Some pharmacological effects of 17(S) methyl-ω-honiytrans-Δ2-PGE1 (ONO 1206)

17(s) methyl-ω-hamo-trans-Δ²-PGE, (ONO 1206) produced qualitatively similar effects to PGE₁ in several systems.It was 18.4 and 25.6 times respectively more potent than PGE₁ in inhibiting ADP-induced baboon and human platelet aggregation in vitro. Intravenous infusion of ONO 1206 in baboon also produced ex-vivo inhibition of ADP-induced platelet aggregation.However, this was accompanied by a significant fall in blood pressure and an increase in heart rate. The potent relaxant effect of ONO 1206 on human respiratory tract smooth muscle in vitro suggests that this compound may be a bronchodilator in man.     

The Ratio of ADP- to TRAP-Induced Platelet Aggregation Quantifies P2Y12-Dependent Platelet Inhibition Independently of the Platelet Count

Objective

This study aimed to assess the association of clinical factors with P2Y₁₂-dependent platelet inhibition as monitored by the ratio of ADP- to TRAP-induced platelet aggregation and conventional ADP-induced aggregation, respectively.

Background

Controversial findings to identify and overcome high platelet reactivity (HPR) after coronary stent-implantation and to improve clinical outcome by tailored anti-platelet therapy exist. Monitoring anti-platelet therapy ex vivo underlies several confounding parameters causing that ex vivo platelet aggregation might not reflect in vivo platelet inhibition.

Methods

In a single centre observational study, multiple electrode aggregometry was performed in whole blood of patients after recent coronary stent-implantation. Relative ADP-induced aggregation (r-ADP-agg) was defined as the ratio of ADP- to TRAP- induced aggregation reflecting the individual degree of P2Y₁₂-mediated platelet reactivity.

Results

Platelet aggregation was assessed in 359 patients. Means (± SD) of TRAP-, ADP-induced aggregation and r-ADP-agg were 794 ± 239 AU*min, 297 ± 153 AU*min and 37 ± 14%, respectively. While ADP- and TRAP-induced platelet aggregation correlated significantly with platelet count (ADP: r = 0.302; p<0.001; TRAP: r = 0.509 p<0.001), r-ADP-agg values did not (r = -0.003; p = 0.960). These findings were unaltered in multivariate analyses adjusting for a range of factors potentially influencing platelet aggregation. The presence of an acute coronary syndrome and body weight were found to correlate with both ADP-induced platelet aggregation and r-ADP-agg.

Conclusion

The ratio of ADP- to TRAP-induced platelet aggregation quantifies P2Y₁₂-dependent platelet inhibition independently of the platelet count in contrast to conventional ADP-induced aggregation. Furthermore, r-ADP-agg was associated with the presence of an acute coronary syndrome and body weight as well as ADP-induced aggregation. Thus, the r-ADP-agg is a more valid reflecting platelet aggregation and potentially prognosis after coronary stent-implantation in P2Y₁₂-mediated HPR than conventional ADP-induced platelet aggregation.     

Isolation of homogeneous phospholipase A2 from human platelets

Phospholipase A₂ from human blood platelets has been purified to homogeneity by treatment of the platelet homogenate with H₂SO₄, followed by affinity chromatography of the extract. The platelet phospholipase is a soluble, heat-stable protein of MW 44000. The purified enzyme inhibits ADP-induced platelet aggregation.     

Comparison of the vasodepressor action of ZK 36 374, a stable prostacyclin derivative,PGI2 and PGE1 with their effect on platelet aggregation and bleeding time in rats

ZK 36 374, a new, chemically stable prostacyclin derivative, was compared with PGE₁ and PGI₂ with respect to its action on platelet aggregation in vitro, on bleeding time and on arterial blood pressure in conscious rats. The time of occlusion of a hole in a polyethylene (PE) tube of an AV-shunt between the left carotid artery and the right jugular vein by a microthrombus was considered as an index of bleeding time. All three substances inhibited the ADP-induced aggregation of human and rat platelets. In human PRP, ZK 36 374 was 17 times more active than PGE₁ and 2 – 5 times as potent as PGI₂. In contrast, in rat PRP, PGI₂ was 9.2 and 3.4 times as potent as PGE₁ and ZK 36 374, respectively. Similar differences in potency were found in the in vivo experiments where these substances given by an intravenous infusion to conscious rats prolonged bleeding time and depressed mean arterial pressure in a dose-dependent manner. ZK 36 374 was also orally active. At oral doses of 1, 2 and 3 mg/kg this new compound caused a dose-dependent prolongation of bleeding time and a fall in arterial blood pressure. In conclusion, the results show that ZK 36 374 is an intravenously and orally active prostacyclin derivative which may be of therapeutic value for occlusive peripheral vascular diseases.     

