The Effects of Two New Antithrombotic Agents (IM Idazoquinazoli Nones) on Platelet Shape and Aggregation

Recently, one member of a new series of compounds was reported as a potent, nontoxic and long lasting antithrombotic agent, based on in vitro and in vivo animal tests (Bristol Labs; Fleming et al (1975), J. Pharmacol. Exp. Ther. 194, 435).We here report on the effects of this compound, 6-methyl-l,2,3,5-tetrahydroimidazo [2,1-b]quinazolin-2-one hydrochloride monohydrate (BL-3459), and its metabol ical ly more stable 6,7-dichloro analogue (BL-4162) , on rabbit and human platelet shape change and aggregation, and compare them with other agents known to affect platelet adenosine 3′:5′-cyclic monophosphate (cAMP). In aggregometer studies with citrated (0.29%) platelet-rich plasma (PRP), both BL-compounds were found to inhibit platelet shape change and aggregation induced by ADP, thrombin, serotonin and adrenaline-serotonin. Typically for human PRP, aggregation induced by 10 μM ADP was inhibited by 90% with 10 μM BL-4162 or 0.1 μM prostaglandin E1 (PGE1), and by 60% with 10 μM BL-3459. In corresponding rabbit PRP tests, 60% inhibition was caused equally by 1 μM BL-3459 or BL-4162, and by 0.05 μM PGE1,Both BL-compounds, like methylxanthines, were found to potentiate the inhibitory effect of PGE1 on platelet aggregation but did not potentiate the action of methylxanthines. Moreover, they both slightly increased the basal level of rabbit cAMP and potentiated the elevation of cAMP by PGE1, These BL-compounds are potent inhibitors of human and rabbit shape change and aggregation and appear to act by a mechanism distinct from that of PGE1.

Effects of Acetylsalicylic Acid on Human Platelet Function In Vivo at Salicylate Steady State

10.1055/s-0038-1661074 ◽

1984 ◽

Vol 51 (02) ◽

pp. 269-271 ◽

Cited By ~ 2

Author(s):

R Simrock ◽

A Missalla ◽

P Schwidtal ◽

V Lischke ◽

H K Breddin

Keyword(s):

Steady State ◽

Platelet Aggregation ◽

Acetylsalicylic Acid ◽

Human Platelet ◽

Shape Change ◽

Clinical Importance ◽

Tissue Extract ◽

SummaryThe results of clinical trials concerning the use of acetylsalicylic acid (ASA) as antithrombotic drug are contradictory. Inhibition by ASA of platelet prostaglandin synthesis and aggregation is prevented by its metabolite salicylic acid (SA) in animals and in human platelets in vitro. It was suggested that ASA might produce its own inhibitor, thereby diminishing its efficiency in thromboembolic disease.In four healthy male subjects there was no difference in inhibition of collagen-induced platelet aggregation after the administration of 500 mg ASA alone or at salicylate steady state (3 g SA daily). But the inhibition of tissue-extract-induced platelet shape change was diminished and shortened by pretreatment with SA. We conclude that SA does not inhibit the effects of ASA on human platelet aggregation in vivo in therapeutic dose ranges. The clinical importance of the SA/ASA-interaction on tissue-extract-induced platelet shape change remains to be clarified.

The Effect of Barbituric Acid Derivatives on Platelet Function in Vitro and in Vivo

10.1055/s-0038-1649080 ◽

1973 ◽

Vol 30 (02) ◽

pp. 315-326

Author(s):

J. Heinz Joist ◽

Jean-Pierre Cazenave ◽

J. Fraser Mustard

Keyword(s):

Platelet Aggregation ◽

Platelet Function ◽

Barbituric Acid ◽

Platelet Rich Plasma ◽

Inhibitory Effect ◽

Primary Response ◽

Sodium Pentobarbital ◽

Barbituric Acid Derivatives

SummarySodium pentobarbital (SPB) and three other barbituric acid derivatives were found to inhibit platelet function in vitro. SPB had no effect on the primary response to ADP of platelets in platelet-rich plasma (PRP) or washed platelets but inhibited secondary aggregation induced by ADP in human PRP. The drug inhibited both phases of aggregation induced by epinephrine. SPB suppressed aggregation and the release reaction induced by collagen or low concentrations of thrombin, and platelet adherence to collagen-coated glass tubes. The inhibition by SPB of platelet aggregation was readily reversible and isotopically labeled SPB did not become firmly bound to platelets. No inhibitory effect on platelet aggregation induced by ADP, collagen, or thrombin could be detected in PRP obtained from rabbits after induction of SPB-anesthesia.

