Aggregation Of Washed Platelets Research Articles

Licofelone, an inhibitor of cyclooxygenase and 5-lipoxygenase, specifically inhibits cyclooxygenase-1-dependent platelet activation

5-Lipoxygenase/cyclooxygenase inhibitors, possessing anti-inflammatory action and gastric safety due to cyclooxygenase-2 and 5-lipoxygenase inhibition and antiplatelet activity due to cyclooxygenase-1 blockade, would be beneficial in the treatment of ischemic disease because they may reduce, at the same time, inflammation, underlying the atherosclerotic process, and platelet activation, responsible for acute thrombotic events. In this study, we characterized the antiplatelet effects of the new 5-lipoxygenase/cyclooxygenase inhibitor licofelone ([2,2-dimethyl-6-(4-chlorophenyl)-7-phenyl-2,3,dihydro-1 H-pyrrolizine-5-yl]-acetic acid. Licofelone completely prevented platelet aggregation induced in platelet-rich plasma by threshold aggregating concentrations of arachidonic acid (0.87±0.14 mM) at threshold inhibitory concentrations of 0.75±0.35 μM ( n=5). Platelet-rich plasma aggregation induced by threshold aggregating concentrations of collagen/adrenalin (0.3±0.05 μg/ml and 0.4±0.1 μM, respectively) was reduced to 3.2±2% of control at licofelone 100 μM, ( P<0.05, n=6). Washed platelet aggregation induced by threshold aggregating concentrations of thrombin (0.07±0.01 U/ml) was only partially affected by licofelone at concentrations one or two order of magnitude higher than those fully preventing arachidonic acid-induced aggregation (44±11% of control at 100 μM, P<0.05, n=7). Failure to prevent aggregation triggered by high concentrations of collagen/adrenalin in aspirin-treated platelets supports cyclooxygenase-1 as a specific target of licofelone. In fact, licofelone inhibited thromboxane B 2 (TxB 2) production by all the agonists tested at concentrations between 0.5 and 50 μM. At this concentration, TxB 2 production was reduced at values similar to those of unstimulated platelets. These results indicate that, at clinically relevant concentrations, licofelone exerts a potent antiplatelet effect mediated by the inhibition of cyclooxygenase-1 activity.

Pharmacological characterization of N-tert-butyl-N'-[2-(4'-methylphenylamino)-5-nitrobenzenesulfonyl]urea (BM-573), a novel thromboxane A2 receptor antagonist and thromboxane synthase inhibitor in a rat model of arterial thrombosis and its effects on bleeding time.

The present study was undertaken to characterize the antiplatelet and antithrombotic effects of BM-573 [N-tert-butyl-N'-[2-(4'-methylphenylamino)-5-nitrobenzenesulfonyl]urea], an original combined thromboxane receptor antagonist and thromboxane synthase inhibitor in rats, and to determine its effects on mice bleeding time. Intraperitoneal injection of a single dose of 5 mg/kg BM-573 to rats inhibited U-46619 (9,11-dideoxy-9,11-methanoepoxy-prostaglandin F(2))-induced washed platelet aggregation 30 min and 1, 2, and 4 h after drug administration with a maximum antiplatelet effect observed after 1 and 2 h. In a rat model of thrombosis induced by ferric chloride application on the abdominal aorta, BM-573 significantly reduced the thrombus weight by 92.53, 80.20, 64.75, and 18.21% at doses of 5, 2, 0.5, and 0.2 mg/kg, respectively. Time to occlusion of abdominal aorta in the BM-573-treated group (41.50 +/- 5.21 min) was significantly prolonged compared with the vehicle-treated rats (16.16 +/- 0.79 min). Like furegrelate, seratrodast, and acetylsalicylic acid, BM-573 did not affect the tail bleeding time induced by tail transection in mice compared with vehicle-treated mice. Moreover, BM-573, a close derivative of the loop diuretic torasemide, failed to induce a significant increase in diuresis in rat and did not produce a decrease in blood glucose concentration as observed with the sulfonylurea glibenclamide. In conclusion, we have demonstrated that the nitrobenzenic sulfonylurea BM-573, an original combined thromboxane receptor antagonist and thromboxane synthase inhibitor, is a potent antithrombotic agent that does not affect bleeding time. Moreover, BM-573 lost the diuretic property of torasemide and has no impact on glycemia.

