Diabetic Retinopathy And Thromboxane Like Substance

Mapping Intimacies ◽

10.1055/s-0038-1652115 ◽

1981 ◽

Author(s):

M A Lazzari ◽

M Gimeno ◽

N M Sutton ◽

J R Lopez

Keyword(s):

Diabetes Mellitus ◽

Arachidonic Acid ◽

Diabetic Retinopathy ◽

Risk Factor ◽

Platelet Aggregation ◽

Platelet Rich Plasma ◽

Thromboxane A2 ◽

Initial Step ◽

Platelet Activity

Diabetes Mellitus (DM) is a risk factor in the development of vasculopathies and its complications. It produces also its own microangiopathy. Evidence was reported of increased platelet activity in DM in different assays. Platelets aggregation and the arachidonic cycle could play a key role in the increased tendency to thrombosis. A disorder of ratio TXA2/PGI2, two opposing prostaglandin derivatives, could be the initial step. We intended to evaluate a thromboxane like substance (TLS) produced from platelet rich plasma (PRP) and to compare between normals and diabetic retinopathy (DR) patients. TLS was measured in 16 controls and 16 patients. Assay was done with the aggregating activity developed in PRP (considered TLS) after addition of arachidonic acid (f.c. 2 mM). The supernatant of the PRP (100 μl) was taken 40 sec. after the aggregation started and were added to a normal PRP treated with aspirin (f.c. 40 μl/ml) adjusted to 250.000 - 300.000 pl/μl and the degree of platelet aggregation measured in a Chrono Log Aggregometer. TLS was inactivated after its incubation during 2 min. at 37°C. This finding suggests this activity is due to TXA2.The results obtained (expressed in % of platelet aggregation) were: controls x 16.37% ± 6.28 and DR x 36.00% ± 9.72.The increase detected in the DR group supports previous experimental reports suggesting the role of the thromboxane A2 in vaso occlusive complication of diabetes mellitus.

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Testosterone Potentiation of Ionophore and ADP Induced Platelet Aggregation : Relationship to Arachidonic Acid Metabolism

Thrombosis and Haemostasis ◽

10.1055/s-0038-1653405 ◽

1981 ◽

Vol 46 (02) ◽

pp. 538-542 ◽

Cited By ~ 42

Author(s):

R Pilo ◽

D Aharony ◽

A Raz

Keyword(s):

Arachidonic Acid ◽

Platelet Aggregation ◽

Unsaturated Fatty Acids ◽

Human Platelet ◽

Platelet Rich Plasma ◽

Arachidonic Acid Metabolism ◽

Ionophore A23187 ◽

Low Concentrations ◽

Induced Aggregation

SummaryThe role of arachidonic acid oxygenated products in human platelet aggregation induced by the ionophore A23187 was investigated. The ionophore produced an increased release of both saturated and unsaturated fatty acids and a concomitant increased formation of TxA2 and other arachidonate products. TxA2 (and possibly other cyclo oxygenase products) appears to have a significant role in ionophore-induced aggregation only when low concentrations (<1 μM) of the ionophore are employed.Testosterone added to rat or human platelet-rich plasma (PRP) was shown previously to potentiate platelet aggregation induced by ADP, adrenaline, collagen and arachidonic acid (1, 2). We show that testosterone also potentiates ionophore induced aggregation in washed platelets and in PRP. This potentiation was dose and time dependent and resulted from increased lipolysis and concomitant generation of TxA2 and other prostaglandin products. The testosterone potentiating effect was abolished by preincubation of the platelets with indomethacin.

