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Y Tokumitsu

Publications and source records attributed to Y Tokumitsu.

At least 55 records · Page 3Linked to original sources
PubMed1990

Activation of glucose transport by activatory receptor agonists of adenylate cyclase in rat adipocytes.

1. Catecholamine, glucagon, and adrenocorticotropic hormone stimulated 2-deoxyglucose (2-DG) uptake via an increase in glucose transporters in plasma membranes, similarly to insulin. 2. In contrast to the action of insulin, the stimulating effects of these agonists on 2-DG uptake were abolished when Gi was not activated. 3. The mode of the 2-DG uptake stimulation was partially different among these agonists.

Adenylyl Cyclases↗
PubMed1990

Effects of repeated administrations of facteur thymique sérique (FTS) on biochemical changes related to aging in senescence-accelerated mouse (SAM).

Superoxide dismutase (SOD) activity,malondialdehyde (MDA) content and monoamine oxidase B (MAO-B) activity were measured in the brain, liver and kidney of a normal aging strain (R/1) and an accelerating aging strain (P/8) senescence-accelerated mice (SAM) at 9-10 months of age, and the effects of facteur thymique sérique (FTS) were examined. The activity of Cu,Zn-SOD in the kidney and MAO-B in the liver was significantly low and high in SAM-P/8 compared to SAM-R/1. FTS enhanced the activity of Mn-SOD and Cu,Zn-SOD in the kidney of SAM-P/8 and Cu,Zn-SOD activity in the brain of both SAM-P/8 and SAM-R/1. It decreased the activity of MAO-B in the liver and the contents of malondialdehyde (MDA) in the brain and kidney of SAM-P/8. Thus, FTS affects the biochemical factors related to senescence in SAM-P/8, a particular senescent animal model, and may thus possibly be effective as an anti-senescent medicine.

Aging↗
PubMed1989

A pertussis toxin-sensitive GTP-binding protein plays a role in the G0-G1 transition of rat hepatocytes following establishment in primary culture.

Acute spontaneous c-myc gene expression and sustained increase of a GTP-binding protein(s) (G-protein) which is sensitive to islet-activating protein (IAP), pertussis toxin, occurred early during primary culture of adult rat hepatocytes. Following these earlier events, DNA synthesis was demonstrated in response to EGF and insulin. Addition of IAP immediately after plating of primary cultures inhibited c-myc expression and the hormone-induced DNA synthesis. Addition at 24 h or later following cell inoculation, however, produced only weak effects on DNA synthesis, even though the IAP-sensitive G-proteins were completely inactivated. We conclude that the IAP-sensitive G-protein(s) plays a role in the earlier process(es) of the G0-G1 transition, which is essential for the initiation of growth factor-dependent DNA synthesis.

Adenosine Diphosphate Ribose↗
PubMed1989

Pertussis toxin attenuates 5-hydroxytryptamine1A receptor-mediated inhibition of forskolin-stimulated adenylate cyclase activity in rat hippocampal membranes.

The inhibition of forskolin-stimulated adenylate cyclase activity by 5-hydroxytryptamine (5-HT) receptor agonists was measured in rat hippocampal membranes isolated from animals treated with vehicle or islet-activating protein (IAP; pertussis toxin). In vehicle-treated animals, 5-HT, 8-hydroxy-2-(di-n-propylamino)tetralin, buspirone, and gepirone were potent in inhibiting forskolin-stimulated adenylate cyclase activity with EC50 values of 60, 76, 376, and 530 nM, respectively. IAP treatment reduced by 30-55% the 5-HT1A agonist inhibition of adenylate cyclase activity via 5-HT1A receptors. The data indicate that the inhibitory guanine nucleotide-binding protein or Go (a similar GTP-binding protein of unknown function purified from brain) mediates the 5-HT1A agonist inhibition of hippocampal adenylate cyclase.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1988

Possible involvement of pertussis toxin substrates (Gi, Go) in desipramine-induced refractoriness of adenylate cyclase in cerebral cortices of rats.

