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Biomedical subjects

M Tamura

Publications and source records attributed to M Tamura.

At least 361 records · Page 20Linked to original sources
PubMed1996

Adrenomedullin-sensitive receptors are preferentially expressed in cultured rat mesangial cells.

By using cultured rat mesangial cells, we compared the effects on cyclic nucleotide levels of adrenomedullin with those of the structurally related peptides, calcitonin gene-related peptide (CGRP) and amylin. Adrenomedullin potently increased cAMP levels 7-fold in a time- and concentration-dependent manner. Its EC50 was 3 x 10(-9) M. CGRP was less potent (2-fold) with an EC50 of 10(-7) M, and amylin had no effect on cAMP levels. All three peptides failed to increase cGMP levels. Treatment of cells with near maximal concentrations of adrenomedullin (10(-7) M) and CGRP (10(-6) M) had no additive effect on cAMP levels. Human adrenomedullin-(22-52)-NH2, a putative adrenomedullin receptor antagonist, inhibited the production of cAMP elicited by adrenomedullin (IC50: 7 x 10(-8) M) and CGRP (IC50: 5 x 10(-8) M). Human CGRP-(8-37), a CGRP receptor antagonist, conversely, reduced the cAMP elevation caused by these peptides with a lower potency (IC50: 10(-6) M for both peptides). This demonstrated that human adrenomedullin-(22-52)-NH2 was a more effective antagonist for adrenomedullin- and CGRP-specific receptors than human CGRP-(8-37). Results suggest that receptors sensitive to adrenomedullin are preferentially expressed in cultured rat mesangial cells. Immunohistochemical study showed almost no immunoreactive adrenomedullin and CGRP, if any, in the cells. Adrenomedullin may regulate mesangial function as either a paracrine or circulating hormone via a cAMP- but not a cGMP-dependent mechanism.

Adrenomedullin↗
PubMed1996

Effects of cardiac output on Doppler transmitral and transtricuspid flow velocity patterns in very low birth weight infants.

We studied effects of cardiac output on Doppler transmitral and transtricuspid flow velocities in 24 appropriate for gestational age premature infants. We measured peak flow velocity of early diastole (peak E) and atrial contraction (peak A), ratio of peak flow velocity of early diastole to atrial contraction (peak E/A), total flow velocity-time integral, the first third filling fraction, peak filling rate normalized to stroke volume, and deceleration time (DT). Cardiac output was calculated as the product of the aortic flow velocity-time integral, aortic valve area, and heart rate. The cardiac output increased significantly with advancing gestational age and body weight (r = 0.78 and 0.86, P < 0.01, respectively). With increasing cardiac output, the transmitral as well as transtricuspid peak E, peak E/A, and total flow velocity-time integral increased significantly without any change in the peak filling rate normalized to stroke volume, peak A, and deceleration time. The transmitral as well as transtricuspid peak E did not correlate with the heart rate. Although these results do not establish whether changes in ventricular relaxation process or in cardiac output is responsible for the progressive increase in the peak E and peak E/A. Unchanged peak filling rate normalized to stroke volume of the left and right ventricles suggest that changes in cardiac output with maturity is, in fact, one of the important contributory factors. This evidence should be borne in mind in interpreting ventricular diastolic filling as an index of ventricular diastolic function in premature infants.

Blood Flow Velocity↗
PubMed1996

Experimental liver fibrosis induced in rats receiving high doses of alcohol and alternating between regular and vitamin-depleted diets.

Liver fibrosis was induced in rats by simulating human alcoholic eating and drinking patterns. Alcohol addiction was established by gradually increasing the ethanol concentration in the drinking water; salts were added at the terminal stage. The hepatocytes of rats receiving alcohol concentrations exceeding 50% (v/v) (similar to vodka) exhibited alcoholic hyaline (Mallory bodies). Alcoholic liver fibrosis was induced by alternating between regular and autoclaved (vitamin-depleted) diets, simulating the irregular eating habits of human alcoholics. In the livers of rats receiving 70% (v/v) ethanol (comparable to absinthe) with 25% saline and fed the alternating diets, pericellular fibrosis was induced. No significant difference in calorie intake between control and alcohol rats was detected except when rats underwent drinking bouts (heavy drinking phase). This indicates that neither a high-fat diet nor a choline-depleted diet is necessary to induce the alcoholic fibrosis seen in human alcoholics.

