Biomedical subjects

H Arita

Publications and source records attributed to H Arita.

At least 145 records · Page 8Linked to original sources

PubMed1988

Characterization of thromboxane A2/prostaglandin H2 (TXA2/PGH2) receptors of rat platelets and their interaction with TXA2/PGH2 receptor antagonists.

Characterization of thromboxane A2/prostaglandin H2 (TXA2/PGH2) receptors of rat platelets was performed on both intact platelets and crude membrane fractions. The binding of [3H]U46619, a stable TXA2 mimetic, to intact platelets was found to be saturable and displaceable. Scatchard analysis of equilibrium binding at 24 degrees revealed a single class of binding sites with a Kd of 37 nM and a Bmax of 160 fmol/10(8) platelets. The binding affinity of [3H]U46619 to the platelet membrane fractions was remarkably and specifically enhanced by addition of Mg2+ without alteration of the maximum density level. Kinetic analysis for [3H]U46619 binding to the membrane fractions in the presence of 20 mM MgCl2 gave a K1 of 6.9 x 10(6) M-1 min-1 and a K-1 of 0.25 min-1, yielding a Kd (K-1/K1) of 36 nM; the value corresponded well to Kd values from Scatchard analysis in both intact (37 nM) and crude membrane fractions (39 nM). A series of TXA2/PGH2 receptor antagonists completely suppressed U46619 binding to rat platelets as well as collagen-induced platelet aggregation. The rank order of binding affinities to rat platelets (intact platelets or crude membranes) among the respective antagonists correlated well with (a) that of human platelet membrane fraction and (b) the potencies for suppression of collagen-induced platelet aggregation in rat. These results may support our proposed mechanism of TXA2/PGH2 action in collagen-stimulated platelets [K. Hanasaki et al., Thromb. Res. 46, 425 (1987)] and also suggest that they may provide a simple technique for evaluating synthetic TXA2/PGH2 receptor antagonists.

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

PubMed1988

Retinol induces platelet aggregation via activation of phospholipase A2.

All-trans-retinol induced aggregation of rabbit platelets, and this effect could be inhibited by a cyclooxygenase inhibitor and a thromboxane A2 (TXA2) receptor antagonist, indicating an essential role for endogenously produced TXA2. We found a two-phase arachidonic acid release in retinol-stimulated platelets. The first phase was induced by the action of retinol alone and not inhibited by TXA2 receptor antagonist. The second phase was induced via synergistic action of retinol and initially generated small amount of TXA2, and was inhibited by the antagonist. Moreover, we discussed that the arachidonic acid release may be mediated by the action of phospholipase A2.

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

PubMed1988

Different effects of two thromboxane A2/prostaglandin H2 receptor ligands, U46619 and S-145, on rabbit platelets.

Stimulation of rabbit platelets with U46619 induced platelet shape change, aggregation and secretion of ATP. However, S-145, which specifically binds to the thromboxane A2/prostaglandin H2 receptor like U46619, induced only shape change. Both compounds rapidly elevated cytoplasmic Ca2+ concentration although only U46619 evoked the formation of inositol phosphates. Chelating external Ca2+ with EGTA did not affect the S-145-induced platelet shape change while intracellular Ca2+ movement was severely reduced. These results suggest an essential role of phospholipase C in the induction of platelet aggregation and secretion and that some factor other than Ca2+ and phospholipase C participates in platelet shape change.

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

PubMed1988

Characterization of a new compound, S-145, as a specific TXA2 receptor antagonist in platelets.

S-145, a newly synthesized thromboxane A2 (TXA2) receptor antagonist, was investigated for its effects on platelet TXA2 receptors. In rat washed platelets, S-145 (100 nM) completely suppressed both U46619-induced shape change and collagen-induced shape change and aggregation, whereas aggregation responses provoked by ADP and thrombin were unaffected by S-145. S-145 had no effect on the cAMP levels in rat platelets as well as no inhibitory activity for the bindings of 3H-PGE1, 3H-Iloprost, 3H-PGD2 and 3H-PGF2 alpha to rat platelet membranes. TXB2 formation was not affected by S-145 (10 microM) in rat washed platelets. S-145 antagonized not only the collagen-induced aggregation but also the binding of 3H-U46619 in rat washed platelets with stereospecificity and high potency, which exerted an IC50 of 4.7 nM or a Ki of 2.5 nM, respectively. The potent activity of S-145 in inhibition of 3H-U46619 binding to crude platelet membranes was seen in rat as well as rabbit and human. These results demonstrate that S-145 is a highly potent and selective antagonist for platelet TXA2 receptors.

