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

1981 ◽  
Vol 46 (02) ◽  
pp. 538-542 ◽  
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.

Human Platelet Aggregation Induced by the Synthetic Endoperoxide Analogue U-46619 is Independent From Secretion, Prostaglandin Production and Extracellular Calcium

1979 ◽  
Author(s):  
G. Di Minno ◽  
L. Bianchi ◽  
G. de Gaetano ◽  
M.J. Silver
Keyword(s):  
Arachidonic Acid ◽  
Platelet Aggregation ◽  
Acid Metabolism ◽  
Human Platelet ◽  
Platelet Rich Plasma ◽  
Arachidonic Acid Metabolism ◽  
Extracellular Calcium ◽  
Reversible Aggregation ◽  
Human Platelet Aggregation ◽  
Aspirin Ingestion

U-46619 is a stable analogue of cyclic prostaglandin endoperoxides which induces human platelet aggregation independently from nucleotide secretion. We studied platelet aggregation, 14C-5 HT release and malondialdehyde (MDA) production induced by this compound in stirred or unstirred platelet-rich plasma (PRP) samples from 11 healthy volunteers. Each subject was tested both before and 90 min after aspirin ingestion (500 mg). The threshold aggregating concentration (TAC) of U-466l9 ranged between 240 and 900 nM. Aggregation was maximal between 30 and 60 min after venepuncture and was concentration-dependent (60-7, 200nM). At concentrations below the TAC, U-466l9 induced primary reversible aggregation without detectable l4C-5 HT release. At TAC or higher concentrations aggregation and release proceeded as parallel events. Neither MOA production nor intracellular LDH loss could be detected in any of the tested situations. Aspirin ingestion did not modify the above pattern of platelet responses. In unstirred samples l4C - 5 HT release occurred to the same extent as in stirred platelet suspensions. Addition to citrated PRP of Na2 - EDTA did not affect either aggregation or release. It is suggested that aggregation and secretion may be independent, parallel responses of platelet activation by U-466l9 and do not require either extracellular calcium or activation of endogenous arachidonic acid metabolism. (Supported by the Italian CNR and NIH).

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

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.

Effects of Ethanol on Pathways of Platelet Aggregation In Vitro

1988 ◽  
Vol 59 (03) ◽  
pp. 383-387 ◽  
Author(s):  
Margaret L Rand ◽  
Marian A Packham ◽  
Raelene L Kinlough-Rathbone ◽  
J Fraser Mustard
Keyword(s):  
Arachidonic Acid ◽  
Platelet Aggregation ◽  
Platelet Rich Plasma ◽  
Secondary Phase ◽  
Primary Phase ◽  
Rabbit Platelet ◽  
Membrane Phospholipids ◽  
Rabbit Platelets ◽  
Induced Aggregation

SummaryEthanol, at physiologically tolerable concentrations, did not affect the primary phase of ADP-induced aggregation of human or rabbit platelets, which is not associated with the secretion of granule contents. Potentiation by epinephrine of the primary phase of ADP-induced aggregation of rabbit platelets was also not inhibited by ethanol. However, ethanol did inhibit the secondary phase of ADP-induced aggregation which occurs with human platelets in citrated platelet-rich plasma and is dependent on the formation of thromboxane A2. Inhibition by ethanol of thromboxane production by stimulated platelets is likely due to inhibition of the mobilization of arachidonic acid from membrane phospholipids, as ethanol had little or no effect on aggregation and secretion induced by arachidonic acid or the thromboxane mimetic U46619. Rabbit platelet aggregation and secretion in response to low concentrations of collagen, thrombin, or PAF were inhibited by ethanol. Inhibition of the effects of thrombin and PAF was also observed with aspirin-treated platelets. Thus, in addition to inhibiting the mobilization of arachidonate for thromboxane formation that occurs with most agonists, ethanol can also inhibit aggregation and secretion through other effects on platelet responses.

Diabetic Retinopathy And Thromboxane Like Substance

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.

Dependence of Human Platelet Functional Responses on Divalent Cations: Aggregation and Secretion in Heparin- and Hirudin-Anticoagulated Platelet-Rich Plasma and the Effects of Chelating Agents

1981 ◽  
Vol 45 (02) ◽  
pp. 173-179 ◽  
Author(s):  
Bruce Lages ◽  
Harvey J Weiss
Keyword(s):  
Platelet Aggregation ◽  
Chelating Agents ◽  
Human Platelet ◽  
Platelet Rich Plasma ◽  
Divalent Cations ◽  
Normal Subjects ◽  
Concentration Addition ◽  
Functional Responses ◽  
Induced Aggregation

