Search PubMed⌕ Search

Biomedical subjects

F Hirata

Publications and source records attributed to F Hirata.

At least 55 records · Page 3Linked to original sources
PubMed1987

Regulation of prostaglandin formation by glucocorticoids and their second messenger, lipocortins.

Glucocorticoids induce the synthesis of a family of phospholipase inhibitory proteins, lipocortins. This family of lipocortins includes inhibitory proteins on phospholipase A2, phospholipase C and phosphatidylinositol phospholipase C. Hence, glucocorticoids reduce the formation of prostaglandins and leukotrienes by inhibiting cellular phospholipases, enzymes that degrade membrane phospholipids to release arachidonic acid, a precursor. The induction by glucocorticoids requires 1 h for the synthesis of mRNA and 5 h for the synthesis of proteins in various tissues and cells. However, glucocorticoids often exert their suppressive effects before the induction of lipocortins. This is now attributed to the nonenzymic formation of the adducts between glucocorticoids and lipocortins. These adducts are easily inserted into the membranes and more resistant to digestion of proteases, thus being more biologically potent with respect to suppression of the release of arachidonic acid, a precursor of prostaglandins and leukotrienes.

Animals↗
PubMed1987

Adrenergic regulation of beta-endorphin secretion from anterior pituitary in conscious rats: effects of thyroid state.

In conscious, chronically cannulated, unrestrained rats, systemic administration of catecholamines increases the plasma levels of beta-endorphin-like immunoreactivity (beta Ei). In euthyroid rats, this effect is mediated by both alpha 1 and beta-adrenergic receptors; the rise in plasma beta Ei caused by isoproterenol is blocked by 1 mg/kg propranolol, and the similar effects of norepinephrine and phenylephrine are blocked by 0.1 mg/kg prazosin. Both types of responses are completely suppressed by a 4-h pretreatment of rats with 0.1 mg/kg dexamethasone, indicating the anterior pituitary origin of the beta Ei released. Prior sectioning of the pituitary stalk does not significantly reduce the response to either phenylephrine or isoproterenol, suggesting that both agents act directly on the pituitary. Hypothyroidism induced by surgical thyroidectomy does not influence the beta Ei response to isoproterenol, which remains sensitive to block by propranolol or suppression by dexamethasone. However, neither norepinephrine nor phenylephrine is able to increase plasma beta Ei in the hypothyroid animals. Both isoproterenol and phenylephrine remain fully effective in rats made hyperthyroid by daily injections of 40 micrograms/kg T3 for 4 days. We propose that in unstressed rats catecholamines increase plasma beta Ei by a direct action on the anterior pituitary via either alpha 1- or beta-adrenergic receptors, and that expression of the alpha 1-, but not the beta-adrenergic response is regulated by thyroid hormones.

Animals↗
PubMed1986

Aspirin inhibits phospholipase C.

We have shown previously that aspirin (ASA) ingestion by normal human volunteers inhibits peripheral blood monocyte phospholipase C (PLC) activities ex vivo. In order to explore further the mechanism of action of ASA, normal human monocytes and differentiated human U937 cells were treated with ASA and other salicylates. Cells preincubated with ASA were found to have decreased PLC activities. Phospholipase A2 activities were not affected by salicylates. Sodium salicylate and salicylic acid, nonacetylated relatives of ASA also inhibited PLC activity. This effect was dose and time dependent and addition of cycloheximide or actinomycin D to the preincubation mixture abrogated the inhibitory effect of salicylates on PLC. This PLC inhibitory protein induced by ASA appears distinct from lipocortin, a phospholipase A2 inhibitory protein inducible by corticosteroids.

Annexins↗
PubMed1986

Isolation and characterization of lipocortin (lipomodulin).

Lipocortin is a phospholipase inhibitory protein whose synthesis is induced in various cells by glucocorticoids. At least three species with molecular weights of 40,000, 30,000, and 15,000 are presently known. This protein mimics the anti-inflammatory action of glucocorticoids in vitro as well as in vivo. The synthesis of the protein appears to be associated with the MHC genes.

Animals↗
PubMed1986

Lipocortin output by human endometrium in vitro.

Lipocortin was found to be secreted by human endometrium incubated for 1-2 days under organ culture conditions. Levels of lipocortin in the culture medium, measured by RIA, were increased by dexamethasone (10(-8)-10(-6) M) and decreased by progesterone (10(-8)-10(-6) M). Both steroids, however, decreased prostaglandin F2 alpha (PGF2 alpha) output, also estimated by RIA. These results suggest that lipocortin does not mediate the inhibition of PGF2 alpha production evoked by progesterone. Dexamethasone may inhibit PGF2 alpha production by mechanisms involved in the inhibition by progesterone in addition to those mediated by an elevation in the levels of lipocortin, a phospholipase inhibitor.

Annexins↗
PubMed1985

Glutaraldehyde pretreatment blocks phospholipase A2 modulation of adrenergic receptors.

