Inhibitory effect of OP-41483.alpha-CD, a prostacyclin analog, on peripheral vascular lesion models in rats.

The effect of a chemically stable prostacyclin analog, OP-41483 alpha-cyclodextrin clathrate (OP-41483.alpha-CD), on vascular lesions, platelet aggregation and blood pressure were examined and compared with those of prostaglandin E1 alpha-cyclodextrin clathrate (PGE1.CD) in in vivo rat models. 1) In the laurate (1 mg/leg, i.a.)-induced arterial thrombotic model, OP-41483.alpha-CD (1 microgram/kg/min, i.v.) prevented the progression of femoral arterial vascular lesions and enhanced the development of collaterals in the femoral artery. PGE1.CD did not inhibit the progression of vascular damages. 2) In the model of vasoconstriction induced by epinephrine (0.05 mg/tail, s.c.) and ergotamine (2 mg/kg, s.c.), OP-41483.alpha-CD and PGE1.CD, at 1 microgram/kg/min, inhibited the progress of of tail gangrene and lessened the decrease in tail cutaneous blood flow. 3) OP-41483.alpha-CD (1 microgram/kg/min) suppressed the ADP (0.1 mg/kg/min, i.v.)-induced decrease in the number of circulating platelets without affecting the change in blood pressure. In contrast, PGE1.CD (3 micrograms/kg/min) inhibited ADP-induced thrombocytopenia with a decrease in blood pressure. These results indicate that OP-41483.alpha-CD has antiplatelet and cutaneous blood flow improving activities that are greater than its hypotensive effect and may be of therapeutic potential in peripheral vascular diseases.     

Studies on antiplatelet effects of OP-41483, a prostaglandin I2 analog, in experimental animals. II. Mechanism of its antiplatelet effect

The mechanism for the inhibition of platelet functions by a prostaglandin I2 analog, OP-41483, was studied with guinea pig platelets. OP-41483, and PGI2 as well, inhibited aggregation, ADP release and thromboxane formation of platelets with IC50 values of 4.3-5.8 ng/ml and 0.6-0.9 ng/ml, respectively. The ligand binding study using [3H]-OP-41483 suggested that OP-41483 bound with different affinities to two classes of binding sites on platelets. The dissociation constant of OP-41483 for the higher affinity site corresponded to the IC50 values of its antiplatelet effect. PGI2 as well as OP-41483 displaced [3H]-OP-41483 previously bound to platelets, thus indicating that both agents exerted their antiplatelet effects by binding to the same site on platelets. OP-41483 and PGI2 activated adenylate cyclase and raised cyclic AMP levels in platelets. However, their inhibitory effect on platelet aggregation was not fully antagonized by an adenylate cyclase inhibitor, 2',5'-dideoxyadenosine (DDA), at a concentration completely inhibiting the increase of cyclic AMP. Moreover, this DDA-resistant effect of OP-41483 disappeared in the presence of calcium chloride (10(-4)-10(-3) M). OP-41483 and PGI2 inhibited thrombin-induced Ca++ influx into platelets. The inhibition of Ca++ influx was not reversed by DDA. Based on these results, we speculate that the inhibitory effects of OP-41483 and PGI2 on platelet functions are produced through dual mechanisms: one mediated by activation of adenylate cyclase and the other by an inhibition of Ca++ influx; and these two mechanisms seem to be independent of each other.     

Effect of a prostaglandin E1 derivative (OP-1206) and acetylsalicylic acid on electrically induced thrombosis in guinea-pig mesenteric artery and its modification by an inhibitor of prostaglandin I2 synthetase, tranylcypromine