Animals↗
PubMed1996

Enhanced glomerular profilin gene and protein expression in experimental mesangial proliferative glomerulonephritis.

Profilin is a cytoplasmic protein that binds to actin monomer and regulates actin polymerization. In a number of experimental and human glomerular diseases, the mesangial cell expresses alpha-smooth muscle actin and undergoes a phenotypic change to myofibroblast. We used a rat model of mesangial proliferative nephritis induced with antibody to the Thy 1 antigen present on mesangial cells to investigate whether profilin is upregulated. We amplified and sequenced rat profilin cDNA by the reverse-transcribed-polymerase chain reaction (RT-PCR). The nucleotide and amino acid sequences were highly conserved across the mammalian profilins. We raised affinity purified antibody to rat profilin in rabbits immunized with a synthetic profilin peptide (EFTMDLRTKS). At 7 days after disease induction, enhanced expression in both profilin mRNA and protein was demonstrated in the isolated glomeruli by RT-PCR and Western blot analysis. These results suggest that profilin may be involved in the pathogenesis of glomerulonephritis by reorganizing actin cytoskeleton.

Amino Acid Sequence↗
PubMed1996

Species specificity of anticoagulant activity of activated human protein C: involvement of factor V as well as protein S.

Activated protein C (APC) possesses species specificity in its anticoagulant activity. Human APC exerts only weak activity in rat plasma compared with that in human plasma. The present study was undertaken to estimate the difference in interaction of human and rat factors with human APC and to assess the cause of the species specificity. Human or rat protein S (PS), factor V, or factor VIII was used to supplement human plasma depleted of each respective factor, and the anticoagulant activity of human APC was measured in term of the elongation of activated partial thromboplastin time (APTT). The activity of human APC in rat PS- or factor V-supplemented plasma was weaker than that in the human PS- or factor V-supplemented plasma. Furthermore, using purified human and rat factor V, human APC showed weaker inactivation of rat factor V than human factor V. Equal anticoagulant activity was observed in human or rat factor VIII-supplemented plasma. And there was a little difference in the interaction of APC with its inhibitors in human or rat plasma during a few minutes of incubation as judged by measurement of residual activity by an enzyme capture assay. From these results factor V as well as PS seems to play a major role in the species specificity of APC.

Animals↗
PubMed1996

Spermine suppresses the activation of human neutrophil NADPH oxidase in cell-free and semi-recombinant systems.

Spermine, a cellular polyamine, down-regulates O2- generation in human neutrophils stimulated by receptor-linked agonist [Ogata, Tamura and Takeshita (1992) Biochem. Biophys. Res. Commun. 182, 20-26]. In this study, to elucidate the mechanism for the inhibition, the effect of spermine on cell-free activation of the O2- generating enzyme (NADPH oxidase) was examined. Spermine suppressed the SDS-induced activation of NADPH oxidase in a dose-dependent manner with an IC50 of 18 microM. The inhibition was specific for spermine over its precursor amines, spermidine and putrescine. Spermine did not alter the Km for NADPH or the optimal concentration of SDS for activation. The amine was inhibitory only when added before activation, indicating that it affects the activation process rather than the enzyme's activity. An increased concentration of cytosol partly prevented the inhibition by spermine. In semi-recombinant cell-free system, spermine inhibited the activation of NADPH oxidase as effectively as in the cell-free system (IC50 = 13 microM). Pretreatment of each recombinant cytosolic component with spermine revealed that they (especially p67phox) are sensitive to spermine. These results suggest that spermine interacts with cytosolic component(s) and impairs the assembly of NADPH oxidase.

