General pharmacology of pergolide in animals. 1st communication: cardiovascular, respiratory and autonomic nervous system studies.

Pergolide mesylate ((8 beta)-8-[(methylthio)methyl]-6-propylergoline monomethanesulfonate, LY 127,809, CAS 66104-23-2) is a novel and potent dopamine agonist marketed for treating the symptoms of Parkinson's disease. The potential secondary pharmacological effects of this agent on the cardiovascular, respiratory, and the autonomic nervous systems were examined. Pergolide exhibited significant pharmacological effects in cardiovascular and autonomic tests at high oral or intravenous doses. The reference dopamine agonist, bromocriptine, exhibited effects qualitatively similar to, but at doses generally higher than, pergolide, in parallel with its lower therapeutic potency relative to pergolide. In summary, these studies confirm the pharmacological selectivity of pergolide at low doses, and indicate the potential for secondary pharmacological side effects upon cardiovascular function at significant multiples of the clinical dose.     

Effects of ethanol and hemolysis on in vivo and in vitro platelet aggregation

In vivo and in vitro platelet function were measured in male rats after intravenous injection of ethanol or water. There was a dose-related ethanol suppression of platelet aggregation induced by extravasation. Increased volumes of preformed microaggregates were seen in samples taken directly from the vena cava after injection of ethanol in doses that caused hemolysis. Lower doses of ethanol produced no demonstrable microaggregates or hemolysis: however, extravasation-induced aggregation was inhibited. Hemolysis was noted after intravenous injection of water, which also reduced the total volume and mean aggregate size of platelet aggregates induced by extravasation. Blood drawn from the inferior vena cava after induction of hemolysis had an increased volume of microaggregates, regardless of the agent producing hemolysis. In vitro studies revealed changes in spontaneous and ADP-induced aggregation only at very high concentrations of ethanol (greater than 3,000 mg/dl) and no effects at ethanol levels that altered in vivo aggregation. Ethanol, in doses that do not hemolyze erythrocytes, decreases platelet aggregation.     

Diacylglycerol overcomes aspirin inhibition of platelets: evidence for a necessary role for diacylglycerol accumulation in platelet activation

Aspirin, an inhibitor of cyclooxygenase, inhibits platelet aggregation in response to many stimuli. Previous studies suggested an important and necessary role for protein kinase C (PKC) in platelet aggregation and secretion. Therefore, the effects of aspirin on sn-1,2-diacylglycerol (DAG), the endogenous activator of PKC, were investigated. Specifically, we sought to determine whether inhibition of DAG production is critical for aspirin action on platelets. Total DAG mass was measured using the DAG kinase assay. At low doses of gamma-thrombin (4 nM), aspirin (5 mM) completely inhibited secondary aggregation; this inhibition was associated with near-complete inhibition of DAG production. Inhibition of collagen-induced aggregation by aspirin (50 microM) was also associated with complete inhibition of collagen-stimulated DAG production and secondary aggregation. Concomitantly, aspirin reduced phosphorylation of the 40-kDa protein, a specific PKC substrate strongly suggesting inhibition of PKC in response to aspirin. To determine the physiologic significance of the inhibition of DAG production by aspirin, reconstitution studies were conducted with dioctanoylglycerol (diC8), a cell-permeable DAG. Under conditions in which aspirin completely inhibited secondary aggregation induced by gamma-thrombin, collagen, or arachidonic acid, diC8 overcame aspirin inhibition of agonist action and reconstituted secondary aggregation. DiC8 exerted these effects at low concentrations (2-3 microM), which caused minimal aggregation of control platelets. Phorbol 12,13-dibutyrate, a phorbol ester that directly activates PKC, mimicked the effects of diC8 in overcoming aspirin inhibition of collagen-induced platelet activation. However, subthreshold concentrations of the calcium ionophore ionomycin, arachidonic acid, or gamma-thrombin were unable to overcome aspirin inhibition of collagen-induced platelet aggregation, suggesting that the ability to overcome aspirin inhibition is not shared by other second messengers and is not due to nonspecific synergy. These studies constitute evidence that inhibition of DAG production and subsequent PKC activation are crucial to the antiaggregatory effects of aspirin. They also support the hypothesis that DAG production and PKC activation may be the final common pathway for induction of secondary aggregation.     