Unresponsiveness of forearm hemodynamics to omega-3 polyunsaturated fatty acids and asprin

Prostaglandin synthesis has been reported to change with aspirin ingestion via cyclooxygenase enzyme inhibition and with marine oil supplementation via an increase in the metabolism of 3-series eicosanoids. This study investigated the effects of pharmacological manipulations of prostaglandin metabolism on forearm hemodynamics and blood pressure. The agents studied were omega-3 fatty acids and aspirin.In the omega-3 fatty acid study, two groups of normal volunteers (N=10/group) supplemented their diets with either marine oil capsules or placebo. Hemodynamic variables (Mercury-in-Silastic forearm plethysmography) were measured initially and weekly for 4 weeks. There were no significant differences between the two groups in blood pressure, forearm blood flow, venous capacitance, or forearm vascular resistance. Parallel changes occurred for forearm blood flow and venous capacitance. Six normal volunteers took daily dosages of aspirin, increasing from 162 to 6200 mg. Hemodynamic measurements, ADP-induced platelet aggregation, and serum salicylate levels were obtained daily. Maximu inhibition of platelet aggregation occurred after 162 mg. (serum salicylate = 17.7+/−6.4 mg/l). Though serum salicylate levels rose to 165.0+/−20.0 mg/l, no significant changes occurred in blood pressure or forearm blood flow. Even at aspirin levels 16- fold greater than those required to impair platelet aggregation, the changes in forearm vascular resistance were not found to be significant. These results suggest that under resting conditions in normotensive males, neither pharmacological inhibition nor stimulation of vascular prostaglandin metabolism alters to forearm vascular resistance or arterial blood pressure.     

Duration of activity of the acid, methyl ester and amide of an orally active platelet aggregation inhibitory prostanoid in the rat

The prostanoid 3-oxa-4,5,6-trinor-3,7-inter- -phenylene PGE₁ (OI-PGE₁) has been shown to be a more potent inhibitor of ADP-induced human platelet aggregation than PGE₁. OI-PGE₁ inhibits ex vivo ADP-induced platelet aggregation for 60 minutes after an oral dose of 20 mg/kg to rats. Present studies compare duration of ex vivo inhibition to ADP-induced platelet aggregation in the rat by OI-PGE₁, its methyl ester and amide after administration by various routes. All oral (p.o.) and intraduodenal (i.d.) doses were 20 mg/kg and all intravenous (i.v.) doses were 1 mg/kg. OI-PGE₁ and its methyl ester had the same duration of activity after i.v. (60 min.) and p.o. (60 min.) administration, however, the methyl ester, when administered i.d., had a longer duration of activity than the free acid i.d. (>90 min. vs. 60 min.). OI-PGE₁-amide had significantly longer duration than the acid or methyl ester after i.v. (>120 min.), p.o. (>240 min.) or i.d. (>240 min.) administration. Present data suggest that in the rat (1) intestinal absorption of OI-PGE₁-methyl ester is more efficient than it is for the free acid and (2) due to metabolic and/or distributional differences between OI-PGE₁ and its amide, the amide has a much greater duration of activity.     

Platelet function in stored heparinised autologous blood is not superior to in patient platelet function during routine cardiopulmonary bypass

Background

In cardiac surgery, cardiopulmonary bypass (CPB) and unfractionated heparin have negative effects on blood platelet function. In acute normovolemic haemodilution autologous unfractionated heparinised blood is stored ex-vivo and retransfused at the end of the procedure to reduce (allogeneic) transfusion requirements. In this observational study we assessed whether platelet function is better preserved in ex vivo stored autologous blood compared to platelet function in the patient during CPB.