Treatment of rat cerebral cortical membranes with phospholipase A2 affects, in a parallel fashion, beta-, alpha 1- and alpha 2-adrenergic receptor binding, but not the affinity of these receptors for their respective ligands. Pretreatment of membranes with 0.1 percent glutaraldehyde blocks the effects of phospholipase A2 on adrenergic receptor binding. The results support the hypothesis that desensitization or "masking" of adrenergic receptors may involve changes in membrane lipid composition. Furthermore, glutaraldehyde may prove a useful tool in the investigation of the dynamic roles of lipids in receptor function and more specifically, their regulation and coupling to physiological events.

Adrenergic alpha-Antagonists↗
PubMed1985

Inhibition of phospholipases by Met-Leu-Phe-Ile-Leu-Ile-Lys-Arg-Ser-Arg-His-Phe, C terminus of middle-sized tumor antigen.

The N and C terminals and tyrosine-phosphorylating site of the middle-sized tumor antigen of polyoma virus were chemically synthesized. The sequences of these peptides were Met-Asp-Arg-Val-Leu-Ser-Arg-Ala-Asp-Lys (N-MT), Met-Leu-Phe-Ile-Leu-Ile-Lys-Arg-Ser-Arg-His-Phe (C-MT), and Glu-Glu-Glu-Glu-Tyr-Met-Pro-Met-Glu (MT-Tyr), respectively. Among these peptides, the C-MT peptide inhibited phospholipase A2 (EC 3.1.1.4), phospholipase C (EC 3.1.4.3), and phospholipase D (EC 3.1.4.4). In addition, phosphatidylinositol-specific phospholipase C (EC 3.1.4.10) was also inhibited by this peptide. To study the mechanism of the inhibition, kinetic analysis was performed using phospholipase A2 from porcine pancreas. The degree of inhibition of phospholipase was dose dependent, and maximal inhibition was observed at pH 8.8. This peptide inhibited phospholipase A2 in a competitive manner for low-affinity sites of Ca2+, and in a noncompetitive manner for phospholipid substrates. When a fatty acid in the 2 position of the glycerol moiety of phosphatidylcholine was replaced by palmitic acid (C16:0), oleic acid (C18:1), linoleic acid (C18:2), eicosatrienoic acid (C20:3), or arachidonic acid (C20:4), the degree of inhibition of phosphatidylcholine hydrolysis by the C-MT peptide decreased. Inhibition of phospholipase A2 by the C-MT peptide was reversed by low concentrations of sodium deoxycholate but not by Triton X-100 or Nonidet P40, nonionic detergents. These detergents and the modification of acyl groups altered the micellar state of phospholipids. These results, taken together, suggest that the binding of the C-MT peptide near the low-affinity Ca2+ binding sites modifies the interaction of phospholipid substrates with the active center of phospholipase A2.

Animals↗
PubMed1985

Adrenergic receptors: possible mechanism of inverse regulation of alpha- and beta-receptors.

Many physiologic and pathologic conditions, including bronchial asthma, are associated with inverse changes in alpha- and beta-receptor-mediated responses in various tissues. The direction of the change elicited by a given stimulus is tissue specific, as exemplified by the actions of thyroid hormones: In the rat heart, hypothyroidism reduces beta- and increases alpha-receptor responses, whereas in the rat liver it has the opposite effects. A similar increase in beta- and decrease in alpha-receptor responses in the rat liver is triggered by a number of different conditions, including glucocorticoid deficiency, that appear to represent lower levels of cellular differentiation. Among these, incubation of isolated hepatocytes in a serum-free buffer triggers the conversion of the receptor response in vitro within 4 hours, without parallel changes in the density or affinity of receptor binding sites. This change can be acutely reversed by an endogenous inhibitor of membrane phospholipase A2, or accelerated by an activator of phospholipase A2, suggesting that changes in the activity of this enzyme are involved in the conversion of the hepatic adrenoceptor response. The glucocorticoid-induced increase in beta-receptors in cultured human lung adenocarcinoma cells also appears to be mediated indirectly through the induction of an endogenous inhibitor (lipomodulin) of membrane phospholipase A2. The possible relevance of altered membrane phospholipid metabolism in the pathomechanism of asthma and in the associated glucocorticoid-sensitive changes in adrenergic receptor mechanisms is discussed.

Animals↗
PubMed1984

Inhibition of leukocyte chemotaxis by Glu-Glu-Glu-Glu-Tyr-Pro-Met-Glu and Leu-Ile-Glu-Asp-Asn-Glu-Tyr-Thr-Ala-Arg-Gln-Gly.

Chemotaxis of rabbit peritoneal leucocytes stimulated by fMet-Leu-Phe, a synthetic chemoattractant, was inhibited by Glu-Glu-Glu-Glu-Tyr-Pro-Met-Glu (MT peptide) and Leu-Ile-Glu-Asp-Asn-Glu-Tyr-Thr-Ala-Arg-Glu-Gly (Src peptide). Both peptides did not inhibit the binding of [3H] formyl-NLe-Leu-Phe, a chemoattractant, to neutrophils, suggesting that the peptides inhibit the events distal to the chemotactic receptors. These peptides blocked the release of arachidonic acid from phospholipids in neutrophils stimulated with chemoattractants, whereas they had no effect on phospholipase A2 activity itself. The peptides markedly reduced the phosphorylation of lipomodulin, a phospholipase inhibitory protein, in either intact cells or isolated plasma membranes. Lipomodulin immunoprecipitated by monoclonal anti-lipomodulin antibody had phosphorylserine and phosphoryltyrosine as analyzed upon electrophoresis. The MT peptide which does not contain threonine or serine was phosphorylated by isolated plasma membranes. These results, taken together, suggest that a tyrosine phosphorylating kinase is involved in biochemical events of chemotactic receptors, and that lipomodulin is a substrate for this kinase.

