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Biomedical subjects

N Inagaki

Publications and source records attributed to N Inagaki.

At least 181 records · Page 10Linked to original sources
PubMed1992

Antiallergic mechanisms of beta-adrenergic stimulants in rats.

Antiallergic mechanisms of beta-adrenergic stimulants were investigated in rats. Isoproterenol administered intravenously inhibited IgE antibody-mediated homologous passive cutaneous anaphylaxis (PCA) and histamine-induced cutaneous reaction (HCR) elicited at the same time in the same rats significantly. The inhibition of PCA was more potent than that of HCR, suggesting that PCA is inhibited by at least 2 mechanisms. One is the inhibition of vascular permeability increase. In vivo histamine release in the rat peritoneal cavity caused by intravenous antigen was inhibited by the intravenous administration of isoproterenol or salbutamol dose-dependently. On the contrary, when the histamine release in the peritoneal cavity was caused by intraperitoneal antigen, isoproterenol or salbutamol administered simultaneously with antigen failed to inhibit the reaction. Furthermore, antigen-induced histamine release from sensitized peritoneal exudate cells in vitro was not inhibited by isoproterenol or salbutamol. These results indicate that the primary target of beta-adrenergic stimulants is the vascular endothelium, and that the direct inhibition of chemical mediator release from mast cells does not play an important role for the inhibition of PCA and in vivo histamine release in the peritoneal cavity in rats. Beta-adrenergic stimulants therefore may prevent intravenously administered antigen from activating sensitized mast cells through affecting endothelial cells.

Albuterol↗
PubMed1992

Circadian rhythm of histamine release from the hypothalamus of freely moving rats.

Using an in vivo microdialysis technique coupled with HPLC-fluorometry, the release of neuronal histamine from the anterior hypothalamic area was monitored continuously in conscious, freely moving rats under a 12:12 h light:dark cycle. Spontaneous locomotor activity of the rats was measured simultaneously using a locomotor activity counter. Histamine release gradually increased in the second half of the light period (1400-2000) and the average histamine release during the dark period (2000-0800, 0.20 +/- 0.02 pmol/30 min) was significantly higher than that during the light period (0.12 +/- 0.01 pmol/30 min). This clear circadian change in the release suggests that the central histaminergic system is related to the circadian rhythm of rats.

Animals↗
PubMed1992

Studies on the anti-allergic mechanism of glucocorticoids in mice.

Glucocorticoids inhibit IgE antibody-mediated passive cutaneous anaphylaxis (PCA) and chemical mediator-induced cutaneous reactions elicited in the mouse ear. In the present study, we investigated the effect of actinomycin D, a protein synthesis inhibitor, on dexamethasone-caused inhibition of PCA and histamine-induced cutaneous reaction in the mouse ear. Tyrosine aminotransferase (TAT) activity in the liver, which was estimated as an index for protein synthesis, significantly increased by the administration of hydrocortisone, prednisolone and dexamethasone. Significant increase in TAT activity was observed from 2 h after glucocorticoid administration and peaked at 4 h, and declined gradually thereafter. Cycloheximide even at high doses of 100 and 300 mg/kg failed to affect the increase in TAT activity by dexamethasone. On the contrary, actinomycin D at doses of 1 and 10 mg/kg abrogated the TAT activity increase by dexamethasone almost completely. Treatment with 1 mg/kg of actinomycin D, however, failed to affect the inhibition of PCA and histamine-induced cutaneous reaction by dexamethasone. These results suggest that glucocorticoids exhibit their inhibitory action of PCA and chemical mediator-induced cutaneous reactions in mice through a mechanism resistant to actinomycin D treatment.

Animals↗
PubMed1992

Active cutaneous anaphylaxis (ACA) in the mouse ear.

Active cutaneous anaphylaxis (ACA) was studied in the ear of female BALB/c mice. Mice were immunized with ovalbumin in the presence of aluminium hydroxide gel or complete Freund's adjuvant (CFA). Two weeks after the immunization, ACA was elicited in the mouse ear by injecting 10 microliters of antigen solution intradermally into the ear lobe. ACA was assessed by the amount of extravasated dye, which was given intravenously just after the antigen injection. Antiallergic drugs (tranilast, ketotifen and azelastine), antihistamines (chlorpheniramine, diphenhydramine and mequitazine), beta-stimulants (isoproterenol and salbutamol), theophylline and glucocorticoids (hydrocortisone, prednisolone and dexamethasone) inhibited the reaction significantly. These drugs inhibited both ACA in mice immunized with alum-precipitated antigen and ACA in mice injected with CFA-emulsified antigen similarly. ACA in the mouse ear might be a useful tool for studying drugs for allergy.