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ADRENALINE (ADR) INTERACTIONS WITH THROMBIN AND COLLAGEN -EFFECTS ON PLATELET ARACHIDONATE RELEASE AND 5HT SECRETION AND ROLE OF ENDOGENOUSLY FORMED THROMBOXANE A2 (TxA2)

10.1055/s-0038-1643384 ◽

1987 ◽

Author(s):

Y Patel ◽

S Krishnamurthi ◽

V V Kakkar

Keyword(s):

Arachidonic Acid ◽

Platelet Aggregation ◽

Adenylate Cyclase ◽

Synergistic Effects ◽

Thromboxane A2 ◽

Human Platelets ◽

Presence And Absence ◽

Pre Treatment ◽

Arachidonate Release

We have examined the effect of combinations of ADR + thrombin (T) and ADR + collagen (C) on platelet arachidonate release and 5HT secretion, and assessed the role of endogenously formed TxA2 on these responses using indomethacin (I). Washed, human platelets prelabelled with [3H]-arachidonic acid (AA) or [14C]-5HT were used, ADR was added 10 sec before T or C and the reaction was terminated 3 min later. In the range 1-100μM, ADR induced no detectable aggregation or 5HT secretion but potentiated platelet aggregation when added with sub-threshold concentrations of T or C, which on their own induced no aggregation. At 2-4 fold higher concentrations of T and C (threshold for 5HT secretion), 5HT secretion and AA/TXB2 release were also potentiated by ADR (1-10μM) by 30-50%. Pre-treatment of platelets with I (10μM) abolished threshold T and C-induced 5HT secretion, as well as its potentiation by ADR. However, approximately 2-fold and 5-fold higher concentrations of T and C respectively were able to induce 'I-insensitive'secretion, which was further potentiated by ADR. In I-treated platelets, C-induced AA release and its potentiation by ADR were also abolished suggesting a role for endogenously formed TxA2 This was confirmed by addition of the TxA2 mimetic, U46619 (0.3μM), which potentiated C-induced AA release in the presence and absence of ADR, even though it induced no AA release on its own or, in combination with ADR alone in the absence of collagen. The latter suggests agonist specificity regarding the ability of TxA2 to synergistically stimulate AA release. Finally, unstirred platelets in PRP pre-incubated with ADR (10μM) for 120 min lost their responsiveness to ADR, when eventually stirred; however, these 'ADR-desensitised' platelets when washed and resuspended, were able to demonstrate synergistic effects on secretion when stimulated with ADR+T or ADR+C. This is analogous to the previously demonstrated ability of ADR to inhibit adenylate cyclase even in 'ADR-desensitised' platelets and re-inforces the separation regarding the mechanisms underlying the various effects of ADR on platelets.

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Pharmacologic inhibition of thromboxane synthetase and platelet aggregation: modulatory role of cyclooxygenase products

Blood ◽

10.1182/blood.v63.6.1460.bloodjournal6361460 ◽

1984 ◽

Vol 63 (6) ◽

pp. 1460-1466

Author(s):

V Bertele ◽

A Falanga ◽

M Tomasiak ◽

C Chiabrando ◽

C Cerletti ◽

...

Keyword(s):

Arachidonic Acid ◽

Platelet Aggregation ◽

Platelet Rich Plasma ◽

Normal Subjects ◽

Gas Chromatography Mass Spectrometry ◽

Thromboxane Synthetase ◽

High Resolution Gas Chromatography ◽

Pharmacologic Inhibition

Dazoxiben , an imidazole-derived selective inhibitor of thromboxane A2 (TxA2) synthetase, prevented TxB2 synthesis in vitro in platelet-rich plasma from 16 normal subjects. Inhibition of TxB2 synthesis was accompanied by increased generation of PGE2, PGF2 alpha, and PGD2, as shown by radioimmunoassay, thin-layer radiochromatography, and high- resolution gas chromatography-mass spectrometry. Even at dazoxiben concentrations (40–80 microM) above those inhibiting TxB2 synthesis, platelet aggregation induced by threshold concentrations of arachidonic acid was inhibited in only 4 of 16 subjects, referred to as responders. The remaining 12 individuals were defined as nonresponders. The aggregating effect of arachidonic acid and of the prostaglandin- endoperoxide analog U-46619 was potentiated by PGE2 and prevented by PGD2 at concentrations within the range of those detected in dazoxiben - treated platelet-rich plasma. The antiaggregating effect of dazoxiben was counteracted by PGE2 (in responders) and was potentiated by PGD2 (in nonresponders). Platelets from responders and nonresponders did not differ in the amount of immunoreactive PGE2 material or in their sensitivity to U-46619 or PGD2. It is concluded that inhibition of thromboxane synthetase does not per se prevent platelet aggregation. The functional result of thromboxane suppression appears to be modulated by an interplay of the prostaglandin-endoperoxides, PGE2 and PGD2, which are formed in excess.