Effects of Plumbagin on Platelet Aggregation and Platelet-Neutrophil Interactions

The effects of plumbagin were investigated on platelet aggregation in vitro and ex vivo, on the binding of thrombin-stimulated platelets to neutrophils, and platelet aggregation induced by intact neutrophils and N-formyl-methionyl-leucyl-phenylalanine (fMLP) or platelet activating factor (PAF) activated neutrophils, by use of the methods of Hamburger, McEver and Born, respectively. The results showed that plumbagin in vitro significantly inhibited adenosine diphosphate (ADP)-, arachidonic acid (AA)-, or platelet activating factor (PAF)-induced platelet aggregation, in a concentration-dependent manner. The medium inhibitory concentrations (IC 50 ) were 39.4, 82.7 and 38.1 microM, respectively. Intragastric plumbagin at 10 mg/kg markedly suppressed platelet aggregation induced by ADP, AA, or PAF. Plumbagin decreased the binding between thrombin-stimulated platelets and neutrophils with an IC 50 of 62.9 microM. Plumbagin significantly inhibited washed platelet aggregation stimulated by fMLP- or PAF-activated neutrophils. The IC 50 values were 54.3 and 47.6 microM, respectively. On the other hand, plumbagin and aspirin increased the inhibition of intact neutrophils on AA-induced platelet aggregation. It is suggested that plumbagin inhibited platelet aggregation in vitro and ex vivo, suppressed the binding of activated platelets to neutrophils, inhibited platelet aggregation induced by activated neutrophils, and increased inhibition of intact neutrophils on platelet reactivity. Abbreviations. DMSO:dimethyl sulphoxide fMLP: N-formyl-methionyl-leucyl-phenylalanine ADP:adenosine diphosphate AA:arachidonic acid PAF:platelet activating factor

The in vivo pharmacological profile of CS-747, a novel antiplatelet agent with platelet ADP receptor antagonist properties.

1. CS-747 is a novel antiplatelet agent that generates an active metabolite, R-99224, in vivo. CS-747 itself was totally inactive in vitro. This study examined in vivo pharmacological profiles of CS-747 after single oral administration to rats. 2. Orally administered CS-747 (0.3 - 10 mg kg(-1)) partially but significantly decreased [(3)H]-2-methylthio-ADP binding to rat platelets. CS-747 (3 mg kg(-1), p.o.) treatment neutralized ADP-induced decreases of cyclic AMP concentrations induced by prostaglandin E(1), suggesting that metabolites of CS-747 interfere with G(i)-linked P2T receptor. 3. CS-747 (0.3 and 3 mg kg(-1), p.o.) markedly inhibited ex vivo washed platelet aggregation in response to ADP but not to thrombin. CS-747 also exhibited a marked inhibition of ADP-induced ex vivo platelet aggregation in PRP with a rapid onset (<0.5 h) and long duration (>3 days) of action (ED(50) at 4 h=1.2 mg kg(-1)). 4. R-99224 (IC(50)=45 microM) inhibited in vitro PRP aggregation in a concentration-related manner. 5. CS-747 prevented thrombus formation in a dose-related manner with an ED(50) value of 0.68 mg kg(-1). CS-747 was more potent than clopidogrel (6.2 mg kg(-1)) and ticlopidine (>300 mg kg(-1)). 6. CS-747, clopidogrel, and ticlopidine prolonged the bleeding time. The order of potency of these agents in this activity was the same as that in antiaggregatory and antithrombotic activities. 7. These findings indicate that CS-747 is an orally active and a potent antiplatelet and antithrombotic agent with a rapid onset and long duration of action, and warrants clinical evaluations of the agent.