Animals↗
PubMed1992

Mechanisms for glucocorticoid inhibition of immediate hypersensitivity reactions in rats.

The inhibitory mechanisms of immediate hypersensitivity reactions by glucocorticoid (GC) were studied in rats. Homologous passive cutaneous anaphylaxis (PCA) mediated by IgE antibodies and cutaneous reactions caused by histamine, serotonin and leukotriene C4 were elicited at the same time in the same rats. Three kinds of GC, hydrocortisone, prednisolone and dexamethasone, inhibited all these reactions significantly. Although mediator-induced cutaneous reactions were inhibited transiently around 2 hours after GC administration, inhibition of PCA was more potent and lasted longer. A time lag seemed to be essential for both inhibitions. IgE antibody-mediated histamine release in vivo in the rat peritoneal cavity was also inhibited by GC administration significantly, and the inhibition was long lasting when compared to those of the mediator-induced cutaneous reactions. Tyrosine amino-transferase (TAT) activity in the rat liver increased significantly by GC administration, and the increased TAT activity was completely abrogated by simultaneous administration of 5 mg/kg of cycloheximide (CH). In the same experimental condition, although inhibition of histamine-induced cutaneous reaction by GC was completely abrogated, the inhibition of PCA elicited at the same time in the same rats was only partially attenuated. Furthermore, the same dose of CH little affected the dexamethasone inhibition of histamine release in the rat peritoneal cavity, although the increase of TAT activity in the liver of the same rats was completely abrogated. These results demonstrate that PCA is inhibited by GC through at least 2 mechanisms, inhibition of mediator release from mast cells and non-specific inhibition of vascular permeability increase caused by released mediators. Although the latter action of GC is dependent upon protein synthesis, the former seems to be mediated by a unique mechanism independent of protein synthesis.

Animals↗
PubMed1992

Expression of GLUT1 and GLUT2 glucose transporter isoforms in rat islets of Langerhans and their regulation by glucose.

Previous studies revealed that rat islets express the GLUT2-liver facilitative glucose transporter isoform, a glucose carrier with a low affinity for glucose but a high capacity for glucose transport. These studies indicated the presence of a second glucose transporter in rat islets; however, they did not indicate to which of the five known facilitative glucose transporters it corresponded. In this study, we isolated RNA from rat islets of Langerhans and confirmed the presence of GLUT2 mRNA. In addition, we present data indicating that the second isoform expressed in islets is the GLUT1-erythrocyte isoform. The effect of culturing islets in 5.5, 8.3, or 11.1 mM glucose on the levels of GLUT1 and GLUT2 mRNA also was examined. The levels of GLUT1 and GLUT2 mRNA were two- and threefold higher, respectively, in islets cultured for 24 h in 11.1 mM glucose compared with those incubated in the presence of 5.5 mM glucose. Therefore, the previously observed increase in GLUT2 mRNA levels in the islets of rats made hyperglycemic by chronic infusion of glucose can be mimicked in vitro, implying that glucose regulates GLUT2 mRNA expression.

Animals↗
PubMed1992

Glucose as regulator of glucose transport activity and glucose-transporter mRNA in hamster beta-cell line.

To investigate the role of glucose in regulating glucose transporters in pancreatic beta-cells, we studied the hamster clonal beta-cell line HIT-T15, which retains responsiveness to glucose. Northern blot analysis demonstrates that GLUT2 and GLUT1 mRNA are abundant in HIT cells. After a 24-h culture with various concentrations of glucose (0-22.2 mM [0-400 mg/dl]), the GLUT2 mRNA level in HIT cells increased by 40% at 22.2 mM (400 mg/dl) glucose compared with 11.1 mM (200 mg/dl) without a change in mRNA stability. It also decreased proportionally to the reduction of glucose concentration. Glucose deprivation resulted in a decrease of GLUT2 mRNA to an almost undetectable level, with a marked increase in the degradation rate of mRNA. In contrast, the GLUT1 mRNA was not affected by glucose. We show that glucose uptake is highest in HIT cells incubated at 2.8-5.5 mM (50-99 mg/dl) glucose for 24 h, and that levels in cells cultured at 0 mM (0 mg/dl) and 22.2 mM (400 mg/dl) glucose decrease to approximately 20% of the maximum level. This decrease is consistent with the effects of glucose on glucose-stimulated insulin secretion in HIT cells. Our results indicate that glucose is involved in regulating GLUT2 mRNA and glucose uptake activity and that the glucose responsiveness of the insulin secretion correlates with the glucose-induced change in glucose uptake activity in HIT cells.