Cell-Free System↗
PubMed1996

Changes in left ventricular volume and systolic function before and after the closure of ductus arteriosus in full-term infants.

Using echocardiographic techniques, the change in left ventricular (LV) volume and its effect on systolic function were studied before and after the closure of ductus arteriosus in 18 full-term infants. Examinations were performed twice in each infant, within 6 h after birth and on day 5, and the patency of the ductus with left-to-right shunt was confirmed at the first examination by Doppler echocardiography. A biplane Simpson's rule method was used for volume measurements. The LV end-diastolic volume, stroke volume, and cardiac output were more than 1.3-fold before the ductal closure, and the ejection fraction showed the similar change. However, the mean normalized systolic ejection rate, an index of contractility, and heart rate showed no significant difference. The Frank-Starling curve was obtained from the relationship between the LV end-diastolic and stroke volumes, and the LV performance was operated at a higher level on that curve when the ductus was open. Our data indicated that LV cardiac output was significantly higher during the patency of the ductus arteriosus and that this high cardiac performance might depend more on the Frank-Starling response to the volume load through the ductus arteriosus than on the increase of LV contractility and heart rate.

Cardiac Output↗
PubMed1996

Interpretation of BOLD MRI signals in rat brain using simultaneously measured near-infrared spectrophotometric information.

The purpose of this paper is to investigate the origin of the signal changes in the blood oxygenation level dependent effect (BOLD) and the influence of oxygen metabolism by utilizing near-infrared spectrophotometry (NIRS), which can measure deoxyhemoglobin (deoxyHb) content in blood vessels and redox states of cytochrome oxidase in whole tissue. Simultaneous MRI and NIRS measurements of the rat head were performed by changing oxygen concentrations in the inhalant gas. The signal intensity based on the BOLD effect depended on the influence of both arterial and venous blood deoxygenation in the brain, whose relative contributions differed at various points. In this paper, it is noteworthy that the differential apparent transverse relaxation rate between two conditions in the brain areas was linearly correlated with deoxyHb content determined by NIRS, except in severe hypoxia, and that no reduction of cytochrome oxidase occurred under the same conditions. These results indicate that the influence of hemodynamic changes on the signal intensity of the BOLD effect, and therefore functional MRI, can be elucidated by the NIRS information to determine actual changes of blood deoxygenation and blood volume.

Animals↗
PubMed1996

Establishment of a novel chondrocyte-like cell line derived from transgenic mice harboring the temperature-sensitive simian virus 40 large T-antigen gene.

We established a clonal chondrocyte-like cell line (TC6, TC stands for large T immortalized chondrocyte-like cell line) derived from articular cartilage of transgenic mice harboring a temperature-sensitive simian virus 40 large T-antigen gene. TC6 cells exhibited spindle-like or polygonal morphology and grew well at 33 degrees C in alpha-minimal essential medium supplemented with 0.5% fetal bovine serum. After confluence, these cells formed nodules that were positive for staining with alcian blue. Northern blot analysis demonstrated that these cells expressed messenger RNAs (mRNA) of the genes encoding cartilage-specific proteins such as type II procollagen, link protein, and aggrecan. Furthermore, the expression of type II procollagen and link protein genes in TC6 cells was regulated by parathyroid hormone and basic fibroblast growth factor, suggesting the presence of the receptors for the hormone and cytokine. The expression of link protein mRNA in TC6 cells was regulated in a time-dependent manner and was enhanced in culture within a week and increased continuously up to 10-fold by the end of 4 weeks. Expression of mRNAs encoding type II procollagen and versican/PG-M also increased moderately during the culture period. TC6 cells expressed type I procollagen mRNA, however, its level declined along with time in culture in contrast to the enhancement of the genes encoding cartilage-specific molecules in these cells. Interestingly, alkaline phosphatase mRNA expression was barely detectable in the TC6 cells in their growing phase while it was enhanced dramatically more than 7-fold by day 14 in culture. These results indicate that the TC6 cells could serve as an excellent model for the studies on chondrocyte physiology.

