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H Arita

Publications and source records attributed to H Arita.

At least 109 records · Page 6Linked to original sources
PubMed1991

cAMP negatively regulates mRNA levels of actin and tropomyosin in rat cultured vascular smooth muscle cells.

The isoform expression patterns of actin and actin-binding proteins have been reported to be good markers for phenotypic modulation of rat vascular smooth muscle cells. In order to elucidate the regulatory mechanism of actin and tropomyosin isoform expression on a molecular basis, we examined the effects of various agents on the isoform expression patterns of actin and tropomyosin at the mRNA level in smooth muscle cells. We found that cAMP-elevating agents induced drastic decreases in the amounts of alpha-smooth muscle type actin and alpha-tropomyosin transcripts, the expression of other actin and tropomyosin isoforms being also repressed, but to a lesser extent. The results of the experiment involving RNA synthesis inhibitors strongly suggest that activation of some mRNA-specific degradation machinery by cAMP might be responsible at least for the rapid disappearance of alpha-smooth muscle type actin and alpha-tropomyosin transcripts in smooth muscle cells.

1-Methyl-3-isobutylxanthine↗
PubMed1991

Kinetic studies on stereospecific recognition by the thromboxane A2/prostaglandin H2 receptor of the antagonist, S-145.

1. The mechanism for the stereospecific recognition of the antagonist S-145 by the thromboxane A2 (TXA2)/prostaglandin H2 (PGH2) receptor was examined by ligand-binding techniques in rat vascular smooth muscle cells (VSMCs) and in human platelet membranes. 2. Scatchard analysis revealed the existence of a single class of binding sites with the same maximum number for both [3H]-(+)-S-145 and [3H]-(-)-S-145 in both cell types. The dissociation constants (Kd) for the binding of the (+)-isomer in rat VSMCs and human platelet membranes were, respectively, 0.40 +/- 0.03 and 0.20 +/- 0.02 nM, each value being lower than that for the (-)-isomer (3.57 +/- 0.74 and 2.87 +/- 0.08 nM, respectively). 3. The rank orders of potency (Ki) for a series of TXA2/PGH2 ligands at inhibiting [3H]-(+)-S-145 binding were highly correlated with those determined for [3H]-(-)-S-145 binding in both cell preparations. 4. Kinetic analysis of the binding of both radioligands revealed a much lower dissociation rate constant (k-1) and a slightly greater association rate constant (k1) for the (+)-isomer compared to those for the (-)-isomer. 5. These results suggest that it is at the stage of dissociation from the TXA2/PGH2 receptor that the stereochemistry of the optical isomers of S-145 confers their difference in affinity for these receptors in rat VSMCs and human platelet membranes.

Animals↗
PubMed1991

Opposing effects of 5-hydroxytryptamine on two types of medullary inspiratory neurons with distinct firing patterns.

1. Activity of inspiratory neurons was recorded extracellularly from the caudal portion of the nucleus ambiguous (0-3.5 mm rostral to the obex) in decerebrated, spontaneously breathing cats. Using a micropressure ejection method, we tested the responsiveness of the inspiratory neurons to direct applications of serotonin (5-HT) and noradrenaline (NA) in comparison with applications of glutamate and control artificial cerebrospinal fluid (ACSF) by means of a multibarreled micropipette. 2. We made detailed examinations of 52 inspiratory neurons that were excited by glutamate but did not react to control ACSF. Those inspiratory neurons were further classified into two subgroups based on the differences in firing patterns: inspiratory neurons with an augmenting firing pattern ["augmenting I units" (22/52)] and inspiratory neurons with a decrementing firing pattern ["decrementing I units" (30/52)]. 3. Although application of NA produced predominantly inhibitory effects on both the decrementing (22/30) and augmenting I units (20/22), application of 5-HT resulted in distinct or opposing effects on these two types of inspiratory neurons: the decrementing I units (25/30, 83%) were excited by 5-HT, whereas the augmenting I units (17/22, 77%) were inhibited by 5-HT. 4. The excitation of the decrementing I units with 5-HT was characterized by a long onset-latency of response and a prolonged recovery process. The increase in firing rate occurred not only during the inspiratory active phase but also during the expiratory phase.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

[Effect of (+)-S-145 calcium salt dihydrate, an orally active antagonist of the thromboxane A2/prostaglandin endoperoxide receptor, on platelet aggregation].