Animals↗
PubMed1991

Histamine-induced cyclic AMP accumulation in type-1 and type-2 astrocytes in primary culture.

Histamine-induced cyclic AMP (cAMP) accumulation was studied in purified primary cultures of type-1 and type-2 astrocytes from neonatal rat brain. Histamine induced remarkable cAMP accumulation in type-1 astrocytes in a dose-dependent manner (EC50 = 1.2 x 10(-5) M, Emax = 1100% of control). In contrast, histamine had no significant effect on cAMP accumulation in type-2 astrocytes. Famotidine, an H2-antagonist, dose-dependently inhibited histamine-induced cAMP accumulation in type-1 astrocytes (Ki = 3 x 10(-8) M), but mepyramine (10(-6) M), an H1-antagonist, had no effect. Dimaprit and impromidine, H2-agonists, stimulated cAMP accumulation, but 2-pyridylethylamine, an H1-agonist, did not stimulate it nor augment the H2-agonist-induced cAMP accumulation. These results indicate that (1) histamine induces cAMP accumulation in type-1 astrocytes but not in type-2 astrocytes, and that (2) histamine-induced cAMP accumulation in type-1 astrocytes is mediated by H2-receptors without significant augmentation via H1-receptors.

Animals↗
PubMed1991

Arachidonic acid metabolism during antigen and ionophore activation of the mouse bone marrow derived mast cell.

This study has examined the metabolism of arachidonic acid in the mouse bone marrow-derived mast cell (BMMC) during immunologic and nonimmunologic activation. The predominant pools of endogenous arachidonate in the mast cells were found in ethanolamine (46%), choline (39%) and inositol (14%) containing glycerolipids. Initial studies established conditions where equilibrium labelling of these major phospholipids in the BMMC could be reached. Upon challenge, arachidonate was lost from all major phospholipid classes (phosphatidylethanolamine greater than phosphatidylcholine greater than phosphatidylinositol). There was a small but significant increase in the amount of label associated with phosphatidic acid during cell activation. Arachidonate was distributed among 1-acyl, 1-alkyl and 1-alk-1-enyl-linked subclasses of PC and PE. The rank order of loss of labelled arachidonate from the major PE and PC subclasses during antigen and ionophore activation was 1-alk-enyl-2-arachidonoyl-GPE greater than 1-acyl-2-arachidonoyl-GPC greater than 1-acyl-2-arachidonoyl-GPE greater than 1-alkyl-2-arachidonoyl-GPC. Labelled products released into the supernatant fluids and free arachidonic acid within the cell accounted for the bulk of arachidonate lost from phospholipids. Labelled products in the supernatant fluids were composed of LTB4, LTC4, PGD2 and free arachidonic acid. BMMC phospholipids were also labelled for 24 hr with [3H]choline, [3H]myoinositol or [14H]ethanolamine and labelled 2-lyso phospholipids were measured after cell activation. Radioactivity in lysophospholipids from PC, PE and PI increased significantly between 30 s and 2 min after antigen activation and then declined. Taken together, these studies suggest that arachidonate is mobilized predominantly from PE and in particular 1-alk-1-enyl-2-arachidonoyl-GPE by the direct removal of arachidonate from the sn-2 position of the molecule. Most of this arachidonate is then released from cells as eicosanoids or free fatty acid.

Animals↗
PubMed1991

Organization of the histaminergic system in the brain of the teleost, Trachurus trachurus.

To accumulate phylogenetic information on the central histaminergic system, we investigated the histaminergic system in the brain of a teleost, the jack mackerel (Trachurus trachurus), using the indirect immunofluorescent method with antiserum against histamine. A small number of histamine-immunoreactive cell bodies were observed in the posterior hypothalamus around the posterior recess. Histamine-immunoreactive fibers innervated the telencephalon, diencephalon, tegmentum, and rostral part of the medulla oblongata. The immunoreactive fibers were very sparse or absent in the olfactory bulb, optic tectum, cerebellum, caudal part of the medulla oblongata, spinal cord, and hypophysis. Ascending fiber bundles were seen in the basal hypothalamus, supplying fiber collaterals to the telencephalon and diencephalon, whereas descending fibers were observed in the midline of the lower brainstem. These findings suggest that the central histaminergic system of the jack mackerel is homologous to those of mammals, reptiles, and amphibians, although poorly developed compared with them. The histamine-immunoreactive neuronal cell bodies found in the border area between the mesencephalon and rhombencephalon of the river lamprey were not detected in the brain of the jack mackerel.

