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R Korbut

Publications and source records attributed to R Korbut.

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

A biological method for studying the interaction between platelets and vascular endothelium.

A segment of fresh rabbit thoracic aorta (RbA) was turned inside out and superfused (1.5 ml/min) with citrated (3.8%) or heparinized (10 U/ml) blood of rabbit and the superfusate was discarded. RbA gained in weight due to deposition of thrombi on its endothelial surface. These thrombi were mainly composed of platelets. The interaction between platelets and endothelium was augmented in RbAs from animals with atherosclerosis and in RbAs pretreated with aspirin (110 microM) or 15-HPETE (150 microM) or by the enzymatic system generating oxygen free radicals (xanthine:xanthine oxidase - 100 microM: 0.1 U/ml). On the other hand, this interaction was impaired by superoxide dismutase (20 U/ml) or catalase (0.2 U/ml). Finally, the dissipation of thrombi by thromboxane A2-synthetase inhibitor--dazoxiben was found to be related to an increase in endothelial generation of prostacyclin.

Animals↗
PubMed1990

Immediate release of a nitric oxide-like factor from bovine aortic endothelial cells by Escherichia coli lipopolysaccharide.

Incubation of human washed platelets with bovine aortic endothelial cells (ECs) treated with indomethacin resulted in an inhibition of thrombin-induced platelet aggregation that was dependent on the number of ECs added. Preincubation of ECs with Escherichia coli lipopolysaccharide (LPS; 0.5-2.0 micrograms/ml) for 1 min significantly enhanced their inhibitory activity. This effect was potentiated by superoxide dismutase (60 units/ml) and reversed by oxyhemoglobin (5-10 microM), indicating that the inhibition was due to the release of endothelium-derived relaxing factor (nitric oxide). When the ECs were pretreated with NG-monomethyl-L-arginine (30-300 microM) before LPS, the antiaggregatory activity was strongly reduced. The reduction of activity by NG-monomethyl-L-arginine was reversed by L-arginine (100 microM) but not by D-arginine (100 microM). Under similar conditions, LPS also enhanced the antiaggregatory activity of ECs grown on beads. The immediate enhancement by LPS of the release of endothelium-derived relaxing factor from endothelial cells may contribute to the rapid fall in blood pressure associated with endotoxin shock in vivo.

Animals↗
PubMed1990

Sodium nitroprusside modulates the fibrinolytic system in the rabbit.

1. We have investigated the effect of sodium nitroprusside (NP) and glyceryl trinitrate (GTN) on fibrinolysis in anaesthetized rabbits ex vivo and in vitro by measurement of euglobulin clot lysis time (ECLT), plasma levels of tissue plasminogen activator (t-PA) activity, plasma t-PA antigen levels and plasminogen activator inhibitor (PAI-1) activity. 2. In vivo, NP (30 micrograms kg-1), GTN (30 micrograms kg-1) and prostacyclin (3 micrograms kg-1) caused similar transient decreases in left ventricular systolic pressure. However, while prostacyclin induced near-maximal inhibition of ex vivo platelet aggregation, NP or GTN had no effect. 3. Ex vivo, NP caused a significant decrease in ECLT and an increase in plasma t-PA activity. 4. Intravenous co-administration of t-PA (30 micrograms kg-1) with NP caused substantial prolongation of plasma t-PA activity, without affecting t-PA antigen levels. 5. In whole blood in vitro, NP (30 micrograms kg-1) prevented the time-dependent increase in PAI-1 activity and inhibited inactivation of added t-PA (10 ng ml-1). 6. We propose that NP exhibited fibrinolytic activity through increased t-PA activity as a result of inhibition of PAI-1 release from platelets. These results could have important therapeutic consequences when t-PA and nitrate treatments are combined.

Animals↗
PubMed1990

The use of oxyhaemoglobin to explore the events underlying inhibition of platelet aggregation induced by NO or NO-donors.

1. Full inhibition of thrombin-induced platelet aggregation was elicited by the least maximal platelet inhibitory concentrations of nitric oxide (NO; 7 +/- 1 microM) or NO-donors which included sodium nitroprusside (NaNp; 80 +/- 13 microM) 3-morpholinosydnonimine (SIN-1; 3 +/- 0.1 microM) or endothelial cells (EC; 2.36 +/- 0.12 x 10(5) added 1 min before thrombin. Oxyhaemoglobin (oxyHb; 10 microM) administered 30s to 10 min after stimulation with thrombin caused a time-dependent reversal of the inhibition induced by these agents. OxyHb was ineffective when these agents were co-incubated with the non-selective phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX, 0.05 mM). 2. OxyHb did not reverse the platelet inhibition with IBMX (0.2 mM) or that caused by a selective guanosine 3'; 5'-cyclic monophosphate (cyclic GMP) phosphodiesterase inhibitor 2-O-propoxyphenyl-8-azapurin-6-one, (M & B 22948; 20 microM). In addition, oxyHb did not reverse the inhibition with iloprost (1 nM) which inhibits platelet aggregation through stimulation of adenylate cyclase. 3. The inhibition of platelet aggregation by NO (7 +/- 1 microM) or NaNp (80 +/- 13 microM) was accompanied by a 13 fold increase in cyclic GMP levels occurring within 15 s of addition of these agents. In the continued presence of NO or NaNp, the reversing effect of oxyHb given 1 min after thrombin was associated with a pronounced decrease in cyclic GMP levels. 4. We conclude that the inhibition of platelet aggregation by activators of guanylate cyclase depends in the first few minutes on continuous stimulation of the enzyme in order to maintain intracellular concentrations of cyclic GMP, except when its breakdown is inhibited. 5. The addition of agents such as oxyHb after the inhibition of platelet aggregation offers another way of investigating the biochemical changes involved in maintaining platelets in an inactive state.

