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T Obata

Publications and source records attributed to T Obata.

At least 55 records · Page 3Linked to original sources
PubMed2000

Reserpine attenuates interstitial adenosine-mediated activation of ecto-5'-nucleotidase in rat hearts in vivo.

We examined whether reserpine-induced norepinephrine (NE) depletion attenuated the products of adenosine in rat heart. A flexibly mounted microdialysis technique was used to measure the concentration of interstitial adenosine and to assess the activity of ecto-5'-nucleotidase in rat hearts in situ. The microdialysis probe was implanted in the left ventricular myocardium of anesthetized rats and perfused with Tyrode solution containing adenosine 5'-monophosphate (AMP) at rate of 1.0 microliter/min. The baseline level of dialysate adenosine was 0.51 +/- 0.09 microM. The introduction of AMP (100 microM) through the probe increased markedly the dialysate adenosine to 8.95 +/- 0.86 microM, and this increase was inhibited by ecto-5'-nucleotidase inhibitor, alpha, beta-methyleneadenosine 5'-diphosphate (AOPCP, 100 microM), to 0.66 +/- 0.38 microM. Thus, the level of dialysate adenosine is a measure of the ecto-5'-nucleotidase activity in the tissue in situ. AMP concentration for the half-maximal effect of adenosine release (EC(50)) was 107.3 microM. The maximum attainable concentration of dialysate adenosine (E(max)) by AMP was 21.1 microM. However, the EC(50) and E(max) values with reserpinized animals were 106.9 and 7.1 microM, respectively. Electrical stimulation of the left stellate ganglion increased significantly dialysate adenosine concentration, from the control level of 8.66 +/- 0.96 microM to 12.38 +/- 1.11 microM. After stimulation, dialysate adenosine returned to near the prestimulation level. When corresponding experiments were performed with reserpinized animals, the effect of electrical stimulation was abolished. Tyramine (endogenous catecholamine trigger) increased the adenosine concentration in a concentration-dependent manner. However, the elevation of adenosine concentration with reserpinized animals was not observed. These results suggest that reserpine attenuates NE-induced adenosine via stimulation of alpha(1)-adrenoceptor and protein kinase C mediated activation of ecto-5'-nucleotidase in rat heart.

5'-Nucleotidase↗
PubMed2000

Potassium chloride depolarization enhances MPP+-induced hydroxyl radical generation in the rat striatum.

We determined that extracellular potassium ion concentration, [K+]o-induced depolarization, enhances 1-methyl-4-phenylpyridinium ion (MPP+)-induced hydroxyl radical (*OH) generation in the rat striatum. Rats were anesthetized, and sodium salicylate in Ringer's solution (0.5 nmol/microl/min) was infused through a microdialysis probe to detect the generation of *OH as reflected by the non-enzymatic formation of 2,3-dihydroxybenzoic acid (DHBA) in the striatum. Induction of high concentration KCl (70 mM) drastically increased formation of *OH trapped as DHBA by the action of MPP+. When dopamine (DA) was administered to the high KCl-treated animals, a marked elevation of DHBA was observed, compared with MPP+-only-treated animals, that showed a positive linear correlation between DA and *OH formation trapped as DHBA (R2 = 0.979) in the dialysate. When corresponding experiments were performed with iron (II), the same results were obtained: a positive linear correlation between the release of iron (II) and DHBA (R2 = 0.988) in the dialysate. These results suggest that [K+]o-induced depolarization enhances the formation of *OH products of efflux/oxidation due to MPP+.

1-Methyl-4-phenylpyridinium↗
PubMed2000

An increase of the native interstitial adenosine concentration during histidine application.

