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T Segawa

Publications and source records attributed to T Segawa.

At least 109 records · Page 6Linked to original sources
PubMed1988

Structure-activity relationship of hylambatin and its fragments as studied in the guinea-pig ileum.

Hylambatin (Hyl), a dodecapeptide isolated from the skin of the African frog, Hylambates maculatus, belongs to the family of tachykinin or physalaemin-like peptides. Hylambatin and its 12 fragments were tested in the guinea-pig ileum preparation for contractile activities. All fragments except 3 had contractile activities. The C-terminal fragment as short as the octapeptide sequence was at least as active as the parent molecules. The heptapeptide fragment (Hyl6-12) and the hexapeptide fragment (Hyl7-12) were less active and the C-terminal pentapeptide fragment (Hyl8-12) and the N-terminal hexapeptide fragment (Hyl1-6) were much less active. The N-terminal pentapeptide fragment (Hyl1-5) and the N-terminal fragment from which the N-terminal Asp or Asp-Pro residues were removed (Hyl2-6, Hyl3-6), were inactive at doses used.

Animals↗
PubMed1988

Exponential increases in pulmonary intravascular and extravascular fluid volumes by overperfusion with dextran 70 in anesthetized dogs.

In the lung overperfused by dextran 70, it is not known how intravascular blood volume and extravascular water volume increase as a function of pulmonary microvascular pressure. To determine their characteristics, we produced an overperfusion state (high pressure and high blood flow) by infusing dextran 70 (100 ml/kg over 30 min) into 15 anesthetized dogs. Using the thermal and dye dilution technique, we simultaneously estimated the pulmonary blood volume (PBV) and the extravascular lung thermal volume (EVLTV), and correlated mathematically these variables with pulmonary artery end-diastolic pressure (PAEDP). Here, we defined PAEDP as the pulmonary microvascular pressure. From the values determined before, during and after dextran 70 infusion, we obtained the following exponential relations. PBV(ml/kg) = 30[1-0.902(e-0.021PAEDP(mmHg)) EVLTV(ml/kg) = 5.15(e0.027PAEDP (mmHg)) From these mathematical relations, we conclude that: (1) the pulmonary blood volume increases rapidly at low pressure and slowly at high pressure; and (2) the pulmonary extravascular water volume increases slowly at low pressure and then increases rapidly at high pressure. In addition, this equation indicates that the critical pressure from which the pulmonary extravascular water volume exceeds the upper limit of its normal volume is about 17 mmHg in PAEDP. Infusion of dextran 70 increased plasma macromolecular osmotic pressure from 20.8 +/- 0.6 (mean +/- SD) mmHg before infusion to 43.7 +/- 1.4 mmHg after infusion. Therefore, dextran 70 does not change the critical microvascular pressure against pulmonary edema.

Animals↗
PubMed1988

Chronic effects of imipramine and lithium on postsynaptic 5-HT1A and 5-HT1B sites and on presynaptic 5-HT3 sites in rat brain.

The effects of chronic treatment with imipramine, a tricyclic antidepressant, or lithium, an antimanic-depressive illness drug, on postsynaptic serotonin-1A (5-HT1A) and 5-HT1B sites and on presynaptic 5-HT3 sites in the frontal cortex and hippocampus from rat brains were studied. Chronic i.p. administration (21 days) of imipramine reduced the maximum number of binding sites (Bmax) for postsynaptic 5-HT1A as monitored by the radioligands 3H-5-HT or 3H-8-hydroxy-2-(di-n-propylamino)tetralin (3H-8-OH-DPAT), but did not change the Bmax for postsynaptic 5-HT1B and presynaptic 5-HT3 in either the frontal cortex or the hippocampus. Chronic i.p. administration (21 days) of lithium reduced the Bmax for postsynaptic 5-HT1A sites in the hippocampus, but not in the frontal cortex. There was a specific difference between imipramine and lithium regarding the inhibitory effect on postsynaptic 5-HT1A sites in the frontal cortex. In addition, lithium decreased the affinity of presynaptic 5-HT3 sites in the hippocampus. These findings may be also consistent with the inhibitory effect of lithium on presynaptic autoreceptors, which results in an increase of 5-HT release. It is concluded that enhanced 5-HT neurotransmission which develops during chronic treatment with imipramine or lithium seems tob e related to the down-regulation of postsynaptic 5-HT1A receptors in addition to postsynaptic 5-HT2 receptors, which may also have an important role in the antidepressant effects of these drugs.

Animals↗
PubMed1987

Neurotensin receptors on the rat liver plasma membranes.

