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Biomedical subjects

A Imai

Publications and source records attributed to A Imai.

At least 217 records · Page 12Linked to original sources
PubMed1987

Regulation by phosphatidylinositol of rat pituitary plasma membrane and endoplasmic reticulum phosphatidylinositol synthase activities. A mechanism for activation of phosphoinositide resynthesis during cell stimulation.

The mechanism of signal transduction used by a large number of extracellular regulatory molecules involves hydrolysis and resynthesis of phosphoinositides. We recently demonstrated that during stimulation by thyrotropin-releasing hormone of rat pituitary (GH3) cells phosphatidylinositol (PtdIns) resynthesis occurs within the plasma membrane as well as the endoplasmic reticulum (Imai, A., and Gershengorn, M. C. (1987) Nature, 325, 726-728). In this report, we have studied regulation of PtdIns synthase (CDP-diglyceride-inositol phosphatidyltransferase, EC 2.7.8.11) activities associated with plasma membranes and endoplasmic reticulum isolated from GH3 cells. Exogenously added PtdIns noncompetitively inhibited membrane-associated and solubilized PtdIns synthase activities by up to 84 to 91%; half-maximal inhibition occurred between 0.03 and 0.1 mM PtdIns. Similar inhibition of PtdIns synthase activities were observed when PtdIns content of both membrane fractions was increased in vivo in intact GH3 cells prior to assay in vitro. These findings demonstrate that PtdIns synthase activities associated with plasma membrane and endoplasmic reticulum fractions isolated from GH3 cells are inhibited by the product, PtdIns. Because PtdIns levels decrease and PtdIns resynthesis is activated in both membrane fractions during stimulation of GH3 cells by thyrotropin-releasing hormone, it seems likely that activation of PtdIns synthase(s) during cell stimulation occurs by release of this enzyme(s) from inhibition by its product.

Animals↗
PubMed1987

Three-dimensional mapping of local cerebral perfusion in alcoholic encephalopathy with and without Wernicke-Korsakoff syndrome.

Seventeen severe chronic alcoholic patients with and without Wernicke-Korsakoff syndrome (WKS) were examined prospectively after being treated by withdrawal from alcohol. The WKS patients also received thiamine supplements. Three-dimensional measurements of local cerebral blood flow (LCBF) and local partition coefficients (L lambda) were made utilizing xenon contrast computed tomography (Xe CT-CBF). Results were displayed as color-coded brain maps before and after treatment and these were correlated with neurological and cognitive examinations. Before treatment chronic alcoholics without WKS (n = 10) showed diffuse reductions of LCBF values throughout all gray matter including hypothalamus, vicinity of nucleus basalis of Meynert, thalamus, and basal ganglia. Similar, but more severe, reductions were seen in patients with WKS (n = 7), however, white matter perfusion was also reduced. In WKS, most prominent reductions of LCBF were also seen in hypothalamus and basal forebrain nuclei but thalamus, basal ganglia, and limbic systems were severely reduced. After treatment, both groups with alcoholic encephalopathy showed marked clinical improvement and cerebral perfusion was restored toward normal. Chronic alcohol abuse, in the absence of thiamine deficiency, reduces CBF by direct neurotoxic effects. If thiamine deficiency is also present, more severe and localized hemodynamic reductions are superimposed.

Adult↗
PubMed1987

Phosphatidylinositol depletion in GH3 rat pituitary cells inhibits sustained responses to thyrotropin-releasing hormone. Reversal with myo-inositol.

