The effect of defibrotide on thromboembolism in the pulmonary vasculature of mice and rabbits and in the cerebral vasculature of rabbits.

1. Administration of bovine thrombin (100 u kg-1) into the carotid artery of rabbits induces a sustained accumulation of 111 Indium-labelled platelets within the cranial vasculature over the subsequent 3 h. 2. Intracarotid (i.c.) administration of defibrotide (64 mg kg-1 bolus plus 64 mg kg-1 h-1 for 1 h) prior to i.c. thrombin (100 u kg-1) significantly reduces the ability of thrombin to induce cranial thromboembolism in rabbits. 3. Intravenous (i.v.) administration of thrombin (20 u kg-1) in rabbits induces a reversible accumulation of radiolabelled platelets into the thoracic circulation which is significantly reduced by i.v. administration of defibrotide (64 mg kg-1 bolus plus 64 mg kg-1 h-1 for 1 h) prior to i.v. thrombin. In contrast, platelet accumulation in response to adenosine diphosphate (ADP; 20 micrograms kg-1, i.v.) or platelet activating factor (PAF; 50 ng kg-1, i.v.) is not significantly affected by this treatment. 4. Intravenous administration of the nitric oxide (NO)-synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME; 10 mg kg-1) potentiates platelet accumulation induced by low dose thrombin (10 u kg-1, i.v.) within the pulmonary vasculature of rabbits. The potentiated response is significantly abrogated following pretreatment with defibrotide (64 mg kg-1 bolus plus 64 mg kg-1 h-1 for 1 h, i.v.). 5. Intravenous injection of human thrombin (1250 u kg-1) to mice induces death within the majority of animals which is significantly reduced by pretreatment with defibrotide (150-175 mg kg-1, i.v.).(ABSTRACT TRUNCATED AT 250 WORDS)     

The role of nitric oxide as an endogenous regulator of platelet and neutrophil activation within the pulmonary circulation of the rabbit.

1. Intravenous (i.v.) administration of adenosine diphosphate (ADP), platelet activating factor (PAF) and thrombin induced a dose-related accumulation of 111indium-labelled platelets within the thoracic region of anaesthetized rabbits. 2. I.v. administration of the inhibitor of NO biosynthesis, L-NG-nitro arginine methyl ester (L-NAME; 10 mg kg-1) significantly potentiated the peak platelet accumulation induced by ADP, PAF and thrombin. Additionally L-NAME prolonged the disaggregation of platelets in comparison to D-NAME (10 mg kg-1). Such changes were reversible by the administration of L-arginine (900 mg kg-1). 3. I.v. administration of PAF induced a small accumulation of 111indium-labelled neutrophils within the pulmonary circulation which could be greatly potentiated by pretreatment of the animals with L-NAME. In contrast, thrombin administration did not cause significant accumulation of 11indium-labelled erythrocytes in the pulmonary circulation of anaesthetized rabbits. 4. Intracarotid (i.c.) administration of thrombin induced a marked accumulation of radiolabelled platelets within the cranial vasculature which was not potentiated by the prior administration of L-NAME (at either 10 mg kg-1 or 100 mg kg-1). 5. These results suggest that endogenous NO may regulate platelet and polymorphonuclear leukocyte activation within the pulmonary but not the cerebral circulation of rabbits.     

Endothelin-1 inhibits platelet aggregation in vivo: a study with 111indium-labelled platelets.