Effects of cadralazine on the respiration, circulation, kidney, autonomic nervous system, digestive system, blood and so on

The general pharmacological effects of cadralazine and its major metabolite ISF 2405 were studied by comparing them with those of hydralazine. Cadralazine at 3.0 mg/kg, i.v., increased respiratory movement and heart rate and decreased blood pressure in cats. Cadralazine at 3.0 mg/kg, i.v., inhibited the hypertensive response induced by adrenaline, but showed little effect on the hypotensive response induced by acetylcholine in cats. Cadralazine and ISF 2405 at 10(-4) g/ml had negative chronotropic effects on isolated guinea-pig atria. The drug at 2.5 mg/kg, p.o., inhibited the passage of BaSO4 in the gastrointestinal tract in mice. The drug at 5.0 mg/kg, i.d. or more inhibited gastric secretion in rats. Cadralazine, except at higher doses, had little effect on spontaneous gastric motility and uterine spontaneous movement in rats. Cadralazine at 2.5 mg/kg, p.o., or more reduced or tended to reduce urine volume and urinary excretion of electrolytes. The drug showed little effect on coagulation and osmotic fragility in blood cell in rats nor on hemolysis and platelet aggregation in rabbits. ISF 2405, however, showed slight or moderate influence on hemolysis at concentrations as high as 0.01-1.0%. Cadralazine at 5.0 mg/kg, p.o. or more antagonized carrageenin-induced hind paw edema in rats. In conclusion, these effects of cadralazine were found to be qualitatively identical with those of hydralazine.     

The effect of the antiarrhythmic, prajmalium bitartrate, on human thrombocyte function

Studies of the in vitro effects of the antiarrhythmic drug prajmalium bitartrate (PBT, Neo-Gilurytmal) showed inhibitory effects on platelet aggregation and thromboxane production. PBT inhibited the primary and secondary phases of aggregation induced by adrenaline (epinephrine) or adenosine diphosphate (ADP). Platelet aggregation stimulated with collagen, platelet activating factor (PAF), and the thromboxane mimetic 9,11-azo-prostaglandin H2 (U 44064) was inhibited. The secondary phase of aggregation induced by ristocetin and aggregation caused by arachidonic acid (AA) were inhibited in samples from some donors (responders) but not in others (nonresponders). Platelet aggregation by the ionophore calcimycine (A 23187) was not inhibited, but small doses of calcimycine abolished the PBT-induced inhibition of aggregation caused by ADP. Thromboxane production of platelets with collagen of ADP was inhibited by higher concentrations of PBT, whereas AA-induced thromboxane synthesis remained unchanged. The observed antiplatelet activities of PBT are thought to result from calcium and sodium channel blocking properties of the drug.     

Behavioral characterization of the new potent nonselective dopamine agonist pergolide.

Pergolide (LY127809, CAS 66104-23-2), a non-selective dopamine agonist, was evaluated for broad behavioral properties in a wide range of pharmacological tests. The selective dopamine2(D2) agonist, bromocriptine, served as a reference standard for those tests where behavioral activity was noted with pergolide. Pergolide and bromocriptine were administered orally to mice at doses of 0.3-30 and 3-300 mg/kg, respectively. Both compounds produced biphasic effects on spontaneous activity, increased hexobarbital-induced sleep time, and lowered mouse body temperature. Qualitative changes with pergolide were observed with some mice showing hyporeactiveness, ptosis, slowed respiration and placing loss. Reserpine-induced hypothermia was reversed by pergolide with significant increases in the body temperature of reserpine-treated mice. However, a further reduction in the body temperature of reserpinized hypothermic mice was seen following bromocriptine administration. Acetic acid-induced writhing and performance on the rotarod were both impaired by higher doses of pergolide. Bromocriptine administration also reduced writhing at higher doses but did not alter performance on the rotarod. Pergolide had no effect on seizure activity as evaluated by electroshock, pentylenetetrazol (pentetrazol) or strychnine. Oxotremorine-induced tremors and salivation, grip strength, and tail-flick were not affected by pergolide. Neither pergolide nor bromocriptine altered established shuttle-avoidance behavior in rats at oral doses of 0.1 to 30 mg/kg. Behavioral assessment of pergolide in dogs was complicated by severe emetic responses at clinically relevant doses greater than 0.003 mg/kg. In summary, these data suggest that pergolide produces a behavioral profile which is characteristic of dopaminergics.(ABSTRACT TRUNCATED AT 250 WORDS)     