Animals↗
PubMed1996

Characterization, molecular cloning and expression of megakaryocyte potentiating factor.

We examined whether the conditioned media of 64 kinds of cell lines, which have been maintained by a protein-free culture system, could produce megakaryocyte potentiating (Meg-POT) activity. In these cell lines, HPC-Y5, established from human pancreatic cancer, was shown to have the highest level of activity. The megakaryocyte potentiating factor (MPF) was purified from its conditioned medium by a combination of ion-exchange chromatography, gel filtration and reversed-phase HPLC. The purified MPF showed Meg-POT activity almost equal to human (Hu) interleukin 6 (IL-6) in the presence of murine IL-3 in a colony-forming assay with mouse bone marrow cells. The molecular weight of MPF was estimated to be 33 kDa by SDS-PAGE. Glycopeptidase F digestion and amino sugar analysis of the factor demonstrated that MPF is a glycoprotein carrying at least one N-linked sugar chain. The N-terminal amino acid sequence of MPF was determined to be Leu-Ala-Gly-Glu-Thr-Gly-Gln-Glu-Ala-Ala-Pro-Leu-Asp-Gly-Val-Leu-Ala-Asn. The same or homologous amino acid sequence has not been found in known proteins, demonstrating that MPF may be a novel cytokine which has Meg-POT activity. Then, we isolated HuMPF cDNA from an HPC-Y5 cDNA library using polymerase chain reaction and plaque hybridization methods. The HuMPF cDNA encodes a polypeptide consisting of 622 amino acids, including a signal peptide of 33 amino acids, and with a deduced molecular weight of 68 kDa, although HPC-Y5 cells secrete a 33 kDa form of HuMPF. HuMPF cDNA does not show any significant homology with other known sequences. The cDNA was expressed in COS-7 and Chinese hamster ovary (CHO) cells, and Meg-POT activity was detected in their culture supernatant. The COS-7 cells secreted only a 33 kDa recombinant (r)HuMPF, however, an additional 30 kDa form was detected in the culture medium of CHO cells. The 33 kDa rHuMPF from CHO cells showed Meg-POT activity, but not the purified 30 kDa rHuMPF. The difference in structure and activity between the 33 and 30 kDa forms of HuMPF was ascribed to the existence in the 33 kDa form of the C-terminal 25 amino acid residues. The expression of MPF mRNA was examined by Northern blot analysis using labeled MPF cDNA as a probe. MPF mRNA was detected in HPC-Y5 cells, with an approximate molecular size of 2.4 kb. We also examined the expression of the MPF gene in various human tissues, and the 2.4 kb band was detected only in lung. Then, the immunohistocytochemical analysis and in situ hybridization revealed that MPF-producing cells were identified as lung macrophages. MPF may exhibit other biological activities such as regeneration of the lung tissues.

Amidohydrolases↗
PubMed1996

Cerebral hypoxia after hyperventilation causes "re-build-up" phenomenon and TIA in childhood moyamoya disease. A near-infrared spectroscopy study.

Near-infrared spectroscopy was used to monitor the sequential changes in the cerebral oxygenation state during and after hyperventilation in two children with moyamoya disease. Hyperventilation induced the build-up phenomenon and a decrease in the concentration of oxy-hemoglobin ([oxy-Hb]) and total hemoglobin ([t-Hb]). The termination of hyperventilation was followed by partial recovery of [oxy-Hb] and [t-Hb]. Subsequently, however, [oxy-Hb] and [t-Hb] decreased again and cytochrome oxidase was reduced. These impairments of the cerebral hemodynamics and oxygen metabolism were closely associated with the re-build-up phenomenon on EEG and with transient ischemic attacks (TIA). The present study implies that cerebral hypoxia after hyperventilation is closely related to the re-build-up phenomenon and ischemic attacks in children with moyamoya disease.

Anastomosis, Surgical↗