SummaryThe dependence of ADP- and epinephrine-induced platelet aggregation and secretion on extracellular divalent cations was examined by quantitating these responses in citrate-, heparin-, and hirudin-anticoagulated platelet-rich plasma. ADP-induced 14C-5HT secretion in heparin-PRP and hirudin-PRP was generally decreased, relative to that in citrate-PRP, without corresponding reductions in aggregation, whereas in response to epinephrine, both aggregation and secretion were decreased in heparin-PRP, and abolished in hirudin-PRP. In heparin-PRP, but not in hirudin-PRP, the degree to which these responses were altered was highly variable among normal subjects, and was dependent on the anticoagulant concentration. Addition of citrate restored the extent of ADP-induced secretion and of epinephrine-induced aggregation and secretion in heparin-PRP to that observed in citrate-PRP, and increased the extent of ADP-induced secretion in hirudin-PRP. Addition of EDTA or EGTA, however, had no effect on ADP-induced secretion in heparin-PRP. These results suggest that ADP-induced aggregation and secretion, as well as responses to ADP vs. epinephrine, have different dependencies on extracellular or surface-bound divalent cations. The variable responses observed in heparin-PRP may reflect direct interactions of heparin with platelets, and this variability may account for the conflicting results of previous studies.

scholarly journals Calcium ionophore synergizes with bacterial lipopolysaccharides in activating macrophage arachidonic acid metabolism.

1988 ◽  
Vol 167 (2) ◽  
pp. 623-631 ◽  
Author(s):  
A A Aderem ◽  
Z A Cohn
Keyword(s):  
Arachidonic Acid ◽  
Acid Metabolism ◽  
Calcium Ionophore ◽  
Arachidonic Acid Metabolism ◽  
Ionophore A23187 ◽  
Rapid Release ◽  
Lipoxygenase Products ◽  
Order Of Magnitude ◽  
Bacterial Lipopolysaccharides

LPS, a major component of Gram-negative bacterial cell walls, prime macrophages for greatly enhanced arachidonic acid [20:4] metabolism when the cells are subsequently stimulated. The LPS-primed macrophage has been used as a model system in which to study the role of Ca2+ in the regulation of 20:4 metabolism. The Ca2+ ionophore A23187 (0.1 microM) triggered the rapid release of 20:4 metabolites from LPS-primed macrophages but not from cells not previously exposed to LPS. Macrophages required exposure to LPS for at least 40 min before A23187 became effective as a trigger. A23187 (0.1 microM) also synergized with PMA in activating macrophage 20:4 metabolism. The PMA effect could be distinguished from that of LPS since no preincubation with PMA was required. A23187 greatly increased the amount of lipoxygenase products secreted from LPS-primed macrophages, leukotriene C4 synthesis being increased 150-fold. LPS-primed macrophages, partially permeabilized to Ca2+ with A23187, were used to titrate the Ca2+ concentration dependence of the cyclooxygenase and lipoxygenase pathways. Cyclooxygenase metabolites were detected at an order of magnitude lower Ca2+ concentration than were lipoxygenase products. The data suggest that Ca2+ regulates macrophage 20:4 metabolism at two distinct steps: an increase in intracellular Ca2+ regulates the triggering signal and relatively higher Ca2+ concentrations are required for 5-lipoxygenase activity.

The Effects Of Chemical Alterations Of The Benzoic Acid Nucleus On Platelet Function And Prostacyclin Activity In The Arterial Wall

1981 ◽  
Author(s):  
B A Killackey ◽  
J J Killackey ◽  
R B Philp
Keyword(s):  
Arachidonic Acid ◽  
Platelet Aggregation ◽  
Benzoic Acid ◽  
Platelet Function ◽  
Platelet Rich Plasma ◽  
Atp Release ◽  
Rabbit Aorta ◽  
Arachidonic Acid Metabolism ◽  
Second Phase ◽  
Benzoic Acid Derivatives

The effects of a series of benzoic acid derivatives (ASA analogs) on prostacyclin (PGI2) synthesis by rabbit aorta rings and on human platelet function were examined to determine if antiplatelet activity could be separated from anti-PGI2 activity.Rings of rabbit aorta were incubated with or without drugs in Tris 0.05 M, pH 7.5 for 6 m at room temperature (R.T.). Supernatant was then transferred to platelet-rich plasma incubated at 37°C for 3 m. ADP was added 60 s later and aggregation was measured and compared to controls. Rings were also incubated with 14C-arachidonic acid (14C-AA) for 60 m at R.T. in Tris with or without drugs. Products were extracted and measured by radio-T.L.C. along with known standards. Platelet aggregation and release of ATP were measured using a ChronoLog Lumi aggregometer. The effects of these agents on PGI2 activity were similar to their effects on platelet aggregation. ASA however did not exhibit the marked inhibitory potency that it had on the second phase of platelet aggregation and ATP release. Changing the 2-acetoxy group of A.S.A. to a 2-acetyl or 3-propionyloxy resulted in a loss of inhibitory activity in both systems. 2-Propionyloxy substitution resulted in a similar spectrum of activity to ASA. The effects of these agents on the metabolism of 14C-AA by rabbit aorta rings generally confirmed the bioassay results although some of the agents had novel effects on blood vessel arachidonic acid metabolism.Despite potential species differences, this study demonstrates an inability to separate antiplatelet and anti-PGI2 effects with this series of benzoic acid derivatives. Further study of the effects of these agents on the metabolism of 14C-AA by rings of rabbit aorta may lead to a better understanding of PGI2 formation.

