein of SD rats on days 15 to 22 after CCI. Vehicle-treated rats and sham-operated rats without nerve injury were also prepared as controls. In all rats, we observed pain behavior, and measured the latency period of paw withdrawal from the thermal stimuli and, with von Frey filaments, the mechanical pain threshold, before surgery and on days 14 and 22 after CCI. B/N-Katholiek rats, which congenitally lack plasma kininogen and release no kinin, were also tested for hyperalgesic parameters. Expression of kinin receptor mRNA in the dorsal root ganglia was detected by RT-PCR. Results: Most of the rats (88%)showed some pain behavior, which was reduced to 67% by a B1 antagonist and to 57% by a B2 antagonist infused between days 15 to 22. Thermal hyperalgesia was significantly reduced from 7.25 ± 0.41 sec (mean ± SEM) to 8.36 ± 0.41 sec in paw withdrawal latency on day 22 by a B1 antagonist and from 7.24 ± 0.19 sec to 8.23 ± 0.21 sec by a B2 antagonist (P < 0.05). Mechanical hyperalgesia was also ameliorated from 0.02 ± 0.007 g force to 0.16 ± 0.08 g force in pain threshold by a B1 antagonist and from 0.03 ± 0.007 g force to 0.10 ± 0.003 g force on day 22 by a B2 antagonist. Moreover, deficient B/N-Katholiek rats showed a low incidence of thermal and mechanical hyperalgesia on day 14. Expression of both B1 and B2 receptor mRNAs was detected in the lumbar dorsal ganglia ipsilateral to the site of the ner ve injury. Conclusion: These data suggests that kinin were at least partly involved in yielding nociceptor hypersensitivity up to day 14 after CCI. Bradykinin and its B1 and B2 receptors were involved in the maintenance of hyperalgesia.

Dexmedetomidine-induced cerebral hypoperfusion exacerbates ischemic brain injury in rats

PurposeDexmedetomidine has been used for purposes of anesthesia and sedation, and experimental studies have demonstrated its neuroprotective effects. However, it has also been shown that the constriction of cerebral vessels in response to high doses of dexmedetomidine decreases cerebral blood flow. We tested the hypothesis that dexmedetomidine-induced cerebral hypoperfusion exacerbates ischemic cerebral injury.MethodsThe effects of dexmedetomidine on cerebral blood flow and mean arterial blood pressure were studied first. Six rats received intravenous infusions of dexmedetomidine in doses ranging from 0.01 to 10 μg·kg−1·min−1. At the end of this phase of treatment, the alpha-2 adrenergic antagonist yohimbine was administered (3 mg·kg−1 ip). Cerebral blood flow and mean arterial blood pressure were recorded continuously. A second series of experiments was then performed using a rat model of transient middle cerebral artery occlusion. Forty-two rats received 1μg·kg−1·min−1 or 10 μg·kg−1·min−1 dexmedetomidine with or without pretreatment with either of the alpha-2 adrenergic antagonists yohimbine or rauwolscine. Five days after middle cerebral artery occlusion and reperfusion, the rat brains were removed and the infarct volumes were measured.ResultsIn the first protocol, increasing the dose of dexmedetomidine significantly decreased cerebral blood flow. Mean arterial blood pressure decreased to 79.9% relative to baseline with a dose of 0.01 μg·kg−1·min−1 dexmedetomidine, and increased to 119.9% relative to baseline with a dose of 10 μg·kg−1·min−1 dexmedetomidine. In the second protocol, the infarct volume in the control group was 9.5% of the total brain volume; the infarct volume increased to 11.3% in rats treated with 1 μg·kg−1·min−1 dexmedetomidine and the volume increased to 24.5% in rats treated with 10 μg·kg−1·min−1 dexmedetomidine. Pretreatment with an alpha-2 adrenergic antagonist, either yohimbine or rauwolscine, reduced the size of these high-dose dexmedetomidine-induced infarct volumes.ConclusionHypertension following the administration of high-dose dexmedetomidine is associated with cerebral hypoperfusion and the exacerbation of ischemic brain injury, possibly through alpha-2-induced cerebral vasoconstriction.

Isoflurane-induced Cerebral Hyperemia in Neuronal Nitric Oxide Synthase Gene Deficient Mice