The effect of (+)-S-145, (1R, 2S, 3S, 4S)-(5Z)-7-(3-phenylsulfonylaminobicyclo [2.2.1] hept-2-yl) heptenoic acid on human and guinea pig platelet aggregation was examined. (+)-S-145 sodium salt inhibited human platelet aggregation induced by arachidonic acid (AA), 9,11-methanoepoxy-PGH2 (U 46619), collagen, ADP or epinephrine with the IC50 being 0.047-0.146 microM in an in vitro system. When (+)-S-145 calcium salt dihydrate was administered orally to guinea pigs, it inhibited AA-, U-46619- or collagen-induced platelet aggregation dose-dependently with the minimum effective dose being 0.03 mg/kg, and the effective duration being maximally 3 hr. The inhibiting potency and effective duration of (+)-S-145 calcium salt dihydrate after multiple administrations, once a day (0.5 mg/kg) for 7 days, were almost the same as those after a single administration. Although (+)-S-145 sodium salt showed a partial agonist effect (shape change) on platelets in vitro, the effect diminished after pretreatment of the platelets with a lower dose of this compound. These data suggest that (+)-S-145 calcium salt dihydrate is an orally effective potent platelet aggregation inhibitor.

Adenosine Diphosphate↗
PubMed1991

[Clinical and pharmacokinetics studies of ceftriaxone upon 2g once daily administration in respiratory tract infections].

Clinical studies on ceftriaxone (CTRX) were conducted with 2 g once daily administration to respiratory tract infections. In addition, CTRX concentrations in serum, sputum and urine were determined. The results obtained are summarized as follows: 1. Clinical responses to CTRX in a total of 29 cases with respiratory tract infections were excellent in 7 cases, good in 13, fair in 8 and poor in 1 with a response rate of 69.0%. 2. CTRX concentrations in serum, sputum and urine (total and free body) were determined in 3 cases after intravenous drip infusion of 2g CTRX. Peak levels in sputum were 2.6 to 7.8 micrograms/ml, and CTRX maintained high sputum levels for 12 to 24 hours after administration.

Aged↗
PubMed1990

A simple and sensitive method for determining transcription initiation site: identification of two transcription initiation sites in rat group II phospholipase A2 gene.

We developed a simple and sensitive method for assigning transcriptional initiation sites, and applied it to characterize the transcriptional unit of rat group II phospholipase A2 (PLA2) gene. Our method involves the primer extension reaction followed by detection of its products by hybridization. Using this method, we were able to map two transcriptional initiation sites on the nucleotide sequence of the core promoter region of PLA2 gene with one-base resolution without any difficulties.

Animals↗
PubMed1990

Receptor-mediated mitogenic effect of thromboxane A2 in vascular smooth muscle cells.

The effects of thromboxane A2 (TXA2) on the proliferation of vascular smooth muscles cells (VSMC) were examined using primary cultures of VSMC from rat aorta. U46619, a stable TXA2 mimetic, stimulated DNA synthesis of VSMC only in the presence of insulin. The effect was concentration-dependent with a half-maximal effect obtained at approximately 1 x 10(-8) M. The mitogenic effect of U46619 was larger than that of endothelin, another mitogen derived from endothelium. Among several TXA2/PGH2 analogs, the proliferative activity was detected only in the agonists, and not in the antagonists or in the metabolite of TXA2. A series of TXA2/PHG2 receptor antagonists completely suppressed the U46619-stimulated DNA synthesis as well as the [3H]SQ29,548 binding to the TXA2/PGH2 receptors in VSMC. The rank order of binding affinities to the receptors among the respective antagonists correlated well with the potencies for suppression of the proliferative effects of U46619. The mitogenic effects of U46619 were also attenuated by the presence of calcium antagonists. U46619 caused activation of phospholipase C with the production of inositol trisphosphate, leading to increases in the intracellular free Ca2+ concentration as measured with the fluorescent indicator fura-2. These results suggest that TXA2 induces mitogenic effects on VSMC through binding to its specific receptors. This effect of TXA2 on the proliferation of VSMC may be related to the development of atherosclerosis.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1990

Enhanced expression of group II phospholipase A2 gene in the tissues of endotoxin shock rats and its suppression by glucocorticoid.