TRH stimulation of rat pituitary (GH3) cells causes biphasic changes in cytoplasmic free Ca2+ concentration [( Ca2+]i) and PRL secretion. It has been proposed, based primarily on indirect evidence, that the first phase effects are mediated by inositol 1,4,5-trisphosphate, which releases Ca2+ from cellular stores, and the sustained effects are mediated by 1,2-diacylglycerol, which activates protein kinase C. To determine more directly if inositol lipid hydrolysis leading to protein kinase C activation is involved in the sustained effects of TRH, GH3 cells were depleted of phosphatidylinositol (PtdIns) by prestimulation and incubation in myo-inositol-free, Li(+)-containing medium. Cells depleted of PtdIns (to 53 +/- 3.2% of control) had unchanged PtdIns 4,5-bisphosphate content, and responded to TRH with a rapid elevation of inositol trisphosphate, and a first phase (or burst) elevation of [Ca2+]i and PRL secretion that was not different from that found in control cells. In contrast, in PtdIns-depleted cells, the prolonged generation of inositol phosphates, which are produced in equimolar amounts with 1,2-diacylglycerol, caused by TRH was virtually abolished, and the second phase (or sustained) elevation of [Ca2+]i and PRL secretion were inhibited by 50% and 40%, respectively. The inhibition of both sustained effects was reversed by adding 100 mM myo-inositol to the medium, which allowed for synthesis of PtdIns. Last, in cells in which protein kinase C was down-regulated by pretreatment with a phorbol ester, the sustained effects of TRH were inhibited also.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Differential regulation by phosphatidylinositol 4,5-bisphosphate of pituitary plasma-membrane and cytosolic phosphoinositide kinases.

Regulation of phosphatidylinositol kinase (EC 2.7.1.67) and phosphatidylinositol 4-phosphate (PtdIns4P) kinase (EC 2.7.1.68) was investigated in highly enriched plasma-membrane and cytosolic fractions derived from cloned rat pituitary (GH3) cells. In plasma membranes, phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] added exogenously enhanced incorporation of [32P]phosphate from [gamma-32P]MgATP2- into PtdIns(4,5)P2 and PtdIns4P to 150% of control; half-maximal effect occurred with 0.03 mM exogenous PtdIns(4,5)P2. Exogenous PtdIns4P and phosphatidylinositol (PtdIns) had no effect. When plasma membranes prepared from cells prelabelled to isotopic steady state with [3H]inositol were used, there was a MgATP2- dependent increase in the content of [3H]PtdIns(4,5)P2 and [3H]PtdIns4P that was enhanced specifically by exogenous PtdIns(4,5)P2 also. Degradation of 32P- and 3H-labelled PtdIns(4,5)P2 and PtdIns4P within the plasma-membrane fraction was not affected by exogenous PtdIns(4,5)P2. Phosphoinositide kinase activities in the cytosolic fraction were assayed by using exogenous substrates. Phosphoinositide kinase activities in cytosol were inhibited by exogenously added PtdIns(4,5)P2. These findings demonstrate that exogenously added PtdIns(4,5)P2 enhances phosphoinositide kinase activities (and formation of polyphosphoinositides) in plasma membranes, but decreases these kinase activities in cytosol derived from GH3 cells. These data suggest that flux of PtdIns to PtdIns4P to PtdIns(4,5)P2 in the plasma membrane cannot be increased simply by release of membrane-associated phosphoinositide kinases from product inhibition as PtdIns(4,5)P2 is hydrolysed.

1-Phosphatidylinositol 4-Kinase↗
PubMed1986

Narcolepsy following cerebral hypoxic ischemia.

A 51-year-old man with non-HLA-DR2 histocompatibility developed classic signs and symptoms of the narcoleptic tetrad soon after recovering from an episode of cardiopulmonary insufficiency, which occurred during induction of surgical anesthesia. Symptoms included excessive daytime sleepiness, hypnagogic hallucinations, sleep paralysis, and cataplexy. The diagnosis was confirmed by repeated polysomnographic examinations in the sleep laboratory. Cerebral hemodynamic changes during the onset of sleep showed remarkable increases of cerebral blood flow during the onset of rapid-eye-movement sleep similar to those reported previously in patients with narcolepsy. Magnetic resonance imaging showed focal regions of abnormal spin-echo signals in the ventral pons.

Anesthesia, Intravenous↗
PubMed1986

Phosphatidylinositol 4,5-bisphosphate turnover is transient while phosphatidylinositol turnover is persistent in thyrotropin-releasing hormone-stimulated rat pituitary cells.