Neurotensin (NT) is now classified as a brain-gut peptide in the central nervous system and gastrointestinal tract. In the present study, we characterized the NT receptors on the rat liver plasma membranes. The specific binding of [3H]NT was time dependent, reversible, and saturable. Scatchard analysis of the specific binding data yielded two classes of binding sites, a high affinity site and a low affinity site. The average maximum number of binding sites (Bmax) amounted to 13.3 +/- 1.1 fmol/mg protein at high affinity site and 122.3 +/- 21.5 fmol/mg protein at low affinity site, respectively. The dissociation constant (Kd) had values of 0.39 +/- 0.01 nM at high affinity site and 8.1 +/- 1.1 nM at low affinity site, respectively. The amount of specifically bound [3H]NT was significantly reduced in the presence of mono and divalent cations, EDTA, EGTA and a peptidase inhibitor bacitracin, NT1-13 competed with [3H]NT for its binding site with an IC50 of 0.19 nM at high affinity site (0.2 nM concentration of [3H]NT) and 0.7 nM at low affinity site (4.0 nM concentration of [3H]NT). Xenopsin, a NT analogue separated from the skin of Xenopus laevis, was equipotent (IC50 0.75 nM) with NT1-13 at 4.0 nM concentration of [3H]NT. C-terminal sequence of NT contains the structure necessary for interaction with NT binding sites whereas N-terminal sequence had no binding activity. Since NT has a hyperglysemic and a hypercholesterolemic effects in rats, these NT receptors on the rat liver plasma membranes may be involved in the hyperglycemia and/or hypercholesteroremia induced by NT.

Amino Acid Sequence↗
PubMed1987

Autogenous regulation of the Saccharomyces cerevisiae regulatory gene GAL80.

We have suggested previously from Northern blot analysis that transcription of the negative regulatory gene GAL80 was controlled positively by another regulatory gene GAL4, and negatively by GAL80 itself, in similar way to GAL1, GAL7 and GAL10 genes encoding galactose-metabolizing enzymes in Saccharomyces cerevisiae. To study further the controlled expression of GAL80, we have exploited the gene fusion technique. We constructed gene fusions consisting of 5' fragments of GAL80 and a 5' truncated lacZ of Escherichia coli, and introduced the GAL80'-'lacZ fusions into wild-type yeast or various GAL4 or GAL80 mutants using multiple-copy or single-copy plasmid vectors. We then studied beta-galactosidase activity in the resultant transformants under uninduced, induced or glucose-repressed conditions. Expression of the GAL80'-'lacZ fusions was clearly under the control of Gal4/Gal80. Next we constructed GAL7'-'lacZ fusions, whose upstream activating sequence (UAS) from GAL7 was replaced with a GAL80 fragment containing a UAS-like sequence located in the 5' flanking region of GAL80. Synthesis of beta-galactosidase directed by the hybrid genes was inducible by galactose exactly like the original GAL7'-'lacZ fusion with a UAS from GAL7. Finally we constructed a GAL7-GAL80 hybrid gene, in which the entire 5' flanking region was derived from GAL7. When the chromosomal GAL80 gene in wild-type yeast was replaced with the hybrid gene, the uninduced level, but not the induced level, of the GAL10-encoded enzyme (uridine diphosphoglucose-4-epimerase) was significantly increased.

Galactose↗
PubMed1987

Histamine acting on H2 receptors stimulates phospholipid methylation in synaptic membranes of rat brain.

Histamine stimulated [3H]methyl group incorporation into phospholipids in crude synaptic membranes of rat whole brain (without cerebellum) in modified Krebs-Ringer solution containing the methyl donor S-adenosyl-[methyl-3H]methionine. The transient increase of [3H]methyl incorporation into lipids peaked within 45 s after addition of histamine (5 or 10 microM) and decreased the basal level in 60 s. Histamine-stimulated [3H]methyl incorporation was increased linearly in a protein concentration-dependent manner. The stimulation was temperature and histamine concentration dependent. TLC analysis of a chloroform/methanol extract indicated that radioactive phospholipids (phosphatidylcholine, phosphatidyl-N,N-dimethylethanolamine, and phosphatidyl-N-monomethylethanolamine) accounted for 60-65% of the total radioactivity recovered. The synaptosomal fraction had the highest specific activity of all the subfractions of crude synaptic membranes (P2). Histamine-induced [3H]methyl incorporation was inhibited by addition of cimetidine (0.01-10 microM) or famotidine (0.01-1.0 microM) in a concentration-dependent manner but not by mepyramine (0.1-10 microM) or diphenhydramine (0.1-10 microM). The stimulation of [3H]methyl incorporation was also observed by addition of impromidine (0.01-10 microM) or dimaprit (1.0 microM-1.0 mM) in a concentration-dependent manner but not by 2-pyridylethylamine (1.0 microM-1.0 mM). These results indicate that phospholipid methylation is induced by histamine acting on H2 receptors in rat brain synaptosomes.