We studied the regulation of group II phospholipase A2 (PLA2-II) gene in vivo, using endotoxin shock rat as a model for systemic inflammation. Administration of endotoxin into rats increased PLA2 activity in the plasma, as described by Vadas and Hay, using endotoxin-challenged rabbit. Specific absorption of this activity by anti-PLA2-II antibody indicated that the released PLA2 was PLA2-II. The levels of PLA2-II mRNA were elevated in the aorta, spleen, lung, and thymus but not in the liver and kidney. The tissues with high PLA2-II mRNA contents released a greater amount of PLA2-II than the tissues of control rats. These results suggest that in endotoxin shock rats, PLA2-II is synthesized de novo in the above tissues and released into circulation. Furthermore, our present study demonstrates that glucocorticoid suppresses the enhanced expression of the PLA2-II gene in the tissues of endotoxin shock rats.

Animals↗
PubMed1990

Glucocorticoids suppress group II phospholipase A2 production by blocking mRNA synthesis and post-transcriptional expression.

We investigated the effects of glucocorticoids on group II phospholipase A2 (PLA2) expression in rat cultured smooth muscle cells. Both forskolin-induced and tumor necrosis factor (TNF)-induced PLA2 release responses were almost completely blocked by 10 and 100 nM dexamethasone, respectively, as assayed by protein blotting and PLA2 activity assays. Dexamethasone-mediated inhibition of PLA2 release appeared to be mediated by the glucocorticoid receptor. Dexamethasone at concentrations greater than 10 nM inhibited forskolin-induced elevation of the group II PLA2 mRNA level but not TNF-induced elevation. These data suggest that the mechanism mediating forskolin-induced mRNA accumulation is sensitive to glucocorticoids, but the mechanism mediating the TNF-induced accumulation is not. Inhibition of TNF-induced PLA2 release by glucocorticoids may be explained by the blocking of post-transcriptional synthesis of the group II PLA2.

Animals↗
PubMed1990

Phorbol ester-induced expression of the common, low-affinity binding site for primary prostanoids in vascular smooth muscle cells.

We showed in an earlier study (Hanasaki, K., and Arita, H. (1989) Biochim. Biophys. Acta 1013, 28-35) that there is a common, low-affinity binding site for primary prostanoids in cultured vascular smooth muscle cells (VSMC). This site, called the "primary prostaglandin (PG) site," can be evaluated by radioreceptor assay using [3H]PGF2 alpha and [3H]PGE1. Comparison of the capacity of several PGF2 alpha analogs to displace both radioligand bindings indicated strict requirements of the 15-hydroxy group as well as the 13,14-double bond in the omega-side chain of prostaglandins for recognition of this site. Treatment of VSMC with phorbol 12-myristate 13-acetate (PMA), a known protein kinase C activator, led to concentration- and time-dependent increases in the binding activities of [3H] PGF2 alpha as well as [3H]PGE1, which could be completely suppressed by the addition of protein kinase C inhibitor, H-7. The PMA effects could be mimicked by phorbol 12,13-dibutylate, but not by inactive phorbol ester. Scatchard analyses revealed an approximately 8-fold increase in the binding density with unaltered binding affinity after PMA treatment. This expression of the primary PG site was blocked by the addition of cycloheximide and actinomycin D. In contrast, PMA did not affect the binding activity for the thromboxane A2/prostaglandin H2 receptor in VSMC. These results suggest that the expression of the primary PG site is regulated by a protein kinase C-dependent mechanism in VSMC.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1990

Group II phospholipase A2 mRNA synthesis is stimulated by two distinct mechanisms in rat vascular smooth muscle cells.