The antithrombotic effect of a prostaglandin E1 derivative, OP-1206 (17S-20-dimethyl-trans-delta 2-PGE1) X alpha-cyclodextrin clathrate (OP-1206 X alpha-CD), was compared with that of acetylsalicylic acid (ASA) in a electrically induced thrombosis model of guinea-pig mesenteric arteries using intact animals and animals subjected to the superfusion of tranylcypromine (TC, 15 mM) over their mesentery. The drug-effect was assessed by the change of the threshold voltage for the thrombus formation. 1) TC (1.5-15 mM) lowered the threshold voltage, and the effect was comparable to its inhibitory effect on PGI2 formation in vitro, suggesting that PGI2 generated in mesenteric arteries acts to prevent thrombus formation. 2) In intact animals, OP-1206 X alpha-CD at doses of 0.01-0.3 mg/kg, p.o. (as OP-1206), significantly and dose-dependently elevated the threshold voltage. ASA (30-1000 mg/kg, p.o.) significantly elevated the threshold voltage, but the effect reached to its maximum at 100 mg/kg and lessened with further increase of ASA. 3) In TC-treated animals, OP-1206 X alpha-CD elevated the threshold voltage dose-dependently, but the elevation of threshold voltage by ASA reached to its plateau level which was significantly lower than that obtained with OP-1206 X alpha-CD at 0.3 mg/kg, indicating that the antithrombotic effect of ASA is incomplete in this model.(ABSTRACT TRUNCATED AT 250 WORDS)     

Changes in arachidonic acid-induced respiratory distress in streptozotocin-diabetic mice]

Using streptozotocin (STZ)-diabetic mice, we examined the respiratory distress induced by arachidonic acid. Male ddY mice were made diabetic by injecting STZ (170 mg/kg, i.p.) 2 weeks prior to the experiment. Control mice received the vehicle (citrate buffer, pH 4.6). The duration of respiratory distress was observed by a slow i.v.-injection of sodium arachidonic acid (AA) into the caudal vein of mice at the dose of 50 mg/kg. Aspirin was i.p.-administered 30 min before AA. OKY-046 (specific thromboxane A2 (TXA2) synthetase inhibitor), OP-41483 (stable prostacyclin analog) and 9, 11 epithia-11, 12-methano-TXA2 (STA2, stable TXA2 analog) were i.v.-administered 30 min before AA. The duration of respiratory distress induced by AA was significantly reduced in STZ-diabetic mice. Aspirin (10-50 mg/kg) and OKY-046 (25-100 mg/kg) enhanced the AA-induced respiratory distress in STZ-diabetic mice. OP-41483 (1-100 micrograms/kg) reduced the AA-induced effect in both control and STZ-diabetic mice. STA2 (10 micrograms/kg) enhanced the AA-induced effect in both control and STZ-diabetic mice. ONO-1078 (1-10 mg/kg) did not affect the AA-induced effect in both control and STZ-diabetic mice. TMK-688 (0.01-1 mg/kg) reduced the AA-induced effect in the control mice, but not in the STZ-diabetic mice. These results suggest an involvement of leukotriene in the respiratory response to AA in diabetic mice, especially when cyclooxygenase and TXA2 synthetase are inhibited.     

Protective effect of WEB 2086, a novel antagonist of platelet activating factor, in endotoxin shock

WEB 2086, a novel specific platelet activating factor (PAF) antagonist derived from triazolodiazepines, inhibited in a dose-related manner the hypotensive and lethal effect of PAF as well as of E. coli endotoxin in the rat. The hypotension induced by endotoxin (15 mg/kg i.v.) or PAF (30 ng/(kg X min) i.v.) in anaesthetized rats was prevented by oral (1-10 mg/kg) and inhibited or reversed by i.v. (0.1-5.0 mg/kg or 0.1-1.0 mg/kg) doses of WEB 2086. Similar oral and i.v. doses of WEB 2086 protected conscious rats from PAF (15 micrograms/kg i.v.)- and endotoxin (7.5 mg/kg i.v.)-induced death. The results obtained with WEB 2086 confirm that PAF has an important role in the pathophysiology of endotoxin shock. This compound may have a therapeutic effect in human septic shock.     

Interactions of saruplase with acetylsalicylic acid, heparin, glyceryl trinitrate, tranexamic acid and aprotinin in a rabbit pulmonary thrombosis model.