General pharmacology of T-2588, a new oral cephem antibiotic

A new oral cephem antibiotic, T-2588, the pivaloyloxymethyl ester of (+)-(6R, 7R)-7-[(Z)-2-(2-amino-4-thiazolyl)-2-methoxyiminoacetamido]-3- [(5-methyl-2H-tetrazol-2-yl)methyl]-8-oxo-5-thia-1-azabicyclo[4.2. 0]oct-2-ene-2-carboxylic acid (T-2525), is mainly absorbed from the intestinal tract and biotransformed to T-2525 thereafter. General pharmacological activities of T-2588 were studied and following results were obtained. On the central nervous system, T-2588 did not show any effects at oral doses of 500-2,000 mg/kg and T-2525 produced only a slight elevation of body temperature in rabbits without any other effects at an intravenous dose of 500 mg/kg. On the respiratory and cardiovascular systems, T-2525 caused a slight hypotension and increased both respiratory rate and femoral blood flow, but no changes were observed in heart rate and electrocardiogram in dogs at an intravenous dose of 500 mg/kg. The T-2525 exerted no significant influence on blood pressure response to isoproterenol, acetylcholine or histamine, but showed a slight tendency to decrease pressor response to adrenaline in dogs at intravenous doses of 100-500 mg/kg. For the renal function in rats, T-2588 had no effects on urine volume, electrolytes and PSP excretion at oral doses of 500-2,000 mg/kg. Intravenous administration of T-2525 caused an increase of sodium excretion at 500 mg/kg and dose-dependent increases of PSP excretion at 20-500 mg/kg. Hematological studies revealed that both T-2588 at oral doses of 500-2,000 mg/kg and T-2525 at intravenous doses of 100-500 mg/kg had no effects on bleeding time in mice, blood coagulation and platelet aggregation in rats. The T-2588 exerted no effect on the gastrointestinal system in rats or mice and had no antiinflammatory activity in rats at oral doses of 500-2,000 mg/kg. The T-2525 scarcely affected the motilities of isolated smooth muscle preparations in experimental animals including stomach, ileum, colon, uterus, vas deferens and trachea at a concentration as high as 10(-3) g/ml. The T-2525 increased bile secretion in rats at intravenous doses of 100-500 mg/kg. The T-2525 slightly decreased the twitch tension of musculus gastrocnemius induced by electrical stimulation in rats at an intravenous dose of 500 mg/kg. These results indicate that T-2588 is a pharmacologically inactive antibiotic.     

Effect of Oriental Plant Drugs on Platelet Aggregation II1. Effect of Qian-Hu Coumarins on Human Platelet Aggregation.

Five kinds of furo- and pyrano-coumarins isolated from Chinese Drug "Qian-Hu", the root of PEUCEDANUM DECURSIVUM Maxim. (= ANGELICA DECURSIVA Fr. et Sav.) and P. PRAERUPTORUM Dunn., and two kinds of furocoumarins isolated from ANGELICA EDULIS Miyabe were tested on their effects on human platelet aggregation induced by 2 microM ADP. Nodakenin ( 1) and nodakenetin ( 2) were found to show the most inhibitory activity against both primary and secondary wave of aggregation induced by 2 microM ADP. Ae-II (= vaginidin) ( 3) and Ae-III (= isopeucenidin) ( 4) showed inhibition against only secondary wave aggregation. Pd-C-V ( 6) and Pd-Ia ( 7) were rather promotive in the primary wave aggregation. Pd-C-II ( 5) and dicoumarol ( 8) showed no activity. Coumarin ( 9) and umbelliferone ( 10), a biosynthetic intermediate of Qian-Hu coumarins, showed also strong activity on primary and secondary platelet aggregation.     

Antiplatelet and antithrombotic effect of D-003.