Stimulating Effect of Biologically Modified Low Density Lipoproteins on ADP-Induced Aggregation of Washed Platelets Persists in Absence of Specific Binding

Oxidized low density lipoproteins are closely associated with atherosclerosis and also might be directly involved in thrombosis because they have been shown to mediate a stimulating effect on human platelets. In this work, we used biologically modified low density lipoproteins (i.e., low density lipoproteins sufficiently oxidized to show specificity for the macrophage scavenger receptor system) to examine if specific binding of the oxidized apolipoprotein moiety to the platelet surface is a prerequisite for the platelet-stimulating effects reported by other authors. We find that biologically modified low density lipoproteins show specific binding to human platelets ( K d=5.83±0.4 μg/mL, 3850±620 sites/platelet) and strongly augment both ADP- and thrombin-induced aggregation of washed platelets. Maleylated albumin, an antagonist of oxidized low density lipoproteins binding to all currently classified scavenger receptors, is able to reduce platelet oxidized low density lipoproteins binding to background levels. Nevertheless, maleylated albumin is not able to exert any kind of normalizing effect on the augmented ADP-induced aggregation response observed in the presence of biologically modified low density lipoproteins. From these data, we conclude that specific binding of oxidatively modified apolipoprotein B to the platelet surface is not essential to the process of platelet stimulation. Therefore, we conclude that these stimulating effects may be mediated by unidentified compounds formed in the lipid phase of the lipoproteins.

Effects of copper-aspirin complex on plasma 6-keto-prostaglandin F1α level and platelet cytosolic calcium in rabbits

Effects of copper-aspirin complex on washed platelet aggregation, thromboxane B2 formation and 6-ketoprostaglandin F1α level were monitored by Born's and Terashita's methods, respectively. The influence of copper-aspirin complex on cytosolic free calcium was examined using the fluorescent indicator, Fura 2-AM. Copper-aspirin complex significantly inhibited arachidonic acid-induced aggregation in washed platelets. The IC50 value was 9.6 μmolL-1. Copper-aspirin complex significantly decreased arachidonic acid-induced thromboxane B2 formation by 87.1% in washed platelets. Ten mg kg-1 of copper-aspirin complex given intragastrically markedly increased the plasma level of 6-keto-prostaglandin F1α . Aspirin, however, reduced both thromboxane B2 formation and 6-keto-prostaglandin F1α level. In the presence of CaCl2 1 mmolL-1, copper-aspirin complex (20, 40 and 80 mu mol L-1) markedly lowered arachidonic acid-induced increase in platelet calcium from the resting level (270±36 nmolL-1) to 213±14, 170±20 and 135±17 nmolL-1, respectively. In the presence of ethylene glycol-bis (β-aminoethyl ether) N,N,N',N'-tetraacetic acid 1 mmolL-1, copper-aspirin complex (20, 40 and 80 mu molL-1) significantly suppressed the release of intracellular calcium induced by arachidonic acid from 127±23 nmolL-1 to 108±17, 93±12 and 70±13 nmolL-1.

Losartan inhibits thromboxane A2-induced platelet aggregation and vascular constriction in spontaneously hypertensive rats.

Our recent studies have shown that the nonpeptide angiotensin II (Ang II) antagonist losartan interacts with thromboxane A2/prostaglandin H2 receptors and inhibits the thromboxane A2 (TxA2) analog U46619-induced vasoconstriction in canine coronary arteries. In this study, we further investigated whether losartan prevents TxA2-induced platelet aggregation and vasoconstriction in spontaneously hypertensive rats (SHRs). Pretreatment with losartan (10 microM) significantly reduced U46619-induced, concentration-dependent washed platelet aggregation. The inhibition is specific for losartan, because another Ang II AT1-receptor antagonist, CV11974 (10 microM), an active metabolite of TCV116, did not block the platelet aggregation caused by U46619. In addition, losartan (10 microM) augmented acetylcholine (ACH)-induced nitric oxide (NO)-dependent vasodilation and abolished the ACH-induced endothelium-derived contracting factor (EDCF)-mediated vasoconstriction in the aortic rings from adult SHRs. U46619 produced dose-dependent vasoconstriction in aortic vessels of SHRs, which was demonstrated to be blocked by the potent, selective TxA2/PGH2 receptor antagonist SQ29,548. Pretreatment with losartan (10(-6)-10(-5) M) inhibited the contractile response of U46619 and shifted the concentration-response curve to the right in a dose-dependent manner. The effective concentration at half maximal contraction (EC50) of U46619 was increased 2.5- and 7.6-fold in the presence of 1 and 10 microM losartan, respectively, without changes in maximal contraction. The active metabolite of losartan, EXP3174, at 1 microM also competitively inhibited U46619-induced contractions in aortic rings of SHRs. In contrast, neither the AT1-receptor antagonist CV11974, the AT2 antagonist PD123319, nor the angiotensin-converting enzyme inhibitor lisinopril, each at concentrations of 1 microM, had any effect on the U46619-induced constriction in aortic rings. In conclusion, losartan, acting as both AT1- and TxA2/PGH2-receptor antagonists, may enhance its therapeutic profile in the treatment of hypertension and cardiovascular disease.