In anesthetized rabbits with pulmonary embolized thrombi the interactions of saruplase (recombinant unglycosylated single-chain urokinase-type plasminogen activator, CAS 99149-95-8) with acetylsalicylic acid (ASA), glyceryl trinitrate (nitroglycerin, GTN), heparin, and the antifibrinolytics tranexamic acid and aprotinin have been studied. Lysis rates were evaluated as reduction of the weight and as reduction of the incorporated 125J-fibrin content of the embolized thrombi. In untreated controls the spontaneous 125J-fibrinolysis was 8.3 +/- 0.7% and the thrombus weight was reduced by 55.3 +/- 4.5% (mainly due to loss of H2O) at 195 min after the thromboembolization. Infusion of saruplase (21.5 micrograms/kg.min) for 60 min significantly increased the 125J-fibrinolysis to 36.8 +/- 3.7% and the reduction of the thrombus weight to 69.9 +/- 2.1%. ASA (50 mg/kg p.o.) by itself did not exert a lytic effect; in combination with saruplase ASA insignificantly augmented the 125J-fibrinolysis rate and significantly further increased the thrombus weight reduction. GTN (5.0 micrograms/kg.min i.v.) neither influenced the spontaneous nor the saruplase-mediated lysis rates. Treatment with heparin (200 IU/kg i.v.-bolus plus 50 IU/kg.min i.v.-infusion) resulted in significant greater thrombus weight reduction than observed in untreated controls; in combination with saruplase heparin significantly intensified the lytic effect. Tranexamic acid (30 mg/kg i.v.) and aprotinin (30.10(3) KIU/kg i.v.) completely abrogated the lytic effect of saruplase. Treatment with saruplase alone produced an insignificant decrease of the plasma level of fibrinogen by 23% to 200 +/- 20 mg/dl. ASA, GTN and aprotinin did not influence this slight fibrinogenolysis in saruplase-treated animals. A slight decrease of plasma fibrinogen levels was observed by heparin, whereas the decrease by tranexamic acid was significant.     

Effects of WEB 2086, a novel antagonist of platelet activating factor, in active and passive anaphylaxis

WEB 2086, a novel specific platelet activating factor (PAF) antagonist derived from triazolodiazepines, inhibited in a dose-related manner the PAF-dependent component of anaphylaxis as well as PAF-induced effects in mice and guinea pigs. In mice a lethal anaphylactic shock and a PAF-induced (100 micrograms/kg i.v.) death was inhibited by i.v. WEB 2086. The ED50 values were 13.6 and 0.37 mg/kg i.v., respectively. In actively sensitized guinea pigs, the anaphylactic lung reaction (bronchoconstriction), but not the corresponding hypotension, was prevented by oral (0.05-0.5 mg/kg) doses of WEB 2086. In contrast, in passively sensitized animals a dose-dependent inhibition of the pulmonary (bronchoconstriction) and blood pressure (hypotension) reaction due to anaphylaxis was achieved by i.v. WEB 2086. Similarly, oral (0.05-0.5 mg/kg) and i.v. (0.005-0.05 mg/kg) WEB 2086 inhibited PAF-induced reduction in respiratory flow (bronchoconstriction) and hypotension in guinea pigs. The ED50 values were 0.070 and 0.066 mg/kg p.o., and 0.017 and 0.015 mg/kg i.v., respectively. In conclusion, PAF seems to play a more major role in passive than in active anaphylaxis in guinea pigs. These results provide further evidence for an important role of PAF in anaphylaxis and support the hypothesis that PAF is involved in asthma and other allergic diseases.     

Effect of a new thromboxane A2 antagonist, S-145, on platelet aggregation

The newly synthesized compound S-145, (+/-)-5(Z)-7-(3-endo-phenylsulfonylamino [2.2.1] bicyclohept-2-exo-yl)heptenoic acid, inhibited arachidonic acid (AA)-, 9,11-methanoepoxy-PGH2 (U46619)-, collagen- and ADP-induced human platelet aggregation in vitro with IC50 values of 0.25, 0.34, 0.22, and 0.08 microM, respectively. The inhibiting potency of this compound to AA- or U46619-induced platelet aggregation was about twice that of ONO-3708 and 1/7-1/14 that of SQ29,548 in human platelets, about 7 times that of ONO-3708 and 1/3-1/7 that of SQ29,548 in guinea pig platelets, and 250-800 times that of ONO-3708 and 1-7 times that of SQ29,548 in rabbit platelets. When S-145 was administered orally to guinea pigs at the dose of 0.1 mg/kg, AA-induced platelet aggregation was completely inhibited at 30 and 60 min after the administration, but not at 3 and 6 hr. The minimum effective doses of S-145 (p.o.) to AA- and collagen-induced platelet aggregation at 60 min after the administration were 0.01 mg/kg and 0.03 mg/kg, respectively. The potency of S-145 (p.o.) to inhibit AA- and collagen-induced guinea pig platelet aggregation was 30-300 times that of ONO-3708 or SQ29,548 and 300-1000 times that of aspirin. These results suggest that S-145 is a thromboxane A2 antagonist showing a potent inhibiting effect on platelet aggregation by oral administration.     