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Role of Cyclic Amp in Platelet Function : Evidence from Inhibition of Adenylate Cyclase in Intact Platelets by Adenosine Analogues

10.1055/s-0039-1680345 ◽

1977 ◽

Author(s):

R. J. Haslam ◽

M. M. L. Davidson ◽

J. V. Desjardins

Keyword(s):

Arachidonic Acid ◽

Platelet Aggregation ◽

Cyclic Amp ◽

Adenylate Cyclase ◽

Platelet Function ◽

Platelet Rich Plasma ◽

Inhibitory Effects ◽

Adenosine Analogues ◽

Inhibitory Activities

Adenosine exerts independent stimulatory and inhibitory effects on the adenylate cyclase activity of platelet particulate fractions (Haslam & Lynham, 1972). Two adenosine analogues, 9-(tetrahydro-2-furyl) adenine (SQ 22536) and 2′, 5′-dideoxyadenosine (DDA) have now been found to show marked non-competitive inhibitory activities only. Basal and PGE1-stimulated adenylate cyclase activities were inhibited ~50% and ~70% respectively by 100 μM SQ 22536 and ~60% and ~80% respectively by 100 μM DDA. Both compounds also inhibited adenylate cyclase in intact platelets, when this was measured as the increase in cyclic [3H]AMP in platelets labelled with [3H] adenine and then incubated with papaverine. At the concentrations tested (10-500 μM), neither SQ 22536 nor DDA induced platelet aggregation or potentiated aggregation and release of [14C] 5-HT induced by suboptimal concentrations of ADP, Arg8-vasopressin, arachidonic acid or collagen added to heparinized or citrated platelet-rich plasma. However, both compounds partially blocked the inhibition by PGE1 or papaverine of aggregation induced by ADP or Arg8-vasopressin. From the concentrations exerting equal effects, DDA was ~3 times as potent in this regard as SQ 22536. Above 100 μM, the anti-inhibitory effects of both compounds decreased. The actions of these compounds in overcoming inhibition of aggregation by PGE1 were correlated with decreases in platelet cyclic [3H]AMP in platelets labelled with [3H] adenine. The results show that cyclic AMP plays no role in the responses of platelets to aggregating agents unless the platelet cyclic AMP level is elevated above the resting level and confirm that the effects of PGE1 on platelet function are mediated by cyclic AMP.

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Pharmacologic inhibition of thromboxane synthetase and platelet aggregation: modulatory role of cyclooxygenase products

Blood ◽

10.1182/blood.v63.6.1460.1460 ◽

1984 ◽

Vol 63 (6) ◽

pp. 1460-1466 ◽

Cited By ~ 45

Author(s):

V Bertele ◽

A Falanga ◽

M Tomasiak ◽

C Chiabrando ◽

C Cerletti ◽

...

Keyword(s):