Identification of a new endogenous platelet-activating factor-like molecule in gingival crevicular fluid

Periodontal disease is an inflammatory disease and the major cause of tooth loss in adults. Bacteria and their products are the causative agents of this disease. Endogenous molecules mediate the inflammatory process and play a major role in its amplification and perpetuation as well as in the ensuing tissue destruction. The relationship between platelet-activating factor (PAF) and periodontal disease has not so far been examined thoroughly. We have isolated a phospholipid molecule with PAF-like activity from gingival crevicular fluid. This molecule, purified on HPLC, causes washed platelet aggregation with EC50 value 0.1 microM, based on phosphorus determination. It acts through PAF-receptors and is inactivated by PAF-acetylhydrolase. In addition, this phospholipid presents biological activity towards human platelets. The combination of the results obtained from the chemical and enzymic treatments, the biological assays as well as results from the electrospray analysis, leads to the conclusion that this phospholipid is a hydroxyl-PAF analogue with relative molecular mass 703. This PAF-like molecule may be implicated in periodontal disease.

Synthesis of a new phosphoglycolipid with biological activity towards platelets

Various synthetic as well as naturally occurring compounds have been found to exhibit platelet-activating factor (PAF)-like activity or to act as specific PAF inhibitors. In this work we have synthesized a new phosphoglycolipid, methyl 2,3,4-tri- O-acetyl-6-(1′- O-stearoyl-2′- O-acetyl- dl-glycero-3′-phosphoryl)-α- d-glucopyranoside ammonium salt, using a combination of known synthetic steps. This phosphoglycolipid was first purified on TLC (Rf 0.7, using chloroform/methanol/water, 65:25:4, v/v/v as solvent system). It was further purified onto a high performance liquid chromatography silica column with an elution system that contained acetonitrile and methanol (retention time 13.5 min). Its identification was based on chemical determinations and electrospray mass spectrometry analysis. The above compound induced washed platelet aggregation with an EC 50 value at 2 × 10 −4 M. The aggregation curve was biphasic, the first wave of which was through the PAF way while the second one was through the ADP way. Treatment with acetylhydrolase resulted in a rapid decrease of the first wave of aggregation and in a slow decrease of the second wave. In lower concentrations, the phosphoglycolipid inhibited PAF- and thrombin-induced aggregation with IC 50 values of the order of 10 −7 M. In conclusion, this phosphoglycolipid has a diverse biological activity. The PAF-like activity of this new lipid enforces the conception that PAF is a member of a large family consisting of lipid mediators.