Inhibition of ADP-Induced Responses in Human Platelets by Agents Elevating the Cyclic AMP Level: Comparison of Aggregation and Shape Change

10.1055/s-0038-1661208 ◽

1984 ◽

Vol 52 (03) ◽

pp. 333-335 ◽

Cited By ~ 4

Author(s):

Vider M Steen ◽

Holm Holmsen

Keyword(s):

Inhibitory Action ◽

Human Platelet ◽

Platelet Rich Plasma ◽

Shape Change ◽

Inhibitory Effect ◽

Human Platelets ◽

Inhibitory Effects ◽

Early Step ◽

Stimulus Response ◽

Sequential Relationship

SummaryThe inhibitory effect of cAMP-elevating agents on shape change and aggregation in human platelets was studied to improve the understanding of the sequential relationship between these two responses.Human platelet-rich plasma was preincubated for 2 min at 37° C with prostaglandin E1 or adenosine, agents known to elevate the intracellular level of cAMP. Their inhibitory effects on ADP-induced shape change and aggregation were determined both separately and simultaneously. The dose-inhibition patterns for shape change and aggregation were similar for both PGE1 and adenosine. There was no distinct difference between the inhibitory action of these two inhibitors.These observations suggest that elevation of the intracellular concentration of cAMP interferes with an early step in the stimulus-response coupling that is common for aggregation and shape change.

Inhibition of Human Platelet Aggregation by the Proteolytic Effect of Streptokinase (SK). Role of the Factor VIII Related Antigen

10.1055/s-0039-1689380 ◽

1975 ◽

Cited By ~ 1

Author(s):

R. Castillo ◽

S. Maragall ◽

J. A. Guisasola ◽

F. Casals ◽

C. Ruiz ◽

...

Keyword(s):

Platelet Aggregation ◽

Factor Viii ◽

Platelet Rich Plasma ◽

Gel Filtration ◽

Inhibitory Effect ◽

Factor Viii Related Antigen ◽

Human Factor Viii ◽

Induced Aggregation

Defective ADP-induced platelet aggregation has been observed in patients treated with streptokinase. This same effect appears “in vitro” when adding SK to platelet rich plasma (PRP). Classic hemophilia and normal platelet poor plasmas (PPP) treated with SK inhibit the aggregation of washed platelets; plasmin-treated normal human serum also shows an inhibitory effect on platelet aggregation. However, von Willebrand SK-treated plasmas do not inhibit the aggregation of washed platelets. The same results appear when plasmas are previously treated with a rabbit antibody to human factor VIII.This confirms that the antiaggregating effect is mainly linked to the digested factor VIII related antigen.The inhibition of ADP-induced platelet aggregation has been proved in gel filtration-isolated and washed platelets from SK-treated PRP.Defective ristocetin-induced platelet aggregation has also been observed- This action does not appear in washed platelets from SK-treated PRP in presence of normal PPP, but it does in presence of SK-treated PPP, which suggests that the inhibition of the ristocetin-induced aggregation is due to the lack of factor VIII and not to the factor VIII-related products.Heparin, either “in vivo” or “in vitro”, has corrected the antiaggregating effect of SK.

Kinetics of ADP-induced human platelet shape change: apparent positive cooperativity

Canadian Journal of Physiology and Pharmacology ◽

10.1139/y80-009 ◽

1980 ◽

Vol 58 (1) ◽

pp. 45-52 ◽

Cited By ~ 10

Author(s):

John G. Milton ◽

W. Yung ◽

C. Glushak ◽

M. M. Frojmovic

Keyword(s):

Light Transmission ◽

Human Platelet ◽

Platelet Rich Plasma ◽

Shape Change ◽

Hill Coefficient ◽

A Value ◽

The Hill ◽

Kinetics Of ◽

Type Response ◽

The kinetics of ADP-induced human platelet shape change have been examined. Initial velocities of platelet shape change were estimated by two methods: (1) the slope of the initial decrease in light transmission through stirred, citrated platelet-rich plasma, and (2) direct examination of platelet morphologies by phase-contrast microscopy. In both cases, a value of the Hill coefficient, NH, significantly greater than 1 is obtained (2.0 ± 0.2 and 1.8 ± 0.2, respectively). The observed elevated value of NH is not due to a substantial fraction of the ADP being platelet bound, the presence of factors in the plasma, platelet heterogeneity, or the influence of the rate of platelet shape change reversion. Our observations suggest that ADP-induced platelet shape change may be a positively cooperative or "threshold" type response.