1-Methyl-3-isobutylxanthine↗
PubMed1989

Interaction between stimulators of adenylate and guanylate cyclases in human leukocytes, platelets and arteries.

Buffered solutions (pH 5-pH 8) of glyceryl trinitrate (GTN), sodium nitroprusside (NaNP), S-nitroso-N-acetylpenicillamine (SNAP), molsidomine and its active metabolite (SIN-1) at concentrations of 30 microM were each tested at 37 degrees C for the release of nitric oxide (NO) by its co-oxidation to NO3 along with oxidation of oxyhaemoglobin to methaemoglobin. Apart from GTN and molsidomine, three other stimulators of guanylate cyclase released NO in a pH-dependent manner. Optimum for the release of NO by SIN-1 was at pH 7.4 and therefore this guanylate cyclase stimulator was chosen for studies on interaction with the adenylate cyclase stimulator iloprost, a stable prostacyclin analogue. Human platelets, neutrophils and strips of coronary arteries were used as targets to study this interaction. SIN-1 and iloprost synergized in the inhibition of collagen-induced platelet aggregation and protection of neutrophils against the release of lactate dehydrogenase, whereas no synergism between these drugs was observed in their vasorelaxant action. It is concluded that pharmacological synergism between adenylate and guanylate cyclase stimulators is not a general rule, but occurs only in certain types of cells.

Adenylyl Cyclases↗
PubMed1989

Interaction between NO donors and iloprost in human vascular smooth muscle, platelets, and leukocytes.

Endothelium-derived relaxing factor (EDRF) and donors of nitric oxide (NO) (glyceryl trinitrate, SIN-1--a metabolite of molsidomine--S-nitroso-N-acetyl-penicillamine, and sodium nitroprusside) but not prostacyclin and its analog, iloprost, relax strips of rabbit aorta. Strips of human coronary artery also relax when exposed to NO donors and prostacyclin; in this artery, SIN-1 and iloprost exert additive but not synergistic relaxant action. In mildly activated human platelets and leukocytes, SIN-1 and iloprost have a synergistic suppressive action. A similar synergistic thrombolytic effect between NO and prostacyclin was observed in whole rabbit blood in interactions with rabbit aortic endothelium. These findings suggest that because of this cell-selective synergism between NO donors and prostacyclin analogs, the concomitant use of molsidomine and iloprost for the treatment of ischemic heart and peripheral vascular disease should be attempted.

Adenylyl Cyclases↗
PubMed1987

On the mechanism of thrombolytic action of thromboxane synthetase inhibitors.

Using our in vivo model for studying drugs which prevent deposition of thrombi or dissipate thrombi formed in extra-corporeal circulation over a collagen strip superfused with arterial blood of anaesthetized and heparinized cats, we have found that dazoxiben--a thromboxane synthetase inhibitor--possesses not only antithrombotic but also thrombolytic potency in vivo (ED50 = 3.8 mg/kg i.v.). The thrombolytic potency of dazoxiben was antagonized by aspirin at a dose of 50 mg/kg i.v. Moreover, dazoxiben stimulated the generation of prostacyclin in isolated rat aortic slices incubated in platelet rich plasma, but not in platelet poor plasma. It is suggested that the thrombolytic potency of thromboxane synthetase inhibitors after their systemic administration is associated with the release of prostacyclin and/or prostacyclin-stable metabolites by the vascular endothelium owing to feeding of prostacyclin synthetase with prostaglandin endoperoxides accumulated in platelets following the inhibition of thromboxane synthetase.

Animals↗
PubMed1987

On the mechanism of antithrombotic action of flavonoids.