Modulatory effect of 8-iso-PGE 2 on platelets

1. 1. 8-Iso-PGE 2 induced either reversible or irreversible aggregation of platelets in human platelet-rich plasma (PRP) or in the suspension of washed platelets (WP). The values of EC 50 for irreversible aggregation in PRP and WP were 4 and 2 μM, respectively. 2. 2. In rabbit PRP, 8-iso-PGE 2 (0.1-100 μM) itself did not induce or induced only reversible aggregation. 3. 3. 8-Iso-PGE 2 (0.1-20μM) potentiated adenosine diphosphate-(ADP) induced platelet aggregation in both human and rabbit. The same effect also was found for adrenaline-induced platelet aggregation in rabbit. 4. 4. The lower concentrations (0.2-0.5 μM) of 8-iso-PGE 2 decreased, and higher concentrations (1–2 μM) increased platelet aggregating factor- (PAF) induced aggregation in human PRP. In rabbit PRP, 8-iso-PGE 2 (0.02–200 μM) had only a decreasing effect on PAF-induced aggregation. 5. 5. The results suggest that low concentrations of 8-iso-PGE 2 can amplify or weaken platelet aggregation induced by various aggregatory agents.

The synergism of hydrogen peroxide with plasma S-nitrosothiols in the inhibition of platelet activation.

Earlier studies have shown that inhibition of aggregation of washed platelets (WP) by NO was enhanced almost 100-fold by H2O2. In the present study, the interactions of H2O2 with nitrosothiols, the influence of the presence of plasma and the mechanism of the synergism were investigated. H2O2 strongly enhanced the inhibitory effects of S-nitrosoglutathione (GSNO) on thrombin-induced aggregation of WP. S-Nitrosoalbumin also inhibited platelets, and this was similarly enhanced by H2O2. The synergism with H2O2 was demonstrable for both exogenous GSNO and NO in the presence of plasma when platelets were stimulated with collagen. The inhibition of platelets by GSNO and H2O2 was completely inhibited by guanylate cyclase inhibitors. Synergism was also observed whether the H2O2 was added simultaneously or 1 min before or after the GSNO (or NO). This suggests that the action of H2O2 follows the occupation by NO of haem sites in guanylate cyclase and that a prior reaction between NO and H2O2 was not required. In the absence of exogenous GSNO or NO, H2O2 inhibited activation of platelets in plasma, an effect abolished by guanylate cyclase inhibitors. This suggested that endogenous NO donors in plasma or NO synthesized in platelets may interact with H2O2. Addition of NG-nitro-L-arginine methyl ester (hydrochloride) (L-NAME) decreased the effects of the H2O2 by 25%, indicating that the major endogenous source of NO in platelet-rich plasma was not derived from platelet synthesis of NO but from NO donors in plasma, such as nitrosothiols. Inhibition by H2O2 was also enhanced by beta-mercaptosuccinate, a glutathione peroxidase inhibitor that protects the H2O2. These results suggest a potent synergism of H2O2 with endogenous plasma nitrosothiols that inhibit platelet function through an intracellular mechanism involving guanylate cyclase.

381 Different influence of thrombolytic and physiological doses of single-chain urokinase-type plasminogen activator on washed platelets aggregation

381 Different influence of thrombolytic and physiological doses of single-chain urokinase-type plasminogen activator on washed platelets aggregation

Modulation of human platelet function by food flavonoids.