1. A non-invasive technique for the scintigraphic determination of 111indium-labelled platelet aggregation stimulated with submaximal doses of adenosine diphosphate (ADP, 56 micrograms kg-1 i.v.), collagen (100 micrograms kg-1 i.v.), platelet-activating factor (PAF, 0.1 microgram kg-1 i.v.) or thrombin (18 iu kg-1 i.v.) was used to investigate the platelet-inhibitory effects of endothelin 1 (ET-1) in anaesthetized rabbits in vivo. 2. ET-1 (1 nmol kg-1 i.v.) inhibited ADP-stimulated platelet aggregation in vivo; a maximum inhibition of 78% of the control value was reached at 3 min, with 45% inhibition at 15 min, and a return to control values at 30 min after injection of the peptide. 3. ET-1 (1 nmol kg-1 i.v.) inhibited in vivo platelet aggregation in response to collagen or PAF by 86% and 52%, respectively, but had no effect on thrombin-induced platelet aggregation. 4. Indomethacin (5 mg kg-1 i.v.) abolished the ET-1-induced inhibition of ADP-stimulated platelet aggregation and significantly potentiated and prolonged the pressor response brought about by ET-1. 5. In conclusion, the data demonstrate that ET-1 potently inhibits platelet aggregation in the anaesthetized rabbit in vivo by releasing a hypotensive and anti-aggregatory cyclo-oxygenase product, presumably prostacyclin, into the circulation.     

Regulation of platelet function by catecholamines in the cerebral vasculature of the rabbit.

1. 111In-labelled platelets were monitored continuously in the cerebral and pulmonary vascular beds of anaesthetized rabbits. Dopamine can, depending upon the concentration, either potentiate or inhibit thrombin-induced platelet accumulation in the cerebral vasculature of rabbits by unknown mechanisms. The effects of specific adrenergic and dopaminergic receptor antagonists were tested upon dopamine's actions on intracarotid (i.c.) thrombin-induced (80 u kg-1) platelet accumulation in the cerebral vasculature. The effect of adrenaline on the response to thrombin in this vascular bed was also investigated. 2. Thrombin-induced platelet accumulation was significantly (P<0.01) potentiated by dopamine (100 microgkg-1 min-1, i.c.) and this effect was significantly inhibited by infusion of the alpha-adrenoceptor antagonist, phentolamine. 3 A higher dose of dopamine (2 mg kg-1 min-1, i.c.) inhibited thrombin-induced platelet accumulation. The beta-adrenoceptor antagonist, propranolol, did not significantly alter this inhibitory effect whereas it was abolished by the dopamine D1 selective antagonist, SCH23390. 4 Adrenaline (when administered i.c. by bolus injection or infusion) had no significant effect on thrombin-induced accumulation at any of the doses tested. 5 Potentiation of in vivo platelet accumulation by dopamine therefore seems to occur via alpha-adrenergic receptors. However, the inhibitory effect of dopamine appears to be exerted via the activation of dopamine D1 receptors and not via beta-adrenergic receptors. Our findings confirm that dopamine, but not adrenaline, can modify platelet function in the cerebral vasculature and these observations may have implications for current and potential therapeutic uses of dopamine and selective dopaminergic compounds.     

Comparison of desulfatohirudin (REVASC) and heparin as adjuncts to thrombolytic therapy with reteplase in a canine model of coronary thrombosis.