D-003 is a mixture of higher primary aliphatic saturated acids purified from sugar cane wax whose main component is octacosanoic acid followed by triacontanoic, dotriacontanoic, and tetratriacontanoic acids. The aim of this study was to evaluate the effects of D-003 on: ex vivo platelet aggregation, arterial thrombosis and bleeding time in rats. In addition, time course of antiplatelet effects of D-003 was also investigated on ex vivo platelet aggregation in guinea-pigs. D-003 (25-200 mg kg(-1)) orally administered at single or repeated doses (3 days) inhibited platelet aggregation induced by collagen (2.2 microg ml(-1)) and ADP (2 micromol l(-1)) in rats, and collagen (0.25 microg ml(-1)) induced aggregation in guinea-pigs in a dose-dependent manner. Single doses of D-003 (5-500 mg kg(-1)) administered orally 2 h before induction of arterial thrombosis significantly inhibited the reduction of rectal temperature. D-003 administered at a single dose (50-200 mg kg(-1)) 2 h before the experiment significantly increased the bleeding time in a dose-dependent manner. The time-course effects of D-003 on platelet aggregation, arterial thrombus formation, and bleeding time showed no effect 0.5 h after dosing, and maximal effects exhibited 1-2 h after treatment, whereas no significant effects were found 4 h after treatment.     

Aspirin in Cardiovascular Disorders

Clinical trials of aspirin (acetylsalicylic acid) for cardiovascular disorders have employed doses defined for other pharmacological effects of the drug (such as analgesic effects). Antioxidant and anti-inflammatory mechanisms with different dose-response relationships may contribute to the clinical effect of aspirin in cardiovascular disease. The optimal aspirin dose remains uncertain. Although the difference between 325 mg/day and 81 mg/day of aspirin sounds trivial, finding an optimal aspirin dose has enormous potential to reduce ischemic events. Large aspirin doses have not been associated with proportionally greater benefit. For patients with ischemic heart disease, overall consensus defines a range between 75 and 160 mg/day for the secondary prevention of myocardial infarction, stroke, and vascular death. Any benefit of aspirin must be measured against its adverse effects, principally gastrointestinal hemorrhage. The potential for adverse bleeding events may be lower with a 81mg dose, while maintaining clinical benefit. Although current aggregate data is reassuring about aspirin administration, it is increasingly clear that existing aspirin studies are insufficient to conclusively determine an optimal aspirin dose. Platelets can be activated by pathways that are not blocked by aspirin, and the dose of aspirin needed to fully suppress platelet aggregation may be higher in some patients as a result. Higher doses of aspirin than are currently used (75-325 mg/day) may be required in these patients to achieve desired antithrombotic effects. Better understanding of aspirin-resistant populations will facilitate identification of patients who require higher aspirin doses or alternative forms of antiplatelet therapy.     

Effects of Chinese drugs "xiebai" and "dasuan" on human platelet aggregation (Allium bakeri, A. sativum)

Adenosine (1), guanosine (2), and tryptophan (3), as well as beta-sitosterol beta-D-glucoside (4) were isolated from the n-butanol-soluble fraction of Xiebai, the tuber of Allium bakeri Reg., which was recognized to have an anti-platelet aggregation effect. Moreover, 1 and 2 were also isolated from the n-butanol-soluble fraction of Dasuan, the tuber of A. sativum L. Compound 1 showed a significant inhibitory activity against both the primary and secondary wave aggregation of human platelet induced by 2 microM ADP, whereas compounds 2-4 showed no or very low inhibitory effects. The structure-activity relationships on human platelet aggregation with regard to 1, 2 and their derivatives, adenosine 2'-monophosphate (5), adenosine 5'-monophosphate (6), adenosine triphosphate (7), guanosine 3'-monophosphate (8), and guanosine 5'-monophosphate (9), and guanylyl(3'----5')adenosine (10) are discussed. Compounds 5-7 and 10 also inhibited the primary and secondary wave aggregation with a dose-dependent response.     

