Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.21.5 (thrombin)
 33,306 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Induction of NO synthase expression by interleukin-1 beta in cultured vascular smooth muscle cells from rat aortas was accompanied by simultaneous induction of GTP: cyclohydrolase I. This enzyme regulates the de novo synthesis pathway for tetrahydrobiopterin, an essential cofactor for the catalytic conversion of L-arginine to L-citrulline and NO by inducible NO synthase. Inhibition of GTP: cyclohydrolase attenuated NO production by interleukin-1 beta-stimulated smooth muscle cells. Peptide growth factors such as fibroblast growth factor, platelet-derived growth factor and transforming growth factor beta 1 and the protease thrombin have been shown to modulate the production NO by cytokine-treated smooth muscle cells. These peptide agonists also regulated the induction of NO synthase and GTP: cyclohydrolase mRNA expression.
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PMID:Growth factor regulation of interleukin-1 beta-induced nitric oxide synthase and GTP: cyclohydrolase expression in cultured smooth muscle cells. 750 72

Experiments were designed to examine whether or not insulin-like growth factor I (IGF-I), which is produced by vascular cells in response to injury, affects the production of nitric oxide evoked by the inducible nitric oxide synthase in cultures of smooth muscle cells from the rat aorta. Nitric oxide production was assessed indirectly by the measurement of nitrite accumulation and nitric oxide synthase activity by determining the formation of L-citrulline from L-arginine. Nitric oxide synthase was induced in vascular smooth muscle cells that had been exposed to interleukin-1 beta (IL-1 beta) or tumor necrosis factor-alpha (TNF-alpha). IGF-I inhibited, in a concentration-dependent manner, the production of nitrite and L-citrulline evoked by IL-1 beta or TNF-alpha. The inhibition caused by IGF-I required the presence of the growth factor during the induction of nitric oxide synthase. Two IGF-I-related proteins, IGF-II and insulin, also inhibited, but to a smaller extent, the release of nitrite and the formation of L-citrulline stimulated by IL-1 beta. Under bioassay conditions, the perfusates from columns containing IL-1 beta-treated smooth muscle cells relaxed rings of rat aorta without endothelium that had been contracted with phenylephrine; these relaxations were reversed by nitro-L-arginine. Addition of IL-1 beta-treated vascular smooth muscle cells to indomethacin-treated platelets inhibited their aggregation to thrombin; methylene blue prevented this inhibition. Control smooth muscle cells or cells exposed to IGF-I alone did not have such effects.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Insulin-like growth factor I inhibits induction of nitric oxide synthase in vascular smooth muscle cells. 750 7

This brief overview discusses the ability of mediators associated with vascular injury, such as interleukin-1 beta and tumour necrosis factor alpha, to activate vascular smooth muscle cells to produce nitric oxide or a related donor of nitric oxide. The cytokines cause the synthesis of nitric oxide synthase(s), which catalyzes the conversion of L-arginine to nitric oxide and L-citrulline. The production of nitric oxide can be modulated by factors produced by vascular cells and formed elements of the blood (e.g. platelet-derived growth factor, transforming growth factor beta), but also by those generated at sites of vascular injury from inactive precursors circulating in the blood (e.g. thrombin, plasmin). The production of nitric oxide by vascular smooth muscle cells may contribute to the homeostasis of blood vessels at sites of injury. In particular, nitric oxide may prevent the local development of vasospasms, unwanted proliferation of smooth muscle cells, and also help to control coagulation and the formation of the thrombus.
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PMID:Role of the L-arginine-nitric oxide pathway in vascular smooth muscle. 750 37

Although high-density lipoprotein (HDL) has been found to decrease platelet function per se, little is known regarding the mechanism of its platelet inhibitory effect. In this study, we confirmed the inhibitory effect of HDL on platelet aggregation and 14C-serotonin release in thrombin-activated washed human platelets. The inhibition of platelet function was associated with an increase in nitric oxide synthase activity, measured as the conversion of 3H-L-arginine to 3H-L-citrulline as well as nitrite release in the platelet supernates. The inhibition of platelet function by HDL was reversed by preincubation of washed platelets with an inhibitor of nitric oxide synthase, NG-nitro-L-arginine methyl ester (L-NAME), and potentiated by co-incubation with the precursor of nitric oxide, L-arginine. These observations suggest that HDL decreases platelet function by increasing nitric oxide synthase activity in human platelets.
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PMID:Inhibitory effect of high-density lipoprotein on platelet function is mediated by increase in nitric oxide synthase activity in platelets. 752 5