Two potent inflammatory mediators, interleukin 1 (IL-1) and tumor necrosis factor (TNF) as well as lipopolysaccharide (LPS) increased group II phospholipase A2 (PLA2) mRNA levels, which resulted in enhanced secretion of the PLA2 enzyme from rat smooth muscle cells. cAMP-elevating agents also stimulated the release of PLA2 and increased the mRNA, but IL-1, TNF and LPS did not affect cAMP levels. Furthermore, the effects of TNF and cAMP-elevating agents were not additive but synergistic. Therefore, we concluded that the level of rat group II PLA2 mRNA is controlled at least by two distinct mechanisms, one involves cAMP and the other is mediated by TNF, IL-1 and LPS. This study also suggests important roles of group II PLA2 in pathogenesis of vascular inflammation.

1-Methyl-3-isobutylxanthine↗
PubMed1990

Mitogenic response of near-diploid mouse cell line m5S/1M induced by epidermal growth factor.

A nonmalignant near-diploid cell line m5s/1M, established by Sasaki and Kodama (J. Cell. Res., 131:114-122, 1987), was shown to respond to the epidermal growth factor (EGF). The m5s/1M cells showed high sensitivity to post-confluence inhibition of cell division and formed a uniform monolayer after the cells had become confluent. The addition of EGF resulted in loss of contact-dependent inhibition of growth and caused a massive piling up of a multilayered array of cells after they had become confluent. When EGF was removed from the medium, the cell number decreased rapidly, and the cells formed a uniform monolayer at the density observed in the absence of EGF. m5S/1M cells have high- and low-affinity receptors for EGF (approximately 40,000 receptors per cell), and the apparent dissociation constants of the EGF-binding reactions were 3.3 nM and 0.15 nM, respectively. The effect of EGF on the intracellular mobilization of Ca2+ and the formation of inositol phosphates was studied by using the calcium-sensitive fluorescent indicator fura 2 and [3H]inositol. EGF had no effect either on the mobilization of cytosolic free calcium [( Ca2+]i) or on the formation of inositol phosphates in m5s/1M cells, whereas bradykinin induced a rapid increase in both [Ca2+]i and inositol phosphates. Analysis of the glycosphingolipid (GSL) composition of m5S/1M cells showed that globotriaosylceramide (Gb3Cer), which is known to be a Burkitt lymphoma-associated antigen, is specifically expressed in the EGF-treated cells. The expression of Gb3Cer is dependent on the presence of EGF, with a reversible shift in GSL composition being observed in the presence or absence of EGF.

Animals↗
PubMed1990

Synthesis of thromboxane receptor antagonists with bicyclo[3.1.0]hexane ring systems.

Thromboxane A2 receptor antagonists 11a, 15a, 26a, 30a, 34a, 36a, 46a, 52a, 61a, 72a, and 82a, which contain 6-oxabicyclo[3.1.0]hexane, 6-thiabicyclo[3.1.0]hexane, bicyclo[3.1.0]hexane, or 6,6-dimethylbicyclo[3.1.0]hexane ring systems with heptenoic and (phenylsulfonyl)amino side chains, and their corresponding sodium salts and methyl esters were synthesized. This study then examined the inhibitory effects of their sodium salts for the platelet aggregation induced by arachidonic acid with rabbit platelet-rich plasma and platelet aggregation induced by collagen with rat washed platelets.

Animals↗
PubMed1990

In vivo study on medullary H(+)-sensitive neurons.

Using the micro pressure ejection technique, we examined responses of medullary neurons with nonphasic discharges (164 units) to direct application of acidified mock cerebrospinal fluid (CSF, pH 6.85-7.05) in decerebrated spontaneously breathing cats. We found 16 H(+)-sensitive cells; they were excited promptly on application of approximately 500 pl of acidified mock CSF in the vicinity of the neuron under investigation, whereas they were unaffected by microejection of the control mock CSF (pH 7.25-7.60). Of the 16 H(+)-sensitive cells, 10 units were further found to be excited by transcapillary stimulation of the central chemoreceptors by using a method of intravertebral arterial injection of CO2-saturated saline. The discharges increased in a similar time course to that of ventilatory augmentation. Distributions of these 10 specific H(+)-sensitive cells were found in the vicinity of nucleus tractus solitarii as well as deep in the ventrolateral medulla. The present results suggest a possibility that pH-dependent central chemoreceptors, if any, would be located in two distinct medullary regions described in this study.

Animals↗