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Biomedical subjects

K Iwata

Publications and source records attributed to K Iwata.

At least 19 recordsLinked to original sources
PubMed2006

Tissue Doppler-derived index of left ventricular filling pressure, E/E', predicts survival of patients with non-valvular atrial fibrillation.

OBJECTIVES: To investigate whether the ratio of early transmitral flow velocity (E) to early diastolic mitral annular velocity (E') predict prognosis in patients with non-valvular atrial fibrillation. METHODS: 230 patients with non-valvular atrial fibrillation were enrolled and studied. According to E/E' value, patients were divided into groups with lower (group A with E/E' 15) E/E'. RESULTS: During follow up (average 245 days), 21 (9.1%) deaths were documented. All cause death (15/90 (16.7%) v 6/140 (4.3%)), cardiac death (10 (11.1%) v 2 (1.4%)) and congestive heart failure (16 (17.8%) v 8 (5.7%)) were more common in group B than in group A (all p < 0.01). A Kaplan-Meier survival curve showed that the cumulative survival rate was significantly lower in group B than in group A (log rank p = 0.0013). By multivariate logistic regression analysis, E/E' (chi(2) = 4.47, odds ratio (OR) 1.05, 95% confidence interval (CI) 1.01 to 1.11, p = 0.03) and age (chi(2) = 6.45, OR 1.06, 95% CI 1.01 to 1.11, p = 0.02) were independent predictors of mortality. CONCLUSION: The Doppler-derived index of left ventricular filling pressure, E/E', is a powerful predictor of the clinical outcome of patients with non-valvular atrial fibrillation.

Aged↗
PubMed2005

High ambient ammonia promotes growth in a ureogenic goby, Mugilogobius abei.

Mugilogobius abei has the ability to produce large amounts of urea when exposed to high ambient ammonia. Despite this metabolically costly approach, and reports of growth inhibition effects of ammonia on fish, M. abei exposed to ammonia shows no adverse effects on growth. To investigate this observation the growth of M. abei was measured at room temperatures for 8 weeks at a constant ration level under solitary and grouped conditions, in 20% SW with or without (control) 2 mM NH(4)Cl. Furthermore, pituitary mRNA levels of growth hormone, oxygen consumption, incorporation of external (15)N-ammonia into amino acid and protein fractions as well as behavioral activities were also examined. The specific growth rates of ammonia-exposed fish under grouped condition over the 8 weeks were significantly higher than those of control, while those rates under solitary condition were not significantly different between the treatments. The pituitary of ammonia-exposed fish had higher growth hormone mRNA than in control fish. The use of (15)N isotope revealed that M. abei can actively use external ammonia as a supplementary nitrogen source. Oxygen consumption of ammonia-exposed fish was significantly lower than that of control fish. Locomotor activity and aggressive behavior under grouped condition were significantly reduced in ammonia-exposed fish as compared to those of control. These combined alterations in the ammonia-exposed fish may result in the higher growth rates.

Amino Acids↗
PubMed2005

Fusing EEG and fMRI based on a bottom-up model: inferring activation and effective connectivity in neural masses.

The elucidation of the complex machinery used by the human brain to segregate and integrate information while performing high cognitive functions is a subject of imminent future consequences. The most significant contributions to date in this field, known as cognitive neuroscience, have been achieved by using innovative neuroimaging techniques, such as electroencephalogram (EEG) and functional magnetic resonance imaging (fMRI), which measure variations in both the time and the space of some interpretable physical magnitudes. Extraordinary maps of cerebral activation involving function-restricted brain areas, as well as graphs of the functional connectivity between them, have been obtained from EEG and fMRI data by solving some spatio-temporal inverse problems, which constitutes a top-down approach. However, in many cases, a natural bridge between these maps/graphs and the causal physiological processes is lacking, leading to some misunderstandings in their interpretation. Recent advances in the comprehension of the underlying physiological mechanisms associated with different cerebral scales have provided researchers with an excellent scenario to develop sophisticated biophysical models that permit an integration of these neuroimage modalities, which must share a common aetiology. This paper proposes a bottom-up approach, involving physiological parameters in a specific mesoscopic dynamic equations system. Further observation equations encapsulating the relationship between the mesostates and the EEG/fMRI data are obtained on the basis of the physical foundations of these techniques. A methodology for the estimation of parameters from fused EEG/fMRI data is also presented. In this context, the concepts of activation and effective connectivity are carefully revised. This new approach permits us to examine and discuss some future prospects for the integration of multimodal neuroimages.

Brain↗
PubMed2004

Clinical significance of alendronate in postmenopausal type 2 diabetes mellitus.