Pharmacological studies of loperamide, an anti-diarrheal agent. II. Effects on peristalsis of the small intestine and colon in guinea pigs (author's transl)

Effects of loperamide on peristalsis in the guinea pig intestines were investigated in comparison with those of morphine and atropine. The following results were obtained. The ejection of intraluminal fluid produced by the peristaltic contraction of the isolated ileum was suppressed by loperamide at a concentration of 10(-8) or 2 X 10(-8) g/ml. Peristalsis in the intestinal loop of anesthetized guinea pigs was inhibited by i.v. administration of loperamide at a dose of 0.03 mg/kg. Morphine (0.03 mg/kg i.v.) and atropine (0.05 mg/kg i.v.) also inhibited the peristaltic contraction. The effect of loperamide continued longer than that of morphine. Peristalsis in the colonic loop of anesthetized guinea pigs was inhibited by i.v. administration of loperamide at a dose of 0.01 or 0.03 mg/kg. Morphine (0.1 mg/kg i.v.) and atropine (0.03 mg/kg i.v.) also inhibited the peristaltic contraction of the colonic loop. Loperamide (0.01 or 0.03 mg/kg i.v.) and morphine (0.1 mg/kg i.v.) caused a slight and temporary increase of resting level of intraluminal pressure with inhibition of peristalsis in the colonic loop. These results suggest that loperamide suppresses the peristaltic contraction caused by distension of the intestinal lumen.     

Prevention of reocclusion following tissue type plasminogen activator-induced thrombolysis by the RGD-containing peptide, echistatin, in a canine model of coronary thrombosis

We evaluated the effect of the RGD-containing peptide, echistatin, on thrombolysis time and acute reocclusion in a canine model of coronary thrombosis/thrombolysis. Occlusive thrombus formation was induced by electrical injury, via a stimulating electrode, to the endothelial surface of the circumflex coronary artery in the open-chest, anesthetized dog in the presence of a critical stenosis. Fifteen minutes after occlusive thrombus formation, dogs received either an intravenous infusion of vehicle (saline at 0.1 ml/min) or echistatin (15 micrograms/kg/min i.v.). Heparin was given as an initial bolus (100 U/kg i.v.) 15 min after thrombus formation and repeated at hourly intervals (50 U/kg). This dose of heparin increased activated partial thromboplastin time to 1.5- to 2.5- fold over control. Thrombolysis was induced with recombinant tissue-type plasminogen activator (tPA) at a total dose of 1 mg/kg, intravenously administered over 90 min with 10% given as an initial bolus. The vehicle-treated animals reperfused at 48 +/- 9 min with a reperfusion incidence of 60% (3/5). The echistatin-treated animals reperfused at 46 +/- 5 min with a reperfusion incidence of 100% (5/5). After stopping the tPA infusion, acute reocclusion occurred in 100% (3/3) of the vehicle-treated dogs and in only 20% (1/5) of the echistatin-treated dogs. Echistatin caused a greater than 5-fold increase in buccal mucosa bleeding time and almost completely inhibited ex vivo platelet aggregation to ADP, collagen, and U-46619. Residual thrombus wet weight, determined at the end of the experiment, was significantly lower for the echistatin group (2.1 +/- 0.2 mg) compared to the vehicle group (5.8 +/- 0.7 mg).(ABSTRACT TRUNCATED AT 250 WORDS)     