Flavonoids, a group of polyphenolic natural compounds, represent an important source of antioxidants in the human diet [ 1,2]. Although the mechanism of action of flavonoids is not well understood, these compounds have been found to be inversely related to mortality from coronary heart disease[3]. Aggregation of platelet is fundamental to a wide range of physiological processes, i.e. in the events ranging from normal blood coagulation to the extremes of thrombosis and atherosclerosis [4,5], therefore the aim of this study was to investigate the effects of several dietary flavonoids (catechin, myricetin, querectin, apigenin and morin) and a-tocopherol on platelet function. Platelet iich plasma (PRF') was prepared from blood collected in sodium citrate (10% v/v of 3.8% citrate solution) from healthy volunteers who had not taken any medication for at least 14 days prior to phlebotomy. Platelets were counted in PRP and adjusted to a constant platelet count (2.5x108/ml) with platelet poor-plasma (PPP), obtained by further centrifugation of the blood remaining after removal of PRP. Washed platelets (WP) were prepared from PRP as described [6]. Aggregation of platelets was induced by either collagen or ADP. Maximal amplitude of aggregation of PRP was obtained with lOpg/ml collagen and 10 pM ADP, whereas WP were aggregated with collagen only. The inhibitory effects of flavonoids and vitamin E were initially evaluated at different times of preincubation either with PRP or WP with the compound dissolved in ethano1:water at a final ethanol concentration of 0.13%. Control samples were preincubated with vehicle alone. Aggregatory responses in the absence or presence of these compounds were evaluated by measuring the amplitude curves with different concentrations of these compounds in three separate experiments using platelets from different subjects. Plasma levels of fibrinogen, vitamin E and vitamin C of these volunteers were determined and were found to be within the normal range. Apigenin, quercetin, morin and a-tocopherol did not inhibit platelet aggregation in PRP induced by collagen, ADP, or arachidonic acid (AA) (n=5). Conversely, catechin inhibited collagen-induced aggregation by approximately 4.3% (n=7) whereas myricetin inhibited AA-induced aggregation by 75%, ADP-induced aggregation by 21 % and collagen-induced aggregation by 5% in PRP (n=2). In contrast to PRP, aggregation of WP was significantly inhibited by these flavonoids except apigenin and a-tocopherol (Table). Minimum concentration of flavonoids required to inhibit 50% platelet aggregation (Icso) induced by collagen was determined for these flavonoids. The IC50 value for myricetin was 57f6 pM whereas for morin and catechin the values were very high, 323f78 pM and 591f 65 @4 (n=3), respectively. Table: % inhibition of platelet aggregation by various flavonoids tn WP

Effect of Therapy with Recombinant Human Interferon-γ on the Release of Nitric Oxide by Neutrophils and Mononuclear Cells from Patients with Chronic Granulomatous Disease

The aim of this study was to investigate the effect of recombinant human interferon-gamma (rHuIFN-gamma) therapy on the release of nitric oxide (NO) by neutrophils (NEU) and mononuclear cells (MON) from patients with chronic granulomatous disease (CGD). Five patients with this rare disease received rHuIFN-gamma (50 micrograms/m2 of body surface, given by subcutaneous injection three times a week) for 6 months. Clinical and laboratory evaluations were performed before and after 1 and 6 months of rHuIFN-gamma therapy. Nitric oxide release by NEU and MON was assessed by the ability of these cells to inhibit thrombin-induced washed platelet aggregation. The nitrite (NO2-) and nitrate (NO3-) levels in the supernatant of cultured NEU and MON, as well as in plasma and urine (24 h diuresis), were quantified by high-performance liquid chromatography (HPLC). Conventional immunologic tests for assessing phagocyte and lymphocyte functions and humoral immunity were also performed. Therapy with rHuIFN-gamma for 6 months did not enhance NO synthesis by NEU or MON from the patients with CGD. The urinary but not plasma levels of NO2- and NO3- were elevated after rHuIFN-gamma therapy. Phagocyte and lymphocyte functions as well as humoral immunity were not affected by rHuIFN-gamma therapy. Although few patients were available for the study, we conclude that therapy with rHuIFN-gamma for 6 months did not enhance the synthesis of NO by NEU and MON in CGD patients. Whether the increased excretion of NO2- and NO3- in the urine of CGD patients after rHUIFN-gamma therapy reflects an induction of NO-synthase in cells other than leukocytes remains to be investigated.

The release of nitric oxide and superoxide anion by neutrophils and mononuclear cells from patients with sickle cell anaemia

