New galanin(1-15) analogues modified in positions 9, 10 and 11 act as galanin antagonists on glucose-induced insulin secretion.

Galanin (GAL) is a 29-amino-acid residue peptide originally isolated from porcine upper small intestine. GAL exhibits various physiological activities, such as effects on hormones release, smooth muscles contractions, gastric acid secretion, neurons degeneration and feeding. One of the biological actions of GAL is the inhibition of insulin secretion from the pancreatic beta-cells. In our studies we have designed several new 15-amino-acid-residue galanin fragment analogues modified in positions: 6, 8, 9, 10, 11 and tested for their effects on glucose-induced insulin secretion from isolated rat pancreatic islets of Langerhans. In vitro insulin secretion was studied during static incubation. All peptides were tested at two concentrations: 0.1 microM and 1 microM. Among the analogues derived from GAL(1-15)NH(2) peptide: [Phe(9)]GAL(1-15)NH(2) and [Pro(11)]GAL(1-15)NH(2) were found to be the potent antagonists against the inhibitory effect of GAL on glucose-induced insulin secretion from the isolated rat pancreas. These analogues block the GAL-mediated inhibition of insulin secretion. The present studies have shown that analogues: [Phe(9)]GAL(1-15)NH(2) and [Pro(11)]GAL(1-15)NH(2) may be a key compounds for developing a more potent GAL antagonists.

Salutary effects of tachykinin receptor antagonists in a rat model of postoperative ileus.

BACKGROUND: Postoperative ileus (PI) is a common surgical complication treated mainly with supportive measures. Tachykinins control gastrointestinal motility and modulate somatic and visceral pain sensation; therefore, the effect of tachykinin receptor antagonists in a rat model of PI using NK(1-3) antagonists, SR140333, SR48968, and SR142801, was investigated. MATERIALS AND METHODS: Intestinal transit was measured as Evans blue migration after varied nociceptive stimuli: skin incision (SI), laparotomy (LAP), or laparotomy plus gut manipulation (L + M) in anesthetized rats. RESULTS: Diethyl ether anesthesia and SI did not influence the intestinal transit of the dye in comparison to untreated animals--UN: 61.17 +/- 5.47, 62.10 +/- 8.30, and 56.70 +/- 4.10 cm, respectively. In contrast LAP and L + M have significantly reduced intestinal motility to 26.40 +/- 2.07 and 9.70 +/- 1.15 cm, respectively. SR140333 (3-30 microg/kg), SR48968 (1-30 microg/kg), and SR142801 (3-10 microg/kg) reversed the additional inhibitory effects of gut manipulation subsequent to LAP dose-dependently, the dye transit returning with the use of the most effective antagonist doses up to 25.28 +/- 1.08, 21.70 +/- 0.19, and 25.0 +/- 1.34 cm. The combinations of submaximal doses of NK(1) and NK(3), NK(2) and NK(3) and NK(1), and NK(2) and NK(3) antagonists were not more effective than a single-agent regimen. On the other hand SR140333 and SR48968 (NK(1) + NK(2) antagonists) acted additively, the intestinal transit reaching 26.60 +/- 0.85 cm. SR140333, SR48968, and SR142801 have not affected the intestinal passage in UN rats or those undergoing SI or LAP. CONCLUSIONS: SR140333, SR48968, and SR142801 exert a salutary action on suppressed gut motility following surgical manipulation of the gut, the combination of NK(1) and NK(2) antagonists being most beneficial.

The contractile effects of several substituted short analogues of porcine galanin in isolated rat jejunal and colonic smooth muscle strips.

The activity of short porcine galanin (Gal) analogues was tested in vitro using rat jejunal and colonic smooth muscle strips. Peptides evoked concentration-dependent tissue contractions yielding typical response curves in concentration range from 0.3 nM to 300 microM, with a characteristic fall-down effect at the supramaximal concentrations. Gal(1-15) was less potent than Gal(1-29). Furthermore, [D-Trp(2)]Gal(1-15), [endo-Trp(2),Cle(4)]Gal(1-15), [D-Leu(4)]Gal(1-15), [des-Leu(4)]Gal(1-15), [Hse(6)]Gal(1-15), [Dab(14)]Gal(1-15), [Dpr(14)]Gal(1-15) or [Arg(14)]Gal(1-15) showed a considerable decrease in potency compared to Gal(1-15) in jejunal and/or colonic smooth muscle cells. Functional evidence confirmed that the integrity of both N- and C-terminals must be preserved in order to preserve a full excitatory myogenic potential of the peptide in rat jejunum and colon. Besides, amino acids located in positions 2, 4, 6 and 14 play a crucial role in recognition and activation of molecular domains responsible for Gal action in the intestinal smooth muscle.