Effect of acetylsalicylic acid on plasma thromboxane B2 and platelet aggregation in man

The effect of acetylsalicylic acid (ASA) on plasma thromboxane A2 (TXA2) and platelet aggregation was studied in 12 healthy, non-smoking, male students, in a double-blind, cross-over study, after single doses and 14-days on ASA 50, 100, 250 and 1000 mg/day. Platelet production of TXA2 was assessed by measuring the thromboxane B2 (TXB2) content of clotted venous blood by RIA. Platelet aggregation induced by ADP and adrenaline was studied by the method of Born. All doses of ASA completely suppressed the production of TXB2 within 3 h, with the exception of the 50 mg dose, which effected only 61% suppression (p less than 0.001). After administration for 14 days the suppression was complete, even including the lowest dose. At that time ASA had blocked the secondary phase of adrenaline- and ADP-induced platelet aggregation. It is concluded that the maximal antithromboxane and antiaggregatory effects, which last for at least 24 h, can be achieved by continuous daily administration of ASA 50 mg.     

General pharmacology of nizatidine in animals

Nizatidine (N-[2-[[[2-[(dimethylamino)methyl-4-thiazolyl]- methyl]thio]ethyl]-N'-methyl-2-nitro-1,1-ethenediamine, LY139037, Axid) is a novel, potent, and selective H2-antagonist. The potential secondary pharmacologic effects of this agent on the cardiovascular, respiratory, gastrointestinal, renal, hepatic, autonomic, and central nervous systems as well as effects on circulating blood glucose and the acute inflammatory response were examined. Nizatidine was generally inactive in the tests conducted in mice, rats, guinea pigs, rabbits, and dogs. Nizatidine and the reference H2-antagonist, cimetidine, both produced effects upon the cardiovascular and respiratory systems by intravenous administration in anesthetized dogs at doses in excess of the intended clinical exposure. In summary, these studies confirm the selective pharmacologic activity of nizatidine and indicate a low potential for secondary pharmacologic side effects to be encountered clinically.     

Pharmacokinetics and pharmacodynamics of Ro 44–3888 after single ascending oral doses of sibrafiban, an oral platelet aggregation inhibitor, in healthy male volunteers

AIMS: This study constituted the first administration of the oral platelet inhibitor, sibrafiban, to humans. The aim was to investigate the pharmacokinetics and pharmacodynamics of Ro 44-3888, the active principle of sibrafiban, after single ascending oral doses of sibrafiban. Particular emphasis was placed on intersubject variability of the pharmacokinetic and pharmacodynamic parameters of Ro 44-3888. METHODS: The study consisted of three parts. Part I was an open ascending-dose study to determine target effect ranges of sibrafiban. Part II, a double-blind, placebo-controlled, parallel-group study, addressed the intersubject variability of pharmacokinetic and pharmacodynamic parameters of the active principle at a sibrafiban dose achieving an intermediate effect. Part III was a double-blind, placebo-controlled, ascending-dose design covering the complete plasma concentration vs pharmacodynamic response curve of sibrafiban. RESULTS: At sibrafiban doses between 5 mg and 12 mg, the pharmacokinetics of free Ro 44-3888 in plasma were linear whereas those of total Ro 44-3888 were non-linear because of the saturable binding to the glycoprotein IIb-IIIa receptor. Saturation of the GP IIb-IIIa receptor was reached at plasma concentrations of 15.9 ng ml-1. At sibrafiban doses up to 2 mg, ADP-induced platelet aggregation was inhibited by 50%, whereas the inhibition of TRAP-induced platelet aggregation was about 20-30%. At the higher doses, ADP-induced platelet aggregation was almost completely inhibited while a clear dose-response could be observed with TRAP-induced inhibition of platelet aggregation at sibrafiban doses of 5 to 12 mg. Ivy bleeding time increased very steeply with dose with a significant prolongation observed at doses of 5 to 7 mg of sibrafiban (5-7 min, >30 min in one case). At a sibrafiban dose of 12 mg, the stopping criterion for dose escalation (prolongation of the Ivy bleeding time >30 min in three out of four subjects per dose group) was reached. The interindividual coefficients of variation of the integrated pharmacokinetic and pharmacodynamic parameters (AUC and AUE) were below 20%, thus lying well within the pre-set level of acceptance. CONCLUSIONS: With a low intersubject variability of its pharmacokinetic and pharmacodynamic parameters, linear pharmacokinetics and pharmacodynamic effects closely related to its plasma concentrations, Ro 44-3888 has good pharmacological prerequisites for a well controllable therapy of secondary prevention of arterial thrombosis in patients with acute coronary syndrome.     