Animals↗
PubMed1991

Type-2 astrocytes show intracellular Ca2+ elevation in response to various neuroactive substances.

The effects of various neuroactive substances on the intracellular free Ca2+ concentration ([Ca2+]i) in cultured type-2 astrocytes were examined by fura-2-based microfluorometry. Type-2 astrocytes showed [Ca2+]i elevation in response to all the substances examined, i.e. carbachol (10(-4) M), histamine (10(-4) M), noradrenaline (10(-4) M), serotonin (10(-4) M), substance P (10(-6) M), vasopressin (10(-6) M) and glutamate (10(-4) M). Not all type-2 astrocytes, however, responded to these substances at the concentrations tested, and the percentages of astrocytes showing a Ca2+ response differed depending on the substance. These results indicate that type-2 astrocytes are potential targets for widely diverse neuroactive substances and heterogeneous in response to them.

Animals↗
PubMed1991

Histamine-induced inositol phosphate accumulation in type-2 astrocytes.

Histamine elicited dose-dependent accumulation of [3H]inositol phosphates in type-2 astrocytes, but not in type-1 astrocytes. The ED50 was about 2.4 x 10(-6) M and the maximal response was obtained at 10(-4) M. This response was dose-dependently inhibited by H1-antagonists, mepyramine and D- and L-chlorpheniramine. Furthermore, D- and L-chlorpheniramine showed stereoselectivity in the inhibition. On the other hand, an H2-antagonist, famotidine, and an H3-antagonist, thioperamide, did not inhibit the response. These results indicate that histamine stimulates accumulation of inositol phosphates in type-2 astrocytes via H1-receptors.

Animals↗
PubMed1991

Single type-2 astrocytes show multiple independent sites of Ca2+ signaling in response to histamine.

Intracellular Ca2+ plays an important role in signal transduction as a second messenger. In various types of cells, inositol 1,4,5-trisphosphate-induced elevations of intracellular free Ca2+ concentration ([Ca2+]i) have been reported to be uniform in single cells or originate at discrete sites from which they then propagate throughout the cells. These observations so far imply that a single cell functions as a minimal unit for inositol 1,4,5-trisphosphate-induced Ca2+ signaling. In this study, we examined the effects of histamine on [Ca2+]i of type-2 astrocytes using fura-2-based digital imaging fluorescence microscopy and found an unusual type of Ca2+ signaling in these cells. Histamine induced [Ca2+]i elevation in type-2 astrocytes by means of histamine H1 receptors. Submaximal concentrations of histamine (10(-7)-10(-6) M) evoked multiple sites of oscillatory [Ca2+]i elevation in single type-2 astrocytes. These Ca2+ "hot spots" were localized in the processes of the astrocytes but not in the cell bodies. The time courses of [Ca2+]i oscillations in different hot spots were not synchronized, indicating that each of them formed an independent compartment of Ca2+ signaling. When higher concentrations (10(-5)-10(-4) M) of histamine were added, [Ca2+]i in the processes remained elevated at high levels and [Ca2+]i elevations propagated from the processes to the cell bodies. These results suggest that individual processes of type-2 astrocytes can form minimal units for Ca2+ signaling in response to submaximal concentrations of histamine and that single type-2 astrocytes may function as multiple units for Ca2+ signaling.

Animals↗
PubMed1991

Tissue distribution and species difference of the brain type glucose transporter (GLUT3).

