Atsushi Kohjitani

Dexmedetomidine enhances the local anesthetic action of lidocaine via an α-2A adrenoceptor

BACKGROUND: Clonidine, an &agr;-2 adrenoceptor agonist, is a common adjunct in both central and peripheral blocks. Dexmedetomidine, a more selective &agr;-2 adrenoceptor agonist, is also known to enhance central neural blockades. Its peripheral effect, however, has not been fully elucidated. Thus, we evaluated the effect of dexmedetomidine and other &agr;-2 adrenoceptor agonists on the local anesthetic action of lidocaine at the periphery and explored the mechanism involved. METHODS: &agr;-2 Adrenoceptor agonists, including dexmedetomidine, clonidine, and oxymetazoline, combined with lidocaine were intracutaneously injected into the back of male guinea pigs. The test of six pinpricks was applied every 5 min until 60 min after the injection. The number of times which the prick failed to elicit a response during the 60-min period was added and the sum served as an anesthetic score indicating the degree of local anesthesia. Differences from the control value within the group were analyzed using an analysis of variance followed by a post hoc Dunnett’s test. Furthermore, we evaluated the antagonism of the effect of dexmedetomidine by yohimbine, an &agr;-2A, 2B, and 2C adrenoceptor antagonist, or prazosin, an &agr;-1, &agr;-2B, and 2C adrenoceptor antagonist, analyzed using a two-way analysis of variance. RESULTS: All &agr;-2 adrenoceptor agonists enhanced the degree of local anesthesia of lidocaine in a dose-dependent manner. Furthermore, yohimbine inhibited the effect of dexmedetomidine, whereas prazosin did not. CONCLUSION: We demonstrated that &agr;-2 adrenoceptor agonists enhanced the local anesthetic action of lidocaine, and suggest that dexmedetomidine acts via &agr;-2A adrenoceptors.

Role of the hyperpolarization-activated cation current (Ih) in pacemaker activity in area postrema neurons of rat brain slices

To clarify the functional properties of the hyperpolarization‐activated cation current (Ih) as a pacemaker current in area postrema neurons, whole‐cell recordings were made in visually identified cells in rat brain slices. The activation of Ih was identified in approximately 62 % of area postrema neurons tested. The cells displaying Ih showed a depolarizing ‘sag’ in responses to hyperpolarizing current injection in current‐clamp mode. The reversal potential for the Ih was −36 mV, and this was shown to depend on the external concentration of Na+ and K+ ions. Extracellular Cs+ ions (2 mM) and ZD7288 (100 μm), a potent selective Ih channel antagonist, blocked Ih and induced a membrane potential hyperpolarization, suggesting the sustained activation of Ih near the resting potential and a contribution from Ih to membrane potential maintenance at more depolarized levels. In contrast, extracellular Ba2+ ions caused a depolarization of the membrane potential, suggesting the blockade of inward rectifier K+ currents. ZD7288 decreased the spontaneous discharge rate by prolonging the slow depolarization between two spikes, with minimal effect on the amplitude of the afterhyperpolarization or action potential waveforms. Ih stabilized the latency of rebound action potentials. Ih was weakly activated by external 8‐bromoadenosine 3′,5′ cyclic monophosphate (1 mM) or forskolin (50‐100 μM), indicating that the Ih channel subtypes in area postrema cells could be modulated by intracellular cAMP. Our findings indicate that Ih contributes to the subthreshold membrane and firing properties of rat area postrema neurons and may regulate their resting membrane potential and firing patterns.

Ketamine and midazolam differentially inhibit nonadrenergic noncholinergic lower esophageal sphincter relaxation in rabbits: role of superoxide anion and nitric oxide synthase.