Arachidonic Acid ◽

Platelet Aggregation ◽

Platelet Rich Plasma ◽

Normal Subjects ◽

Gas Chromatography Mass Spectrometry ◽

Thromboxane Synthetase ◽

High Resolution Gas Chromatography ◽

Pharmacologic Inhibition

Abstract Dazoxiben , an imidazole-derived selective inhibitor of thromboxane A2 (TxA2) synthetase, prevented TxB2 synthesis in vitro in platelet-rich plasma from 16 normal subjects. Inhibition of TxB2 synthesis was accompanied by increased generation of PGE2, PGF2 alpha, and PGD2, as shown by radioimmunoassay, thin-layer radiochromatography, and high- resolution gas chromatography-mass spectrometry. Even at dazoxiben concentrations (40–80 microM) above those inhibiting TxB2 synthesis, platelet aggregation induced by threshold concentrations of arachidonic acid was inhibited in only 4 of 16 subjects, referred to as responders. The remaining 12 individuals were defined as nonresponders. The aggregating effect of arachidonic acid and of the prostaglandin- endoperoxide analog U-46619 was potentiated by PGE2 and prevented by PGD2 at concentrations within the range of those detected in dazoxiben - treated platelet-rich plasma. The antiaggregating effect of dazoxiben was counteracted by PGE2 (in responders) and was potentiated by PGD2 (in nonresponders). Platelets from responders and nonresponders did not differ in the amount of immunoreactive PGE2 material or in their sensitivity to U-46619 or PGD2. It is concluded that inhibition of thromboxane synthetase does not per se prevent platelet aggregation. The functional result of thromboxane suppression appears to be modulated by an interplay of the prostaglandin-endoperoxides, PGE2 and PGD2, which are formed in excess.

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Reconstituted High Density Lipoprotein (rHDL) Modulates Platelet Activity In Vitro and Ex Vivo

Thrombosis and Haemostasis ◽

10.1055/s-0037-1615194 ◽

1998 ◽

Vol 80 (08) ◽

pp. 316-320 ◽

Cited By ~ 44

Author(s):

Martin Spycher ◽

Jan Doran ◽

Peter Lerch

Keyword(s):

Body Weight ◽

Arachidonic Acid ◽

Platelet Aggregation ◽

High Density Lipoprotein ◽

Ex Vivo ◽

Platelet Rich Plasma ◽

Density Lipoprotein ◽

High Density ◽

Platelet Activity

SummaryA reconstituted high density lipoprotein (rHDL) prepared for clinical use was tested for its influence on platelet activity modulated by various stimuli. In a first series of in vitro experiments, rHDL was added to blood in a concentration series, and platelet rich plasma (PRP) was isolated. Platelets were stimulated with arachidonic acid, collagen, epinephrine or ADP, and platelet aggregation was assessed. rHDL mediated a dose dependent inhibition of the platelet activity. With purified platelets rHDL inhibited the release reaction induced by collagen, but not by thrombin, as measured by CD62P (P-Selectin) expression on the plasma membrane. Ex vivo experiments were performed with PRP from volunteers, previously infused with 25 mg rHDL/kg body weight and 40 mg rHDL/kg body weight, respectively. Platelet activity in PRP was assessed before, and up to 30 h after the end of the rHDL infusion. A transient inhibition of the platelet aggregation induced by arachidonic acid and collagen was observed which was more pronounced in the group receiving 40 mg rHDL/kg body weight. In both groups of experiments, in vitro and ex vivo, the inhibition of the platelet activity was also dependent on the stimulus used.

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Stimulated Platelet Aggregation, Thromboxane B2 Formation and Platelet Sensitivity to Prostacyclin - A Critical Evaluation

Thrombosis and Haemostasis ◽

10.1055/s-0038-1650170 ◽

1981 ◽

Vol 45 (03) ◽

pp. 204-207 ◽

Cited By ~ 42

Author(s):

Wolfgang Siess ◽

Peter Roth ◽

Peter C Weber

Keyword(s):

Arachidonic Acid ◽

Platelet Count ◽

Platelet Aggregation ◽

Reliable Method ◽

Platelet Rich Plasma ◽

Critical Evaluation ◽

Vascular Diseases ◽

Thromboxane B2 ◽

Test Time ◽

Stimulation Of

SummaryPlatelets have been implicated in the development of atherosclerotic and thrombotic vascular diseases. Evaluation of platelet aggregation in relation to endogenously formed compounds which affect platelet function may provide information of clinical and pharmacological relevance. We describe a method in which thromboxane B2 (TXB2) formation was analyzed following stimulation of platelet-rich plasma (PRP) with ADP, 1-epinephrine, collagen, and arachidonic acid. In addition, we determined platelet sensitivity to prostacyclin following ADP- and collagen-induced platelet aggregation. The parameters under study were found to depend on the platelet count in PRP, on the type and dose of the aggregating agent used, and on the test time after blood sampling. By standardization of these variables, a reliable method was established which can be used in clinical and pharmacological trials.