OBJECTIVES: To examine early changes in biochemical markers of bone turnover and bone mineral density (BMD) in a clinical trial of anti-resorptive agent alendronate versus alfacalcidol in postmenopausal women with type 2 diabetes mellitus. METHODS: 12 subjects (mean age; 73.1 +/- 6.3 yrs, duration of diabetes; 13.2 +/- 3.7 yrs) were administered alendronate sodium (5 mg/day) and 12 subjects (mean age; 70.7 +/- 7.8 yrs, duration of diabetes; 12.8 +/- 2.0 yrs) were administered alfacalcidol (0.5 microg/day) for 12 months. Urinary N-telopeptide cross-linked collagen type I (NTx), one of biochemical markers, and radial bone mineral density (BMD) were measured as a marker of bone turnover. RESULTS: After 12 months, urinary NTx did not change in women with alfacalcidol treatment, however urinary NTx significantly decreased after alendronate treatment. The BMD significantly decreased by 3.33% (p<0.05) in women with alfacalcidol treatment, while the BMD did not decrease in women with alendronate treatment. CONCLUSION: Alendronate that produces reduction in urinary NTx and inhibition of decrease in BMD may have a clinical significance to reduce the risk of bone fracture in postmenopausal type 2 diabetic women.

Aged↗
PubMed2003

A new model of experimental parotitis in rats and its implication for trigeminal nociception.

A rat model of chronic parotitis was developed following a direct injection of Complete Freund's adjuvant (CFA) into the unilateral parotid gland via the parotid duct without skin incision. The nocifensive behavior, plasma extravasation in the parotid gland, and trigeminal Fos protein expression, a marker of neuronal activation, were analyzed in this model and compared to that of the saline-injected rats. A significant reduction of the escape threshold to mechanical stimulation of the lateral face on the ipsilateral side to the CFA injection was observed at 1-6 days after CFA injection as compared to that of the pre-CFA control ( P<0.01). The lateral face region contralateral to the CFA injection also showed mechanical hyperalgesia at 1-6 days after injection ( P<0.05). The plasma extravasation was significantly increased in the parotid gland ipsilateral to CFA injection as compared to that of the parotid gland with saline injection at 3 days after injection as shown by Evans' blue dye extravasation ( P<0.05). Bilateral expression of Fos protein-like immunoreactive cells was observed in the transition zone between the trigeminal spinal nucleus interpolaris (Vi) and caudalis (Vc) and paratrigeminal nucleus (Pa5). On the other hand, a significant unilateral expression of Fos protein-positive cells was observed on the ipsilateral side of the upper cervical (C2) dorsal horn ( P<0.05). This model of parotitis can be used to study trigeminal pain mechanisms associated with sialadenitis. A unique feature of this preparation is that the inflammation was limited to the parotid gland after intraductal injection of CFA, allowing analysis of peripheral input from a defined orofacial region. The model will be useful in developing new strategies to treat chronic orofacial pain.

Animals↗
PubMed2003

Hard-food mastication suppresses complete Freund's adjuvant-induced nociception.

The effect of food hardness during mastication on nociceptive transmission in the spinal cord was studied by analyzing complete Freund's adjuvant (CFA) induced nocifensive behavior and Fos expression. The behavioral study showed that the shortening of the withdrawal latency following CFA injection into the hind paw was depressed after a change in the given food hardness from soft to hard. The depression of nocifensive behavior in the rats with hard food was reversed after i.v. injection of naloxone. Fos protein-like immunoreactive cells (Fos protein-LI cells) were expressed in the superficial and deep laminae of the L4-6 spinal dorsal horn after s.c. injection of CFA into the hind paw during soft food mastication. The number of Fos protein-LI cells was decreased in the rats with hard food mastication followed by soft food. This reduction of Fos protein-LI cells following change in food hardness was reversed after i.v. application of naloxone. Furthermore, the depression of Fos protein-LI cells following hard food intake was significantly inhibited after bilateral inferior alveolar nerve transection or bilateral ablation of the somatosensory cortex. These findings suggest that the change in food hardness during mastication might drive an opioid descending system through the trigeminal sensory pathway and somatosensory cortex resulting in an antinociceptive effect on chronic pain. However, IAN transection and cortical ablation did not induce 100% reversal of Fos expression, suggesting other than trigeminal sensory system may be involved in this phenomena, such as the pathway through the brainstem reticular formation.

Animals↗
PubMed2003

Adjustment of the occlusal vertical dimension in the bite-raised guinea pig.

In humans, the inappropriate occlusal vertical dimension (OVD) causes several orofacial disorders, such as bruxism and pain in the masticatory muscles and temporomandibular joint. However, it is still unclear how strictly the OVD is adjusted. To answer this question, we studied the temporal change of the OVD in bite-raised young guinea pigs. The OVD was raised by fixation of a bite-raising appliance to the lower incisors, and increased by either 3 or 1.5 mm at the first molars. After the space produced between the upper and lower molars was filled within 10 days due to eruption of the molars, the appliance was removed. In the bite-raised animals, the raised OVD was reduced until it attained that observed in the control animals, after which the OVD increased according to cranial growth. These results show that the OVD is developmentally changed and strictly controlled.