Animals↗

PubMed1988

Identification of thromboxane A2 receptor in cultured vascular endothelial cells of rat aorta.

The binding site for [3H]SQ29,548, a potent and selective thromboxane A2 (TXA2) receptor antagonist, was studied in cultured vascular endothelial cells (VEC) of the rat aorta. Specific binding of [3H]SQ29,548 to rat VEC at 24 degrees C was saturable, displaceable and of high affinity. Scatchard analysis of equilibrium binding studies indicated that rat VEC contain a single class of binding sites with a Kd of 2.7 nM. The number of maximum binding sites (25.8 fmol/10(6) cells) for [3H]SQ29,548 on rat VEC was respectively 23 and 3.2 times more than that on rat platelets and rat vascular smooth muscle cells. Four TXA2 receptor antagonists and U46619 completely suppressed [3H]SQ29,548 binding to rat VEC, whereas other prostanoids, such as PGD2, PGF2 alpha, PGE1 and Iloprost, displaced the ligand binding only at considerably higher concentrations. These results suggest that the specific receptor for TXA2 is present in rat vascular endothelial cells.

Animals↗

PubMed1988

Locations of medullary neurons with non-phasic discharges excited by stimulation of central and/or peripheral chemoreceptors and by activation of nociceptors in cat.

The activity of medullary neurons (146 units) with non-phasic discharges was recorded extracellularly in decerebrated, spontaneously breathing cats. The firing rate changes were studied during injections of 100% CO2-saturated saline into the vertebral artery and into the carotid artery. Thirty-nine of the 146 units were excited by the vertebral artery injections in the same time course as ventilatory augmentation. Eighteen of the 39 units did not react to peripheral chemoreceptor stimulation, i.e. they responded exclusively to central chemoreceptor stimulation. These 18 units were distributed in the caudal ('C') chemoceptive area of the ventral surface, in the vicinity of ventral respiratory group (VRG) neurons, and in the dorsal area ventral to the solitary tract. Twenty-one of the 39 units were excited by peripheral chemoreceptor stimulation, i.e. neurons with integrations of central and peripheral chemoreceptor inputs. They were densely packed in the nucleus paragigantocellularis lateralis, although also found in and around the rostral VRG neurons. Fifty-one of the 146 non-phasic units were excited (44) or inhibited (7) immediately after the vertebral artery injections, and their discharges returned to pre-injection levels prior to or during the early period of ventilatory augmentation. They also reacted to skin pinching, i.e. neurons with nociceptive action, and were found scattered variously in the ventral half of the medulla. Fourteen of the 146 units reacted to both chemoreceptor and nociceptor stimulations. The remaining 42 units were non-responsive. In summary, the distributions of the tonically active neurons excited by the central and/or peripheral chemoreceptors were not restricted to the ventral surface of the medulla.

Action Potentials↗

PubMed1988

Specific receptors for thromboxane A2 in cultured vascular smooth muscle cells of rat aorta.

The specific binding site for thromboxane A2 (TXA2) was studied in cultured vascular smooth muscle cells (VSMC) of the rat aorta. [3H]SQ29,548, a potent and selective TXA2 receptor antagonist, displayed high-affinity and specificity, as well as saturable and displaceable binding to rat VSMC in culture. Scatchard analysis of equilibrium binding at 24 degrees C revealed a single class of binding sites with a Kd of 1.7 nM and a Bmax of 8.0 fmol/10(6) cells. A series of TXA2 receptor antagonists completely suppressed [3H]SQ29,548 binding to rat VSMC, and the rank order of their inhibitory potencies (Ki) correlated well with the potencies for suppression of the U46619-induced contraction of rat thoracic aorta. These results suggest that specific binding sites for [3H]SQ29,548 represent the TXA2 receptor in rat VSMC.

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

PubMed1988

Induction of hypermetabolism in guinea pigs by endotoxin infused through the portal vein.