To evaluate the efficiency of coupling between beta-receptor and adenylate cyclase catalyst via a GTP-binding protein, Gs, in the brain membrane two parameters were employed: a beta-agonist-induced increase in the membrane GTP-dependent adenylate cyclase activity and a beta-agonist-induced shortening of the lag time preceding the onset of the steady-state activation by guanyl-5'-yl-beta-gamma-imidodiphosphate [Gpp(NH)p] of the membrane cyclase. Both parameters showed lower values in membranes from desipramine-treated rats compared with untreated rats. Thus, coupling of beta-adrenergic receptors to adenylate cyclase in the brain membrane was impaired by the desipramine treatment. Rats once injected intraventricularly with islet-activating protein (IAP), pertussis toxin, were subjected to desipramine treatment, for the purpose of studying effects of another kind of the GTP-binding protein (Gi), which loses its function as a signal transducer on being ADP-ribosylated selectively by the toxin. IAP treatment did not impair the beta-receptor coupling by itself, since neither of the above two parameters for the coupling were reduced by IAP treatment. Moreover, the first parameter was normalized, though the second one was not, by superimposition of the IAP treatment upon the desipramine-treated rats. It seems likely, therefore, that Gi interacts with a Gs-adenylate cyclase coupling in an inhibitory fashion in brain membranes. The desensitization might be overcome when the inhibitory interaction of Gi on the subsequent process is attenuated by IAP treatment.

Adenosine Diphosphate Ribose↗
PubMed1987

P2-purinergic receptors are coupled to two signal transduction systems leading to inhibition of cAMP generation and to production of inositol trisphosphate in rat hepatocytes.

Stimulation of P2-purinergic receptors by ATP resulted in activation of phosphorylase, which was associated with marked production of inositol trisphosphate (Ins-P3), in rat hepatocytes. ATP also inhibited forskolin-induced accumulation of cAMP in the presence of a phosphodiesterase inhibitor. On the contrary, adenosine or AMP never inhibited the cAMP accumulation, but increased hepatocyte cAMP; the stimulation was antagonized by a methylxanthine. Thus, P1-purinergic receptors are linked to adenylate cyclase in a stimulatory fashion in hepatocytes. Various kinds of purine nucleotides stimulating P2-receptors can be divided into two groups on the basis of their relative abilities to stimulate Ins-P3 production and to inhibit cAMP accumulation; the first group including adenosine 5'-O-(3-thiotriphosphate) (ATP gamma S), ADP, 5-adenylyl imidodiphosphate, GTP, and guanosine 5'-O-(3-thiotriphosphate) has an efficacy similar to that of ATP, and the second group of nucleotides including alpha, beta-methyleneadenosine 5'-triphosphate, beta, gamma-methyleneadenosine 5'-triphosphate (App(CH)2)p), and GDP exerts considerable inhibitory effects on cAMP accumulation, but only slight effects on inositol lipid metabolism. Treatment of hepatocytes with islet-activating protein, pertussis toxin, blocked the nucleotide-induced inhibition of cAMP accumulation, but exerted only a small effect on Ins-P3 production. In membranes prepared from hepatocytes, forskolin-stimulated adenylate cyclase was inhibited by GTP. This GTP-induced inhibition of the enzyme was susceptible to islet-activating protein and dependent on the concentration of ATP (or its derivatives, ATP gamma S or App(CH2)p). It is concluded that there are two types of P2-purinergic receptors: one is linked to adenylate cyclase via an inhibitory guanine nucleotide regulatory protein (Gi) and the other is linked to phospholipase C.

1-Methyl-3-isobutylxanthine↗
PubMed1986

Desensitization of beta-adrenergic receptor-coupled adenylate cyclase in cerebral cortex after in vivo treatment of rats with desipramine.