Background The authors previously reported that ketamine and midazolam inhibited nitric oxide-mediated nonadrenergic noncholinergic (NANC) lower esophageal sphincter (LES) relaxation via nitric oxide-3′,5′-cyclic guanosine monophosphate pathway modulation. The mechanisms inhibiting the NANC relaxation by ketamine and midazolam were investigated. Methods The isometric tension of circular distal esophageal muscle strips from Japanese White rabbits was examined. NANC relaxation was induced by KCl (30 mm) in the presence of atropine (3 × 10−6 m) and guanethidine (3 × 10−6 m). Nitric oxide synthase activity in the absence and presence of ketamine and midazolam was analyzed using the biochemical conversion of L-[3H]arginine to L-[3H]citrulline. Results The ketamine-induced inhibition of the NANC relaxation was partly reversed by superoxide dismutase (200, 400 U/ml) but not by catalase (100 U/ml). Ketamine concentration-dependently inhibited the relaxation induced by N-ethylethanamine:1,1-diethyl-2-hydroxy-2-nitrosohydrazine (diethylamine NONOate) and S-nitrosoglutathione. The NANC relaxation itself was not affected by superoxide dismutase. The midazolam-induced inhibition of the NANC relaxation was reversed neither by superoxide dismutase nor by catalase, and midazolam did not affect the relaxations induced by nitric oxide donors. The nitric oxide synthase activity was concentration-dependently suppressed by midazolam, but there was no marked effect of ketamine. Pyrogallol, a superoxide generator, inhibited the NANC and the diethylamine NONOate-induced relaxations. The pyrogallol-induced inhibition of the NANC relaxation was reversed by superoxide dismutase. Conclusion These findings suggest that ketamine inhibits NANC LES relaxation by the extracellular production of superoxide anion, and that midazolam inhibits it by the inhibition of nitric oxide synthase activity.

Cholesterol sulfate induces expression of the skin barrier protein filaggrin in normal human epidermal keratinocytes through induction of RORα.

Cholesterol sulfate is abundant in the human epidermis and is a putative natural ligand for retinoic acid receptor-related orphan receptor alpha (RORα). Although direct binding of cholesterol sulfate is expected to activate RORα, cholesterol sulfate can also induce RORα expression and increase RORα target gene expression. The purpose of this study was to determine whether cholesterol sulfate induces profilaggrin expression, a precursor of the barrier protein filaggrin in the epidermis, through activation of RORα by directly binding to RORα, or through increased RORα expression. Immunohistochemical and polymerase chain reaction (PCR) analyses showed that RORα was expressed in normal human epidermal keratinocytes (NHEKs) and that its expression increased during keratinocyte differentiation in parallel with that of profilaggrin and cholesterol sulfotransferase, which catalyzes the synthesis of cholesterol sulfate. Exogenous cholesterol sulfate significantly increased both RORα and profilaggrin expression in NHEKs, whereas no effect on profilaggrin expression was observed in cells in which RORα was knocked down with small interfering RNA (siRNA). Additionally, a luciferase reporter gene assay revealed that exogenous RORα dose-dependently increased the activity of the profilaggrin gene promoter even in the absence of cholesterol sulfate, and that this response involves activator protein-1. In conclusion, the results of this study indicate that cholesterol sulfate induces filaggrin expression through increased RORα expression. Further studies are required to fully elucidate the mechanisms involved.

Regulation of SULT2B1a (pregnenolone sulfotransferase) expression in rat C6 glioma cells: Relevance of AMPA receptor-mediated NO signaling