The aim of this work was to investigate the release of nitric oxide and superoxide by neutrophils and mononuclear cells from patients with sickle cell anaemia. Nitric oxide release was assayed by the ability of leucocytes to inhibit thrombin-induced washed platelet aggregation. Superoxide release was assessed by a cytochrome c reduction assay. Neutrophils from sickle cell anaemia patients released nitric oxide in a similar manner to those from healthy controls, because inhibition of platelet aggregation by neutrophils from sickle cell anaemia or from healthy controls was blocked by the inhibitor of nitric oxide synthesis N(omega)-nitro-L-arginine methyl ester (300 microM), but not by N(omega)-nitro-D-arginine methyl ester (300 microM) and was reversed by L-arginine (1 mM). Additionally, a similar number of neutrophils from sickle cell anaemia patients and from healthy controls was required to inhibit platelet aggregation. Mononuclear cells from sickle cell anaemia patients inhibited platelet aggregation only in the presence of superoxide dismutase (60 U ml(-1)). Phorbol 12-myristate 13-acetate (PMA, 30 nM)- or zymosan (100 particles/cell)-induced release of superoxide by mononuclear cells from sickle cell anaemia patients was significantly higher than that observed in mononuclear cells from healthy controls (P<0.001 and P<0.01 respectively, Mann-Whitney test). The levels of superoxide released by neutrophils from sickle cell anaemia patients were similar to those from healthy controls. We conclude that mononuclear cells from sickle cell anaemia patients release more superoxide than those from healthy controls, when stimulated with PMA or zymosan in vitro. Considering that superoxide inactivates nitric oxide, that nitric oxide is an important endogenous vasodilator, and that superoxide produces oxidant damage, this greater production of superoxide by mononuclear cells from sickle cell anaemia patients may represent an additional risk factor for the obstruction of the microcirculation and tissue damage in these patients.

Effects of Beraprost Sodium, a Prostacyclin Analogue, on Diabetic Neuropathy in Streptozotocin-Induced Diabetic Rats

The effects of beraprost sodium (BPS), a stable prostacyclin analogue, on motor nerve conduction velocity and nerve blood flow of the sciatic nerve were investigated in streptozotocin-induced diabetic rats, and they were compared with the effects of epalrestat (aldose reductase inhibitor). Treatment with BPS for 4 weeks significantly inhibited the decrease in motor nerve conduction velocity and nerve blood flow dose-dependently, but epalrestat had no effect on nerve blood flow. Morphological changes of the myelinated fibers of the sciatic nerve were observed macroscopically. The mean axonal area and the mean circularity index of diabetic control rats were significantly less than that of normal rats, while after 6 weeks of BPS treatment, these decreases of the axonal area and the circularity index were inhibited. The enlargement of the mean lumen area of microvessels in the diabetic rats was significantly inhibited after 6 weeks of BPS treatment. Additionally, augmentation of the washed platelet aggregation in diabetic rats was significantly normalized by BPS. It was suggested that BPS is effective on diabetic neuropathy via amelioration of the decrease of blood supply to the structure. The effects of BPS on platelets might also contribute to the improvement of neuronal circulatory deficiency.

Regulation of platelet-activating factor production in gastric epithelial cells.

The authors have previously reported that platelet-activating factor (PAF), a phospholipid mediator with potent proinflammatory activities, is produced in the gastric mucosa and stimulates gastric acid secretion in humans and animals. In the present study they used the human gastric tumour cells HGT1 (clone 6) to examine whether PAF production is regulated by neuromediators. PAF was extracted by ethanol and assayed by the washed platelet aggregation test. HGT1 cells produced PAF spontaneously (110 +/- 20 pg 10(6) cells). The addition of vasoactive intestinal peptide (VIP; 10(-9) to 10(-7) mol L(-1)) or of histamine (10(-5) to 10(-3) mol L(-1)) increased PAF production by three- to fivefold, while the addition of carbachol (10(-7) to 10(-4) mol L(-1)) increased PAF production up to sevenfold. PAF production was also increased up to 10- to 13-fold, in a dose- and time-dependent manner, by the addition of calcium and two- to threefold by the addition of phorbol myristate acetate (PMA; 10(-7) to 10(-5) mol L(-1)). However, the addition of dibutyryl cyclic AMP (dBcAMP; 10(-6) to 10(-4) mol L(-1) was without any effect. This is the first report showing PAF production by gastric epithelial cells in response to histamine, VIP and carbachol. Furthermore, the findings are consistent with a central role of calcium in this production. The results of this study, together with those of previous studies from the authors' laboratory, support the hypothesis that PAF is a physiological mediator of gastric acid secretion.