Methodology/Principal Finding

We measured platelet aggregation responses pre-CPB, 5 min after the start of CPB, at the end of CPB, and after unfractionated heparin reversal, using multiple electrode aggregometry (Multiplate®) with adenosine diphosphate (ADP), thrombin receptor activating peptide (TRAP) and ristocetin activated test cells. We compared blood samples taken from the patient with samples taken from 100 ml ex-vivo stored blood, which we took to mimick blood storage during normovolemic haemodilution. Platelet function declined both in ex-vivo stored blood as well as in blood taken from the patient. At the end of CPB there were no differences in platelet aggregation responses between samples from the ex vivo stored blood and the patient.

Conclusion/Significance

Ex vivo preservation of autologous blood in unfractionated heparin does not seem to be profitable to preserve platelet function.     

Inhibition of ADP-induced platelet activation by 7-chloro-4-nitrobenz-2-oxa-1,3-diazole: Covalent modification of aggregin,a putative ADP receptor

ADP-induced platelet responses play an important role in the maintenance of hemostasis. There has been disagreement concerning the identity of an ADP receptor on the platelet surface. The chemical structure of 7-chloro-4-nitrobenz-2-oxa-1,3-diazole (NBD-Cl) shows considerable resemblance to that of the adenine moiety of adenine-based nucleotides. The reagent has been previously used by other investigators as an affinity label for adenine nucleotide-requiring enzymes, such as mitochondrial ATPase and the catalytic subunit of cAMP-dependent protein kinase. Since ADP-induced platelet responses depend on the binding of ADP to its receptor, we investigated the effect on ADP-induced platelet responses and the nature of ADP-binding protein modified by NBD-Cl. NBD-Cl inhibited ADP-induced shape change and aggregation of platelets in platelet-rich plasma in a concentration- and time-dependent manner. NBD-Cl also inhibited ADP-induced shape change, aggregation, exposure of fibrinogen binding sites, secretion, and calcium mobilization in washed platelets. NBD-Cl did not act as an agonist for platelet shape change and aggregation. Covalent modification of platelets by NBD-Cl blocked the ability of ADP to antagonize the increase in intracellular levels of cAMP mediated by iloprost (a stable analogue of prostaglandin I₂). NBD-Cl was quite specific in inhibiting platelet aggregation by those agonists, e.g., ADP, collagen, and U44619 (a thromboxane mimetic), that completely or partially depend on the binding of ADP to its receptor. Autoradiogram of the gel obtained by SDS-PAGE of solubilized platelets modified by [¹⁴C]-NBD-Cl showed the presence of a predominant radiolabeled protein band at 100 kDa corresponding to aggregin, a putative ADP receptor. The intensity of this band was considerably decreased when platelets were either preincubated with ADP and ATP or covalently modified by a sulfhydryl group modifying reagent before modification by [¹⁴C]-NBD-Cl. These results (1) indicate that covalent modification of aggregin by NBD-Cl contributed to loss of the ADP-induced platelet responses, and (2) suggest that there is a sulfhydryl group in the ADP-binding domain of aggregin. © 1996 Wiley-Liss, Inc.     

Prevention of blockage of partially obstructed coronary arteries with prostacyclin correlates with inhibition of platelet aggregation

Coronary arteries (circumflex or left anterior descending) of anesthetized dogs were partially obstructed to approximately 5% of the normal lumen size by fitting a plastic cylinder around the vessel. Under these conditions, blood flow in the artery was not maintained but, instead, gradually declined over a few minutes until the vessel was completely blocked. Shaking the plastic obstructor restored blood flow temporarily, however, flow gradually declined again to zero. Sometimes flow was spontaneously restored by immediate increases that occurred at irregular intervals while, on other occasions, blood flow had to be restored by shaking the obstructor every time the rate declined to near zero. Intravenous infusion of prostacyclin (PGI₂) at 15 to 150 ng/kg/min reversed and prevented the blockage of the coronary arteries. The efficacy of PGI₂ in preventing blockage correlated with inhibition of ADP-induced platelet aggregation in platelet rich plasma prepared from blood samples withdrawn from the dogs during PGI₂ infusion. Other coronary vasodilators, nitroglycerin and PGE₂, that have no antiaggregatory effects, failed to prevent blockage whereas PGE₁ and indomethacin, which do block aggregation, also prevented blockage of the vessels. PGI₂ or its precursor, PGH₂, dripped topically on the obstructed site prevented the blockage of the artery. This local effect of PGI₂ could be obtained with amounts too small to cause systemic inhibition of platelet aggregation. The results show that PGI₂ prevents blockage of partially obstructed coronary arteries and this effect correlates with inhibition of platelet aggregation. Furthermore, the data suggest that locally produced PGI₂ may have a local antiaggregatory effect without inhibiting platelet aggregation in the general circulation.     