Synthesis and biological properties of new chimeric galanin analogue GAL(1-13)-[Ala10,11]ET-1(6-21)-NH2.

Several chimeric peptides consisting of the N-terminal fragment of galanin (GAL) and C-terminal fragments of other bioactive peptides (e.g. substance P, bradykinin, neuropeptide Y, mastoparan) have been synthesized and reported as high-affinity galanin receptor antagonists. Recently we have synthesized a new chimeric peptide, GAL(1-13)-[Ala(10,11)]ET-1(6-21)-NH(2), consisting of the N-terminal fragment of GAL and the C-terminal fragment of endothelin-1 (ET-1) analogue. This chimera was previously shown to be a moderate-affinity ligand to hypothalamic galanin receptors with a K(D) value of 205 nM. However, its biological action has been unknown so far. In our studies we characterized the biological properties of this new chimeric analogue, investigating its action on rat isolated gastric smooth muscles and influence on insulin secretion from rat isolated islets of Langerhans. Data acquired in the course of our studies suggest that analogue GAL(1-13)-[Ala(10,11)]ET-1(6-21)-NH(2) does not seem to be a potent galanin receptor antagonist in the gastrointestinal tract.

The role and interactions of nitric oxide (NO), carbon monoxide (CO), and prostanoids in the pathogenesis of postoperative ileus in rats.

The effects of heme oxygenase (HO) inhibitors, zinc-protoporphyrin-IX (ZnPP-IX), and tin protoporphyrin-IX (SnPP-IX) and their interactions with L-arginine/nitric oxide synthase (NOS) and cyclooxygenase (COX) pathways were investigated in postoperative ileus in rats. Intestinal transit was measured as Evans blue migration after skin incision, laparotomy or laparotomy plus gut evisceration and handling. Laparotomy and small intestinal manipulations increased blood plasma nitrites/nitrates level 1.88-fold. N(omega)-nitro-L-arginine methyl ester, indomethacin, a selective COX-1 blocker (resveratrol) and COX-2 antagonists (nimesulide, DuP-697, NS-398) reversed the additional inhibitory effects of gut manipulation subsequent to laparotomy. In contrast, N-(3-(aminomethyl)benzyl)acetamidine or S-methylisothiourea, highly selective inducible NOS blockers, remained ineffective. ZnPP-IX and SnPP-IX overturned the effects of laparotomy on dye propulsion, but were only partially effective after laparotomy and gut handling attenuating the additional inhibitory influences of gut manipulation, the intestinal transit reaching 89.21%, 92.87%, 53.46%, and 48.56% of respective controls transit. Salutary effects of L-NAME, ZnPP-IX, and SnPP-IX were dose-dependent, L-arginine or hemin (HO substrate) sensitive. Administration of indomethacin and resveratrol subsequent to SnPP-IX reversed the inhibitory effects of laparotomy and manipulation, amounting to 93.91% and 87.43% of controls. On the other hand, L-NAME injected after SnPP-IX abolished the salutary effects of the latter, study dye migration reached 25.18% of control rat. Therefore we demonstrated that nitric oxide, carbon monoxide, and prostanoids play a role in the pathogenesis of postoperative ileus albeit in different mechanisms. Laparotomy stimulated HO activity, whereas gut manipulation led to an excessive constitutive NOS stimulation accompanied by augmented prostanoid synthesis by COX-1. Unaffected synthesis of either NO or CO enables a return of gastrointestinal transit during postoperative period, whereas a pharmacological blockade of two complementary metabolic pathways provides a most effective measure against postoperative ileus development.

Antiaggregatory activity of hypoglycaemic sulphonylureas.