Endotoxin has been suspected of inducing hypermetabolism in animals. To delineate its mechanism more precisely, three experiments were performed using male Hartley guinea pigs that involved intermittent or continuous administration of endotoxin intraperitoneally for seven days and continuous infusion of low-dose endotoxin through the portal vein for five days. The doses of endotoxin were 0.3 mg, 0.36 mg, and 0.014 mg per 100 g of body weight per day, respectively. Hypermetabolic response was induced only in the experiment involving the infusion of endotoxin through the portal vein; the hypermetabolic response was correlated significantly with endotoxin levels in the plasma. These results indicate that endotoxin translocated from the gut into the mesenteric vein will induce hypermetabolism more readily than endotoxin translocated into the peritoneal cavity.

Animals↗

PubMed1988

Synthesis and in vitro activity of various derivatives of a novel thromboxane receptor antagonist, (+/-)-(5Z)-7-[3-endo-[(phenylsulfonyl)amino]bicyclo[2.2.1] hept-2-exo-yl]heptenoic acid.

Several sulfonyl derivatives (13a-t) of (+/-)-(5Z)-7-(3-endo-aminobicyclo[2.2.1]hept-2-exo-yl)heptenoic acid (VI) were synthesized via its methyl ester 10. Sulfonylation of 10 with 11a-t followed by saponification yielded 13a-t. Inhibitory concentrations (IC50) of the corresponding sodium salts 14a-t for platelet aggregation were measured with rat washed platelets (WP) and rabbit platelet-rich plasma (PRP). IC50 values of some derivatives for contraction of the rat aorta were also measured. The IC50 values for rat WP increased from 2.9 to 26 nM in the order of 14a, 14c, 14d, and 14b for derivatives with an arylsulfonyl residue, depending on the number of of intervening methylene groups. Methyl derivative 14e exhibited a higher IC50 value than n-hexyl derivative 14f. Substitution with a p-methyl, p-fluoro-, or p-chloro group in 14a retained or slightly reduced its IC50 value, while a p-n-pentyl or p-oxycarbonyl group augmented it significantly. The representative 14a suppressed (15S)-15-hydroxy-11,9-(epoxymethano)prosta-5(Z),13(E)-dienoic acid (U-46619) induced aggregation of human WP with an IC50 value of 7.7 nM, which corresponds well to the IC50 value of 3 nM obtained for each displacement by 14a of [3H]-U-46619 or (5Z,15 xi)-9 alpha, 11 alpha-(dimethylmethano)-15-hydroxy-16-(3-[125I]iodo- 4-hydroxyphenyl)-17,18,19,20-tetranor-13-aza-11a-carbathrombo-5-en oic acid [( 125I]-PTA-OH) bound to human WP. Synthesis of thromboxane A2 (TxA2) in human WP stimulated by thrombin was not inhibited by 14a at a concentration up to 10 microM. From these observations, the corresponding acid 13a (S-145) was concluded to be a potent TxA2 receptor antagonist.

Animals↗

PubMed1988

Molecular analysis of enterotoxin plasmids of enterotoxigenic Escherichia coli of 14 different O serotypes.

A total of 104 isolates of enterotoxigenic Escherichia coli derived from diarrheal patients from more than 10 countries were examined for serotype and toxigenicity. The transferability and molecular structure of the enterotoxin plasmids from each isolate were also examined. Enterotoxin plasmids from serotypes such as O6, O25, O27, O126, O128, and O159, which are frequently associated with E. coli diarrhea (classical strains) generally did not transfer by conjugation from clinical isolates, whereas those from serotypes such as O7, O17, O80, O98, O139, O150, and O153, which are rarely associated with diarrhea (rare strains) transferred almost always from the clinical isolates by conjugation. Analyses of enterotoxin plasmids by restriction endonucleases and DNA-DNA hybridization with the enterotoxin probes revealed that the strains with the same O serotype and toxigenicity carry closely related enterotoxin plasmids. These results suggest that classical strains resulted from the dissemination of ancestral clones which received enterotoxin plasmids long ago, while the rare strains acquired the enterotoxin plasmids recently by conjugation and have not yet been spread to the same degree as the ancestral clones.

Cloning, Molecular↗

PubMed1988

Rapid and transient excitation of respiration mediated by central chemoreceptor.