Depletion of Platelet Amine Storage Granules by the Antithrombotic Agent, Suloctidil

10.1055/s-0038-1651919 ◽

1977 ◽

Vol 38 (04) ◽

pp. 1010-1017 ◽

Cited By ~ 12

Author(s):

David C. B. Mills ◽

Donald E. Macfarlane

Keyword(s):

Energy Balance ◽

Animal Models ◽

Human Platelet ◽

Platelet Rich Plasma ◽

Oxidation Products ◽

Antithrombotic Agent ◽

Amine Storage ◽

Storage Granules ◽

Amine Storage Granules

SummarySuloctidil, a compound with antithrombotic properties in animal models, causes depletion of human platelet serotonin stores during 1–5 hr incubation with platelet-rich plasma in vitro. This effect is not attended by leakage of cytoplasmic nucleotides or by alterations in cyclic AMP metabolism, malondialdehyde production or energy balance. 5HT uptake was also inhibited but uptake of adenine was not. 5HT released by suloctidil appeared in the supernatant as oxidation products, though the amine also accumulated when re-uptake was blocked by imipramine.

A Comparative Study of the Effects of Adrenoceptor Antagonists on Platelet Aggregation and Thromboxane Generation

10.1055/s-0038-1657878 ◽

1985 ◽

Vol 54 (02) ◽

pp. 480-484 ◽

Cited By ~ 17

Author(s):

I A Greer ◽

J J Walker ◽

M McLaren ◽

A A Calder ◽

C D Forbes

Keyword(s):

Platelet Aggregation ◽

Vascular Disease ◽

Platelet Rich Plasma ◽

Thromboxane A2 ◽

Inhibitory Effect ◽

Dependent Manner ◽

Wide Range ◽

The Right

SummaryPlatelet aggregation and thromboxane A2 have been implicated in the pathogenesis of several forms of vascular disease. The aim of this study was to determine the effect of a wide range of adrenoceptor antagonists on platelet aggregation, and thromboxane A2 production, from normal human platelet rich plasma in vitro. Labetalol, pindolol and propranolol inhibited platelet aggregation to collagen in a dose dependent manner. Increasing the concentration of collagen “shifted” the dose response curve to the right. These 3 drugs also significantly inhibited thromboxane A2 generation in response to collagen but not to arachidonic acid. This effect was independent of any inhibitory effect of these drugs on platelet aggregation, and occurred at a drug concentration close to that obtained in vivo. Atenolol, metoprolol, prazosin and timolol were similarly assessed but had no effect on either platelet aggregation or thromboxane A2 generation. This ability of labetalol, pindolol, and propranolol to inhibit platelet aggregation and thromboxane generation, may be of clinical benefit in view of the increasing evidence implicating thromboxane A2 in the pathogenesis of vascular disease.

48740 RP INHIBITS PLATELET SHAPE CHANGE INDUCED BY PAF-ACETHER IN VITRO.

10.1055/s-0038-1643487 ◽

1987 ◽

Author(s):

G Jung ◽

P Sedivy

Keyword(s):

Sodium Citrate ◽

Light Transmission ◽

Platelet Rich Plasma ◽

Shape Change ◽

Maximum Amplitude ◽

Maximal Velocity ◽

Maximal Amplitude ◽

Plasma Properties ◽

Platelet shape change (PSC) is the first measurable physiological response to platelet pro-aggregant agonists such as PAF-acether (PAF) (1). The laser thromborheometer (2) was used to assess the PSC (detected as decrease in light scattering as 2 of maximal velocity) and the platelet aggrega tion (detected as increase in the light transmission as 2 of maximal velocity and maximal amplitude) in citrated platelet -rich plasma (cPRP) (1 volume 3.8 2 sodium citrate ± 9 volumes blood) from 12 volunteers of either sex. PAF concentrations ranging from 0.1 to 1 yM induced PSC (range of velocities : 13.2-69.8 2 of maximal velocity, n = 12) and platelet aggregation (range of velocities : 9.3-22.2 2 of maximal velocity and maximum amplitude of aggregation always superior to 20 2, n = 12). These effects were inhibited by 48740 R.P., 3-(3- pyridy1)-1H,3H pyrrolo [1 , 2-c] thiazo1e-7-carboxamide (100200 yM) a selective and competitive PAF-antagonist (3). For instance, 100 yM 48740 RP decreased by 76.4 ± 3.5 (mean ± S.E.M., n = 3) PSC evoked by 0.1 yM of PAF. Furthermore, 48740 RP was also able to reduce PSC in heparinized platelet - r ich plasma (hPRP). The antagonist effects of 46740 RP could be overcome by increasing PAF concentrations in the cPRP and hPRP. During this study, 6 volunteers were found, in whom even concentrations of PAF up to 10.5 pM failed to induce an amplitude of aggregation in cPRP greater than 20 2 whereas PSC was in the range of 19.1-79.4 2 of maximal velocity. These responses to PAF which were antagonized by 48740 RP were not due to an alteration in plasma properties ; thus, they are proposed to result from undetermined changes occuring at the level of the platelet (e.g.) decreased number of PAF-operationa1 receptors or alteration of the excitation - response pathways). In conclusion, 48740 RP is an antagonist of PAF-evoked aggregation and PSC in cPRP from volunteers responding either normally or poorly to PAF. (1) LAPETINA E.G. et al. J. Biol. Chem. 258, 7241 (1983). (2) JUNG G. et al. Nouv. Rev. Fr. H6matol. 27, 103 (1985). (3) SEDIVY P. et al. Thromb. Haemost. 54, 185 (1985).