We examined whether histidine can increase the production of interstitial adenosine via noradrenaline (NA) release-mediated activation of ecto-5'-nucleotidase in the ventricular myocardium, with use of microdialysis techniques in in situ rat hearts. The microdialysis probe was implanted in the left ventricular myocardium of anesthetized rat hearts and the tissue was perfused with Tyrode's solution containing adenosine 5'-monophosphate (AMP) through the dialysis probe at a rate of 1.0 microl/min. Adenosine in the dialysate collected during perfusion with Tyrode's solution containing 100 microM AMP (through the probe) originated from the hydrolysis of AMP catalyzed by endogenous ecto-5'-nucleotidase, so that the level of adenosine reflected the activity of ecto-5'-nucleotidase in this tissue. In the presence of NA (10 microM), histidine, a scavenger of highly active singlet oxygen (1O2), significantly increased concentration of adenosine. Histidine (5-50 mM) increased the level of AMP-primed dialysate adenosine in a concentration-dependent manner. When histidine (25 mM) was infused to rat myocardium, small increase in the levels of adenosine were observed. However, when corresponding experiments were performed with NA (10 microM)-pretreated animals, a marked elevation of the level of adenosine in rat heart dialysate was obtained. To confirm the possible mechanism of interaction between 1O2 and NA, we examined the effect of histidine in ischemic-reperfused rat hearts. In the presence of histidine (25 mM), a marked elevation of NA and adenosine was observed. However, when corresponding experiments were performed with reserpinized rat hearts, the elevation of both NA and adenosine was not observed in ischemia-reperfused rat hearts. These results indicate that histidine increases interstitial adenosine concentration via NA release-mediated activation of ecto-5'-nucleotidase.

5'-Nucleotidase↗
PubMed2000

Nicorandil increases adenosine 5'-monophosphate-primed interstitial adenosine via activation of ecto-5'-nucleotidase in rat hearts.

With the use of microdialysis techniques, we examined the effects of nicorandil, a hybrid of an ATP-sensitive K+ (K ATP) channel opener and a nitrate compound, on the production of interstitial adenosine in rat hearts in situ. The level of dialysate adenosine measured under a constant supply of adenosine 5'-monophosphate (AMP) reflected the activity of endogenous ecto-5'-nucleotidase. Nicorandil (0.3-3mM) increased the level of AMP (100 microM)-primed dialysate adenosine in a concentration-dependent manner, and this effect was completely abolished by the guanylate cyclase inhibitor, methylene blue (100 microM), but not by the K ATP channel blocker, glibenclamide (10 microM). Another K ATP channel opener, cromakalim (0.1-1mM), did not increase the production of AMP-primed dialysate adenosine. These results suggest that nicorandil increases the level of interstitial adenosine via cyclic guanosine monophosphate-mediated activation of ecto-5'-nucleotidase.

5'-Nucleotidase↗
PubMed2000

MR in vivo imaging of oxygen suppression effect of soft contact lens on the human cornea.

The O(2) suppression effect of a soft contact lens on the human cornea was measured using dynamic magnetic resonance imaging (MRI) of the anterior chamber transcorneally exposed to O(2). Dynamic T(1)-weighted fast spin echo imaging of anterior chambers (TR = 2 s, TE = 15 ms, 5-mm slice) was performed both before and during oxygen supply to a full goggle placed on the face of volunteers wearing a soft contact lens on one eye and nothing on the other eye as a control. Within 15 min after O(2) administration, significantly lower intensity changes were obtained in the anterior chambers of the eyes with the contact lens than in those of the eyes without one, suggesting that dynamic MRI of the anterior chamber transcorneally exposed to O(2) can be used to evaluate the O(2) suppression effect of a soft contact lens on the cornea.

Anterior Chamber↗
PubMed2000

The protooncogene TCL1 is an Akt kinase coactivator.

Human T cell prolymphocytic leukemia can result from chromosomal translocations involving 14q32.1 or Xq28 regions. The regions encode a family of protooncogenes (TCL1, MTCP1, and TCL1b) of unknown function. In yeast two-hybrid screening, we found that TCL1 interacts with Akt. All TCL1 isoforms bind to the Akt pleckstrin homology domain. Both in vitro and in vivo TCL1 increases Akt kinase activity and as a consequence enhances substrate phosphorylation. In vivo, TCL1 stabilizes the mitochondrial transmembrane potential and enhances cell proliferation and survival. In vivo, TCL1 forms trimers, which associate with Akt. TCL1 facilitates the oligomerization and activation of Akt. Our data show that TCL1 is a novel Akt kinase coactivator, which promotes Akt-induced cell survival and proliferation.