Antithrombotic effect of TRK-100, a novel, stable PGI2 analogue

TRK-100, a stable PGI2 analogue structurally different from carbacyclines, was compared with other antiplatelet drugs for its effect on platelet functions using animal models. TRK-100 (10-300 nM) inhibited rat platelet aggregation induced by ADP (3 microM), collagen (12.5 micrograms/ml) and A23187 (10 microM), and its potency was about 1/3-1/7 that of PGI2. TRK-100 (0.3-3 mg/kg, p.o.) dose-dependently inhibited rabbit platelet adhesion (ED50: 2.2 mg/kg), and its effect lasted over at least 5 hr. In contrast, aspirin and ticlopidine (both at 300 mg/kg, p.o.) showed only a slight inhibition (4-7%). In the thrombocytopenia induced by collagen injection in rats, TRK-100 (3-300 micrograms/kg, i.v.; 0.1-3 mg/kg, p.o.) dose-dependently inhibited a decrease in platelet number, and its ED50 was 0.48-0.62 mg/kg orally and 13.7-16.4 micrograms/kg intravenously, while the inhibition by aspirin and ticlopidine (both at 1000 mg/kg, p.o.) was 40 and 37%, respectively. In the experimental thread thrombosis in rats. TRK-100 (0.03-3 mg/kg, p.o.) dose-dependently inhibited thrombus formation, and its ED50 was 0.46 mg/kg, being 21 and 87 times as potent as aspirin and ticlopidine, respectively. These results reveal that TRK-100 has a potent antiplatelet activity and is orally and intravenously effective for a variety of thrombosis models, suggesting that it may have a therapeutic value as an antithrombotic drug.     

Effect of BW443C81, a novel opioid, on non-cholinergic bronchoconstrictor responses and neurogenic plasma extravasation in the guinea pig.

The novel, peripherally acting opioid peptide, BW443C81, which attenuates airway sensory nerve impulses, was examined on non-cholinergic (NC) constrictor responses in vitro and in vivo and neurogenic plasma extravasation in vivo in guinea-pig airways. Non-cholinergic contractions of guinea pig isolated bronchi, evoked by electrical field stimulation, were concentration-dependently inhibited by BW443C81 and morphine (10 nmol/1-100 mumol/l). In anaesthetised, artificially ventilated guinea pigs, frequency-related NC bronchoconstrictor responses evoked by antidromic electrical stimulation of the vagus nerves were reduced by BW443C81 (100 micrograms/kg/min i.v. infusion) and morphine (1 mg/kg i.v.). Neurogenic plasma extravasation produced by bilateral electrical vagal nerve stimulation in spontaneously breathing, anaesthetised guinea pigs was also inhibited by BW443C81 (1 mg/kg i.v.). The inhibitory effects of BW443C81 were reversed/prevented by naloxone. BW443C81 inhibits NC bronchoconstrictor responses and neurogenic plasma extravasation in guinea pig airways, consistent with its previously described mu-opioid receptor-mediated inhibitory action on airway sensory nerve function.     

Pharmacological studies of loperamide, an anti-diarrheal agent. III. Interaction between loperamide and various agonists in the guinea pig intestine (author's transl)

To clarify the mode of action of loperamide, the interaction with various agonists was investigated in guinea pig intestines. The following results were obtained. Prostaglandin E1 (0.1 microgram) or acetylcholine (1 approximately 3 microgram) injection into the mesenteric artery at 10 min intervals caused a constant rise of intraluminal pressure of the intestinal loop in situ. Loperamide (0.01 approximately 0.1 mg/kg i.v.) markedly suppressed the response induced by prostaglandin E1. Morphine (0.1 approximately 1.0 mg/kg i.v.) and atropine (0.01 mg/kg i.v.) also suppressed the response. The intestinal response induced by acetylcholine was inhibited markedly by atropine and slightly by loperamide (0.1 mg/kg i.v.) but not by morphine. Contractions of the isolated ileum induced by coaxial stimulation, BaCl2, nicotine and serotonin were suppressed by loperamide (10(-9) approximately 2 X 10(-7) g/ml). Morphine, methadone and codeine showed the same effect as loperamide but the activity was weaker than that of loperamide. Contractions of isolated ileum induced by acetylcholine, histamine and bradykinin, and Ca-contraction in the depolarized taenia coli were inhibited by relatively high concentrations of loperamide (2 X 10(-7) g/ml or above). These results suggest that loperamide suppresses the function of cholinergic neurons in the intestines.     