Anti-aggregation action of hypochlorite on the thrombocytes

Sodium hypochlorite at concentrations higher than 1 mM suppresses ADP-dependent aggregation of blood platelets. The effect was associated with the process of cell modification. Blood platelet aggregation may be depressed partially by ADP destruction. Products of ADP-sodium hypochlorite interaction may lead to the induction of blood platelet aggregation, which is not so intensive than the ADP-induced one.     

Quantification of the Blood Platelet Reactivity in the ADP-Induced Model of Non-Lethal Pulmonary Thromboembolism in Mice with the Use of Laser Doppler Flowmetry

IntroductionThe paper describes an alternative method for quantification of in vivo ADP-induced thromboembolism. The aim of the studies was to develop a method of quantification which would not require either extravasation or labelling of platelets. Our proposed approach is based on the monitoring of changes of blood flow with the use of laser Doppler flowmetry.ResultsThe injection of ADP resulted in a dose-dependent reduction of the blood flow in the mesentery. These responses were fully attributable to blood platelet aggregation, as shown by the lack of the effect in platelet-depleted mice, and significantly reduced responses in mice pretreated with cangrelor and eptifibatide. No platelet aggregate formation in mesenteric vessels was revealed by intravital microscopy, while ex vivo imaging showed accumulation of fluorescent labelled platelets in the lung.ConclusionsInjection of ADP to the venous system results in the formation of platelet aggregates predominantly in the lung. This results in reversible blood flow cessation in peripheral blood vessels. The measurement of this blood flow cessation in the mesentery allows indirect measurement of ADP-induced pulmonary thromboembolism. We suggest that this approach can be useful for in vivo screening for antiplatelet drug candidates.     

9α-homo-9,11-epoxy-5,13-prostadienoic acid analogues: Specific stable agonist (SQ 26,538) and antagonist (SQ 26,536) of the human platelet thromboxane receptor

A newly synthesized 9α-homo-9,11-epoxy-5,13-prostadienoic acid analogue, SQ 26,536, (8(R)9(S)11(R)12(S)-9α-homo-9,11-epoxy-5(Z), 13(E)-15S-hydroxyprostadienoic acid) inhibited arachidonic acid (AA)-induced platelet aggregation with an I₅₀ value of 1.7 μ . SQ 26,536 did not inhibit prostaglandin (PG) synthetase activity of bovine seminal vesicle microsomes or thromboxane (Tx) synthetase activity of lysed human blood platelets. SQ 26,536 also inhibited platelet aggregation induced by epinephrine (secondary phase), 9,11-azoPGH₂ and collagen but did not inhibit the primary phase of epinephrine-induced aggregation or ADP-induced platelet aggregation. SQ 26,538 (8(R)9(S)11(R)12(S)-9α-homo-9-, 11-epoxy-5(Z),13(E)-15R-hydroxyprostadienoic acid), a 15-epimer of SQ 26,536, induced platelet aggregation with an A₅₀ value of 2.5 μ . SQ 26,536 competitively inhibited SQ 26,538-induced platelet aggregation with a K_i value of 3 μ . Neither indomethacin, a PG synthetase inhibitor, nor SQ 80,338 (1-(3-phenyl-2-propenyl)-1H-imidazole), a Tx synthetase inhibitor, inhibited SQ 26,538- or 9,11-azoPGH₂-induced platelet aggregation. These data indicate that SQ 26,536 and SQ 26,538 are stable antagonist and agonist, respectively, of the human blood platelet thromboxane receptor.     