Adaptation, Physiological↗
PubMed2001

Crystallization and preliminary X-ray analysis of aspartate racemase from Pyrococcus horikoshii OT3.

Aspartate racemase from Pyrococcus horikoshii OT3 (P. AspR) has been crystallized in three crystal forms by the sitting-drop vapour-diffusion method. The crystals belong to the space groups P2(1), P2(1)2(1)2(1) and P3(1)21 (or P3(2)21). The crystals of space group P2(1) diffract X-rays beyond 1.7 A resolution under 90 K liquid-nitrogen cryoconditions with synchrotron radiation and were selected for structure determination. Two heavy-atom derivatives of this crystal form were obtained by the soaking method, which afforded the initial electron-density map.

Amino Acid Isomerases↗
PubMed2001

Genome analysis of Agrobacterium tumefaciens: construction of physical maps for linear and circular chromosomal DNAs, determination of copy number ratio and mapping of chromosomal virulence genes.

The phytopathogenic bacterium Agrobacterium tumefaciens is unique in that it possesses both linear and circular DNA chromosomes in addition to a plant-tumor-inducing (Ti) plasmid. We analyzed the two chromosomal DNA molecules in strain MAFF301001, whose Ti plasmid has already been sequenced completely. Physical maps of the chromosomal DNAs were constructed by Southern hybridization experiments using Pme I and Swa I fragments and short fragments bridging the Swa I fragments with special care to avoid any missing fragment. Hybridization with 16S rDNA probe showed one rDNA locus on the linear chromosome and two loci on the circular chromosome. For this bacterium to be pathogenic, not only Ti plasmid but also chromosomal genes are required. The chromosomal virulence (chv) genes (chvA, chvB, chvD, chvE, chvG, chvH, and chvI) and the chromosomal genes affecting the virulence [acvB, pgm(exoC), glgP, miaA, and ros] were successfully mapped onto 5 different regions in the chromosomal physical maps. These chv genes and the chromosomal genes affecting the virulence other than pgm and glgP were found on the circular chromosome, whereas the pgm and glgP genes were located on the linear chromosome. In contrast to the large terminal inverted repeats of Streptomyces linear chromosomal DNA, no hybridization signal was detected between left and right terminal fragments of the linear A. tumefaciens chromosome. Quantitative analysis of DNA fragments indicated that the copy numbers of the two chromosomal DNAs and the Ti plasmid are identical.

Agrobacterium tumefaciens↗
PubMed2001

Full-genome nucleotide sequence of a hepatitis E virus strain that may be indigenous to Japan.

We identified hepatitis E virus (HEV) RNA in serum from a Japanese patient with acute hepatitis, who had never been abroad. The full-genome nucleotide sequence of the HEV isolate (JRA1) from this patient was composed of 7227 nucleotides excepting the poly(A) tail and had ORF1 coding for 1703 amino acids (aa), ORF2 coding for 660 aa, and ORF3 coding for 122 aa. This Japanese strain showed approximately 87% nucleotide similarity to human and swine strains reported from the United States, while it had only 73-76% similarity to Asian and Mexican strains. Here we report the characteristics of the HEV-JRA1 isolate, which might be the first example of an indigenous strain(s) of HEV in Japan.

Amino Acid Sequence↗
PubMed2001

Temporal facilitation of the flexor reflex induced by C-fiber activity: comparison between adult and aged rats.

We investigated the wind-up phenomenon of the flexor reflex in adult and aged rats. The sural nerve was stimulated at C-fiber strength and reflex activity was recorded from the semitendinosus muscle. The wind-up rate, the increment rate of the C-fiber response (i.e. activity from 100 to 600 ms after stimulation) by successive stimuli (five train pulses), was decreased exponentially with increasing stimulus intervals from 3 to 20 s. The time constant of the decay for the aged rats was 9.2+/-3.2 s (mean+/-SD), which was significantly longer than for the adult rats (6.4+/-2.9 s). The findings indicate that the effects of C-fiber activation on the spinal nociceptive pathways attenuate more slowly in aged rats as compared with adult rats.

Action Potentials↗
PubMed2001

Daunorubicin attenuates tumor necrosis factor-alpha-induced biosynthesis of plasminogen activator inhibitor-1 in human umbilical vein endothelial cells.