Platelet inhibition by aspirin is diminished in patients during carotid surgery: a form of transient aspirin resistance?

2004 ◽  
Vol 92 (07) ◽  
pp. 89-96 ◽  
Author(s):  
David Payne ◽  
Chris Jones ◽  
Paul Hayes ◽  
Sally Webster ◽  
A. Naylor ◽  
...  
Keyword(s):  
Arachidonic Acid ◽  
Platelet Aggregation ◽  
Platelet Rich Plasma ◽  
Platelet Inhibition ◽  
Aspirin Resistance ◽  
Arachidonic Acid Metabolism ◽  
Significant Rise ◽  
Control Group

SummaryThe majority of patients who suffer peri-operative thromboembolic complication while undergoing vascular procedures do so despite taking aspirin. This study examined the antiplatelet effect of aspirin during surgery in patients undergoing carotid endarterectomy (CEA). Fifty patients undergoing CEA were standardised to 150 mg aspirin daily for ≥2 weeks. Platelet aggregation in response to arachidonic acid (AA) was measured in platelet rich plasma prepared from blood taken prior to, during, and at the end of surgery. Spontaneous platelet aggregation was also studied, as was the role of physiological agonists (ADP, collagen, thrombin, and epinephrine) in mediating the in vivo and in vitro responses to AA. Eighteen patients undergoing leg angioplasty, also on 150 mg aspirin, without general anaesthesia, served as a control group. In the CEA patients aggregation induced by AA (5 mM) increased significantly from 7.6 ± 5.5% pre-surgery to 50.8 ± 29.5% at the end of surgery (p <0.0001). Aggregation to AA was even greater in samples taken mid-surgery from a sub-set of patients (73.8 ± 7.2%; p = 0.0001), but fell to 45.9 ± 7.4% by the end of surgery. The increased aggregation in response to AA was not due to intra-operative release of physiological platelet agonists since addition of agents that block/neutralise the effects of ADP (apyrase; 4 µg/ml), thrombin (hirudin; 10 units/ml), or epinephrine (yohimbine; 10 µM/l) to the samples taken at the end of surgery did not block the increased aggregation.The patients undergoing angioplasty also showed a significant rise in the response to AA (5 mM), from 5.6 ± 5.5% pre-angioplasty to 32.4 ± 24.9% at the end of the procedure (p <0.0001), which fell significantly to 11.0 ± 8.1% 4 hours later. The antiplatelet activity of aspirin, mediated by blockade of platelet arachidonic acid metabolism, diminished significantly during surgery, but was partially restored by the end of the procedure without additional aspirin treatment.This rapidly inducible and transient effect may explain why some patients undergoing cardiovascular surgery remain at risk of peri-operative stroke and myocardial infarction.

Inhibition Of Platelet Aggregation, Malonyldialdehyde And Thromboxane Formation By Hydroperoxides Of Arachidonic Acid

1981 ◽  
Author(s):  
D Aharonv ◽  
J B Smith ◽  
M J Silver
Keyword(s):  
Arachidonic Acid ◽  
Platelet Aggregation ◽  
Platelet Rich Plasma ◽  
Human Platelets ◽  
Lipoxygenase Pathway ◽  
Dose Dependent Fashion ◽  
Induced Aggregation ◽  
Layer Chromatography ◽  
Dose Dependent ◽  
Thromboxane Formation

The arachidonate hydroperoxides 12-HPETE and 15-HPETE were biosynthesized from arachidonic acid using partially purified human platelet lipoxygenase or soybean lipoxidase respectively, and isolated by thin layer chromatography. Both compounds inhibited the arachidonic acid- induced aggregation of washed human platelets, suspended in calcium-free Krebs Henseleit solution, in a dose dependent fashion at concentrations between 1 and 50 uM. No inhibition was seen with up to 100 uM of these hydroperoxides when platelet -rich plasma was used. 12-HPETE (in micromolar concentrations) inhibited the formation of both thromboxane B2 (radioimmunoassay) and malonyldialdehyde (spectrophotometrie assay) when washed platelets were incubated with arachidonic acid. The 12-hydroxide, 12-HETE also inhibited platelet aggregation and thromboxane formation, but was less potent than 12-HPETE. We suggest that arachidonate hydroperoxide generated in platelets via the lipoxygenase pathway modulates platelet aggregation induced by arachidonic acid by inhibiting thromboxane formation.

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