Cangrelor increases the magnitude of platelet inhibition and reduces interindividual variability in clopidogrel-pretreated subjects

BackgroundInadequate platelet inhibition despite aspirin and clopidogrel therapy during and after a percutaneous coronary intervention is associated with an impaired clinical outcome. Cangrelor, a direct and reversible P2Y₁₂ inhibitor that is currently in development, has the potential to achieve higher levels of inhibition of ADP-induced platelet aggregation than clopidogrel. The aim of the present study was to compare the magnitude of platelet inhibition in clopidogrel-pretreated patients before and after the in vitro addition of a subtherapeutic dose of cangrelor. MethodsBlood samples were drawn from patients pretreated with clopidogrel and aspirin who were undergoing elective percutaneous coronary intervention (n=39). Platelet function analysis with ‘classical’ light transmittance aggregometry (both peak and late aggregation [at 6 min]) was performed before and after the in vitro addition of cangrelor (0.25 μmol/l) to platelet-rich plasma (PRP). After an incubation period of five minutes, platelet aggregation was induced by 5 and 20 μmol/l ADP. ResultsThe in vitro addition of 0.25μmol/l cangrelor to the PRP from clopidogrel-treated subjects resulted in an additional reduction in ADP-induced platelet aggregation. For ADP concentrations of 5 and 20 μmol/l, peak aggregation showed a decrease of 75 and 85%, respectively (p<0.001 for both), while late aggregation was almost completely diminished (p=0.003 and p<0.001, respectively). Furthermore, the interindividual variation in inhibition of ADP-induced platelet aggregation by clopidogrel was greatly reduced after the addition of cangrelor. ConclusionWe demonstrate that the in vitro addition of even a subtherapeutic dose of cangrelor to the PRP of clopidogrel-pretreated patients results in an additional reduction of ADP-induced platelet aggregation. Moreover, cangrelor was able to diminish the interindividual variation observed in clopidogrel-inhibited platelet aggregation. (Neth Heart J 2009;17:195–8.)     

Thrombocyte aggregation in plasma and whole blood during hyperventilation (hypocapnia) in cats

Platelet aggregation in platelet rich plasma (PRP) and whole blood was simultaneously studied in acute experiments on cats in hypocapnic conditions. ADP-induced aggregation increase was determined in PRP and whole blood. Contradictory results were obtained during platelet aggregation induced by collagen and arachidonic acid: increased aggregation in PRP and decreased aggregation in whole blood. The data obtained suggest that ADP is a risk factor for the onset of intravascular thrombosis.     

Variations of glycoprotein IIb–IIIa (αIIb/β3-integrin) content in healthy donors. The influence on platelet aggregation activity and efficacy of aspirin action

The effects of content of a fibrinogen receptor, glycoprotein (GP) IIb–IIIa (αIIb/β3-integrin), GP IIIa genetic polymorphism (substitution Leu33Pro), and fibrinogen concentration in blood plasma on platelet aggregation activity have been investigated in a group of healthy volunteers. In 35 examined donors the GP IIb–IIIa content on platelet surface varied from 40 to 71 × 10³ per platelet. Repeated measurements revealed that the GP IIb–IIIa content coefficient of variation was 9.5%, and deviations from mean levels did not exceed 20%. The level and the rate of platelet aggregation induced by ADP (1.25–20 μM) correlated with GP IIb–IIIa number (r from 0.315 to 0.591) and were higher in the group of donors with high in comparison with low GP IIb–IIIa content (>60 and (40–50) × 10^?3 per platelet, respectively). Aspirin, the inhibitor of thromboxane A₂ synthesis, partially suppressed ADP-induced platelet aggregation. The level of residual aggregation in the presence of aspirin also correlated with GP IIb–IIIa content and increased in subjects with high receptor content. Parameters of ADP-induced aggregation did not differ in donors with genotypes GP IIIa Pro33(?) (Leu33Leu33, n = 20) and Pro33(+) (Leu33Pro33, n = 13, and Pro33Pro33, n = 2) genotype. GP IIb–IIIa content was also not affected by GP IIIa polymorphism. No significant correlations were found between the level and rate of platelet aggregation and fibrinogen concentration in blood plasma. The data obtained indicate that the effects of variations of GP IIb–IIIa content on platelet aggregation are higher than GP IIIa Leu33Pro polymorphism and variations of fibrinogen concentration. High GP IIb–IIIa content is associated with increased platelet aggregation activity and decreased efficacy of aggregation inhibition by aspirin.     