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In Vitro Incorporation and Metabolism of Icosapentaenoic and Docosahexaenoic Acids in Human Platelets - Effect on Aggregation

Thrombosis and Haemostasis ◽

10.1055/s-0038-1661603 ◽

1986 ◽

Vol 56 (01) ◽

pp. 057-062 ◽

Cited By ~ 56

Author(s):

Martine Croset ◽

M Lagarde

Keyword(s):

Arachidonic Acid ◽

Fatty Acid ◽

Platelet Aggregation ◽

Fatty Acid Distribution ◽

Thromboxane A2 ◽

Human Platelets ◽

Aggregation Response ◽

Docosahexaenoic Acids ◽

Membrane Level

SummaryWashed human platelets were pre-loaded with icosapentaenoic acid (EPA), docosahexaenoic acid (DHA) or EPA + DHA and tested for their aggregation response in comparison with control platelets. In fatty acid-rich platelets, an inhibition of the aggregation could be observed when induced by thrombin, collagen or U-46619. The strongest inhibition was observed with DHA-rich platelets and it was reduced when DHA was incorporated in the presence of EPA.Study of fatty acid distribution in cell lipids after loading showed that around 90% of EPA or DHA taken up was acylated into phospholipids and a very small amount (less than 2%) remained in their free and hydroxylated forms. DHA was more efficiently acylated into phosphatidylethanolamine (PE) than into phosphatidylinositol (PI) in contrast to what observed with EPA, and both acids were preferentially incorporated into phosphatidylcholine (PC). EPA inhibited total incorporation of DHA and increased its relative acylation into PE at the expense of PC. In contrast, DHA did not affect the acylation of EPA. Upon stimulation with, thrombin, EPA was liberated from phospholipids and oxygenated (as judged by the formation of its monohydroxy derivative) whereas DHA was much less metabolized, although consistently transferred into PE.It is concluded that EPA and DHA might affect platelet aggregation via different mechanisms when pre-loaded in phospholipids. Whereas EPA is known to alter thromboxane A2 metabolism from endogenous arachidonic acid, by competing with it, DHA might act directly at the membrane level for inhibiting aggregation.

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Decreased Platelet Vitamin C in Diabetes Mellitus; Possible Role in Peraggregatoon

10.1055/s-0039-1687640 ◽

1979 ◽

Author(s):

K.E. Sarji ◽

J. Gonzalez ◽

H. Hempling ◽

J.A. Colwell

Keyword(s):

Ascorbic Acid ◽

Arachidonic Acid ◽

Platelet Aggregation ◽

Vitamin C ◽

Platelet Rich Plasma ◽

Solution Ph ◽

Dose Dependent Fashion ◽

Insulin Dependent Diabetic ◽

Induced Aggregation

To determine whether Vitamin C might relate to the increased platelet sensitivity in the diabetic, we have measured levels of platelet Vitamin C and studied the effects of Vitamin C on platelet aggregation. Ascorbic acid levels in washed platelets from diabetics were significantly lower than from normals (4s.2±3 μg/1010 platelets vs. 2s.s±2 μg/1010 platelets, p<.001). The effects of ascorbic acid on platelet aggregation in vitro were studied by adding ascorbic acid in buffered solution (pH 7.35) prior to-aggregating agents. Ascorbic acid in platelet-rich plasma consistently inhibited platelet aggregation with threshold concentrations of ADP, epinephrine, and collagen. With washed platelets, ascorbic acid inhibited arachidonic, acid-induced aggregation. When platelets were incubated at 37°C for 10 minutes with varying concentrations of ascorbic acid, rewashed, and aggregation with arachidonic acid tested, aggregation was inhibited in a linear dose-dependent fashion. Oral ingestion of ascorbic acid (2 gm/day) for seven days by normal non-smoking males produced a marked inhibition of aggregation. In a similar study, platelets from an insulin-dependent diabetic showed no change in aggregation. These results suggest that platelet levels of ascorbic acid may relate to the hyperaggregat ion of platelets from diabetics.

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