A number of cell types possess an L-arginine-nitric oxide (NO) pathway. We studied the presence of constitutive and inducible forms of NO synthase in human platelets. N omega-nitro-L-arginine, an inhibitor of NO synthase, potentiated thrombin-induced aggregation of washed human platelets, whereas L-arginine inhibited it. The direct evidence for the presence of constitutive form of NO synthase came from the observation of conversion of tritium-labeled L-arginine to tritium-labeled L-citrulline by washed platelets suspended in Ca(++)-rich but not in Ca(++)-free buffer. Incubation of washed platelets in Ca(++)-free buffer with cytokines (tumor necrosis factor-alpha and interferon-gamma) or cytokines plus lipopolysaccharide caused a marked increase in the conversion of [3H]L-arginine to [3H]L-citrulline, suggesting the presence of inducible form of NO synthase. Gel electrophoresis identified an approximately 130 kd protein band with NO synthase in the platelet cytosol, which on isolation converted [3H]L-arginine to [3H]L-citrulline. This 130 kd protein required the presence of Ca++, reduced nicotinamide adenine dinucleotide phosphate tetrahydro-L-biopterin, and flavin adenine dinucleotide for expression of NO synthase activity. Platelet sonicates demonstrated presence of nitrite, and its concentrations were lowered by preincubation of platelets with NG-nitro-L-arginine methyl ester and enhanced in cytokine-treated platelets. Reverse-transcription polymerase chain reaction demonstrated messenger RNA expression of the constitutive endothelial (but not brain) and inducible isoforms of NO synthase in platelets. These observations indicate that human platelet cytosol possesses both constitutive and inducible forms of NO synthase.
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PMID:Identification of constitutive and inducible forms of nitric oxide synthase in human platelets. 753 7

1. Nitric oxide (NO) is released from vascular endothelium following conversion of L-arginine to L-citrulline by calcium-calmodulin-dependent 'constitutive' NO-synthase. 2. Nitric oxide release occurs under basal conditions, in response to chemical stimuli (acetylcholine, bradykinin, thrombin, prostacyclin, serotonin, etc.) and in response to changes in shear stress (effects of blood velocity on vascular endothelium). 3. Analogues of L-arginine inhibit NO and are widely used to study the effects of NO on the cardiovascular system: in intact animals, these inhibitors cause vasoconstriction, leading to an increase in arterial blood pressure (ABP) and bradycardia. 4. Bradycardia induced by NO inhibitors is due, in part, to baroreceptor activity following the increase in ABP and in part to a direct effect on the sino-atrial node. 5. In the intact animals and isolated perfused heart, NO inhibitors cause coronary vasoconstriction and hence a reduction in basal coronary flow. This effect, however, is not seen in isolated coronary vessels. 6. From experiments in which ABP did not change, NO does not appear to have an important role in regulating coronary vasomotor tone under basal conditions. 7. Nitric oxide appears to be involved in the duration of reactive hyperaemia following coronary vascular occlusion but is not involved to any significant extent in the peak amplitude of hyperaemia. 8. Responses to vasodilator stimuli which do not involve NO in the initiation of the vasodilation may be prolonged by the effect of increased blood flow (shear stress) which releases NO and potentiates hyperaemia.
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PMID:Control of coronary blood flow by endothelial release of nitric oxide. 786 29

p-Aminobenzamidine competitively inhibits bovine trypsin, human and bovine thrombin, and human plasmin, all of which act on substrates containing preferentially the L-arginyl side chain at their P1 position. Considering the structural and functional similarity between p-aminobenzamidine and the L-arginyl side chain in trypsin-like serine proteinases, we investigated the interaction of p-aminobenzamidine with mouse brain nitric oxide synthase (NOS), which uses L-arginine as the substrate for generating NO and L-citrulline. p-Aminobenzamidine is a competitive NOS inhibitor (Ki = 1.2 x 10(-4) M, at pH 7.5 and 37.0 degrees C), but not an NO precursor. Therefore, p-aminobenzamidine affects the NO production and the trypsin-like serine proteinase action.
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PMID:Competitive inhibition of nitric oxide synthase by p-aminobenzamidine, a serine proteinase inhibitor. 912 58

