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T Yada

Publications and source records attributed to T Yada.

At least 55 records · Page 3Linked to original sources
PubMed1999

Glucose-sensitive neurons in the rat arcuate nucleus contain neuropeptide Y.

Glucose is known to regulate the activity of the hypothalamic feeding centers. Neuropeptide Y (NPY)-containing neurons in the hypothalamic arcuate nucleus (ARC) have been implicated in the stimulation of feeding. We examined the presence of glucose-sensitive neurons in the ARC and their coincidence with NPY-containing neurons. Cytosolic Ca2+ concentration ([Ca2+]i) in single ARC neurons isolated from rat hypothalamus was measured with fura-2 fluorescence imaging; the cells were then stained immunocytochemically with an anti-NPY antiserum. Lowering the glucose concentration from 10 to 1 mM increased [Ca2+]i in 36 out of 180 neurons (20%), the majority of which (34 neurons, 94%) were immunoreactive for NPY. In conclusion, the ARC contains glucose-sensitive NPY-containing neurons. The suggested role of these neurons is to transduce a reduction in the glucose concentration in the brain to the release of NPY and, subsequently, stimulation of feeding.

Animals↗
PubMed1999

The effect of leptin on feeding-regulating neurons in the rat hypothalamus.

Intense immunoreactivity for the leptin receptor was detected in the hypothalamic arcuate nucleus (ARC), ventromedial nucleus (VMH), and lateral hypothalamus (LH) by immunohistochemistry. Cytosolic Ca2+ concentration ([Ca2+]i) in single neurons isolated from the ARC, VMH and LH was measured with dual wavelength fura-2 fluorescence imaging. A reduction of the superfusate glucose concentration from 10 to 1 mM increased [Ca2+]i in 21% of ARC neurons and 22% of LH neurons. Leptin at 0.1 nM inhibited the [Ca2+]i increase in 66 and 64% of these glucose-sensitive ARC and LH neurons, respectively. Inversely, 10 mM glucose increased [Ca2+]i in 49% of the VMH neurons, and 0.1 nM leptin at 1 mM glucose also increased [Ca2+]i in 84% of these glucose-responsive neurons. These results reveal that leptin inhibits the ARC and LH neurons and stimulates the VMH neurons via the leptin receptor expressed in these cells.

Animals↗
PubMed1999

Effects of prolactin and growth hormone on plasma immunoglobulin M levels of hypophysectomized rainbow trout, Oncorhynchus mykiss.

Immunoglobulin M (IgM) is a major component of the humoral immune system of teleosts. This study examines the effects of hypophysectomy and subsequent replacement with prolactin (PRL) or growth hormone (GH) upon the plasma IgM levels of the rainbow trout (Oncorhynchus mykiss). Plasma IgM levels of the hypophysectomized fish were decreased to 30% of those in sham-operated fish 1 or 4 weeks after operation. Implantation of a cholesterol pellet containing salmon PRL or GH restored plasma IgM levels of the hypophysectomized fish, suggesting important roles for PRL and GH in the regulation of circulating IgM level in trout.

Animals↗
PubMed1999

Insulinotropin PACAP potentiates insulin-stimulated glucose uptake in 3T3 L1 cells.

Pituitary adenylate cyclase-activating polypeptide (PACAP) is localized in pancreatic nerve fibers and islets and potently augments glucose-induced insulin secretion. The present study explored a possible extra-pancreatic action of PACAP. The specific PACAP receptor (PAC1 receptor) was expressed in the rat fat tissue and 3T3-LI adipocytes. PACAP-38 (10 nM) significantly enhanced insulin-induced 2-deoxyglucose uptake by 3T3-L1 adipocytes. Insulin-stimulated phosphatidylinositol 3-kinase activity was further increased by PACAP-38, whereas the tyrosine-phosphorylation of insulin receptor beta-subunit and insulin receptor substrate-1 was unaltered by PACAP-38. These results reveal that PACAP-38 enhances insulin-induced glucose uptake, an effect probably mediated by insulin-stimulated phosphatidyl-inositol 3-kinase, and that PACAP potentiates not only insulin secretion, but also insulin action in adipocytes.