The complementary DNA for the human brain type glucose transporter (GLUT3) was used to determine its tissue specific expression in human, monkey, rabbit, rat, and mouse. Under high stringent conditions, 4.1 and 3.2 kilobase (kb) GLUT3 transcripts in monkey and a single 4.1 kb GLUT3 mRNA in rabbit, rat, and mouse were detected by RNA blot analysis. Although the GLUT3 transcripts were widely distributed, as are the erythrocyte type glucose transporter (GLUT1) transcripts, this mRNA is most abundant in the brain. However, the relative abundance of GLUT3 mRNA in the various regions of the monkey brain shows a different pattern from that of GLUT1 mRNA: GLUT3 is most highly expressed in the frontal lobe of the cerebrum, whereas GLUT1 is most abundant in the basal ganglia and the thalamus. Moderately higher GLUT3 mRNA levels were detected in the parietal lobe of the cerebrum, hippocampus, and cerebellum than the levels of GLUT1 transcripts. We also detected GLUT3 mRNA in adult human psoas major muscle, although it has been reported that the GLUT3 gene is scarcely expressed in adult human skeletal muscle of the thigh. In addition, in the rat and the mouse, no transcripts of the GLUT3 gene were detected in liver, kidney, small intestine, skeletal muscle, or fat besides in brain. Thus, the expression of the GLUT3 gene seems to be restricted to the brain in rodents. These results suggest that the expression of GLUT1 and GLUT3 genes might be regulated by different mechanisms.

Animals↗
PubMed1991

Histaminergic neuron system: morphological features and possible functions.

The histaminergic neuron systems in rat brain have been identified by immunocytochemical techniques using antibodies against histidine decarboxylase or histamine itself. Here, the details of the distribution of the histaminergic neuron networks are presented. Judging from the widespread distribution of the nervous system, it is postulated that the histaminergic neuron system is involved in various brain functions. Some functions, including the circadian rhythms, sleep-arousal cycles, drinking, feeding, thermoregulation, and neuroendocrine controls which were elucidated by administration of alpha-fluoromethylhistidine, a suicide substrate for histidine decarboxylase, are discussed here, although the true functions are still under investigations.

Animals↗
PubMed1991

Histamine H1-receptors on astrocytes in primary cultures: a possible target for histaminergic neurones.

The characteristics of histamine H1-receptors expressed on astrocytes from the cerebral cortex of new born rats were analysed by the [3H]-mepyramine binding assay. The apparent dissociation constant (Kd) was 10.4 nM and the binding capacity (Bmax) of 262 fmol/mg protein. H1-antagonists inhibited the [3H]mepyramine bindings and the isomers of chlorpheniramine showed a stereoselectivity for the inhibition of the bindings. Two distinct populations of cultured astrocytes, type-1 and type-2 astrocytes, were enriched and histamine-induced accumulations of inositol phosphates (IP) and cyclic AMP and histamine-evoked Ca++ signals were examined. Histamine stimulated the accumulation of IP in type-2 astrocytes, but not in type-1 astrocytes. The accumulation of cyclic AMP induced by histamine was observed in type-1 astrocytes, although not in type-2 astrocytes. Histamine-induced Ca++ signals were observed in 17.2% of type-1 astrocytes and in 72.9% of type-2 astrocytes. Histamine-induced Ca++ signals in type-2 astrocytes were antagonized by H1-antagonists, but not by H2- antagonists. Histamine-induced Ca++ signals were classified into 4 patterns, ie. transient, oscillatory, sustained and biphasic. When extracellular Ca++ was omitted or La was added to the extracellular medium, sustained phase of Ca++ signal disappeared and transient and oscillatory patterns were only observed. Phorbol ester inhibited histamine-induced Ca++ signals but pertussis toxin (IAP) and organic voltage dependent Ca++ channel blockers had no effect. Histamine-induced Ca++ elevation appeared initially in processes and then Ca++ wave propagated to the cell soma. Ca++ elevation was observed only in the processes in some cells.

Animals↗
PubMed1991

In vivo release of neuronal histamine in the hypothalamus of rats measured by microdialysis.

Using an in vivo intracerebral microdialysis method coupled with an HPLC-fluorometric method, we investigated the extracellular level of endogenous histamine in the anterior hypothalamic area of urethane-anaesthetized rats. The basal rate of release of endogenous histamine in the anterior hypothalamic area measured by this method was 0.09 +/- 0.01 pmol/20 min. When the anterior hypothalamic area was depolarized by infusion of 100 mM K+ through the dialysis membrane or electrical stimulation at 200 mu A was applied through an electrode implanted into the ipsilateral tuberomammillary nucleus, histamine release increased to 175% and 188%, respectively, of the basal level. These increases were completely suppressed by removal of extracellular Ca2+. The basal release of histamine was also suppressed after infusion of 10(-6) M tetrodotoxin or i.p. administration of 100 mg/kg of alpha-fluoromethylhistidine. On the other hand, 3-fold increase in the basal release was observed after i.p. administration of 5 mg/kg thioperamide. These results clearly indicate that both the basal and evoked release of histamine measured by our method are of neuronal origin.

Animals↗