1. We compared the direct thrombin inhibitor, desulfatohirudin (REVASC) and the indirect thrombin inhibitor, heparin, as adjuncts to thrombolytic therapy with reteplase in a canine model of coronary artery thrombosis. 2. Reteplase (BM 06.022) is a recombinant unglycosylated variant of human tissue-type plasminogen activator. Thrombus formation in anaesthetized open chest dogs was induced by electrical injury. Left circumflex coronary artery blood flow was monitored for 210 min with an electromagnetic flow probe. Twenty eight dogs were randomized to receive i.v. heparin (120 iu kg-1 bolus plus 80 iu kg-1 per h) or i.v. hirudin (2.0 mg kg-1 bolus plus 2.0 mg kg-1 per h) 10 min before thrombolysis preceded by i.v. acetylsalicyclic acid (20 mg kg-1) 5 min prior to anticoagulation. Every dog received an i.v. double bolus injection of 0.14 + 0.14 u kg-1 ( = 0.24 + 0.24 mg kg-1) reteplase, 30 min apart, 1 h after thrombus formation. 3. At comparable reperfusion rates (12 out of 12 vs. 15 out of 16 dogs), hirudin enhanced time to reperfusion (14.3 +/- 1.4 vs. 23.2 +/- 3.4 min; P < 0.05) and completely prevented reocclusion after reperfusion in contrast to heparin (0 out of 11 vs. 7 out of 11 dogs; P < 0.05). Coronary blood flow quality was improved by hirudin as shown by a higher maximum blood flow after reperfusion (130 +/- 14.3 vs. 83 +/- 9.3% of baseline; P < 0.05), a higher blood flow level at 20, 30, 40, and 50 min after onset of thrombolysis (P < 0.05) and a longer cumulative patency time (195 +/- 1.7 vs. 166 +/- 12 min; P < 0.05). Activated partial thromboplastin time and buccal mucosa bleeding time were prolonged (P < 0.05) by either anticoagulant, but did not differ significantly between groups. 4. The direct thrombin inhibitor, desulfatohirudin, enhanced thrombolysis, prevented reocclusion and increased blood flow as compared with the indirect thrombin inhibitor, heparin, when investigated at one dose level each and used in conjunction with reteplase.     

Involvement of superoxide and xanthine oxidase in neutrophil-independent rat gastric damage induced by NO donors.

1. Nitric oxide (NO) and the superoxide anion can interact to form the cytotoxic moiety, peroxynitrite. The involvement and potential source of superoxide in the gastric mucosal damage induced by local infusion of NO donors, has now been investigated in the pentobarbitone-anaesthetized rat. 2. Local intra-arterial infusion of the NO donor, sodium nitroprusside (40 micrograms kg-1 min-1) for 10 min induced macroscopically apparent gastric mucosal injury. 3. This mucosal damage was dose-dependently reduced by prior administration of a systemically acting form of superoxide dismutase conjugated with polyethylene glycol (500-2000 iu kg-1, i.v.). 4. Likewise, the mucosal damage induced by nitroprusside was dose-dependently reduced by prior administration of the xanthine oxidase inhibitor, allopurinol (20-100 mg kg-1, i.p. or 100 mg kg-1, p.o.). 5. Pretreatment with allopurinol (100 mg kg-1, i.p.) also reduced the mucosal injury induced by local intra-arterial infusion of the nitrosothiol, S-nitroso-N-acetyl-penicillamine (40 micrograms kg-1 min-1), but not that induced by local infusion of endothelin-1 (5 pmol kg-1 min-1), indicating specificity of action. 6. Prior administration (4h) of rabbit anti-rat neutrophil serum (0.4 ml kg-1, i.p.), which reduced circulating neutrophils by 90%, did not significantly protect against mucosal injury induced by nitroprusside. 7. Intravenous administration of the platelet-activating factor receptor antagonists, WEB 2086 (1 mg kg-1) or BN 52021 (10 mg kg-1), or the thromboxane synthase inhibitor, OKY 15181 (25 mg kg-1), did not modify mucosal damage induced by nitroprusside, showing lack of involvement of these neutrophil-derived mediators. 8. These findings indicate the involvement of superoxide in the injurious actions of the NO donors, implicating a cytotoxic role of peroxynitrite. Xanthine oxidase, but not neutrophils, appears to be a source of the superoxide.     

Antithrombotic actions of argatroban in rat models of venous, 'mixed' and arterial thrombosis, and its effects on the tail transection bleeding time.