Prevention of thrombosis and rethrombosis and enhancement of the thrombolytic actions of recombinant tissue-type plasminogen activator in the canine heart by DMP728, a glycoprotein IIb/IIIa antagonist.

1. We studied DMP728, a non-peptide glycoprotein (GP) IIb/IIIa receptor antagonist, for prevention of coronary artery thrombosis or rethrombosis in a chronic canine model subjected to arterial injury. 2. In protocol I, DMP728 (1.0 mg kg-1, i.v., n = 8) or saline (n = 8) was administered and a 150 microA anodal current was applied to the intimal surface of the left circumflex coronary artery (LCX). Dogs were monitored for 6 h and again on each of 5 subsequent days. 3. Ex vivo platelet aggregation was inhibited but returned to baseline 1 day after drug administration. Thrombus weight was reduced (saline, 20.7 +/- 5.0 mg; DMP728 1.7 +/- 0.4 mg; P < 0.05), as was infarct size [saline, 27.5 +/- 4.3; DMP728, 1.6 +/- 0.7 (per cent left ventricle); P < 0.05]. All control animals died by day 3, while all but one of the treated dogs survived the entire protocol (P < 0.05). 4. In protocol II, an LCX thrombus was induced and thrombolytic therapy was initiated 30 min later. DMP728 (1.0 mg kg-1, i.v., n = 8) or saline (n = 8) was administered 5 min after recombinant tissue-type plasminogen activator infusion had begun. The incidence of reocclusion was reduced by DMP728 (saline, 4/8; DMP728, 1/8). One day after thrombolysis, 7/8 DMP728-treated animals were alive compared with 1/8 in the control group (P = 0.01). 5. DMP728 inhibited ex vivo platelet aggregation, prevented primary and secondary occlusive thrombus formation, reduced thrombus weight and infarct size and increased survival in a chronic canine model of coronary artery thrombus formation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Triazolodiazepines are potent antagonists of platelet activating factor (PAF) in vitro and in vivo

Summary The triazolodiazepines brotizolam, triazolam and alprazolam inhibited PAF-induced human platelet aggregation in vitro (IC₅₀ = 0.54, 7.6 and 13.7 M, respectively) but showed only a weak or no effect against other aggregating agents (ADP, adrenaline, collagen, serotonin, arachidonic acid). In comparison, flunitrazepam and diazepam, two diazepines without the triazole ring, showed IC₅₀-values of 42 and 260 M, respectively. Flunitrazepam does not possess the specificity shown by the other compounds. Brotizolam and triazolam also inhibited PAF-induced human neutrophil aggregation in vitro, with IC₅₀-values 0.21 and 6.6 M, respectively.In anaesthetized guinea pigs, brotizolam (2.5 to 10 mg/kg p.o. or 0.1 to 0.5 mg/kg i.v.) or triazolam (20 to 100 mg/kg p.o.) inhibited dose-dependently the intrathoracic accumulation and aggregation of ¹¹¹Indium labelled platelets induced by an i. v. infusion of PAF (30 ng/kg × min).Brotizolam at doses of 1 to 10 mg/kg p. o. and 0.1 to 0.5 mg/kg i. v. inhibited dose-dependently the reduction in tidal volume (bronchoconstriction), the systemic hypotension and the lethal effect due to i. v. PAF in guinea pigs. Triazolam inhibited these effects of PAF at doses of 50 to 200 mg/kg p.o.PAF-induced systemic hypotension in rats can be reversed by cumulative i. v. doses (0.05 to 1.0 mg/kg) of brotizolam.In conclusion, these results show that triazolodiazepines, like brotizolam and triazolam, are potent inhibitors of PAF-induced effects in vitro and in vivo. Send offprint requests to J. Casals-Stenzel at the above address     

Effect of the PAF antagonists, CV-3988 and L-652,731 on the pulmonary and hematological responses to guinea pig anaphylaxis