AIMS/HYPOTHESIS: Vascular complications observed in diabetes are often related to altered platelet functions. The most widely used hypoglycaemic drugs for treating Type II (non-insulin-dependent) diabetes mellitus are sulphonylurea derivatives. The purposes of this study were to evaluate the inhibitory effects of hypoglycaemic agents on platelet aggregation, to measure their lipophilicity and identify their structural parameters which assess their antiaggregatory activity. METHODS: An antiaggregatory test in vitro was carried out for 13 sulphonylurea derivatives. Aggregation of platelets, incubated with the agents at concentrations varying from 7.5 to 480 micromol/l, was induced by 10 micromol/l ADP. Drug lipophilicity parameter, log k(w), was measured by gradient HPLC and the agents were subjected to molecular modelling. RESULTS: The most pronounced inhibition of platelet aggregation was by glimepiride, gliclazide, gliquidone, glibenclamide and compound 2A. The IC(25) values were 15.9, 18.6, 20.4, 28.5 and 34.7 micromol/l, respectively. Quantitative structure-activity relationships indicate that antiaggregatory activity is mainly affected by electronic and not by lipophilic properties of the agents. CONCLUSION/INTERPRETATION: Glimepiride appeared to be a more potent ADP-induced platelet aggregation inhibitor in vitro than gliclazide. Antiaggregatory activity was shown for gliquidone and confirmed for glibenclamide. The QSAR analysis supports the hypothesis of a free radical mechanism of action of sulphonylurea derivatives previously suggested for gliclazide.

CGP 41251, a new potential anticancer drug, improves contractility of rat isolated cardiac muscle subjected to hypoxia.

The aim of the present work was to examine the effects of 4'-N-benzoyl staurosporine (CGP 41251), a protein kinase C inhibitor with broad antiproliferative activity in many cell lines, on the rat isolated heart contractility under normoxic and hypoxic conditions. Additionally, we examined the effects of CGP 41251, WB-4101 (alpha1a -adrenoceptor antagonist), chloroethylclonidine (CEC) (alpha1b-adrenoceptor antagonist) and selective damage of endocardial endothelium by Triton X-100 on the protection against hypoxia induced by preconditioning of rat heart tissue. Experiments were performed on rat isolated left ventricular papillary muscle. The following parameters were measured: force of contraction (Fc), velocity of contraction (+dF/dt) and velocity of relaxation (-dF/dt). The temperature of the bath solution was 37 degrees C +/- 0.5 degrees C, and rate of electrical stimulation was 0.5 Hz. At concentrations less than 1 microM CGP 41251 did not cause any changes in contractility of rat heart. At 1 and 3 microM, significant positive inotropic action was observed. Treatment of rat papillary muscle by CGP 41251 at 3 microM reduced decreasing of contractility by simulated hypoxia and reperfusion. Moreover, protective effects of preconditioning was not affected by addition of CGP 41251 neither at 1 nor at 3 microM. Pretreatment with CEC at 3 microM, and selective damage of endocardial endothelium induced by fast (1-s) immersion of papillary muscle in 0.5% Triton X-100, but not pretreatment with WB-4101, abolished the protective effects of preconditioning. The results imply that CGP 41251 improves contractility of heart muscle under normoxic and hypoxic conditions, and does not alter hypoxic preconditioning in rat isolated cardiac tissue. Moreover, it was shown that alpha1b-adrenoceptors and endocardial endothelium are involved in triggering of preconditioning in rat isolated heart muscle.

Increased potency of some substituted short peptide analogues in comparison to galanin(1-15)-NH(2)in rat fundus strips.

The activity of short porcine galanin (Gal) analogues was tested in vitro using rat gastric fundus strips. The peptides contracted longitudinal smooth muscle in a concentration-dependent manner with the following order of potency: Gal(1-29) >[Cit(14)]Gal(1- 15) >[Asp(14)]Gal(1- 15) >[Dab(14)]Gal(1- 15) >[Nle(14)] Gal(1-15) >[Dpr(14)]Gal(1- 15) >[Arg(14)]Gal(1- 15) >[Orn(14)]Gal(1- 15) >Gal(1-15). Only in the case of two peptides, namely [Cit(14)]Gal(1-15) and [Dab(14)]Gal(1-15) did the values of Hill coefficients, estimated from the appropriate concentration-contraction curves, differ significantly from unity. Our results indicate that both N- and C-terminals of Gal molecule contribute towards the affinity and activity of Gal in rat gastric smooth muscle cell receptors, indicating that their integrity is essential for its full excitatory myogenic action. The substitution of histidine with citruline, aspartic acid, norleucine or diaminobutyric acid in position 14 of the amino acid chain led to a considerable increase in potency, suggesting that amino acids located at this position might play a crucial role where the strength of short analogues is concerned.