Flavonols (quercetin and rutin) and flavanes (cyanidol and meciadonol) were studied for their effect on non-enzymatic lipid peroxidation, lipoxygenase and cyclo-oxygenase activities, binding to albumin and platelet membranes. These biochemical properties of four flavonoids were compared with respect to their antithrombotic action in vivo and their efficacy at influencing the platelet-endothelium interaction in vitro. All four flavonoids inhibited the ascorbate-stimulated formation of malondialdehyde by boiled rat liver microsomes (quercetin greater than rutin approximately cyanidol approximately meciadonol) and inhibited platelet lipoxygenase activity (quercetin greater than cyanidol greater than meciadonol greater than rutin) whereas only flavonols, but not flavanes, stimulated cyclo-oxygenase and were bound to platelet membranes. The same two flavonols dispersed platelet thrombi which were adhering to the rabbit aortic endothelium in vitro (EC50 for quercetin was 80 nM and for rutin 500 nM) and prevented platelets from aggregation over blood-superfused collagen strip in vivo (ED50 for quercetin was 5 nmol/kg and for rutin 33 nmol/kg i.v.). Cyanidol and meciadonol were not effective as anti-thrombotic agents. It is concluded that activated platelets adhering to vascular endothelium generate lipid peroxides and oxygen-free radicals which inhibit endothelial biosynthesis of prostacyclin and destroy endothelium-derived relaxing factor (EDRF). Flavonols are anti-thrombotic because they are selectively bound to mural platelet thrombi and owing to their free radical scavenging properties resuscitate biosynthesis and action of endothelial prostacyclin and EDRF. Thus, flavonols release the thrombolytic and vasoprotective endothelial mediators only in these vascular segments which are covered by a carpet of aggregating platelets.

Albumins↗
PubMed1986

Eicosanoid balance at early stages of experimental atherosclerosis. Its relationship with plasma fibrinolytic activity and platelet aggregation.

We have studied generation of eicosanoids in blood vessels and platelets of rabbits in relation to platelet aggregation and plasma fibrinolytic activity at early stages of experimental atherosclerosis. A level of lipid peroxides in plasma augmented progressively from the 2-nd to 12-th week of atherogenic diet. In parallel, platelets generated more TXA2 and 12-HETE while in blood vessels a gradual reduction of prostacyclin formation was observed. Reduction in generation of PGI2 was accompanied by steady formation of PGE2. In the second week of the diet a slight decrease appeared of aggregatory response while later aggregability of platelets was increased. At first, plasma fibrinolytic activity was decreased, but it significantly augmented after 12 weeks of the diet. The above data indicate that changes of arachidonic acid metabolism in platelets and blood vessels appear at a very early stage of atherosclerosis and they influence platelet function and plasma fibrinolytic activity.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1985

Stimulatory cholinergic effect on the release of antiaggregatory activity into the circulation of cat and man and its modification by beta-adrenergic antagonists.

The release of PGI2-like activity into the circulation in response to cholinergic agonists and modification of this response by beta-adrenergic antagonists was investigated in anaesthetized cats and healthy humans. Antiaggregatory activity in the arterial blood was continuously assayed by measuring platelet aggregation on blood superfused collagen strip. In some of the human experiments, after the administration of the drugs, the conversion of [14C]-arachidonate to [14C]-prostaglandins in the pulmonary vascular bed was studied. Cholinergic agonists stimulated the release of PGI2-like activity into the circulation, which effect was potentiated in cats by beta-adrenergic antagonists. In humans the latter agents did not stimulate the conversion of [14C]-arachidonate to prostaglandins in the pulmonary circulation and, moreover, inhibited the stimulatory cholinergic effect. The results suggest that an interplay between cholinergic and beta-adrenergic mediators may be involved, although in a different way in cats and in humans, in the release of PGI2-like activity into the systemic circulation.

Acetylcholine↗
PubMed1984

Release of prostacyclin from the human pulmonary vascular bed in response to cholinergic stimulation.

The ability of the human pulmonary vascular bed to synthesize prostaglandins (PGs) in response to cholinergic stimulation was investigated in healthy male volunteers. In all of them, except controls, carbaminoylcholine (CCh) was injected subcutaneously at a dose of 5 micrograms/kg. In 3 subjects [1-14C]-labelled arachidonate was then infused at a constant rate into the right atrium between 10 and 15 min after the administration of the drug and the blood from the subclavian artery was sampled simultaneously. The arterial content of [14C]-labelled metabolites was extracted, separated by thin-layer chromatography and quantified using liquid scintillation spectrometry. In 8 other subjects PGI2-like activity after the administration of CCh was assayed in the arterial blood and in 1 subject in the venous blood, using a technique for continuous measurement of platelet aggregation on blood-superfused collagen strip. The major portion of [14C]-activity in the radiochromatograms migrated in parallel with the 6-keto-PGF1 alpha standard. No early defined peaks corresponding to any of the unlabelled PGs D2, E2 or F2 alpha, appeared, but in one chromatogram a minor radiopeak corresponding to authentic thromboxane B2 was observed. Also in the platelet aggregation experiments, 5-15 min after the administration of CCh, a significant increase in the PGI2-like activity was observed in the arterial as well as in the peripheral venous blood, which effect of the drug was abolished by pretreatment with atropine and acetylsalicylic acid.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