To define the role of PAF in the acute phase of guinea pig anaphylaxis, we have measured the pulmonary (bronchoconstrictor) and hematological (thrombocytopenia, leukopenia, hemoconcentration, plasma TxB2 increase) responses to PAF infusion and compared these responses to the effect of antigen exposure in actively and passively sensitized guinea pigs. We have also determined the effect of the structurally unrelated PAF antagonists, CV-3988 and L-652,731 on these responses. Intravenous administration of PAF (50-400 ng/kg) caused a dose-related bronchoconstriction, thrombocytopenia, leukopenia, hemoconcentration and increase in plasma TxB2. These PAF-induced responses were inhibited, to a variable degree, by pretreatment with CV-3988 (3 and 10 mg/kg, i.v.) and L-652,731 (3 mg/kg, i.v.). Intravenous administration of ovalbumin to actively or passively sensitized guinea pigs caused bronchoconstriction, thrombocytopenia, leukopenia and hemoconcentration, but there was no increase in TxB2. Moreover, the anaphylactic bronchoconstriction, thrombocytopenia, leukopenia (actively sensitized) and hemoconcentration were not inhibited by CV-3988 (10 mg/kg, i.v.) and L-652,731 (3 mg/kg, i.v.). The different profile of changes produced by PAF and allergic anaphylaxis and the failure to alter the responses to allergic anaphylaxis with PAF antagonists suggest that PAF is not an important mediator of the acute phase of guinea pig anaphylaxis.     

Antiaggregatory, antithrombotic effects of MS-180, a novel platelet glycoprotein IIb/IIIa receptor antagonist

The antiaggregatory and antithrombotic effects of (S)-(-)-ethyl[6-[4-(morpholinoformimidoyl)benzamido]-3,4-dihydro-2 H-1-benzo-pyran-3-yl]acetate hydrochloride (MS-180), a novel platelet glycoprotein IIb/IIIa receptor antagonist, were investigated. Ma-HCl, (S)-(-)-[6-[4-(Morpholinoformimidoyl)benzamido]-3,4-dihydro-2H-1-b enzopyran-3-yl]acetic acid hydrochloride, the hydrochloride salt of Ma (active metabolite), inhibited the binding of fibrinogen to immobilized human glycoprotein IIb/III receptor with an IC50 value of 0.12+/-0.03 nM without affecting binding to either fibronectin or vitronectin receptors. In anesthetized guinea pigs, intraduodenal administration of MS-180 caused dose-dependent inhibition of both ADP- and collagen-induced ex vivo platelet aggregation. At the same dosages, occluded thrombus formation and platelet release reactions were also markedly suppressed. In anesthetized dogs, the bleeding time was prolonged slightly even when submaximal inhibition (< 90%) of ex vivo platelet aggregation was achieved following i.v. administration of Ma-HCl. Aspirin (100 mg/kg) prolonged the bleeding time to the same extent as MS-180 (1 mg/kg), although it suppressed only collagen-induced platelet aggregation. Therefore, MS-180 may be clinically useful for the treatment of thrombotic diseases.     

Roles of prostacyclin, EDRF and active oxygens in leukocyte-dependent platelet adhesion to endothelial cells induced by platelet-activating factor in vitro.

1. The mechanism of polymorphonuclear leukocyte (PMN)-dependent platelet adhesion to cultured endothelial cells induced by platelet-activating factor (PAF) was investigated to determine whether PMNs release or generate any factor(s) capable of inducing platelet adhesion, and the roles of prostacyclin and endothelium-derived relaxing factor (EDRF). 2. Cell-free supernatants, sonicates or rapid filtrates of PAF-stimulated PMN suspensions did not induce platelet adhesion to endothelial cells, but the PMN sonicates induced platelet adhesion when endothelial cells were pretreated with both aspirin and NG-nitro-L-arginine (L-NOARG). Its microphotograph showed that mainly platelet aggregates adhered to the endothelial cell surface. 3. Platelet adhesion induced by the PMN sonicates to aspirin- and L-NOARG-pretreated endothelial cells was dose-dependently prevented by OP-41483 (1-100 nM), and slightly by L-arginine (1 mM). The inhibition of platelet adhesion by OP-41483 and L-arginine was potentiated by their combination. 4. WEB 2170 (3 microM), a PAF antagonist, inhibited platelet adhesion induced by the PMN sonicates. However, PAF alone did not induce significant platelet adhesion to aspirin- and L-NOARG-treated endothelial cells. 5. Platelet adhesion induced by the PMN sonicates was not suppressed by AA-861 and indomethacin. However, both superoxide dismutase and catalase significantly inhibited platelet adhesion, and, in combination, their inhibitory effect was synergistically potentiated. Mannitol had no effect. It was also significantly inhibited by alpha 1-antitrypsin, whereas chymostatin and elastatinal had no effect. 6. PAF-induced platelet adhesion to endothelial cells in the presence of intact PMNs was not suppressed by indomethacin and AA-861, or by protease inhibitors.(ABSTRACT TRUNCATED AT 250 WORDS)     