Animals↗
PubMed2000

Seizure frequency and bilateral temporal abnormalities: a proton magnetic resonance spectroscopy of temporal lobe epilepsy.

Proton magnetic resonance spectroscopy ((1)H-MRS) was performed in seven healthy volunteers and 17 patients with temporal lobe epilepsy (TLE) to clarify the correlation of the severity of epilepsy with bilateral temporal changes in N-acetylaspartate (NAA), choline-containing compounds (Cho) and creatine + phosphocreatine (Cr). Despite unilateral EEG focus, bilateral temporal reduction in NAA /(Cho + Cr) was revealed in patients with intractable seizures. The potential for seizure generation correlated with the NAA /(Cho + Cr) reduction not only on the ipsilateral side but also on the contralateral side. Proton MRS proved to be a useful measurement for obtaining important information about the neuronal changes as well as the lateralization of the epileptogenic focus in TLE patients.

Adult↗
PubMed2000

MAP kinase pathways activated by stress: the p38 MAPK pathway.

A stress-activated serine/threonine protein kinase, p38 mitogen-activated protein kinase (p38 MAPK), belongs to the MAP kinase superfamily. Diverse extracellular stimuli, including ultraviolet light, irradiation, heat shock, high osmotic stress, proinflammatory cytokines and certain mitogens, trigger a stress-regulated protein kinase cascade culminating in activation of p38 MAPK through phosphorylation on a TGY motif within the kinase activation loop. p38 MAPK appears to play a major role in apoptosis, cytokine production, transcriptional regulation, and cytoskeletal reorganization, and has been causally implicated in sepsis, ischemic heart disease, arthritis, human immunodeficiency virus infection, and Alzheimer's disease. The availability of specific inhibitors helps to clarify the role that p38 MAPK plays in these processes, and may ultimately offer therapeutic benefit for certain critically ill patients.

Apoptosis↗
PubMed2000

Fluvastatin, a new inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase, resists hydroxyl radical generation in the rat myocardium.

The aim of this study was to determine whether fluvastatin, an inhibitor of low-density lipoprotein (LDL) oxidation, can resist Cu (II)-induced hydroxyl radical generation (*OH) in the extracellular fluid of rat myocardium. Rats were anaesthetized and sodium salicylate in Ringer's solution (0.5 nmol microL(-1) min(-1)) was infused through a microdialysis probe to detect the generation of *OH as reflected by the non-enzymatic formation of 2,3-dihydroxybenzoic acid (2,3-DHBA) in the myocardium. When Cu (II) (0, 10, 25 or 50 microM) was administered to 1 mM tyramine-pretreated rats, a marked elevation in the levels of 2,3-DHBA was found, indicating a positive linear correlation between Cu (II) and the increase in *OH formation trapped as 2,3-DHBA in the dialysate (r2 = 0.977). In the presence of fluvastatin (100 microM), a marked decrease in the levels of 2,3-DHBA was found. Corresponding experiments performed with iron (II) (0, 10, 25 or 50 microM), showed a marked elevation in the levels of 2,3-DHBA, indicating a positive linear correlation between iron (II) and the increase in *OH formation trapped as 2,3-DHBA in the dialysate (r2 = 0.986). However, in the presence of fluvastatin (100 microM) a small decrease in the level of 2,3-DHBA was found. The results show that iron (II) against LDL oxidation may be insensitive compared with Cu (II). Cu (II)-induced *OH formation may be reduced by inhibiting LDL with fluvastatin.

Animals↗
PubMed2000

[Polyarthralgia as the initial manifestation of isolated ACTH deficiency].