Activated Prothrombin Complex Concentrate

Effect Of A Non-Activated Prothrombin Complex Concentrate (Prothrombinex) On Platelets: In Vitro And In Vivo Studies

10.1055/s-0038-1653035 ◽

1981 ◽

Author(s):

H Ekert ◽

F L Dean ◽

J L Lane

Keyword(s):

Partial Thromboplastin Time ◽

Prothrombin Complex Concentrate ◽

Platelet Rich Plasma ◽

Inhibitory Effect ◽

Activated Partial Thromboplastin Time ◽

In Vivo Studies ◽

Chromogenic Substrates ◽

Chromatography on Sephadex G-200 of the prothrombin complex concentrate, prothrombinex (Px) showed it to have inhibitor and potentiator fractions when tested by the non-activated partial thromboplastin time (NAPTT). The inhibitory effect was related to the heparin content of Px, as it was removed on ECTEOLA-cellulose. The potentiator fraction clotted fibrinogen and this could be inhibited by hirudin. Thrombin-like activity of this fraction was shown using chromogenic substrates. The effect of the potentiator fraction in the NAPTT was markedly enhanced by platelets. Diluted Px and the potentiator fractions caused aggregation of washed platelets which could be inhibited by hirudin. Aggregation was independent of the prostaglandin pathway, as it occurred in washed aspirin-treated platelets. Neither diluted Px nor potentiator fractions aggregated platelets in platelet rich plasma. Infusion of Px was followed by a rise in β-thromboglobulin (β-TG) in 2 of 3 patients two minutes after infusion. This rise could not be ascribed to the presence of β-TG in Px or to the heparin present in Px. These findings suggest that Px has a thrombin-like activity and that its mode of action in patients with factor VIII antibodies may result from its effect on platelets and their interaction with coagulation enzymes.

Lu 23051, A New Potent Inhibitor Of Platelet Aggregation

10.1055/s-0038-1653265 ◽

1981 ◽

Author(s):

H D Lehmann ◽

J Gries ◽

D Lenke

Keyword(s):

Platelet Aggregation ◽

Ex Vivo ◽

Platelet Rich Plasma ◽

Coronary Vessels ◽

Inhibitory Effect ◽

Spontaneously Hypertensive ◽

Dependent Inhibition ◽

Induced Aggregation

6- [p-(2-(Chiorpropionylamino)phenyl] -4.5-dihydro-5-methyl-3(2H)-pyridazinone, LU 23051, is primarily characterized by its strong inhibition of platelet aggregation under in vitro and in vivo conditions. In vitro there is a concentration-dependent inhibition of ADP and collagen induced aggregation in platelet rich plasma of man, rat and dog. The inhibitory concentration EC 33 % is 0.0010-0.030 mg/1 (man: ADP-0.030, col 1.-0.013 mg/l) depending on species and type of aggregation. When administered orally in ex vivo experiments on rats and dogs the substance is found to have a dose-dependent antiaggregatory effect in the range from 0.1-3.16 mg/kg. The ED 33 % is 0.27-0.63 mg/kg.-In addition after oral administration the substance has a good inhibitory effect in models being based on intravascular platelet aggregation. Thus, a dose of 1 mg/kg inhibits laser-induced aggregation in mesenteric venules of rats. Mortality after i.v. injection of collagen in mice is reduced by 50 % after a dose of 0.02 mg/kg. A dose of 0.039 mg/kg prolongs the bleeding time of rats by 50 %. The aggregation-inhibiting action is of long duration (0.1 mg/kg p.o.∼24 h). The substance does not interfere with clotting.Besides its effect on platelet aggregation LU 23051 acts as vasodilatator as well. Dilatation of coronary vessels by 100 % is seen in isolated guinea-pig hearts at a concentration of 0.1 mg/l. In spontaneously hypertensive rats the substance has an anti hypertensive effect. The ED 20 % is 0.36 mg/kg p.o.The combination of antiaggregatory and vasodilatatory effects opens up interesting aspects with respect to the pharmacotherapeutic use of the new substance