The anthracycline antibiotic daunorubicin is reported to induce apoptosis in cells by triggering ceramide generation through de novo synthesis or sphingomyelin hydrolysis. Treatment of human umbilical vein endothelial cells (HUVEC) with daunorubicin markedly decreased the mRNA expression and protein release of plasminogen activator inhibitor-1 (PAI-1). This cellular event was accompanied by a significant increase in the total ceramide content in HUVEC. On the other hand, tumor necrosis factor (TNF)-alpha treatment of HUVEC led to an increase in both PAI-1 mRNA expression and protein release, and an enhancement of total ceramide content was also observed. The stimulating effect of TNF-alpha on PAI-1 synthesis was attenuated by the pretreatment of HUVEC with daunorubicin. Interestingly, the daunorubicin-induced increase in ceramide content was blocked by addition of the potent ceramide synthase inhibitor fumonisin B(1), while the TNF-alpha-induced ceramide increase was not affected by this drug. Fumonisin B(1) treatment restored the daunorubicin-induced decrease in PAI-1 release to approximately 70% of the control, but did not affect the TNF-alpha-induced increase in PAI-1 release. Thus, these data imply the possibility that the subcellular topology of ceramide production determines its lipid mediator function in the regulation of PAI-1 synthesis in HUVEC, because both TNF-alpha and daunorubicin could increase the ceramide levels.

Carboxylic Acids↗
PubMed2001

Early and late outcomes after reoperation for prosthetic valve endocarditis.

OBJECTIVE: Prosthetic valve endocarditis remains a challenging complication after heart valve replacement. To identify predictive risk factors, we have reviewed 30 patients who underwent surgery for prosthetic valve endocarditis between March 1986 and May 1999. METHODS: There were 15 men and 15 women (mean age 51 years). Prosthetic valve endocarditis was classified as early (< or = 1 year after operation) in 10 cases, and as late in the other 20 cases. The most common indication for surgery was moderate to severe congestive heart failure due to prosthetic valve dysfunction in 21 (70%) patients. The average follow-up period was 6.5 years, with a range of 0.3 to 14.1 years. RESULTS: The most common microorganism was Staphylococcus epidermidis in both patients with early (50%) and late prosthetic valve endocarditis (25%). The in-hospital mortality was 13.3% (4/30). There were six late deaths. The actuarial survival at 5 years was 78% and 66% at 10 years. An early onset of prosthetic valve endocarditis was the only significant determinant of both in-hospital mortality (p = 0.005) and overall mortality (p = 0.021). Emergency surgery had a statistically significant relationship with in-hospital mortality (p = 0.045). No significant influence on mortality after reoperation for prosthetic valve endocarditis was found in age, sex, valve position, antecedent native valve endocarditis, or in the type of pathological findings (ring abscess, valve dehiscence, and vegetation). CONCLUSION: Early onset of prosthetic valve endocarditis and emergency surgery were important risk factors for mortality due to prosthetic valve endocarditis.

Adult↗
PubMed2001

Neuronal activity in the putamen and the globus pallidus of rabbit during mastication.

The pattern of jaw movements is changed during a masticatory sequence from ingestion of food to its deglutition. The masticatory sequence is divided into three distinct stages in the rabbit. However, the neural mechanism involved in the alteration of the masticatory stages is still unknown. This study was designed to determine whether neuronal activity in the putamen and globus pallidus is related to the alteration of the masticatory stages. Fifty-three percent of the recorded neurons showed significant alterations of activity during mastication. Of these neurons, 16% changed their firing frequency throughout the masticatory sequence (sequence-related neurons) and 84% changed their firing frequency with the transition of the masticatory stages (stage-related neurons). The stage-related neurons were classified into two groups based on their neuronal activity patterns observed during mastication, i.e. simple type and complex type. The former are the neurons that were either facilitated or inhibited once during mastication, and the latter are those showing the facilitation or inhibition twice or more during mastication. Complex-type neurons were observed more frequently in the globus pallidus than in the putamen. These results suggest that the basal ganglia is involved in mastication and may related to the transition between the masticatory stages.

Animals↗
PubMed2001

Influence of food thickness and hardness on possible feed-forward control of the masseteric muscle activity in the anesthetized rabbit.

The facilitatory masseteric muscle response (FMR) elicited by polyurethane foam strip application between the opposing molars during cortically-induced rhythmic jaw movements (CRJMs) was induced earlier than masticatory force onset. The occurrence of this early response of the FMR (e-FMR) could not be explained by a simple reflex mechanism. One possible mechanism of the e-FMR is the involvement of a feed-forward control mechanism of the masticatory jaw movement. In the present study, experimentally designed polyurethane foam strips with various thickness and hardness were applied during CRJMs and analyzed in terms of how the e-FMR was modulated by the food hardness and thickness. The FMR onset was not related to the strip thickness or the strip hardness. However, the magnitude of the e-FMR increased in a thickness and a hardness-dependent manner. The sensory information of the food properties in the masticatory cycle may make the FMR adequate to chewing of the food in the following cycle, and such modulation may help chewing rhythms remain stable.

Action Potentials↗