Actions of several substituted short analogues of porcine galanin on isolated rat fundus strips: a structure-activity relationship.

The activity of porcine galanin (Gal) fragments and analogues were tested in vitro using rat gastric fundus strips. The peptides contracted longitudinal smooth muscle in a concentration-dependent manner with the following order of potency: [Nle4]Gal(1-15), Gal(-15), [Cle4]Gal(1-15), [Hse6]Gal(1-15), [Va14]Gal(1-15), [Ile4]Gal(1-15), [endoTrip2a, Cle4]Gal(1-15), [desThr3, Cle4]Gal(1-15), [D-Leu4] Gal(1-15), [desLeu4]Gal(1-15). On the contrary [desTrp2, Val4]Gal (1-15) remained inactive up to 10 microM. The values of Hill's coefficients estimated from the appropriate concentration-contraction curves for all analogues except for [Val4]Gal(1-15), [Hse6]Gal(1-15), [endoTrp2a,Cle4]Gal(1-15), [desLeu4]Gal(1-15) and [D-Leu4] Gal(1-15) did not significantly differ from unity. Our results indicate that the integrity of the first four N-terminal amino acids of Gal molecule is essential for the full excitatory myogenic action of the peptide in rat gastric fundus. Similarly, substitution, addition or deletion of amino acid residues in positions two, three, four and six can considerably influence the ability of Gal analogues to interact with Gal receptors. The data acquired in the course of our structure-activity study suggest that both N- and C-terminals of Gal molecule contribute towards the affinity and activity of Gal in rat gastric smooth muscle cell receptors.

Synthesis and hypolipidemic and antiplatelet activities of alpha-asarone isomers in humans (in vitro), mice (in vivo), and rats (in vivo).

A series of alpha-asarone isomers was synthesized and investigated for their hypolipidemic and antiplatelet activity. Considering the hypolipidemic activity in rats at a dose of 80 mg/kg/day, some isomers were more potent than clofibrate at 150 mg/kg. Compound 3 was one of the most active agents elevating the HDL cholesterol level by 56% and lowering the LDL cholesterol level by 46.8% in rats after 7 days of administration. The activities of the platelet aggregation test in vitro were significant but lower than those of the reference substances (indomethacine and acetylsalicylic acid). In the pulmonary thromboembolic in vivo test in mice, two compounds (alpha-asarone (6) and compound 4) produced significant antithrombotic effects at 100 mg/kg, namely 44% and 52% protection against lung microembolia, respectively. alpha-Asarone derivatives form a new group of potential hypolipidemic and/or antithrombotic agents. The compounds 3, 4, and 6 may serve as lead substances whose structural modifications may result in original drugs.

The inhibitory effects of terikalant on the contractile activity of galanin in isolated rat fundus strips.

The maximal responses (E(max)s) of isolated rat gastric fundus strips to 300 n m porcine galanin (Gal) were decreased in a concentration-dependent manner by terikalant (RP 62719). EC(50)of the agent equalled 4.39 microm (2.35-8.22). On the contrary the action of 30 n m of carbachol were not affected by the modulator in concentrations up to 30 microm. It is concluded that potassium currents may contribute to the modulation of Gal myotropic activity in the gut.

Synthesis, structure and antiaggregatory effects of some N-(4,5-dihydro-1H-imidazol-2-yl)indoles.

A series of 1-(4,5-dihydro-1H-imidazol-2-yl)indole derivatives was prepared in order to evaluate their antiaggregatory activity in human platelets. The compounds 4a-m were prepared by reacting N-aryl-N-(4,5-dihydro-1H-imidazol-2-yl)hydroxylamines (2a-d) with monosubstituted acetylene derivatives 3a-b. Imidazoline derivatives 4 were further acetylated or sulfonylated to give amides 5a-c and sulfonamides 6a-c and 7a-c, respectively. Eight compounds were taken as representative aryliminoimidazoline analogs. Among them only one, 4m, showed a good concentration-dependent action against the primary or alpha 2-adrenoreceptor mediated phase of noradrenaline-induced aggregation in platelets.