3T3 Cells↗
PubMed1999

Inhibition by simvastatin, but not pravastatin, of glucose-induced cytosolic Ca2+ signalling and insulin secretion due to blockade of L-type Ca2+ channels in rat islet beta-cells.

1. Hypercholesterolaemia often occurs in patients with type 2 diabetes, who therefore encounter administration of HMG-CoA reductase inhibitors. Alteration of pancreatic beta-cell function leading to an impaired insulin secretory response to glucose plays a crucial role in the pathogenesis of type 2 diabetes. Therefore, it is important to examine the effects of HMG-CoA reductase inhibitors on beta-cell function. 2. Cytosolic Ca2+ concentration ([Ca2+]i) plays a central role in the regulation of beta-cell function. The present study examined the effects of HMG-CoA reductase inhibitors on the glucose-induced [Ca2+]i signalling and insulin secretion in rat islet beta-cells. 3. Simvastatin, a lipophilic HMG-CoA reductase inhibitor, at 0.1-3 microg ml(-1) concentration-dependently inhibited the first phase increase and oscillation of [Ca2+]i induced by 8.3 mM glucose in single beta-cells. The less lipophilic inhibitor, simvastatin-acid, inhibited the first phase [Ca2+]i increase but was two orders of magnitude less potent. The hydrophilic inhibitor, pravastatin (100 microg ml(-1), was without effect on [Ca2+]i. 4. Simvastatin (0.3 microg ml(-1)), more potently than simvastatin-acid (30 microg ml(-1)), inhibited glucose-induced insulin secretion from islets, whereas pravastatin (100 microg ml(-1)) had no effect. 5. Whole-cell patch clamp recordings demonstrated a reversible inhibition of the beta-cell L-type Ca2+ channels by simvastatin, but not by pravastatin. Simvastatin also inhibited the [Ca2+]i increases by L-arginine and KCl, agents that act via opening of L-type Ca2+ channels. 6. In conclusion, lipophilic HMG-CoA reductase inhibitors can inhibit glucose-induced [Ca2+]i signalling and insulin secretion by blocking L-type Ca2+ channels in beta-cells, and their inhibitory potencies parallel their lipophilicities. Precaution should be paid to these findings when HMG-CoA reductase inhibitors are used clinically, particularly in patients with type 2 diabetes.

Animals↗
PubMed1999

Modeling and predicting transcriptional units of Escherichia coli genes using hidden Markov models.

MOTIVATION: The hidden Markov model (HMM) is a valuable technique for gene-finding, especially because its flexibility enables the inclusion of various sequence features. Recent programs for bacterial gene-finding include the information of ribosomal binding site (RBS) to improve the recognition accuracy of the start codon, using this feature. We report here our attempt to extend the model into the total transcriptional unit, enabling the prediction of operon structures. RESULTS: First, we improved the prediction accuracy of coding sequences (CDSs) by employing the models of 'typical', 'atypical' and 'negative (false-positive)' classes as well as the models of RBS and its downstream spacer. The sensitivity of exactly predicting the 204 experimentally confirmed CDSs reached 90.2% in an objective test. Based on the prediction result of CDSs, the positions of the promoters and terminators were predicted. Our model could exactly recognize 60% of 390 known transcriptional units. Thus, the accuracy and significance of this prediction problem is far from trivial. We would like to propose this problem as an open theme in bioinformatics because the ongoing or planned post-sequencing projects will produce much data for future improvements.

Algorithms↗
PubMed1999

Immunohistochemical evaluation of the small and large proteoglycans in pleomorphic adenoma of salivary glands.