Effect of Alkaline Phosphatase on Thromboxane Mimetic Induced Platelet Activation

Recently it has been reported that alkaline phosphatase selectively inhibited thromboxane mimetic induced platelet aggregation and secretion suggesting that the phosphorylation state on the platelet surface may be important for thromboxane induced platelet activation. We report here studies attempting to elucidate the mechanism of action of alkaline phosphatase. Washed human platelet aggregation induced by the thromboxane mimetic IBOP was completely abolished when incubated with alkaline phosphatase (1 unit/ml) for 5 min. The effect was inhibited by co-incubation with 5mM phosphate. Binding studies using [ 125I]BOP showed that niether the affinity of IBOP for the receptor (control: 9.2 ± 2.1 nM, alkaline phosphatase: 7.9 ± 1.8 nM) nor the B max (control: 1780 ± 320 sites/plt. alkaline phosphatase: 1920 ± 290 sites/plt) were effected by alkaline phosphatase treatment. GTPase activity was measured in platelet membranes treated with and without alkaline phosphatase as measured by IBOP induced hydrolysis of [γ 32P]GTP. The EC 50 values for IBOP induced GTPase were similiar whereas the maximum amount of released P i in the control membranes was more than two fold greater than in alkaline phosphatase treated membranes. These studies suggest that thromboxane induced platelet activation may be dependent upon the phosphorylation state of the thromboxane receptor and/or closely associated protein.

Enhancement of thrombotic arterial occlusion following cholesterol feeding in the guinea-pig: A role for thromboxane A 2

We have developed a photochemical model to induce thrombotic occlusion of the guinea-pig femoral artery. Using this model, we investigated the effect of cholesterol feeding on arterial occlusion time in the guinea-pig. Animals were divided into two groups, one on standard diet and the other on standard diet containing 0.5% cholesterol for 3 weeks. The time for femoral artery occlusion was significantly shorter (p > 0.05) in cholesterol fed animals as compared to the control group. In vitro collagen-, U-46619- (a thromboxane A 2 adenosine diphosphate analogue) and (ADP)-induced platelet aggregation responses in whole blood in cholesterol-fed animals were increased 13-, 10- and 4-fold, respectively. U-46619- and collagen-induced washed platelet aggregation responses were also significantly enhanced by cholesterol feeding (p < 0.01). Further, TXA 2 generation by collagen-stimulated washed platelets in cholesterol-fed animals increased similar to the platelet aggregation responses. However, platelet-activating factor (PAF)-induced platelet aggregation in whole blood was relatively unaffected by cholesterol feeding. 11-dehydro TXB 2 levels in plasma were increased significantly by cholesterol feeding. Our observations suggest that increased plasma TXA 2 level and platelet aggregation response to TXA 2 and stimulated TXA 2 synthesis in platelets play a role in enhanced arterial occlusion in cholesterol fed guinea-pigs.

Lys-and Glu-plasminogen potentiate the inhibitory effect of recombinant tissue plasminogen activator on human platelet aggregation

To examine the basis of enhanced thrombolytic effect of tissue-type plasminogen activator (t-PA) in the presence of lys- or glu-plasminogen, studies were performed with human platelet-rich plasma (PRP) and washed platelets (WP). t-PA inhibited platelet aggregation in PRP and this effect was potentiated by lys-plasminogen as well as glu-plasminogen. t-PA inhibited WP aggregation only in the presence of lys- or glu-plasminogen. The potentiation of the effects of t-PA was greater (P<0.05) with lys-plasminogen than with glu-plasminogen. t-PA alone also decreased 14C-serotonin release from WP, and lys- as well as glu-plasminogen reversed this effect of low concentrations of t-PA in WP. Aggregation of WP was also inhibited by plasmin, a proteolytic product of plasminogen. Low, but not high concentrations, of plasmin increased the release of 14C-serotonin. Anti-aggregatory effects of plasmin and lys-plasminogen plus t-PA on platelets were attenuated by preincubation of PRP or WP suspension with aprotinin. These observations suggest enhanced inhibitory effect of t-PA on platelet function in the presence of lys-plasminogen as potential basis of salutary interaction in models of arterial thrombosis.