Different mechanisms of positive chronotropic actions of isoprenaline and noradrenaline on isolated guinea pig right atria revealed by pretreatment with rilmakalim.

In this study we tested the influence of activation of ATP-sensitive K+ channels (KATP) on the changes in automatism induced by isoprenaline, noradrenaline and phenylephrine. Experiments were performed on the spontaneously beating right atria isolated from guinea pig. The rate of spontaneously beating preparations was measured under different experimental conditions. Rilmakalim (formerly HOE 234) was used as an activator of KATP channels. Isoprenaline induced significant, concentration-dependent positive inotropic action. This effect was strongly attenuated only in the presence of selective blockers of beta1- (metoprolol), but not beta2-adrenoceptor subtype (ICI 11855). Pretreatment with 4 microM rilmakalim resulted in a significant increase in the described effects of isoprenaline on automatism of isolated right atria. Phenylephrine (1 to 100 microM) in the presence of 1 microM propranolol, did not cause any changes in automatism of guinea pig right atria. Slight but significant positive chronotropic action induced by noradrenaline at lower concentrations (0.1 to 10 microM) in the presence of 1 microM propranolol was significantly decreased by pretreatment with rilmakalim. However, the effects obtained at higher concentrations (30 and 100 microM) of noradrenaline were enhanced. Interactions mentioned above were prevented by addition of 3 microM glibenclamide. The results imply that positive chronotropic effect of noradrenaline in the presence of propranolol is mediated by adrenoceptor subtype different from alpha1-, beta1- and beta2-adrenoceptors.

Sources of activator Ca2+ for galanin-induced contractions of rat gastric fundus, jejunum and colon.

Galanin (Gal) evoked reproducible contractions of isolated rat gastric fundus, colon and jejunum longitudinal strips in concentrations ranging from 1 nM to 3 microM. EC50 of Gal equalled 12.63, 23.27 and 56.02 nM, respectively. Hill's coefficients were not different from unity in any of the tissues examined. Experiments have been performed in the presence of protease and peptidase inhibitors, a variety of specific antagonists and tetrodotoxin (TTX) to exclude the non-specific stimulatory or inhibitory action of Gal. Gal-evoked contractions were attenuated by diminished extracellular Ca2+ concentration and by diltiazem. Gal activity in gastric fundus and colon, but not in jejunum was inhibited by depleting intracellular Ca2+ stores, thapsigargin, dantrolene, ryanodine, TMB-8, neomycin and U-73122. Our data confirmed that Gal contracts rat fundus, jejunum and colon by stimulating specific receptors, which are coupled both to Ca2+ influx through the voltage-dependent calcium channels and intracellular Ca2+ release from ryanodine- and IP3-sensitive stores (stomach and colon) or the extracellular Ca2+ influx only (jejunum). Phosphatidylinositol-specific phospholipase C (PI-PLC) plays a crucial role in the former but not in the latter signal transduction cascade.

Comparative study of antithrombotic and antiaggregatory activity of acetylsalicylic acid, ticlopidine and a new noncarboxylic acid antiinflammatory pyrazine derivative HF90.

The action of acetylsalicylic acid, ticlopidine and a new pyrazine derivative HF90 selected in preliminary screenings (11, 18, 19) was studied by using the mouse antithrombotic assay according to DiMinno and Silver (22) and in vitro blood platelet aggregation method according to Born (23). Acute pulmonary thromboembolism was induced by injection of a mixture of collagen and epinephrine into the mouse tail vein. The effect of HF90, an acidic pyrazine derivative possessing active methylene moiety, administered at doses of 50 and 100 mg/kg, was compared to the action of the well established antithrombotic agents: ticlopidine (100 mg/kg) and acetylsalicylic acid (20 mg/kg). The compounds were administered i.p. in single doses 1 h and 24 h before the thrombotic challenge or once a day per three consecutive days before the thrombotic challenge. Ticlopidine appeared to provide the better protection against microembolism than acetylsalicylic acid although its effect has not manifested itself immediately after administration. The pyrazine derivative examined has a lower but significant antithrombotic activity. The chemical class of pyrazine derivatives with active methylene moiety (the so called pyrazine CH/NH-acids) (16) provides a new original antiinflammatory pharmacophore and HF90 may serve as the "lead compound" in the search for new agents of pharmacological interest.