Stimulated inositolphospholipid turnover has been proposed to be initiated and sustained by hydrolysis of phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2], which may be replenished by an enhanced flux of phosphatidylinositol (PtdIns) to PtdIns 4-phosphate (PtdIns4P) to PtdIns(4,5)P2. To determine whether there is continued hydrolysis and resynthesis of PtdIns(4,5)P2 in rat pituitary cells (GH3 cells) during stimulation by thyrotropin-releasing hormone (TRH), we investigated the turnover kinetics of the inositolphospholipids and of phosphatidic acid (PtdOH). In cells incubated with 32Pi for 1 min, TRH rapidly and persistently (for at least 30 min) enhanced the rate of 32P-labeling of PtdOH. After a lag time of 1 min, TRH markedly and persistently increased 32P-labeling of PtdIns also. In contrast, TRH caused only a transient increase in 32P-labeling of PtdIns(4,5)P2 that lasted less than 2 min. There was no rapid (before 10 min) effect of TRH on 32P-labeling of PtdIns4P. By 2 min of TRH stimulation, specific 32P radioactivity in PtdOH increased from 3.6% (control) of that in the gamma-phosphate of ATP to 15%; in PtdIns, from 0.07% to 1.3%; and in PtdIns(4,5)P2, from 3.8% to 5.4% (specific 32P radioactivity in PtdIns4P was 1.7% of that in ATP in control and TRH-stimulated cells). In cells exposed to TRH for 4 min and then to 32Pi, 32P-labeling of PtdOH and PtdIns increased, but that of PtdIns(4,5)P2 was not affected. Last, persistent turnover of PtdOH and PtdIns was not caused by initial hydrolysis of PtdIns(4,5)P2 because the turnover of PtdOH and PtdIns could be terminated by displacement of TRH from its receptor by chlordiazepoxide and restarted by reoccupying the receptors with TRH. These data demonstrate that turnover of PtdIns(4,5)P2 is stimulated only transiently, whereas turnover of PtdIns and PtdOH is stimulated persistently by TRH in GH3 cells. Hence, inositolphospholipid turnover in GH3 cells does not occur via continued hydrolysis of PtdIns(4,5)P2 accompanied by enhanced flux of PtdIns to PtdIns4P to PtdIns(4,5)P2, but there is direct and persistent hydrolysis of PtdIns. The dissociation of these actions suggests that there are separate mechanisms involved in coupling TRH-receptor complexes to stimulation of PtdIns(4,5)P2 and PtdIns hydrolysis in GH3 cells.

Animals↗
PubMed1985

Evidence for tight coupling of thyrotropin-releasing hormone receptors to stimulated inositol trisphosphate formation in rat pituitary cells.

The effect of decreasing the concentration of receptors for thyrotropin-releasing hormone (TRH) on the surface of cloned rat pituitary (GH3) cells on TRH-stimulated inositol trisphosphate (Ins-P3) formation was investigated. Incubation of cells with dibutyryl cAMP (Bt2cAMP) for 16 h caused a decrease in [3H] TRH binding to intact cells to a minimum level 37 +/- 9.1% of control. Scatchard analysis of the concentration dependency of [3H]TRH binding showed that the effect of Bt2cAMP was to lower the receptor concentration without affecting its affinity for TRH. Similar decreases in [3H]TRH binding were found in cells incubated with 8-bromo-cAMP, cholera toxin, and sodium butyrate and, as shown previously, with TRH. In cells incubated with 1 mM Bt2cAMP for 16 h, but not for 1 h, the maximum TRH-induced increase in Ins-P3 was inhibited to 25 +/- 3.2% of that in control cells. Inhibition of TRH-induced Ins-P3 formation was also observed in cells treated with 8-bromo-cAMP, cholera toxin, and sodium butyrate for 16 h, and with TRH for 48 h. Inhibition of TRH-induced Ins-P3 formation and lowering of TRH receptor concentration caused by Bt2cAMP occurred in parallel with increasing doses of Bt2cAMP; at 16 h of exposure, half-maximal effects occurred with 0.3 mM Bt2cAMP. The concentration dependency of TRH-induced Ins-P3 formation was the same in control and Bt2cAMP-treated cells; half-maximal effects occurred with 10 nM TRH. These data demonstrate that decreases in TRH receptor concentration caused by several agents that act via different mechanisms are associated with reduced stimulation of Ins-P3 formation and suggest that the TRH receptor is tightly coupled to stimulation of hydrolysis of phosphatidylinositol 4,5-bisphosphate by a phospholipase C.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1985

Prevention of rotavirus infection by oral administration of cow colostrum containing antihumanrotavirus antibody.