A 57-year-old man, employed as a taxi driver, noticed arthralgia of his fingers beginning in May 1999. He was unable to work due to the arthralgia and the accompanying general malaise and anorexia, and was thus admitted to a local hospital in July 1999. Since a diagnosis of rheumatic disease was suspected due to elevated inflammatory reactions and joint symptoms, he was referred to our hospital in September 1999. Although no joint swelling was observed, severe tenderness was present in both the fingers and wrists. His grasping power had decreased markedly and fever was intermittently observed. All autoantibodies aside from antinuclear antibody were negative. Given that hyponatremia (126 mEq/l) and fasting hypoglycemia were demonstrated, an endocrinological examination, in particular for hypopituitary-adrenal function, was performed. Both plasma and urinary cortisol concentrations were very low, and an associated low concentration of plasma ACTH (6.0 pg/ml) was noted. The ACTH circadian rhythm was absent and there was no response to the administration of corticotropin releasing hormone. All other pituitary hormones were secreted at normal levels and brain MRI revealed a normal appearance of a pituitary gland. Based on these findings, the patient was diagnosed as having isolated ACTH deficiency. Arthralgia and general malaise both improved soon after replacement of glucocorticoid, and CRP levels were normalized. Isolated ACTH deficiency should be considered in the differential diagnosis of patients suffering from polyarthralgia, given that fever and increased inflammatory reactions occasionally develop and that rheumatic symptoms are also present, as in the present case.

Adrenocorticotropic Hormone↗
PubMed1999

Protective effect of imidaprilat, an angiotensin-converting enzyme inhibitor on *OH generation in rat myocardium.

We used a flexibly mounted microdialysis technique to the hearts of rats and examined the protective effect of imidaprilat, an angiotensin-converting enzyme (ACE) inhibitor, on the production of hydroxyl free radical (*OH) generation. A microdialysis probe was implanted into the left ventricular myocardium, and dialysate norepinephrine (NE) concentrations were measured as an index of myocardial interstitial NE levels. Sodium salicylate in Ringer's solution (0.5 nmol/microl/min) was directly infused through a microdialysis probe to detect the generation of *OH reflected by the formation of dihydroxybenzoic acid (DHBA) in rat myocardium. When tyramine (1 mM) was directly infused through the microdialysis probe, the level of NE significantly increased in the dialysate and the level of NE increased by 128 +/- 43%. Imidaprilat (5, 25 and 50 microM) decreased the level of tyramine (1 mM)-induced NE in a concentration-dependent manner. Tyramine clearly produced an increase in *OH formation. In the presence of imidaprilat (50 microM), tyramine failed to increase both 2,3- and 2,5-dihydroxylation. Therefore, the effects of imidaprilat on the *OH generation in the sympathetic nerve blockaded hearts by reserpine treatment were not observed. Moreover, to examine the effect of imidaprilat on *OH formation by ischemia/reperfusion of the myocardium, the heart was subjected to myocardial ischemia for 15 min by occlusion of the left anterior descending coronary artery. When the heart was reperfused, elevation of NE and 2,3- and 2,5-DHBA in imidaprilat (50 microM)-pretreated animals was not observed in the heart dialysate. Imidaprilat 2.5 mg/kg i.p. pretreatment at 5 h before coronary occlusion significantly blunted the rise of serum creatine phosphokinase and improved the electrocardiogram 2 h after coronary occlusion. These results suggest that imidaprilat, an ACE inhibitor, is associated with cardioprotective effect due to the suppression of NE-induced *OH generation.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1999

Expression of a dominant negative SHP-2 in transgenic mice induces insulin resistance.

To elucidate the roles of SHP-2, we generated transgenic (Tg) mice expressing a dominant negative mutant lacking protein tyrosine phosphatase domain (DeltaPTP). On examining two lines of Tg mice identified by Southern blot, the transgene product was expressed in skeletal muscle, liver, and adipose tissues, and insulin-induced association of insulin receptor substrate 1 with endogenous SHP-2 was inhibited, confirming that DeltaPTP has a dominant negative property. The intraperitoneal glucose loading test demonstrated an increase in blood glucose levels in Tg mice. Plasma insulin levels in Tg mice after 4 h fasting were 3 times greater with comparable blood glucose levels. To estimate insulin sensitivity by a constant glucose, insulin, and somatostatin infusion, steady state blood glucose levels were higher, suggesting the presence of insulin resistance. Furthermore, we observed the impairment of insulin-stimulated glucose uptake in muscle and adipocytes in the presence of physiological concentrations of insulin. Moreover, tyrosine phosphorylation of insulin receptor substrate-1 and stimulation of phosphatidylinositol 3-kinase and Akt kinase activities by insulin were attenuated in muscle and liver. These results indicate that the inhibition of endogenous SHP-2 function by the overexpression of a dominant negative mutant may lead to impaired insulin sensitivity of glucose metabolism, and thus SHP-2 may function to modulate insulin signaling in target tissues.