1. The antithrombotic action of argatroban, a synthetic thrombin inhibitor, was studied in three models of thrombosis in the rat, and in the tail transection bleeding time test. Heparin was studied as a reference anticoagulant. 2. In the model of venous thrombosis induced by thromboplastin followed by stasis of the abdominal vena cava, argatroban had an ED50 of 125 micrograms kg-1, when administered as an i.v. bolus 5 min prior to the thromboplastin injection: the ED50 of heparin was 42 micrograms kg-1, where ED50 is the dose which reduces the weight of the thrombus by 50% compared with that of the control animals. When the two compounds were administered by continuous i.v. infusion, argatroban (ED50 = 1.5 micrograms kg-1 min-1) had the same potency as heparin (ED50 = 1.2 micrograms kg-1 min-1). 3. Argatroban was active in the arterio-venous shunt model with an ED50 of 0.6 mg kg-1 when the compound was given as a bolus. The ED50 of heparin was 0.04 mg kg-1 under the same conditions. The two compounds had ED50 values of 6 micrograms kg-1 min-1 (argatroban) and 3 micrograms kg-1 min-1 (heparin), when administered by continuous i.v. infusion. 4. When tested against occlusive arterial thrombus formation by electrical stimulation of the left carotid artery, both compounds given as either an i.v. bolus or a continuous infusion led to dose-dependent increases in the duration of post-lesion vessel patency.(ABSTRACT TRUNCATED AT 250 WORDS)     

Endotoxin inhibition of distension-stimulated gastric acid secretion in rat: mediation by NO in the central nervous system.

1. The involvement of nitric oxide in the acute inhibitory effects of low doses of endotoxin, following intracerebroventricular (i.c.v.) or intravenous (i.v.) administration, on gastric acid secretion stimulated by distension or i.v. infusion of pentagastrin has been investigated in the continuously perfused stomach of the anaesthetized rat. 2. The i.c.v. administration of E. coli endotoxin (800 ng kg-1) abolished the acid secretory response induced by gastric distension (20 cm water intragastric pressure) within 30 min of administration. 3. By contrast, submaximal rates of acid secretion induced by i.v. infusion of pentagastrin (8 micrograms kg-1 h-1) were not inhibited by i.c.v. administration of endotoxin (800 ng kg-1). 4. Prior i.c.v. administration of the NO synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME, 800 micrograms kg-1) restored the acid secretory responses to distension in rats treated with endotoxin (i.c.v.). 5. Likewise, i.v. administration of endotoxin (5 micrograms kg-1) abolished the acid secretory response induced by gastric distension within 30 min of administration. Prior i.c.v. injection of L-NAME (800 micrograms kg-1) or its i.v. administration (10 mg kg-1) restored acid secretory responses in rats receiving i.v. endotoxin. 6. The reversal by L-NAME (i.v.) of the acid inhibitory effects of endotoxin (i.v.) was prevented by L-arginine (12 mg kg-1, i.c.v. or 100 mg kg-1, i.v.), but not by its enantiomer D-arginine. 7. The present results imply the existence of an acute response to endotoxin involving NO synthesis in the brain.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of NG-nitro-L-arginine methyl ester on vagally induced gastric relaxation in the anaesthetized rat.

1. The influence of the nitric oxide (NO) biosynthesis inhibitor NG-nitro-L-arginine methyl ester (L-NAME) on the gastric relaxation induced by peripheral vagal stimulation was investigated in the anaesthetized rat. 2. Peripheral vagal stimulation (10 Hz, 10 V, 1 ms for 20 s) induced a reproducible biphasic response: a short-lasting increase followed by a more pronounced decrease in intragastric pressure. This response also occurred in reserpinized animals (5 mg kg-1, i.p., 24 h before the experiment) while atropine (1 mg kg-1, i.v.) abolished the initial increase in intragastric pressure. 3. L-NAME (1-30 mg kg-1, i.v.) induced an increase in arterial blood pressure. L-NAME (1 mg kg-1, i.v.) had no influence on the vagally induced gastric response while L-NAME (10 and 30 mg kg-1 i.v.) significantly changed it: the initial increase in intragastric pressure was enhanced while the decrease in intragastric pressure was reduced or abolished. NG-nitro-L-arginine (L-NNA, 10 mg kg-1, i.v.) had the same effect. 4. An i.v. infusion of phenylephrine (10 micrograms kg-1 min-1) inducing a pressor response similar to that produced by L-NAME (30 mg kg-1, i.v.) did not influence the vagal gastric response. Infusion of L-arginine (300 mg kg-1 bolus, then 100 mg kg-1 h-1) starting 30 min beforehand, reduced the pressor effect and prevented the influence of L-NAME (10 mg kg-1, i.v.) on the vagal gastric response.(ABSTRACT TRUNCATED AT 250 WORDS)     