The neurosteroid pregnenolone sulfate (PREGS), which is synthesized in glial cells, plays a significant role in learning and memory performance. The aim of this study was to investigate the regulation of expression of the steroid sulfotransferase SULT2B1a, which catalyzes the conversion of pregnenolone to PREGS, using the rat C6 glioma cell line. Rat C6 glioma cells expressed the SULT2B1a isoform, which sulfonates pregnenolone, but, neither the SULT2B1b isoform, which catalyzes cholesterol, nor the prototypical steroid sulfotransferase SULT2A1 were expressed in these cells. Increasing concentrations of l-glutamic acid in the presence of cyclothiazide, which prevents AMPA receptor desensitization, attenuated SULT2B1a mRNA expression; however, neither NMDA nor kainic acid had a significant effect. Exposure to the synthetic glutamate analogue alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) in the presence of cyclothiazide also inhibited SULT2B1a expression. Attenuation of SULT2B1a expression by L-glutamic acid was reversed by the selective AMPA/kainate receptor antagonist 2,3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline (NBQX), and partially reversed by the specific neuronal nitric oxide synthase (NOS) inhibitor 7-nitroindazole (7-NI). Induction of inducible NOS by TNF-alpha in combination with lipopolysaccharide (LPS) dramatically attenuated SULT2B1a expression; this was partially reversed by the specific inducible NOS inhibitor N(6)-(1-iminoethyl)-L-lysine hydrochloride (L-NIL). Furthermore, exposure to exogenous NO donors inhibited SULT2B1a mRNA expression, and exposure to sodium nitroprusside, LPS/TNF-alpha and L-glutamic acid in combination with cyclothiazide increased the production of nitrite, a stable degradation product of NO. These findings suggest that expression of SULT2B1a, which catalyzes PREGS production, is inhibited by activation of excitatory amino acid receptors of the AMPA subtype, via facilitation of intracellular NO signaling.

Peripheral N-Methyl-D-Aspartate Receptors Modulate Nonadrenergic Noncholinergic Lower Esophageal Sphincter Relaxation in Rabbits

We investigated the role of peripheral N-methyl-d-aspartate (NMDA) receptors in the myenteric plexus in mediating nonadrenergic noncholinergic (NANC) nitrergic relaxation of the lower esophageal sphincter (LES). Isometric contraction of LES strips from Japanese White rabbits was measured. NANC relaxation was induced by KCl (30 mM) in the presence of atropine and guanethidine. The concentration of 3′,5′-cyclic guanosine monophosphate (cGMP) was measured using a radioimmunoassay. The muscle strips were exposed to diethyldithiocarbamic acid (DETCA; 3 mM) to inactivate Cu/Zn superoxide dismutase. MK801 (5-methyl-10,11-dihydroxy-5H-dibenzo(a,d)cyclohepten-5,10-imine) inhibited NANC relaxation in a concentration-dependent manner (EC50 = 1.5 × 10−5 M), accompanied by a decrease in cGMP production. NMDA induced a concentration-dependent relaxation, which was antagonized by MK801. NMDA stimulated cGMP production, which was inhibited by NG-nitro-l-arginine. Superoxide dismutase (100 U/mL) shifted the concentration-response relationship of MK801-mediated inhibition of NANC relaxation to the right (EC50 = 3.4 × 10−5 M), whereas catalase did not. Treatment with DETCA shifted the concentration-response relationships of pyrogallol-, ketamine- and MK801-mediated inhibition of NANC relaxation to the left. These findings suggest that the peripheral NMDA receptors mediate NANC smooth muscle relaxation, and modulate it, in part, through extracellular production of superoxide anions, thus eliminating the relaxant effect of endogenous nitric oxide.

Intravenous anesthetics inhibit nonadrenergic noncholinergic lower esophageal sphincter relaxation via nitric oxide-cyclic guanosine monophosphate pathway modulation in rabbits