Animals↗
PubMed1999

Prazosin attenuates hydroxyl radical generation in the rat myocardium.

The present study examined whether tyramine-induced hydroxyl radical (*OH) generation via noradrenaline release was attenuated by prazosin. A flexibly mounted microdialysis technique was used to detect the generation of *OH in in vivo rat hearts. The microdialysis probe was implanted in the left ventricular myocardium of anaesthetized rats and Ringer's solution was used. To measure the level of *OH, sodium salicylate in Ringer's solution (0.5 nmol/microl/min) was infused directly through a microdialysis probe to detect the generation of *OH as reflected by the nonenzymatic formation of 2,3-dihydroxybenzoic acid (DHBA). Tyramine (0.1, 0.5 and 1.0 mM) increased the level of 2,3-DHBA in a concentration-dependent manner. However, in the presence of prazosin (10 microM), the effect of tyramine was abolished. To confirm the generation of *OH by a Fenton type reaction, iron (II) was infused through a microdialysis probe. A positive linear correlation between iron (II) and the formation of 2,3-DHBA (R2 = 0.982) was observed. To examine the effect of prazosin on ischemic/reperfused rat myocardium, the heart was subjected to myocardial ischemia for 15 min by occlusion of the left anterior descending coronary artery. When the heart was reperfused, a marked elevation of the level of 2,3-DHBA was observed. However, in the presence of prazosin (10 microM), the elevation of 2,3-DHBA was not observed in ischemic/reperfused rat heart. Prazosin was shown to have a *OH scavenging effect. These results suggest that tyramine-induced noradrenaline causes *OH generation, an effect which is inhibited by prazosin as Na+ channel blocker, but not through its alpha1-adrenoceptor antagonistic action of prazosin.

Adrenergic alpha-Agonists↗
PubMed1999

Simultaneous assay of prostaglandins and thromboxane in the cerebrospinal fluid by gas chromatography-mass spectrometry-selected ion monitoring.

A method of simultaneous analysis of prostaglandins (PGs) and thromboxane (TX) B2 in cerebrospinal fluid (CSF) with GC-MS-SIM was established. Deuterated PGs and TXB2 were used as internal standards: tetra-deuterated PGE2 (d4-PGE2) for PGE2, PGE1 and PGD2; d5-PGF2alpha for PGF2alpha and 9alpha,11beta-PGF2 and 8-epi PGF2alpha; d4-TXB2 for TXB2; and d4-6-keto PGF1alpha for 6-keto PGF1alpha. The PGs and TXB2 were derivatized to the methyl ester of the methoxim dimethyisopropylsilyl (DMiPSi) ether form or the methyl ester of the DMiPSi ether form with simultaneous preparation. Samples were extracted with octadecyl silica gel and purified in two steps with silisic acid gel chromatography between derivatization steps. The calibration curve of each PG and TXB2 was linear from 10 pg to 10 ng with the isotope dilution method. The levels of the seven types of PG and of TXB2 were assayed simultaneously in the cerebrospinal fluid (CSF) from patients with aseptic meningitis. The CSF pattern of the PG and TXB2 concentrations in mumps meningitis differed from those in other types of aseptic meningitis and in disease controls.

Calibration↗
PubMed1999

Protective effect of imidaprilat, a new angiotensin-converting enzyme inhibitor against 1-methyl-4-phenylpyridinium ion-induced *OH generation in rat striatum.