We evaluated rapid and transient changes in phrenic nerve (PN) and internal intercostal (IIC) activities when 0.2-0.5 ml of saline saturated with 100% CO2 was injected into the vertebral artery during various respiratory phases in decerebrated spontaneously breathing cats. The injections evoked an initial transient inhibition of ongoing PN or IIC activity with a mean onset latency of 0.17 s, followed by excitation of subsequent respiratory activities with an onset latency ranging from 0.4 to 2.7 s; the average onset latency of expiratory excitation (1.49 s) was significantly longer than that of inspiratory facilitation (0.89 s). The initial inhibitory responses were analogous to reflex effects of injections of phenyl biguanide, indicating that the initial inhibition was due to activation of vascular nociceptors and the subsequent excitation was due to stimulation of the central chemoreceptors. In addition, CO2-saline injections during hypocapnic apnea developed a quick reappearance of respiratory rhythm, and the first facilitatory effect appeared in tonic IIC activity, which became more active before rhythm started. In summary, the present study, by use of a technique of vertebral arterial injections of 100% CO2-saline, revealed dynamic properties of respiratory control system mediated by central chemoreceptors and vascular nociceptors.

Animals↗

PubMed1988

Effect of cisternal administration of acetazolamide on rapid excitation of central chemoreceptors.

We evaluated rapid and transient changes in phrenic (PN) and internal intercostal (IIC) activities when 0.5 ml of saline saturated with 100% CO2 was injected into the vertebral artery at the C1 level before and after cisternal administration of carbonic anhydrase inhibitor (acetazolamide) in decerebrated, spontaneously breathing cats. Before acetazolamide administration, the injections evoked an initial, transient inhibition of ongoing PN or IIC activity, followed by excitation of subsequent respiratory activities with a short onset latency of less than 3 sec. On the other hand, cisternal administration of acetazolamide abolished both the initial inhibition and the subsequent rapid excitation of respiratory activities, although there still existed a delayed, weak and prolonged excitation of respiration. These results indicated that hydration of CO2 accelerated by carbonic anhydrase within the brain would be essential for the rapid changes in respiratory activity mediated by the central chemoreceptors.

Acetazolamide↗

PubMed1987

Two phasic generation of thromboxane A2 by the action of collagen on rat platelets.

Two-phase thromboxane A2 (TXA2) generation was observed in washed rat platelets stimulated by collagen. One coincided with shape change and the other with aggregation, and both reactions were inhibited by indomethacin. The collagen-induced first phase was not affected by treatment of the platelets with TXA2 receptor antagonist BM13177, while the shape change, the second phase TXA2 generation and aggregation were completely suppressed. U46619, a stable TXA2 mimetic, induced only platelet shape change and not aggregation or endogenous icosanoid mobilization. However, upon addition of U46619 to platelets previously stimulated by collagen in the presence of indomethacin, icosanoids formation was induced together with aggregation. These results suggest that both the collagen-induced initial TXA2 and the occupation of the receptor by collagen might be a trigger for the second-phase TXA2 formation in concert with platelet aggregation.

Animals↗

PubMed1987

Morphological and physiological properties of caudal medullary expiratory neurons of the cat.

The activity of respiratory neurons in the caudal part of the nucleus retroambigualis (NRA) was recorded intracellularly in decerebrated, spontaneously breathing cats. Spinal projections of these neurons were determined by antidromic stimulation at the C3 segment. A high concentration of bulbospinal expiratory (BS-E) neurons was identified in the caudal NRA, whereas the inspiratory (I) neurons, not activated antidromically, were also found to be intermingled in the same region. The BS-E neurons had ramp-like depolarizing potentials during expiration, and repolarized rapidly at the onset of phrenic nerve discharge. The I neurons depolarized abruptly in the early I phase, and repolarized gradually thereafter, namely, they were early-I neurons. Intracellular current injections revealed postsynaptic inhibition of the BS-E neurons during inspiration, as evidenced by inhibitory postsynaptic potential reversal. Using the technique of intracellular labeling with horseradish peroxidase, seven well-stained expiratory cells located in the caudal NRA revealed detailed information about axonal morphology: the axon projected rostrally and dorsomedially for the first 2 mm after emerging from the soma, then turned caudally and ventrally along two different courses, and crossed the midline of the medulla almost at the same rostrocaudal level as the soma. No axon collaterals were observed along the length of the stained portion, indicating that the BS-E neurons cannot influence other respiratory neurons in the brainstem. It has been concluded that the NRA expiratory neurons are involved only in spinal action, and that they receive a postsynaptic inhibition during inspiration.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1987

Analysis of the plasmids of Escherichia coli O148:H28 from travellers with diarrhea.