Reduction of in vivo coronary artery thrombosis by the novel thromboxane antagonist (3R)-3-(4-fluorophenylsulfonamido)-1,2,3,4-tetrahydro-9- carbazolepropanoic acid

The effects of thromboxane (Tx)A2 antagonism were examined in a canine model of platelet-dependent coronary occlusion. The novel TxA2 antagonist (3R)-3-(4-fluorophenylsulfonamido)-1,2,3,4-tetrahydro-9-carbazo lepropanoic acid (Bay u 3405) was studied to ensure that antithrombotic effects seen in vivo were platelet-mediated and did not reflect unspecific compound effects. Bay u 3405 (1, 3, 10 and 30 mg/kg i.v.) inhibited in vivo platelet aggregation and increased the time to thrombotic vascular occlusion by 2.8 h (p less than 0.05) after 30 mg/kg were given. A dose-dependent reduction of intravascular occlusive thrombus growth occurred: thrombus wet weight decreased from 66 +/- 6 mg in vehicle controls to 42 +/- 6 mg, 25 +/- 5 mg, 18 +/- 3 mg and 6 +/- 2 mg after administration of 1, 3, 10 and 30 mg Bay u 3405 i.v., respectively. Electrocardiographic signs for developing myocardial ischemia were largely prevented by the compound. Collagen-induced platelet aggregation ex vivo was inhibited by over 60% in drug-treated animals. The observed delay of thrombotic coronary occlusion reflected an inhibition of platelet aggregation and protection from coronary vasoconstriction at the site of thrombus formation, most likely mediated through blockade of TxA2 receptors.     

Effects of AH-1058, a new antiarrhythmic drug, on experimental arrhythmias and cardiac membrane currents

AH-1058 is a newly synthesized antiarrhythmic agent. We investigated the antiarrhythmic and electrophysiological effects of AH-1058 in experimental arrhythmia models and isolated cardiomyocytes. In the ouabain-induced arrhythmia model of the guinea pig, pretreatment with AH-1058 (0.1-0.3 mg/kg, i.v.) delayed the appearance of premature ventricular complex (PVC) and ventricular fibrillation (VF) induced by intravenous infusion of ouabain. However, disopyramide (10 mg/kg, i.v.) delayed only that of PVC, and verapamil (1 mg/kg, i.v.) failed to affect the ouabain-induced ventricular arrhythmias. In the reperfusion-induced arrhythmia model of the rat, in which 5-min coronary occlusion and 10-min reperfusion were produced, AH-1058 (0.1-0.3 mg/kg, i.v.) inhibited the incidence of both ventricular tachycardia (VT) and VF, whereas disopyramide (5 mg/kg, i.v.) inhibited only reperfusion-induced VF. On the other hand, a higher dose of AH-1058 (1 mg/kg, i.v.) did not affect the aconitine-induced arrhythmias in rats, which were inhibited by disopyramide (5 mg/kg, i.v.). We also confirmed oral activity of AH-1058 in the reperfusion-induced arrhythmia model of the rat. AH-1058, at doses of 2-4 mg/kg, dose-dependently inhibited VT and VF. Electrophysiological experiments with patch-clamp techniques revealed that AH-1058 potently suppressed the L-type Ca2+ currents in isolated cardiomyocytes of the guinea pig. These results suggest that AH-1058 is a potent antiarrhythmic drug having a Ca2+ channel-blocking action. The antiarrhythmic profile of AH-1058 is different from that of disopyramide and verapamil.