Synthesis, structure, and biological activities of some N-(4,5-dihydro-1H-imidazol-2-yl)-1,3-dihydrobenzimidazole derivatives.

A series of novel N-(4,5-dihydroimidazol-2-yl)-1,3-dihydrobenzimidazole derivatives 2a-d, 3a-d and 4a-p were prepared and their structure was determined by IR and NMR spectroscopic data as well as X-ray analysis of carbonitrile 2a. The compounds were studied as potential inhibitors of the human blood platelet aggregation induced by adrenaline or ADP. Compounds of type 3 proved efficacious for the reduction of arterial blood pressure upon intravenous administration to normotensive rats.

[Antagonists of glycoprotein IIb/IIIa as new antiplatelet agents]. / Antagonisci glikoproteiny IIb/IIIa jako nowe srodki przeciwplytkowe.

Blood platelets play an essential role in arterial thrombosis. Platelets activation starts from their binding to membrane receptors what results in consecutive biochemical reactions. Glycoprotein IIb/IIIa receptor of fibrinogen plays a key role in platelet aggregation. Inhibition of activity of glycoprotein IIb/IIIa-fibrinogen receptor complex could prevent thrombus formation by blood platelets. Antagonists of GPIIb/IIIa are synthetic peptides, integrelin, specific monoclonal antibodies and some nonpeptide substances.

Studies on pyrazine derivatives. XXX. Synthesis of pyrazinylamino-1,3-diazacycloalkanes of potential circulatory activity.

A series of pyrazinylamino-1,3-diazacycloalkanes was obtained by reaction of the corresponding substituted aminopyrazines with aliphatic amines. Selected compounds were studied with respect to their potential circulatory activity. The effect on the blood pressure, isolated rat tail artery and heart atria, and an influence on the human blood platelet aggregation were investigated.

Mydriasis elicited by imidazol(in)e alpha 2-adrenomimetics in comparison with other adrenoceptor-mediated effects and hydrophobicity.

alpha 2-Adrenoceptor agonists cause both mydriasis and platelet aggregation. This work is aimed at identifying the factors accompanying and affecting mydriatic activity. For eight imidazol(in)e drugs mydriatic, hypotensive and bradycardic activities were determined in rats. The lipophilicity of the agents was determined chromatographically and calculated theoretically. A correlation was found between the hypotensive and the bradycardic potency and between the mydriatic activity and both the hypotensive and bradycardic activity. Mydriatic activity depended on the lipophilicity of the agents studied. The human platelet antiaggregatory activity of the drugs did not correlate with either the mydriatic or cardiovascular activity and it was independent of lipophilicity. The dependence of the centrally induced effects on lipophilicity and the lack of such a dependence in the case of the in vitro alpha 2-adrenoceptor-mediated platelet aggregation may be interpreted as resulting from heterogeneity of the rat cerebral and the human platelet alpha 2-adrenoceptors. The alpha 2-adrenergic activity of drugs in the model of mydriasis in rats cannot be predicted from their activity in causing human platelet aggregation in vitro.

Comparative studies of antiplatelet activity of nonsteroidal antiinflammatory drugs and new pyrazine CH- and NH-acids.

Nine known nonsteroidal antiinflammatory drugs (NSAID) and three new pyrazine derivatives possessing an active methylene moiety (pyrazine CH/NH-acids) were tested with regards to their in vitro and in vivo antiplatelet activity. Concentrations of the agents were determined which caused 25% and 50% inhibition of aggregation of human blood platelets induced by fixed concentrations of ADP, collagen and epinephrine. The in vivo test consisted in determination of percent protection of mice from pulmonary microembolism caused by injection of a mixture of collagen and epinephrine. The in vitro antiaggregatory activity of the agents studied was rather low, excepting the inhibition of the collagen-induced aggregation by ketoprofen. Several NSAID and two new pyrazine CH/NH-acids appeared highly potent antithrombotic agents in vivo. Activity of NSAID expressed as percent protection against lung thromboembolism in the mouse was demonstrated to depend quantitatively on acid properties of the agents. The new chemical class of pharmacologically active agents, pyrazine CH/NH-acids, offers an original pharmacophore which is distinctive from the carboxylic or enolic functionalities typical for the established NSAID, and as such, may be devoid of some disadvantages of known antiplatelet drugs.