GABAA-receptor-mediated effects of progesterone, its ring-A-reduced metabolites and synthetic neuroactive steroids on neurogenic oedema in the rat meninges.

1. The effects of progesterone, its A-ring-reduced metabolites, allopregnanolone, tetrahydroxydeoxycorticosterone and the synthetic neuroactive steroid alphaxalone were evaluated in a rat model of plasma extravasation within the meninges following unilateral electrical stimulation (ES) of the trigeminal ganglion (0.6 mA, 5 ms, 5 min) or substance P administration (1 nmol kg-1, i.v.). 2. When administered 55 min prior to electrical stimulation, progesterone (> or = 500 micrograms, s.c.) dose-dependently decreased plasma extravasation within the meninges (ED50: 650 micrograms) but not within conjunctiva and tongue. Promegestone (R5020), a non-metabolized progesterone agonist (1000 micrograms, i.p.) was ineffective. The administration of progestrone (> or = 500 micrograms s.c.) 55 min prior to substance P partially suppressed plasma extravasation within the meninges (ED50: 550 micrograms). 3. The GABAA-antagonist, bicuculline (ED50: 8.2 micrograms kg-1, i.p.) but not the GABAB-antagonist, phaclofen (100 micrograms kg-1, i.p.) attenuated the effects of progesterone after electrical stimulation and substance P administration. 4. The metabolites of progesterone, allopregnanolone (3 alpha-hydroxy-5 alpha- pregnan-20-one (THP); ED50: 0.58 micrograms kg-1, i.p.), tetrahydroxydeoxycorticosterone (3 alpha,21- dihydroxy-5 alpha-pregnan-20-one (THDOC); ED50: 1.2 micrograms kg-1, i.p.) as well as the synthetic steroid alphaxalone (3 alpha-hydroxy-5 alpha-pregnane-11,20-dione; ED50: 1.8 micrograms kg-1, i.p.) suppressed plasma extravasation dose-dependently following ES, whereas the epimer of allopregnanolone, 3 beta-hydroxy-5 alpha-pregnan-20-one (100 micrograms kg-1, i.p.), did not. Extravasation caused by SP administration was partially suppressed by allopregnanolone (> or = 1 microgram kg-1, i.p.) (ED50: 2.1 micrograms kg-1). 5. The effect of progesterone (1000 micrograms, s.c.) and allopregnanolone (100 micrograms kg-1, i.p.) on neurogenic plasma extravasation was reversed by bicuculline (10 micrograms kg-1, i.p.) or by a congener, bicuculline-methiodide (10 micrograms kg-1, i.p.) which does not cross the blood brain barrier. 6. Progesterone (1000 micrograms, s.c.) had no effect on mean arterial blood pressure or heart rate when measured for 60 min after administration. 7. These results indicate that neurosteroid modulation of a GABAA-receptor located outside the blood brain barrier suppresses neurogenic and substance P-induced plasma extravasation within the meninges. The findings are consistent with previously reported data showing that valproic acid and muscimol inhibit meningeal oedema by bicuculline-sensitive mechanisms. Drugs which activate GABAA-receptors and its modulatory sites might be clinically effective in the treatment of migraine and cluster headache.     

Nitric oxide mediates the inhibition by interleukin-1 beta of pentagastrin-stimulated rat gastric acid secretion.