Continuous treatment (1-10 days) of rats with desipramine (10 mg/kg, twice per day) caused desensitization of the beta-adrenergic receptor-coupled adenylate cyclase system of cerebral cortical membranes. The decrease in the isoproterenol-stimulated adenylate cyclase activity was more rapid and greater than the decrease in the number of beta-adrenergic receptors in membranes during treatment of the membrane donor rats with desipramine, indicating that the desensitization occurring at an early stage of the treatment was not accounted for solely by the decrease in the receptor number. Neither the guanine nucleotide regulatory protein (N) nor the adenylate cyclase catalyst was impaired by the drug treatment, since there was no decrease in the cyclase activity measured in the presence or absence of GTP, guanyl-5'-yl-beta-gamma-imidodiphosphate [Gpp(NH)p], NaF, or forskolin. Gpp(NH)p-induced activation of membrane adenylate cyclase developed with a lag time of a few minutes in membranes from control or drug-treated rats. The lag was shortened by the addition of isoproterenol, indicating that beta-receptors were coupled to N in such a manner as to facilitate the exchange of added Gpp(NH)p with endogenous GDP on N. This effect of isoproterenol rapidly decreased during the drug treatment of rats. Thus, functional uncoupling of the N protein from receptors was responsible for early development of desensitization of beta-adrenergic receptor-mediated adenylate cyclase in the cerebral cortex during desipramine therapy.

Adenylyl Cyclases↗
PubMed1985

Comparison of basal metabolic activities and hormonal sensitivities between mesenteric and epididymal adipocytes.

The mesenteric adipose tissue, which is present in a considerable amount in the rat but had not been used for the experiments, contained a larger number of adipocytes than the epididymal adipose tissue per wet weight of the tissue. The basal metabolic activities and the responses to epinephrine and insulin in the mesenteric adipocytes were essentially equal to those in the epididymal adipocytes. The mesenteric adipocytes are useful for elucidation of metabolism in white adipose tissue.

Adipose Tissue↗
PubMed1984

Metabolic alterations in normal and streptozotocin-diabetic rats in vivo: influence of prolonged starvation.

We studied the influence of prolonged starvation on carbohydrate metabolism in streptozotocin-diabetic rats compared with normal rats. In streptozotocin (STZ)-diabetic rats, the plasma glucose concentration decreased gradually during prolonged starvation, while it did not change in normal rats. In normal rats, glycogen depletion in the liver occurred within 24 hr of starvation, while in STZ-diabetic rats, glycogen content did not change even after 72 hr of starvation. Impaired glucose tolerance and glycogen deposition in response to oral administration of glucose were observed in STZ-diabetic rats compared with normal animals. STZ-diabetic animals generally had lower glycogen synthase and phosphorylase activities compared with normal rats during starvation. In normal animals, there is a significant correlation between the plasma concentration of free fatty acids and 3-hydroxybutyrate. On the basis of these findings, metabolic alterations in chemically-induced diabetic animals were discussed.

3-Hydroxybutyric Acid↗
PubMed1982

Glycogen storage myopathy with abnormal lactate dehydrogenase.

We studied a 3 year old girl with mental retardation and limb muscle weakness. The muscle glycogen content was 17.4 mg/g tissue, which was approximately three times higher than normal. There were no other known abnormalities noted in this child that could explain the cause of glycogen storage disease. Our in vitro glycolysis study showed marked increase of pyruvate, but no increase in lactate levels. The observed results suggested to us that an abnormal lactate dehydrogenase might account for the abnormal accumulation of glycogen in the muscle.

Child, Preschool↗
PubMed1977

Increased absorption of iodochlorhydroxyquin by rat intestine in the presence of solubilizing agents.

The intestinal absorption of iodochlorhydroxyquin (clioquinol) by the rat was studied by determining the radioactivity in the bile, blood and several organs 90 min after direct application of 125I-labeled clioquinol into the duodenum. The addition of solubilizing agents such as carboxymethyl-cellulose and lauryl sulfate to clioquinol preparation markedly enhanced the intestinal absorption of the drug in either the presence of absence of bile secretion which, by itself, increased the drug absorption. Possible significance of the enhanced absorption of clioquinol by solubilizing agents in the etiology of subacute myelo-optic neuropathy (SMON) in Japan is discussed.

Animals↗