98 Escherichia coli strains of serotype O148:H28 isolated from diarrheal patients from 10 Asian countries and Mexico at Osaka Airport Quarantine were analyzed for enterotoxigenicity and plasmid profile. They were classified into three groups. The first group contained 44 strains that were non-enterotoxigenic and carried 3.9 kb and 50 kb non-enterotoxin plasmids. The second group contained 9 strains that produced LT and ST. They carried a 45 kb enterotoxin plasmid, and 4.6 kb and 9.2 kb non-enterotoxin plasmids. The third group contained 45 strains that produced ST. They carried a 40 kb enterotoxin plasmid, and non-enterotoxin plasmids other than 3.9 kb, 4.6 kb, 9.2 kb and 50 kb. Southern blot hybridization demonstrated that all the non-enterotoxin or enterotoxin plasmids carried by the strains of the same group were identical or similar. These results suggested that the 98 E. coli strains with O148:H28 serotype were derived from three clones, and that the individual strains among each group were derived from a single clonal strain.

Bacterial Toxins↗

PubMed1987

Signal transduction in collagen-stimulated rat platelets is composed of three stages.

A stable thromboxane A2 (TXA2) mimetic, U46619, induced a shape change of rat platelets, but did not induce phosphoinositide breakdown, aggregation or secretion. However, when U46619 was added to platelets which had been previously stimulated with collagen in the presence of indomethacin, all biological responses were induced about 1 min after the occurrence of shape change. Furthermore, two phases of phosphorylation of myosin light chain (MLC) were observed under the same conditions, one coinciding with shape change and the other with aggregation. Similar two-phase Ca2+ mobilization has been observed using aequorin (Nakano, T., Terawaki, A., & Arita, H. (1986) J. Biochem. 99, 1285-1288). From these results, collagen-induced signal transduction is considered to be composed of three stages. The first stage is the initial TXA2 generation. The second stage involves inositol trisphosphate-independent first-phase Ca2+ mobilization and the first-phase MLC phosphorylation by the action of TXA2 alone, leading to the shape change of platelets. The third stage is initiated by an abrupt phosphoinositide breakdown via the synergistic action of TXA2 and occupation of the collagen receptor, and the resulting inositol trisphosphate may induce the second-phase Ca2+ mobilization to produce the second-phase MLC phosphorylation together with aggregation and secretion.

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

PubMed1987

Biphasic action of phospholipase A in collagen-stimulated rat platelets.

The formation of thromboxane A2 (TXA2) in collagen-stimulated rat platelets was successfully divided into two stages, an initial and a second one, by the specific TXA2 receptor antagonist, ONO3708. In the presence of this antagonist, only the initial TXA2 production was observed, without the subsequent platelet shape change and aggregation. Collagen causes the specific cleavage of arachidonic acid from phosphatidylinositol (PI) in the initial stage, whereas in the absence of the antagonist, it caused decrease in the arachidonic acid levels in phosphatidylethanolamine (PE) and PI with concomitant formation of the respective lyso-forms. These results demonstrate that phospholipase A (PLA) preferentially acts on PI to release arachidonic acid which leads to the initial TXA2 production, which might be a trigger for the second release of arachidonic acid from PE and PI.

Arachidonic Acid↗

PubMed1987

Involvement of the Na+/H+ antiporter in activation of rat platelets by collagen.

The rapid Ca2+ increase shown by quin2-loaded platelets was found to be an artifact, probably due to light scattering elicited by collagen. Further findings as to fura2-loaded platelets offered additional support, demonstrating that the initial activation of phospholipase A2 (PLA2) does not require cytoplasmic Ca2+ mobilization. A possible role of the Na+/H+ antiporter as a trigger for collagen-induced activation of PLA2 in rat platelets was presented for the first time.

Animals↗