After immunizing 8-month pregnant Holstein cows with human rotavirus, Wa strain, cow colostrum containing neutralizing antibody to human rotavirus, designated as Rota colostrum, was obtained. After randomly grouping 13 infants from a single orphanage, 6 infants received 20 ml of Rota colostrum every morning and 7 control infants received 20 ml of market milk. One month later, rotavirus associated diarrhea was observed in 6 of the 7 infants given milk and 1 out of the 6 infants given Rota colostrum. Orally administered Rota colostrum significantly protected infants from diarrhea caused by rotavirus (P less than 0.05). Two out of 5 Rota colostrum recipients who were free from diarrhea showed rises in complement fixation (CF) antibody titer after the rotavirus infection epidemic. Thus, Rota colostrum prevented the outbreak of diarrhea but did not prevent immunological responses to natural rotavirus infection. In the therapeutic trial Rota colostrum had no effect on duration of diarrhea, bowel movements or virus shedding in stool. However, there were no side-effects of Rota colostrum.

Administration, Oral↗
PubMed1984

Polyphosphoinositide turnover in rat mast cells stimulated by antigen: rapid and preferential breakdown of phosphatidylinositol 4-phosphate (DPI).

The effect of antigen on the metabolism of polyphosphoinositides was investigated in sensitized rat peritoneal mast cells. Addition of antigen to rat peritoneal mast cells prelabelled with [3H]arachidonic acid resulted in a very rapid decrease in the level of phosphatidylinositol 4-phosphate (DPI) within 5 sec, which appeared to precede the breakdown of phosphatidylinositol (PI), while there was no significant decline of PI 4,5-bisphosphate (TPI). The reduced levels of these phosphoinositides returned almost to control or even slightly higher values by 300 sec in parallel with the antigen-stimulated [32P]phosphate incorporation into these lipids. This early and transient disappearance in DPI prior to that in PI was also observed in [3H]glycerol-prelabelled cells. These data suggest that DPI degradation upon stimulation by antigen in mast cells may be an initial step in the histamine release process.

Animals↗
PubMed1984

Effects of dibutyryl cyclic AMP and forskolin on phospholipid biosynthesis in thrombin-stimulated human platelets.

The influence of forskolin, an adenylate cyclase activator, and of dibutyryl cyclic AMP (Bt2cAMP) on [3H]glycerol incorporation into glycerolipids was investigated in human platelets. It was found that preincubation with 2.5 mM Bt2cAMP produced a 2-4-fold increase in thrombin-induced incorporation into phospholipids compared to platelets activated by thrombin alone. Pretreatment with forskolin, which increased cellular cAMP content, also resulted in an increase in thrombin-stimulated [3H]glycerol incorporation into phospholipids. These findings demonstrate that a rise in platelet cAMP can accentuate thrombin-induced de novo synthesis of phospholipids from [3H]glycerol. Since the content of cellular cAMP was correlated with its ability to inhibit platelet activation monitored by serotonin release, it seems likely that glycerolipid, in particular phospholipid biosynthesis, is involved in controlling platelet activation by thrombin.

Adult↗
PubMed1984

Three different serotypes of human rotavirus determined using an interference test with coxsackievirus B 1.

MA104 cells were used to titrate human rotavirus, and its capacity to render the cells resistant to coxsackievirus B 1 infection enabled us to determine easily the infectious titer of three prototype human rotaviruses. When rabbit antisera prepared against these prototype viruses were used for the neutralization test, the viruses could be discriminated from each other by a specific neutralization test.

Enterovirus B, Human↗
PubMed1984

Differential activation of membrane phospholipid turnover by compound 48/80 and ionophore A23187 in rat mast cells.