Modulation of platelet responsiveness through selective phosphorylation of plasma membrane proteins: Antagonistic eeffects of cyclic AMP and cyclic GMP

³²P phosphorylation of plasma membranes from human blood platelets, under conditions that closely resemble physiological ones (endogeneous phosphate donors and intact platelets in homologous plasma), result in the incorporation of the label mainly in a membrane glycoprotein of apparently high molecular weight (greater than 400 000). Dibutyryl cyclic AMP, an inhibitor of platelet aggregation, specifically increases the degree of phosphorylation of this glycoprotein. Moreover, it has been found that prostaglandin E₁ one of the most potent inhibitors of platelet aggregation which also increases phosphorylation of the same glycoprotein, is significantly more effective than cyclic AMP.Cyclic GMP does not have any apparent effect on platelet aggregation. However, incubation of platelet-rich plasma with both cyclic GMP and cyclic AMP results in a partial recovery of the platelet responsiveness towards ADP-induced aggregation. Coincidently, the degree of phosphorylation of the high molecular weight glycoprotein under these conditions, although still higher than in controls (no nucleotides added), is significantly decreased as compared with cyclic AMP-treated cells. Furthermore, cyclic GMP inhibits the cyclic AMP-dependent protein kinase activity in isolated platelet plasma membranes.These results suggest a central role for this membrane phosphoglycoprotein in the triggering of platelet aggregation and, furthermore, suggest that modulation of its degree of phosphorylation may be exerted through some cyclic AMP/cyclic GMP relationship, which in the basal state might be critical for platelet responsiveness.     

Structural-functional state of platelets at the initial stage of aggregation

ADP-induced changes of light transmission of platelet suspension were studied with a laser aggregometer at concentration variation of both cells and aggregation agents. It was shown that a decrease of light transmission of platelet suspension was due to structure-morphological changes of platelets and pseudopodia formation. An investigation method of platelet aggregation with a small content of cells in the solution permits to fix distinctly the stages of the platelet structural states in the processes of stimulation and aggregation.     

Platelet aggregation inhibitory activity and vasodepressor activity of a series of bicyclo[3.2.0]hetp-6-ylidene iminoxy alkanoic acids with modified lower side chains

Prostacyclin analogues derived from modification of the lower side chain of the bicyclo[3.2.0]hept-6-ylidene iminoxyacetic acid ( ) were studied in inhibition of and platelet aggregation and in the spontaneously hypertensive rat. Iminoxyacetic acids ( ) and iminoxypropionic acid ) were 2.9, 3.0, 1.9 and 2.0 times respectively more potent than PGE₁ in inhibiting ADP-induced aggregation of human platelets . Following intravenous administration at a dose of 90–110 μg/kg in the guinea pig, iminoxyacetic acids ( ), ( ) and iminoxypropionic acid ( ) showed a maximum inhibition of 82–92% with a half life in the range of 14–22 min. Following oral administration at a dose of 1 mg/kg in the guinea pig, iminoxyacetic acids ( ) and ( ) inhibited heterologous platelet aggregation for 4.5 h. Following intravenous administration in spontaneously hypertensive rats, acids )-( ) lowered the mean blood pressure in a dose dependent manner. At a dose of 100 μg/kg, the effect lasted for 20–40 min.     

Influences of prostaglandins on electrophoretic mobility and aggregation of rabbit platelets

Influences of prostaglandin(PG)s on electrophoretic mobilities and aggregation of rabbit platelets were studied. The PGs studied (PGI₂, PGE₁, PGD₂, PGE₂, PGF_2α, PGA₂ and PGA₁) had no effect on platelet electrophoretic mobility. However, both PGE₁ and PGI₂ in 0.3 and 3.0 μM inhibited ADP-induced aggregation and ADP-induced decrease in the mobility. PGD₂ in 0.3 and 3.0, and PGE₂ in 30 μM inhibited the aggregation but did not depress the ADP-induced decrease in the mobility. PGF_2α, PGA₂ and PGA₁ had no effect on the decrease in electrophoretic mobility and on the aggregation caused by ADP.     

Effect of homocysteine, cysteine, and their derivatives on the platelet link of hemostasis system

The influence of homocysteine, homocysteine thiolactone, cysteine and their derivatives on activation and aggregation of human platelets was investigated using the model systems in vitro. It was established that homocysteine and cysteine increased platelet aggregation induced by ADP, epinephrine, or collagen. Their action began in a range of concentrations such as their physiological blood levels (10 microM) and was increasing with the rise of their concentrations. Cysteine increased ADP-induced platelet aggregation, hardly any affect on epinephrine-induced platelet aggregation and depressed collagen-induced platelet aggregation in the highest concentration (1000 microM). Their disulfides and thioethers did not influence platelet aggregation.