Animals↗
PubMed1984

Phosphorylation at a tyrosine residue of lipomodulin in mitogen-stimulated murine thymocytes.

When murine thymocytes were stimulated by mitogens such as concanavalin A, the Ca2+ ionophore A23187, or 4 beta-phorbol 12-myristate 13-acetate, there was a marked increase of 32P incorporation into immunoprecipitable lipomodulin, a phospholipase inhibitory protein. These compounds enhanced 45Ca2+ influx into thymocytes, which, in turn, increased protein phosphorylation, probably by Ca2+- and phospholipid-dependent protein kinase (protein kinase C). Cyclic 8-bromo-AMP, an inhibitor of lymphocyte mitogenesis, blocked the mitogen-stimulated phosphorylation of lipomodulin, although it stimulated the protein phosphorylation via cyclic AMP-dependent kinase (protein kinase A). On electrophoresis, the hydrolysates of 32P-labeled lipomodulin showed a single radioactive spot, which comigrated with authentic phosphotyrosine. The partially purified middle-sized tumor antigen was able to phosphorylate lipomodulin after being phosphorylated by protein kinase C but not by the catalytic subunit of protein kinase A. Our findings suggest that the activity of a tyrosine-specific kinase, which phosphorylates lipomodulin in vivo as well as in vitro, is stimulated by protein kinase C and inhibited by protein kinase A.

Animals↗
PubMed1984

Time-dependent conversion of alpha 1- to beta-adrenoceptor-mediated glycogenolysis in isolated rat liver cells: role of membrane phospholipase A2.

Incubation of isolated rat liver cells in a serum-free buffer leads to the reduction of the glycogenolytic effect of phenylephrine and the simultaneous emergence of a glycogenolytic response to isoproterenol within 4 hr. This conversion of the adrenergic activation of phosphorylase from an alpha 1- to a beta-adrenoceptor-mediated response is associated with no change in the glycogenolytic response to the calcium-linked activator vasopressin, and a reduction of the glycogenolytic response to the cAMP-linked activator glucagon. In vitro incubation of hepatocytes does not influence the density of affinity of [3H]prazosin-labeled alpha 1-receptors and [3H]CGP-12177-labeled beta-receptors. In cells preincubated for 4 hr, a further 30-min incubation with 50 nM lipomodulin, an endogenous inhibitor of membrane phospholipase A2 (EC 3.1.1.4), reverses the adrenergic activation of phosphorylase from a beta- to an alpha 1-receptor-mediated event, whereas in freshly isolated cells lipomodulin does not affect the predominant alpha-receptor response. Conversely, exposure of freshly isolated cells to a monoclonal antibody to lipomodulin in the presence of 10 microM phenylephrine, or to melittin, an activator of phospholipase A2, at 2 micrograms/ml, results in the suppression of the effect of phenylephrine and the emergence of a response to isoproterenol within 30 min. It is proposed that coupling of hepatic alpha 1- and beta-adrenoceptors to postreceptor pathways is regulated in an inverse reciprocal manner by changes in membrane phospholipase A2 activity.

Animals↗
PubMed1984

Glucocorticoid inhibition of zymosan-induced arachidonic acid release by rat alveolar macrophages.

The phospholipase-dependent liberation of arachidonic acid (AA) from membrane phospholipids has been proposed as the rate-limiting step in the synthesis of bioactive AA metabolites, which play an important role in the expression of inflammatory and immune reactions. We have examined the effects of steroids in vitro on the release of AA by rat alveolar macrophages exposed to zymosan. Fluocinolone (1 microM) significantly inhibited the zymosan-induced release of radiolabeled AA from phosphatidylcholine as well as the production of radiolabeled prostaglandin E2. (PGE2). Dose-response curves gave the following rank order of potency: fluocinolone greater than dexamethasone greater than hydrocortisone. The maximal degree of inhibition of radiolabeled AA release observed was approximately 70%. Inhibition was not observed after 3 h of glucocorticoid pretreatment, but maximal inhibition was achieved after 10 h of pretreatment. Pretreatment with gonadal sex hormones (1 microM) did not inhibit AA release. Concurrent incubation of macrophages with hydrocortisone and excess concentrations of the partial glucocorticoid agonist, progesterone, blunted the degree of inhibition observed with hydrocortisone alone. These data are consistent with a receptor-mediated process. The time course suggests a response dependent on new protein synthesis, and the increased concentration of the phospholipase-inhibitory protein, lipomodulin, in steroid-treated cultures is putative evidence of new protein synthesis.

Animals↗