Membrane phospholipid turnover was investigated during histamine release from rat mast cells. Addition of calcium ionophore A23187 (0.5 microgram/ml) to mast cells prelabeled with [3H]glycerol induced the rapid and progressive increase in phosphatidic acid (PA) and 1,2-diacylglycerol (DG), which was concomitant with the small rise in phosphatidylinositol (PI). Loss of the level in triacylglycerol (TG) was very marked. Polyamine compound 48/80 (5 micrograms/ml) was shown to cause rises in PA, 1,2-DG, and PI without any significant changes in TG. Both stimuli increased incorporation of exogenous [3H]glycerol into phospholipids, indicating the involvement of de novo synthesis in phospholipid metabolism. Studies with [3H]arachidonic acid-labeled mast cells showed an enhanced liberation of radioactive arachidonate and metabolites upon histamine release. There were associated decreases of radioactivity in phosphatidylcholine (PC) and TG when exposed to A23187, while phosphatidylethanolamine (PE) was degraded as a result of 48/80 activation. The transient increases of [3H]arachidonoyl-1,2-DG and PA were caused by 48/80, while A23187 showed a gradual rise in the radioactivity in these two lipid fractions. These findings reflect activation of phospholipase C. When mast cells were activated by low concentrations of A23187 (0.1 microgram/ml) and 48/80 (0.5 microgram/ml), different behaviors of PI metabolism were observed. An early degradation of PI and a subsequent formation of 1,2-DG and PA suggest that the lower concentrations of these agents stimulate the PI cycle initiated by PI breakdown rather than de novo synthesis. These results demonstrate that marked and selective changes in membrane phospholipid metabolism occur during histamine release from mast cells, and that these reactions seem to be controlled by the coordination of degradation and biosynthesis, depending on the type and the concentration of stimulants. A23187 stimulates arachidonate release perhaps via the cleavages of PC and TG, whereas 48/80 liberates arachidonate from PE.

Animals↗
PubMed1984

Phospholipid metabolism in human platelets preserved at 22 degrees C: differential effects of storage on phospholipase A2- and C-mediated reactions.

The effects of preservation at 22 degrees C on phospholipid metabolism were studied in human platelets. Stimulation of fresh platelets with thrombin caused a rapid and transient rise of 1,2-diacylglycerol (DG) which was derived from phosphatidylinositol (PI) by its strictly specific phospholipase C. Lysophosphatidylcholine (lysoPC) and lysophosphatidylethanolamine (lysoPE) were also accumulated as a result of the action of phospholipase A2. No significant changes in phospholipid metabolism were detected in platelets preserved at 22 degrees C up to 6 hr. However, platelets stored for more than 12 hr showed (1) an accumulation of both lysoPC and lysoPE before thrombin activation, (2) a subsequent decrease in the formation of lysoPC and lysoPE after thrombin activation when compared to fresh platelets, (3) a threefold lower rate of liberation of arachidonic acid than fresh platelets after activation, and (4) a lower rate and extent of aggregation than fresh platelets. Nevertheless, the amount of 1,2-DG produced during preservation up to 48 hr was similar to that observed in fresh platelets. The results indicate that the markedly enhanced activity of phospholipase A2, but not phospholipase C, that occurs during platelet storage leads to the deterioration of aggregation and arachidonic acid liberation in response to thrombin.

Adult↗
PubMed1984

Phospholipid and fatty acid composition of erythrocyte membrane from wild Japanese serow (Capricornis crispus).

The phospholipid composition and fatty acid composition of the individual phospholipids were determined in erythrocyte membrane of wild Japanese serow, Capricornis crispus, and compared with those of Japanese cattle. Sphingomyelin (SM) contributed more than 50% to the total phospholipids, with only 3% phosphatidylcholine, 30% phosphatidylethanolamine and 11% phosphatidylserine. This phospholipid composition and ratio of phospholipid to protein in erythrocyte membrane of wild serow were quite similar to those of Japanese cattle. However, marked differences in fatty acid composition were found, especially in lignoceric acid 24:0 and nervonic acid 24:1 of sphingomyelin which were major constituents (approximately 60%) of that phospholipid.

Animals↗
PubMed1984

Abnormal phosphatidylinositol-cycle of platelet membrane in schizophrenia--a preliminary study.

Phosphatidylinositol (PI)-cycle in the platelet membrane was examined in eight untreated patients with psychotic symptoms. A defect of PI-cycle in the transformation from 1,2-diacylglycerol into phosphatidic acid was found in three patients, who were diagnosed as having Schizophrenic Disorders or Schizophreniform Disorder according to the DSM-III criteria. Two out of the three patients were reexamined while undergoing neuroleptic medication, and they showed the same abnormality in PI-cycle. Further studies were required to determine the nature of the abnormality in PI-cycle in the platelets of schizophrenics.

Adolescent↗