General pharmacological studies on N-(2,6-dimethylphenyl)-8-pyrrolizidineacetamide hydrochloride hemihydrate. 3rd communication: effect on cardiovascular system

In this general pharmacological study of N-[2,6-dimethylphenyl)-8-pyrrolizidineacetamide hydrochloride hemihydrate (SUN 1165), its effects on the cardiovascular and respiratory systems were studied. SUN 1165, at doses of up to 1.0 mg/kg i.v., had almost no effect. SUN 1165, at doses of 3.0 and 6.0 mg/kg i.v., caused dose-dependent decreases in blood pressure, common carotid, vertebral, coronary, hepatic and femoral artery and portal vein blood flows, cardiac contractility, heart rate and myocardial oxygen consumption. SUN 1165 increased urine volume and urinary excretion of electrolytes in rats at a dose of 100 mg/kg p.o. SUN 1165 decreased renal plasma flow and urinary excretion of electrolytes in anesthetized dogs at 6.0 mg/kg i.v., but at the antiarrhythmic doses (1.0-3.0 mg/kg i.v. in dogs), it had almost no effects on renal function. SUN 1165 had almost no effect on the autonomic nervous systems in anesthetized dogs. These results suggest that SUN 1165 at the antiarrhythmic doses do not have any effects on the respiratory and cardiovascular systems, renal function and autonomic nervous systems in rats and dogs, but that when administered at high doses, it has inhibitory effects on respiratory and cardiovascular system and renal function. In conclusion, SUN 1165 seems to be a novel antiarrhythmic drug relatively free of cardiovascular, respiratory, renal and autonomic effects.     

Inhibitory effect of oral WEB 2086, a novel selective PAF-acether antagonist,on ex vivo platelet aggregation

Summary WEB 2086 is a novel PAF-acether antagonist, whose pharmacological action in man has only been preliminarily defined. Twelve healthy male volunteers received oral doses of 5, 30 and 90 mg and over the following 24 h inhibition of 5 × 10^–8 M PAF-acether-induced platelet aggregation ex vivo was studied as an indicator of pharmacological activity.WEB 2086 inhibited PAF-acether-induced platelet aggregation in all the doses tested, with the maximum effect 1 to 2 h after administration. After 2 h 5- 30- and 90-mg doses caused, respectively, 87, 98 and 100% inhibition. The magnitude and duration of the inhibitory effect was dose-dependent, with a significant action still detectable 10 h after administration of all three doses, and 12 h after administration of the two highest doses (30 and 90 mg).The subjects did not complain of any significant adverse effect and all completed the study.     

Modulation of arachidonate metabolite generation in human blood by oral defibrotide.

Acute intravenous administration in man of defibrotide (CAS 83712-60-1), a polynucleotide derivative, induces increase of 6-keto-PGF1 alpha and PGE2 production from appropriately stimulated whole blood. In the present study including acute and chronic experiments, defibrotide (Prociclide) orally administered during two weeks to healthy volunteers significantly increased the amounts of 6-keto-PGF1 alpha generated after appropriate stimulation in whole blood and in a neutrophilic leukocytes-platelet suspension. Similar effects were observed for PGE2, while TXB2 production was unchanged. Furthermore, platelet aggregation induced by calcium ionophore A23817 and production of leukotriene B4 from whole blood and isolated polymorphonuclear neutrophils were inhibited. The observed results suggest that defibrotide is biochemically active also by the oral route although the pharmacological and clinical value of the observed changes needs to be assessed.     