This study investigated the immunolocalization of small and large proteoglycans (PGs), including decorin, biglycan, PG-M/versican and aggrecan, in salivary pleomorphic adenoma (PA) using monoclonal and polyclonal antibodies. In addition, a polyclonal antibody, A0082, recognizing blood vessels was also used to help identify truly mesenchymal tissues in PA. Decorin reactivity was detected only in tumor capsule and interstitial tissue of non-neoplastic salivary gland, but not in the tumor tissue. Biglycan was frequently revealed throughout the matrix of small chondroid regions and in the peripheral portion of larger chondroid regions. PG-M/versican was mainly localized to the truly mesenchymal tissues in PA and the innermost portion of tumor capsule. On the contrary, aggrecan was extensively expressed in the non-luminal epithelial areas as well as in the myxoid and chondroid areas, but not in the truly mesenchymal tissues. These findings suggest that aggrecan is the most widely distributed PG in PA and may be produced mainly by non-luminal tumor cells. The absence of aggrecan from the truly mesenchymal tissues argues against its origin from this source. Both aggrecan and biglycan may play important roles in the chondroid differentiation and morphogenesis of PA.

Adenoma, Pleomorphic↗
PubMed1999

Role of adenosine in local metabolic coronary vasodilation.

Adenosine has been postulated to mediate the increase in coronary blood flow when myocardial oxygen consumption is increased. The aim of this study was to evaluate the role of adenosine when myocardial oxygen consumption was augmented by cardiac paired-pulse stimulation without the use of catecholamines. In 10 anesthetized closed-chest dogs, coronary blood flow was measured in the left circumflex coronary artery, and myocardial oxygen consumption was calculated using the arteriovenous oxygen difference. Cardiac interstitial adenosine concentration was estimated from coronary venous and arterial plasma adenosine measurements using a previously described multicompartmental, axially distributed mathematical model. Paired stimulation increased heart rate from 55 to 120 beats/min, increased myocardial oxygen consumption 104%, and increased coronary blood flow 92%, but the estimated interstitial adenosine concentration remained below the threshold for coronary vasodilation. After adenosine-receptor blockade with 8-phenyltheophylline (8-PT), coronary blood flow and myocardial oxygen consumption were not significantly different from control values. Paired-pulse pacing during adenosine-receptor blockade resulted in increases in myocardial oxygen consumption and coronary blood flow similar to the response before 8-PT. Coronary venous and estimated interstitial adenosine concentration did not increase to overcome the adenosine blockade by 8-PT. These results demonstrate that adenosine is not required for the local metabolic control of coronary blood flow during pacing-induced increases in myocardial oxygen consumption.

Adenosine↗
PubMed1999

Role of NO and K(+)(ATP) channels in adenosine-induced vasodilation on in vivo canine subendocardial arterioles.

Adenosine (Ado) plays an important role in regulation of coronary vascular tone with nitric oxide (NO) and ATP-sensitive K(+) (K(+)(ATP)) channels. In vitro, it was reported that subendocardial (Endo) arterioles are more sensitive to Ado than subepicardial (Epi) arterioles. The purpose of this study was to observe enhanced vasodilation of Endo arterioles directly and to evaluate possible roles of K(+)(ATP) channels and NO in the different responses of Endo and Epi arterioles to Ado-induced vasodilation. We evaluated dilation of Endo and Epi arterioles (<120 micrometer) of beating canine hearts (n = 19) by Ado (20 and 50 microgram. kg(-1). min(-1) ic) before and after K(+)(ATP) channel blockade (glibenclamide; 200 microgram/kg ic), inhibition of NO synthase [N(G)-nitro-L-arginine methyl ester (L-NAME); 30 microgram. kg(-1). min(-1), 20 min ic], or glibenclamide + L-NAME using a novel needle-probe CCD intravital microscope. Ado induced dose-dependent vasodilation in both Epi and Endo arterioles, but vasodilation was greater in Endo arterioles, i.e., increase at 120 s (maximum dilation) after Ado (50 microgram. kg(-1). min(-1)) was 17% in Endo and 13% in Epi arterioles (P < 0.01). Endo arteriole dilation was attenuated by blockade of K(+)(ATP) channels from 18% (Ado) to 9% (Ado+glibenclamide) increase (P < 0.001) and by inhibition of NO synthase from 17% (Ado) to 9% (Ado+L-NAME) (P < 0.005). Epi arteriole vasodilation was attenuated by blockade of K(+)(ATP) channels from 15 to 9% (P < 0.005) and inhibition of NO from 16 to 10% (P < 0.005). Suppression of vascular response was additive (Endo, 14 to -1%; Epi, 12 to 3%) with glibenclamide + L-NAME. We conclude that 1) the degree of Ado-induced vasodilation was greater in Endo than in Epi arterioles, with higher sensitivity of smaller arterioles in both layers and 2) transmural difference of arteriolar sensitivity to adenosine was abolished or reversed by K(+)(ATP) channel blockade and/or by NO synthase inhibition, indicating crucial involvement of K(+)(ATP) and NO in transmural sensitivity difference.