Background: Nitric oxide (NO) has been reported to play an important role in isoflurane‐induced cerebral hyperemia in vivo. In the brain, there are two constitutive isoforms of NO synthase (NOS), endothelial NOS (eNOS), and neuronal NOS (nNOS). Recently, the mutant mouse deficient in nNOS gene expression (nNOS knockout) has been developed. The present study was designed to examine the role of the two constitutive NOS isoforms in cerebral blood flow (CBF) response to isoflurane using this nNOS knockout mouse. Methods: Regional CBF (rCBF) in the cerebral cortex was measured with laser‐Doppler flowmetry in wild‐type mice (129/SV or C57BL/6) and nNOS knockout mice during stepwise increases in the inspired concentration of isoflurane from 0.6 vol% to 1.2, 1.8, and 2.4 vol%. Subsequently, a NOS inhibitor, Nomega ‐nitro‐L‐arginine (L‐NNA), was administered intravenously (20 mg/kg), and 45 min later, the rCBF response to isoflurane was tested again. In separate groups of wild‐type mice and the knockout mice, the inactive enantiomer, Nomega ‐nitro‐D‐arginine (D‐NNA) was administered intravenously in place of L‐NNA. Brain NOS activity was measured with radio‐labeled L‐arginine to L‐citrulline conversion after treatment with L‐NNA and D‐NNA. Results: Isoflurane produced dose‐dependent increases in rCBF by 25 +/‐ 3%, 74 +/‐ 10%, and 108 +/‐ 14% (SEM) in 129/SV mice and by 32 +/‐ 2%, 71 +/‐ 3%, and 96 +/‐ 7% in C57BL/6 mice at 1.2, 1.8, and 2.4 vol%, respectively. These increases were attenuated at every anesthetic concentration by L‐NNA but not by D‐NNA. Brain NOS activity was decreased by 92 +/‐ 2% with L‐NNA compared with D‐NNA. In nNOS knockout mice, isoflurane increased rCBF by 67 +/‐ 8%, 88 +/‐ 12%, and 112 +/‐ 18% at 1.2, 1.8, and 2.4 vol%, respectively. The increase in rCBF at 1.2 vol% was significantly greater in the nNOS knockout mice than that in the wild‐type mice. Administration of L‐NNA in the knockout mice attenuated the rCBF response to isoflurane at 1.2 and 1.8 vol% but had no effect on the response at 2.4 vol%. Conclusions: In nNOS knockout mice, the cerebral hyperemic response to isoflurane is preserved by compensatory mechanism(s) that is NO‐independent at 2.4 vol%, although it may involve eNOS at 1.2 and 1.8 vol%. It is suggested that in wild‐type mice, eNOS and nNOS contribute to isoflurane‐induced increase in rCBF. At lower concentrations (1.2 and 1.8 vol%), eNOS may be involved, whereas at 2.4 vol%, nNOS may be involved.

Surgical management of severe scoliosis with high risk pulmonary dysfunction in Duchenne muscular dystrophy: patient function, quality of life and satisfaction

In a previous study, the authors reported the clinical and radiological results of Duchenne muscular dystrophy (DMD) scoliosis surgery in 14 patients with a low FVC of <30%. The purpose of this study was to determine if surgery improved function and QOL in these patients. Furthermore, the authors assessed the patients’ and parents’ satisfaction. %FVC increased in all patients after preoperative inspiratory muscle training. Scoliosis surgery in this group of patients presented no increased risk of major complications. All-screw constructions and fusion offered the ability to correct spinal deformity in the coronal and pelvic obliquity initially, intermediate and long-term. All patients were encouraged to continue inspiratory muscle training after surgery. The mean rate of %FVC decline after surgery was 3.6% per year. Most patients and parents believed scoliosis surgery improved their function, sitting balance and quality of life even though patients were at high risk for major complications. Their satisfaction was also high.

L-Arginine Attenuates Ketamine-induced Increase in Renal Sympathetic Nerve Activity

BackgroundIt has been reported that ketamine produces sympathoexcitation by directly stimulating the central nervous system. It also has been shown that nitric oxide (NO) may play a role in signal transduction of the nervous system. Therefore, we hypothesized that the sympathoexcitation of ketamine may be linked to central NO formation. To test this hypothesis, we examined the effects of L-arginine, a substrate of NO formation, on renal sympathetic nerve activity (RSNA) during ketamine anesthesia. MethodsUsing 45 rabbits given basal anesthesia with α-chloralose, we measured changes in heart rate, mean arterial pressure, and RSNA in response to intravenous ketamine (1 mg/kg) and investigated the effect of intravenous L-arginine and D-arginine (bolus 30 mg/kg followed by continuous 30 mg · kg-1 · min-1). The animals were divided into intact, sinoaortic- and vagal-deafferented, and spinal cord-transected groups. ResultsKetamine caused significant increases in RSNA (172 ± 16%), heart rate (12 ± 2 beats/min), and mean arterial pressure (8 ± 1 mmHg) in the intact rabbits. Ketamine also increased RSNA in sinoaortic- and vagal-deafferented rabbits, but not in spinal cord-transected rabbits. L-Arginine attenuated the ketamine-induced Increase in RSNA in intact and deafferented rabbits, whereas D-arginine had no effect on RSNA. In addition, NG-nitro-L-arginine methyl ester, a NO synthase inhibitor, increased RSNA and the increase was attenuated by L-arginine. ConclusionsKetamine may act centrally to increase sympathetic outflow, and the sympathoexcitation may be attenuated by increasing NO formation with L-arginine in the central nervous system.