Activation of platelets and of fibrinolysis by venous occlusion in healthy volunteers and influence of suloctidil in comparison with placebo

The effect of venous occlusion on blood fibrinolytic activity and platelet activation was studied in 10 normal human volunteers. The procedure was used as a model to study the pharmacological effects of 1-(4-isopropylthiophenyl)-2-n-octylaminopropanol (suloctidil, Sulocton) in a double-blind cross-over trial comparing suloctidil 200 mg three times per day versus identical placebo, each given for one week at random, after an initial one-week placebo run-in; blood sampling was done at the end of each period. Statistically significant changes in plasminogen, alpha 2-anti-plasmin, fibrinogen and antithrombin-III were consistently obtained on each occasion and could be ascribed to local haemoconcentration while a much higher increase of plasminogen activator activity occurred. The influence of venous occlusion on plasma beta-thromboglobulin and platelet factor-4 levels was found to be less consistent and under the trial conditions no obvious difference between the regimens studied could be objectified. On the contrary platelet aggregation by collagen was significantly reduced at the end of the suloctidil period.     

Differences in the influence of the interaction between acetylsalicylic acid and salicylic acid on platelet function in whole blood and isolated platelets: influence of neutrophils.

The aim of this study was to characterize the influence of the interaction between acetylsalicylic acid (ASA) and salicylic acid (SA) on the inhibition by ASA of platelet aggregation in platelets isolated from whole blood, and to determine whether leukocytes influence this pharmacological interaction. This in vitro study was done in human blood from which we prepared samples of whole blood, platelet-rich plasma (PRP), PRP plus mononuclear leukocytes, and PRP plus neutrophils. The variables recorded were maximum platelet aggregation intensity, thromboxane B2 (TxB2) production, and nitric oxide (NO) production (N=10 different samples in each type of experiment). Different concentrations of ASA and SA were incubated with all samples. In PRP, the concentration of ASA that inhibited maximum aggregation by 50% (IC50) (281+/-16microM) increased with increasing SA concentration to a maximum of more than 2mM when 500microM SA was used. In whole blood, the IC50 for ASA (24.9+/-1.2microM) decreased with decreasing SA concentrations to 7.9+/-0.8microM with 50microM SA and 15.6+/-0.9microM with 125microM SA, and increased to 46.2+/-2.6microM with 250microM SA and 96.3+/-7.2microM with 500microM SA. In experiments with PRP+neutrophils the IC50 of ASA increased in the presence of all concentrations of SA. The antagonistic interactions were also reflected in the changes in TxB2 production in all samples. In samples of neutrophils incubated with ASA, the curve for NO production was shifted to the right, a finding that paralleled the changes in platelet aggregation. In conclusion, the influence of the interaction between ASA and its metabolite SA on platelet aggregation difference depending on the type of sample, and was antagonistic in PRP but partially agonistic in whole blood. Nitric oxide synthesis showed an additive effect of the two compounds.     

The effects of PGE2 and CL 115,347, an antihypertensive PGE2 analogue, on human blood platelet behaviour and vascular contractility

The effects of prostaglandin E2 (PGE2) and an antihypertensive PGE2 analogue, CL 115,347 (d,l-15-deoxy-16-hydroxy-16 (alpha/beta)-vinyl prostaglandin E2 methyl ester), were examined on human blood platelet behaviour in platelet-rich plasma (PRP) and in whole blood (WB). The effects on baseline tone of isolated human carotid arterial strips were also examined. PGE2 had a biphasic effect on platelet behaviour, potentiating ADP- and collagen-induced aggregation at low concentrations (10(-8)-10(-6) M) and inhibiting aggregation at higher concentrations (10(-5) M). In contrast, low concentrations of CL 115,347 (10(-9)-10(-5) M) had no effect on platelet aggregation and higher concentrations (10(-4) M) potentiated ADP- and collagen-induced aggregation. The effects of PGE2 and CL 115,347 on adrenaline-induced aggregation were different to those of the other aggregating agents since only inhibition of platelet aggregation was observed. In the presence of PGI2 (10(-9)-10(-8) M) however, PGE2 (10(-8)-10(-6) M) was able to potentiate both ADP- and adrenaline-induced aggregation. Results obtained in WB were similar to those obtained in PRP. Both PGE2 and CL 115,347 contracted isolated human carotid arterial strips in a dose-dependent manner, with PGE2 being approximately 20 times more potent than its synthetic analogue. These results indicate that CL 115,347 is less potent than PGE2 in its effects on human blood platelet behaviour and vascular contractility in vitro.