Adenosine↗
PubMed1999

Nitric oxide induces apoptosis via Ca2+-dependent processes in the pancreatic beta-cell line MIN6.

An excessive production of nitric oxide (NO) in response to cytokines has been shown to be the major cause of the destruction of islet beta-cells associated with type 1 (insulin-dependent) diabetes mellitus. The NO-induced beta-cell death is the typical apoptosis. In the present study, we show evidence that supports a tight link between NO, Ca2+, protease and apoptosis in beta-cells. Three different NO donors, SNAP, NOR3 and NOC7, induced apoptosis in a beta-cell line, MIN6 cells, in a concentration-dependent manner. SNAP at 200 microM increased cytosolic Ca2+ concentration ([Ca2+]i) and induced apoptosis. The SNAP-induced apoptosis was blocked by a Ca2+ chelator, BAPTA-AM, and by an inhibitor of a Ca2+-dependent protease, calpain. In conclusion, an excessive NO production induces apoptosis, wherein an increase in [Ca2+]i and resultant activation of calpain play a key role.

Animals↗
PubMed1999

Leptin promotes aggregation of human platelets via the long form of its receptor.

Plasma leptin levels are elevated in most obese individuals, and obesity is accompanied by a high incidence of cardiovascular disease. Therefore, leptin could be involved in the pathogenesis of cardiovascular disease. In the present study, the role of leptin was explored in the regulation of platelet function. The expression of the long form of the leptin receptor was detected in human platelets. At 50 ng/ml, human leptin induced phosphorylation of several proteins of platelets at the tyrosine residue. Neither leptin at concentrations < or = 100 ng/ml nor ADP at concentrations > or = 1 micromol/l affected platelet aggregation. However, after pretreatment with 100 ng/ml leptin for 5 min, 1 micromol/l ADP caused aggregation. Thus, leptin and ADP acted synergistically. At a concentration of 2 micromol/l, ADP induced platelet aggregation, which was markedly enhanced by 30-100 ng/ml leptin in a concentration-dependent manner. This concentration range corresponds to that of plasma leptin levels in obese individuals. At the lower concentrations (< 10 ng/ml) that are observed in normal individuals, leptin had no effect on platelet aggregation. In conclusion, leptin at high concentrations has the novel function of promoting platelet aggregation, which may be a key coupling factor between obesity and the cardiovascular disease associated with syndrome X and diabetes.

Adenosine Diphosphate↗
PubMed1998

In vivo observations of the intramural arterioles and venules in beating canine hearts.