Bolus injection of interleukin-1 beta (2 micrograms kg-1, i.v.) inhibited acid secretion induced by intravenous infusion of pentagastrin (8 micrograms kg-1 h-1) in the continuously perfused stomach of the anaesthetized rat. Administration of interleukin-1 beta did not modify mean systemic arterial blood pressure. Pretreatment with NG-nitro-L-arginine methyl ester (L-NAME, 2-10 mg kg-1, i.v.), but not dexamethasone (5 mg kg-1, s.c. twice over 16 h), restored the acid secretory responses to pentagastrin. The actions of L-NAME were reversed by the prior administration of L-arginine (100 mg kg-1, i.v.), but not by its enantiomer D-arginine (100 mg kg-1, i.v.). L-NAME (5 mg kg-1, i.v.) increased blood pressure but this was not the mechanism by which interleukin-induced acid inhibition was prevented, since similar systemic pressor responses induced by phenylephrine (10 micrograms kg-1 min-1, i.v.), had no such effect. These findings suggest that interleukin-induced inhibition of acid responses to pentagastrin involves synthesis of NO from L-arginine.     

Effects of the endothelin receptor antagonist, SB 209670, on circulatory failure and organ injury in endotoxic shock in the anaesthetized rat.

1. This study investigates the effects of the non-selective ETA/ETB receptor antagonist, SB 209670, on systemic haemodynamics, renal function, liver function, acid-base balance and survival in a rat model of endotoxic shock. 2. Injection of E. coli lipopolysaccharide (LPS, 10 mg kg-1, i.v.) resulted in increases in the serum levels of tumour necrosis factor-alpha (TNF-alpha, maximum 60 min after LPS), endothelin-1, (ET-1; maximum 120 min after LPS), and interferon-gamma (IFN-gamma, maximum 180 min after LPS). 3. Injection of LPS also resulted in a fall in blood pressure from 113 +/- 3 mmHg (time = 0) to 84 +/- 4 mmHg at 360 min (n = 15) as well as a hyporeactivity to the vasoconstrictor responses elicited by noradrenaline (NA, 1 microgram kg-1, i.v.). Pretreatment of rats with a continuous infusion of SB 209670 (3 mg kg-1, i.v. bolus + 100 micrograms kg-1, i.v. infusion commencing 15 min prior to LPS) significantly augmented the hypotension as well as the vascular hyporeactivity to NA caused by endotoxaemia. 4. Pretreatment of LPS-rats with SB 209670 (3 mg kg-1, i.v. bolus given 15 min prior to LPS) or infusion of SB 209670 (bolus dose and infusion as above) resulted in a reduction in 6 h-survival from 71% (control) to 30% and 13%, respectively. 5. Endotoxaemia for 4 h resulted in rises in the serum levels of urea and creatinine (indicators of renal failure), but not in the serum levels of bilirubin, GPT and GOT (indicators of liver dysfunction and/or hepatocellular injury). Pretreatment of LPS-rats with SB 209670 (3 mg kg-1, i.v. bolus 15 min prior to LPS) significantly augmented the serum levels of creatinine, bilirubin, GPT and GOT caused by endotoxin. In addition, endotoxaemia caused, within 15 min, an acute metabolic acidosis (falls in pH, HCO3- and base excess) which was compensated by hyperventilation (fall in PaCO2). Pretreatment of LPS-rats with SB 209670 (3 mg kg-1, i.v. bolus) significantly augmented the metabolic acidosis caused by LPS. 6. Thus, the non-selective ETA/ETB receptor antagonist, SB 209670, augments the degree of (i) hypotension, (ii) vascular hyporeactivity to noradrenaline, (iii) renal dysfunction and (iv) metabolic acidosis caused by endotoxin in the anaesthetized rat. In contrast to rats treated with LPS alone, LPS-rats treated with SB 209670 exhibited liver dysfunction and hepatocellular injury. We propose that the release of endogenous ET-1 serves to maintain blood pressure and subsequently organ perfusion in septic shock.     