L-arginine uptake takes place in human platelets through a saturable high affinity Na(+)-independent process mediated by the y(+) carrier for cationic amino acids. In the present study the effect of thrombin and collagen on L-arginine transport in human platelets was investigated. Thrombin significantly affected L-arginine uptake whereas collagen was uneffective. In particular, thrombin increased Vmax of the uptake by 77%, while it reduced the affinity of the carrier for L-arginine. The effect of thrombin on the transport process did not result in any increase in L-arginine metabolism since no conversion of the amino acid, either to L-citrulline (indicative of the presence of the L-arginine/nitric oxide pathway) or to any other metabolite, could be detected in resting or stimulated platelets.
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PMID:Agonist-regulated L-arginine uptake in human platelets. Evidence against intracellular utilization of the amino acid. 913 60

Activity of both nitric oxide (NO) synthase (NOS) and cyclooxygenase (COX) plays an important role in the regulation of platelet function. NO has been shown to directly activate COX. This study was designed to determine whether products of the COX pathway in turn regulate NOS activity. Human platelets were incubated with aspirin, indomethacin, the selective thromboxane A2 synthase inhibitor U-63557A, or the prostaglandin H2-thromboxane A2-receptor blocker SQ-29548 for 1 h at 37 degrees C. Multiple indexes of the activity of the L-arginine-NO pathway and changes in cytosolic Ca2+ concentration ([Ca2+]i) were measured in platelets. Both aspirin and indomethacin decreased NOS activity, measured as the conversion of L-arginine to L-citrulline and nitrite (+nitrate) formation, in platelets in a concentration-dependent fashion. Aspirin also decreased guanosine 3',5'-cyclic monophosphate accumulation in platelets. The NOS inhibitory effects of these aspirin and indomethacin effects were reversed by coincubation with the thromboxane A2 analog U-46619 or an excess of CaCl2. Incubation of COX inhibitors with platelets was associated with significant reductions in basal as well as thrombin-stimulated [Ca2+]i, and the reduction in [Ca2+]i was reversed by U-46619. Incubation of platelets with U-63557A and SQ-29548 resulted in inhibitory effects on NOS activity qualitatively similar to those of COX inhibitors. The effects of COX inhibitors or U-63557A were not associated with a change in NOS protein expression in platelets. These data suggest that NOS activity in human platelets is inhibited by COX inhibitors, mediated, at least in part, via suppression of thromboxane A2 and [Ca2+]i mobilization in platelets.
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PMID:Cyclooxygenase inhibition decreases nitric oxide synthase activity in human platelets. 936 53

The human placenta contains nitric oxide synthase (NOS) activity, which had been previously found to be localized in the syncytiotrophoblast and the endothelial cells of stem villous vessels. Nitric oxide produced by the syncytiotrophoblast could affect maternal platelet aggregation. The aim of the present study was to examine the effects of substances known to cause platelet aggregation (arginine vasopressin (AVP), the thromboxane A2 mimetic U46619, adenosine diphosphate (ADP) and thrombin) on NOS activity of human placental explants in vitro. Placentae were obtained at term from women with obstetrically uncomplicated deliveries. NOS activity was measured in explants by determining the conversion of [3H]L-arginine to [3H]L-citrulline during 60 min incubations. Either the presence of N-omega-L-arginine or the omission of calcium (in the presence of EDTA) significantly inhibited NOS activity. Adenosine triphosphate (ATP) at concentrations of 100-1000 microM significantly stimulated NOS activity, and was used as a positive control. ADP at a concentration of 1000 microM was found to significantly stimulate NOS activity, however, the other platelet aggregating substances investigated, thrombin (0.1, 10 U/ml), AVP (1, 10, 20 microM) and U46619 (3, 30, 300 nM), had no significant effect on NOS activity. These results show that ATP and ADP can stimulate human placental NOS activity, but provide no evidence that platelet aggregating agents other than ADP can affect the production of NO.
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PMID:Effects of ATP, ADP, thrombin, vasopressin and U46619 on human placental nitric oxide synthase activity. 944 72


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