1. To evaluate the effects of cardiac contraction on intramyocardial (midwall) microvessels, we measured the phasic diameter change of left ventricular intramural arterioles and venules using a novel needle-probe videomicroscope with a CCD camera and compared it with the diameter change in subepicardial and subendocardial vessels. 2. The phasic diameter of the intramural arterioles decreased from 130 +/- 79 ìm in end-diastole to 118 +/- 72 micron (mean +/- S.D.) in end-systole by cardiac contraction (10 +/- 6 %, P < 0.001, n = 21). 3. The phasic diameter in the intramural venules was almost unchanged from end-diastole to end-systole (85 +/- 44 vs. 86 +/- 42 micron, respectively, 2 +/- 6 %, n. s., n = 14). 4. Compared with intramural vessels, the diameters of subendocardial arterioles and venules decreased by a similar extent (arterioles: 10 +/- 8 %, P < 0. 001; venules: 12 +/- 10 %, P < 0.001) from end-diastole to end-systole, respectively, whereas the diameter of the subepicardial arterioles changed little during the cardiac cycle, and subepicardial venule diameter increased by 9 +/- 8 % (P < 0.01) from end-diastole to end-systole. These findings are consistent with our previous report. 5. We suggest that the almost uniform distribution of the cardiac contractility effect and arteriolar transmural pressure between the subendocardium and the midmyocardium, which together constitute the systolic vascular compressive force, accounts for the similarity in the arteriolar diameter changes in both myocardial layers. The smaller intravascular pressure drop from deep to superficial myocardium relative to the larger intramyocardial pressure drop explains the difference in the phasic venular diameter changes across the myocardium.

Animals↗
PubMed1998

Immunohistochemical localization of leptin receptor in the rat brain.

The distribution of leptin receptor in the rat brain was determined by immunocytochemistry and Western blotting. Strong leptin receptor immunoreactivity was detected in the arcuate, paraventricular and ventromedial nuclei of the hypothalamus, and lateral hypothalamic area. The olfactory bulb, neocortex, cerebellar cortex, dorsal raphe nucleus, inferior olive nucleus, nucleus of the solitary tract, dorsal motor nucleus of the vagus nerve also showed intense immunoreactivity. Western blotting analysis yielded a 120-kDa major band.

Animals↗
PubMed1998

Repetitive mitochondrial Ca2+ signals synchronize with cytosolic Ca2+ oscillations in the pancreatic beta-cell line, MIN6.

We examined the relationship between cytosolic Ca2+ concentration ([Ca2+]c) and mitochondrial matrix Ca2+ concentration ([Ca2+]m) in the pancreatic beta-cell line, MIN6. [Ca2+]c was monitored in a single or a group (30 cells) of fura-2-loaded MIN6 cells, and [Ca2+]m was measured in a group (1 x 10[6] cells) of MIN6 cells stably transfected with aequorin targeted at the mitochondria. Exogenous ATP (0.25 mmol/l) produced a single transient increase in [Ca2+]c whereas 22 mmol/l KCl produced a sustained plateau increase. ATP and KCl evoked transient increases in [Ca2+]m but with distinct time courses of [Ca2+]m decline: the [Ca2+]m increase induced by ATP decreased more rapidly than that induced by KCl. Nitrendipine (3 micromol/l), a blocker of L-type Ca2+ channels, inhibited both [Ca2+]c and [Ca2+]m signals in response to KCl and tolbutamide, but not those to ATP. Peak levels of [Ca2+]m increase (around 2 micromol/ l) exceeded those of [Ca2+]c increase (around 500 nmol/l). A rise in glucose concentration from 3 to 30 mmol/l induced oscillations of [Ca2+]c that overlay the sustained increases in [Ca2+]c in single cells. An oscillatory increase in [Ca2+]m was similarly observed in response to glucose. Addition of 10 mmol/l 2-ketoisocaproic acid at 20 mmol/l glucose further increased the plateau level of [Ca2+]c and the frequency of [Ca2+]c oscillations, which were correlated with a further increase in [Ca2+]m. In response to pulsatile exposure to KCl, [Ca2+]c and [Ca2+]m increased synchronously. These data suggest that an oscillatory increase in [Ca2+]m in beta cells, the signal which is thought to be necessary for continuous stimulation of mitochondrial metabolism, is produced synchronously with the [Ca2+]c oscillations.

Adenosine Triphosphate↗