We examined the antioxidant effects of angiotensin-converting enzyme inhibitor on 1-methyl-4-phenylpyridinium ion (MPP+)-induced hydroxyl radical (*OH) formation in extracellular fluid of rat striatum. Rats were anesthetized and sodium salicylate in Ringer's solution (0.5 nmol microl(-1) min(-1) was infused through a microdialysis probe to detect the generation of *OH, as reflected by the non-enzymatic formation of 2,3-dihydroxybenzoic acid (DHBA) in the striatum. MPP+ clearly produced an increase in *OH formation in a concentration-dependent manner. When imidaprilat was infused in MPP+ -pre-treated animals, the formation of dopamine and 2,3-DHBA significantly decreased, as compared with that in the MPP+ -only-treated group. We compared the ability of two non-SH-containing angiotensin-converting enzyme inhibitors (imidaprilat and enalaprilat) with an SH-containing angiotensin-converting enzyme inhibitor (captopril) to scavenge *OH. All three angiotensin-converting enzyme inhibitors were able to scavenge *OH generated by the action of MPP+. However, the changes produced by captopril and enalaprilat were not significant. When dopamine was administered to the MPP+ -pre-treatment group, a marked elevation was observed, showing a positive linear correlation between dopamine and *OH formation (2,3-DHBA) in the dialysate. Moreover, when iron (II) was administered to the MPP+ -pre-treatment group, the same results were obtained: a positive linear correlation (R2 = 0.989) between the release of dopamine and 2,3-DHBA (R2 = 0.989) in the dialysate. When corresponding experiments were performed with imidaprilat-pre-treated animals, the level of 2,3-DHBA decreased. These results suggested that angiotensin-converting enzyme inhibitors may protect against MPP+ -induced *OH formation in the rat striatum.

1-Methyl-4-phenylpyridinium↗
PubMed1999

Tyramine produces interstitial adenosine-mediated activation of ecto-5'-nucleotidase in rat heart in vivo.

We examined the effect of tyramine on the production of adenosine in rat heart. A flexibly mounted microdialysis setup was used to measure the concentration of interstitial adenosine and to assess the activity of ecto-5'-nucleotidase in in vivo rat hearts. The microdialysis probe was implanted in the left ventricular myocardium of anesthetized rats and perfused with Tyrode solution containing adenosine 5'-monophosphate (AMP) at a rate of 1.0 microl/min. The concentration of adenosine in the effluent (dialysate) was measured by high-performance liquid chromatography (HPLC). Dialysate adenosine obtained during perfusion with the AMP-containing solution through the probe originated from the hydrolysis of AMP by endogenous ecto-5'-nucleotidase, and the level of adenosine reflected the activity of ecto-5'-nucleotidase in the tissue. Tyramine (0-4 mM) increased the adenosine concentration measured during the perfusion of AMP (100 microM) in a concentration-dependent manner. Alpha,beta-methyleneadenosine 5'-diphosphate (alpha,beta-meADP, 100 microM), an inhibitor of ecto-5'-nucleotidase, abolished the AMP-induced increase in dialysate adenosine. Tyramine (1 mM) increased the adenosine concentration measured in the presence of 100 microM AMP (i.e., the activity of ecto-5'-nucleotidase) by 65.8 +/- 19.9% (n = 6, P < 0.05), an increase which was inhibited by an antagonist of the alpha1-adrenoceptor (prazosin, 50 microM) or of protein kinase C (chelerythrine, 10 microM). These data provide the first evidence that alpha1-adrenoceptor stimulation and the subsequent activation of protein kinase C can increase adenosine concentrations in the interstitial space of ventricular muscle in vivo, through activation of endogenous ecto-5'-nucleotidase. To examine the effect of tyramine on the production of adenosine by ischemia-reperfusion of the rat myocardium, the heart was subjected to myocardial ischemia for 15 min by occlusion of the left anterior descending coronary artery. When the heart was reperfused, elevation of the level of adenosine in the ischemic zone was observed, but this change was not significant. However, when corresponding experiments were performed with a subsequent systemic administration of tyramine (1 mM), a marked elevation in the level of adenosine was observed. The results suggest that tyramine elevates adenosine via stimulation of alpha1-adrenoceptors and protein kinase C-mediated activation of ecto-5'-nucleotidase in rat heart.

5'-Nucleotidase↗