BackgroundNonadrenergic noncholinergic (NANC) nerves have important roles in the regulation of the lower esophageal sphincter (LES) motility and function. The effects of thiopental, ketamine, and midazolam on NANC LES relaxation were investigated. MethodsThe isometric tension of circular muscle strips from Japanese White rabbits was examined. The NANC relaxation was induced by KCl (30 mm) in the presence of atropine (3 × 10−6 m) and guanethidine (3 × 10−6 m). The modifications of the NANC and sodium nitroprusside (SNP; 10−5 m)-induced relaxation by the anesthetics were examined. The content of 3′,5′-cyclic guanosine monophosphate (cGMP) was measured by radioimmunoassay. ResultsThe KCl-induced relaxation was abolished by pretreating with tetrodotoxin (10−6 m). The NANC relaxation was inhibited in the presence of NG-nitro-l-arginine (L-NNA; 3 × 10−5 m), methylene blue (10−6 m), apamin (10−7 m), and glibenclamide (10−5 m). The SNP-induced relaxation was inhibited by methylene blue but was not affected by tetrodotoxin, L-NNA, apamin, or glibenclamide. Ketamine (EC50 = 8.8 × 10−5 m) and midazolam (EC50 = 4.8 × 10−6 m) suppressed the NANC response in a concentration-dependent manner, leaving SNP-induced response unchanged. Thiopental altered neither of the relaxations. cGMP content was decreased in the presence of ketamine and midazolam. ConclusionThe NANC relaxation was mediated by nitric oxide and by low-conductance calcium- and adenosine triphosphate–sensitive potassium channels of smooth muscle. The modulation of the nitric oxide–cGMP pathway was related, at least in part, to the inhibitory actions of ketamine and midazolam on the NANC LES relaxation.

The relaxing effect of ketamine on isolated rabbit lower esophageal sphincter.

We used ketamine to investigate the effects and intracellular mechanisms of several anesthetics on strips of lower esophageal sphincter (LES) from rabbits.Ketamine induced dose-dependent relaxation of LES preparations. It increased the content of 3 prime,5 prime-cyclic adenosine monophosphate (cAMP) dose-dependently, but decreased that of 3 prime,5 prime-cyclic guanosine monophosphate (cGMP). Pretreatment with nicotinic acid, an inhibitor of adenylate cyclase, along with atropine to block neurogenic effects, antagonized ketamine-induced relaxation. Pretreatment with N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide dihydrochloride (H-89), a selective antagonist for cAMP-dependent protein kinase, similarly antagonized the relaxant effect of ketamine. Cholera toxin and dibutyryl cAMP induced LES relaxation. However, dibutyryl cGMP induced little LES relaxation, and pretreatment with NG-nitro-L-arginine or methylene blue did not alter the relaxant effect. Atropine, propranolol, phentolamine, vasoactive intestinal peptide (VIP) antagonist, and tetrodotoxin did not affect the ketamine-induced relaxation. This response, however, was potentiated in the presence of indomethacin or diphenhydramine. Ketamine-induced relaxation was inhibited in the presence of verapamil. These findings suggest that ketamine induces relaxation of LES, in part, by modulating the activity of adenylate cyclase and in part by inhibiting transmem-brane influx of Ca2+. (Anesth Analg 1997;84:433-7)

Sizes and depths of endotracheal tubes for cleft lip and palate children undergoing primary cheiloplasty and palatoplasty

Background:  Appropriate sizes (internal diameters) and insertion depths of uncuffed preformed endotracheal tubes in children with cleft lip and palate, who generally have delayed growth and development in early infancy have not been elucidated.

Inhalational conscious sedation with nitrous oxide enhances the cardiac parasympathetic component of heart rate variability

OBJECTIVE We investigated the effects of conscious sedation by 30% nitrous oxide inhalation on the cardiac autonomic nervous system in the absence or presence of music listening. STUDY DESIGN The power spectral analysis of heart rate variability (HRV) and cardiovascular parameters were measured in 26 healthy volunteers, who were divided into the control and N(2)O groups. RESULTS Nitrous oxide inhalation attenuated the increase in relative low frequency (LF) power in the control group, but relative high frequency (HF) power remained constant compared to a decreased value in the control group. Nitrous oxide inhibited the increase in the LF/HF ratio. These autonomic balance shifts were observed without hemodynamic changes. Additional music during sedation did not alter HRV variables. CONCLUSIONS Inhalational sedation with nitrous oxide shifted cardiac sympathetic-parasympathetic balance toward a parasympathetic dominance via the suppression of sympathetic activity. Music listening during sedation did not provide further relaxing effects.