Animals↗
PubMed1987

Pressure-volume relationships in the pulmonary "venous" system in living dogs.

In this study, we examined the pressure-volume (P-V) relationships of the pulmonary "venous" (P'V') system in anesthetized living dogs, and assessed compliance by fitting the derived data of the P-V relationships to the exponential function. By definition, the P'V' system consists of the pulmonary veins and the left atrium. The pulmonary "venous" volume (P'V'V) was determined with our modified double indicator dilution method using a single injection and double sampling technique. The mean left atrial pressure (PLA) was measured directly. To observe sequential changes over a wide range of the P-V relationships, dogs were studied from the control state through the volume-loaded state with dextran. The P'V'V ranged from 3.4 to 12.2 ml X kg-1 and the PLA from 3.2 to 40.6 mmHg. We fitted the data of the P-V relationships (n = 24) to the exponential function, yielding an equation: P'V'V (ml X kg-1) = 19(1-0.833(e-0.017PLA(mmHg)). We then differentiated an above equation to estimate the slope of this curve (static compliance), giving the equation: dV/dP (ml X mmHg-1 X kg-1) = 0.269(e-0.017PLA(mmHg)). Therefore, at PLA of 10 mmHg (normal level), the compliance is 0.227 ml X mmHg-1 X kg-1. The compliance, obtained with an application of the present results in dogs to man, (disregarding expected species differences), coincides well with that in man determined with our indirect method.

Animals↗
PubMed1987

Effect of concanavalin A on 5'-nucleotidase activity of rabbit blood platelets.

Ecto-5'-nucleotidase (ecto-5'-NU) of platelets was enhanced by concanavalin A (Con A). This effect of Con A was antagonized by alpha-methyl-D-mannose, a specific antagonist of Con A binding to glycoprotein. Coformycin, an adenosine deaminase inhibitor, did not change the effect of Con A on the ecto-5'-NU. Uptake of adenosine by platelets was not affected by Con A. It was suggested that the ecto-5'-NU of platelet might be a direct and primary site of action of Con A.

5'-Nucleotidase↗
PubMed1986

Influence of pertussis toxin on the effects of guanine nucleotide on adenylate cyclase in rat striatal membranes.

The influence of pertussis toxin on the effects of guanine nucleotide on adenylate cyclase activity were investigated in rat striatal membranes. GTP promoted and inhibited the activity at 1 and 100 microM, respectively. The inhibitory effects of GTP were abolished by pretreatment of the membranes with pertussis toxin. GppNHp (guanyl-5'-y1-beta,gamma-imidodiphosphate) exerted only stimulatory effects and pertussis toxin did not affect the effects of GppNHp. GDP at 10 and 100 microM caused significant inhibition which was completely suppressed by pertussis toxin. It is suggested that guanine nucleotide regulates the affinity of as in stimulatory GTP-binding regulatory protein to either beta gamma or catalytic units of adenylate cyclase in a flip-flop manner. Inhibitory GTP-binding regulatory protein seems to play a regulatory role in inhibiting alpha s activity supplying the beta gamma heterodimer.

Adenylate Cyclase Toxin↗
PubMed1986

Alpha 2-adrenoceptor-GTP binding regulatory protein-adenylate cyclase system in cerebral cortical membranes of adult and senescent rats.

The characterization of [3H]clonidine binding and effects of GTP, forskolin, islet-activating protein (IAP) and cholera toxin on adenylate cyclase activity were investigated in cerebral cortical membranes from 70-day-old and 2-year-old rats. Neither Kd nor Bmax values in [3H]clonidine binding were changed between day 70 and year 2. The activation of adenylate cyclase by forskolin was significantly higher in senescent than in adult animals. The inhibitory effect of adrenaline, which was completely abolished by the pretreatment with IAP/NAD on forskolin/GTP-stimulated cyclase activity, was low in senescent rats compared to that in adult ones. The stimulatory effect of cholera toxin/NAD was also low at the senescent stage compared to that at the adult stage. It is suggested that ligand binding affinity and the density in alpha 2-adrenoceptors do not change between day 70 and year 2 but that GTP binding and/or coupling activity of inhibitory as well as stimulatory GTP binding regulatory protein to catalytic units decrease in synaptic membranes of 2-year-old compared to those of 70-day-old rat brain.

Adenylate Cyclase Toxin↗