Antithrombotic actions of the thrombin inhibitor, argatroban, in a canine model of coronary cyclic flow: comparison with heparin.

1. The antithrombotic action of argatroban, a synthetic thrombin inhibitor, was studied in a canine model of coronary cyclic flow having some of the characteristics of acute unstable angina. Heparin was studied as a reference anticoagulant. 2. Localized endothelial damage was induced in the circumflex coronary artery of anaesthetized open-chest foxhounds and a critical stenosis was applied by use of a Lexan constrictor placed around the artery at the site of endothelial damage. An electro-magnetic flow probe was placed distal to the lesion, and cyclic flow variations (CFVs) were observed, as thrombi formed at the site of the arterial lesion and were dislodged. Test compounds were administered by i.v. infusion commencing 1 h after the appearance of CFVs, and maintained for 1 h. On termination of the treatments, coronary flow was observed for a further 60 min. A series of blood samples were taken at predetermined times throughout each experiment in order to determine the coagulation parameters, thrombin time (TT) activated partial thromboplastin time (aPTT) and for the determination of fibrinopeptide A (FpA) levels before, during and post-treatment. 3. Argatroban and heparin showed antithrombotic effects in this model. Argatroban dose-dependently increased the minimum coronary flow at the nadir of the CFVs from 5.4 +/- 1.7 to 9.1 +/- 2.1 ml min-1 (30 micrograms kg-1 min-1, P = 0.041) and from 2.9 +/- 0.9 to 16.3 +/- 4.5 ml min-1 (100 micrograms kg-1 min-1, P = 0.023, n = 8 dogs at each dose level). Heparin (5 and 15 iu kg-1 min-1) also increased minimum flow, but the increase was not statistically significant at the 5% level, although the P value in animals treated with 15 iu kg-1 min-1 (P = 0.0521, n = 6 dogs) fell just outside this limit. Although neither compound significantly decreased the overall CFV frequency, argatroban (100 micrograms kg-1 min-1) significantly (P < 0.01) decreased the number of large amplitude CFVs (minimum coronary flow < 10 ml min-1) by 63%, and heparin (15 iu kg-1 min-1) caused a 50% decrease in this parameter (P < 0.05). 4. The thrombin times were increased by a factor greater than 10 during antithrombotic treatment, irrespective of the compound or doses used. Heparin treatment induced 17 and > 30 fold increases in aPTT at 5 and 15 iu kg-1 min-1 respectively. However, argatroban produced only 2 and 3 fold increases in aPTT at 30 and 100 micrograms kg-1 min-1, despite significant antithrombotic effects. FpA levels were reduced in the presence of both argatroban and heparin. 5. These data show that, when administered as an intravenous infusion, argatroban is a potent antithrombotic agent in a canine model of coronary cyclic flow.     

The antidyskinetic action of dihomo-gamma-linolenic acid in the rodent

The antidyskinetic action of dihomo-gamma-linolenic acid (DHLA) was assessed against dyskinesias induced in the guinea-pig by dopamine injected into the striatum (200 micrograms bilateral 2 h after nialamide, 75 mg kg-1, i.p.) and in the guinea-pig and rat by 2-di-n-propylamino-5, 6-dihydroxytetralin (tetralin), 0.025 mg kg-1, s.c. Dopamine and tetralin-induced dyskinesias in the guinea-pig were reduced or abolished by DHLA given i.p., 30-100 mg kg-1, given once daily for 5-10 days. Tetralin-induced dyskinesias were antagonized by DHLA given orally to the guinea-pig (50-200 mg kg-1, 5 days) or in the diet to the rat (approximately 200 mg kg-1 daily for 10-14 days). DHLA injected into the striatum (2.5-20 micrograms bilateral, 2-4 days) also antagonized tetralin-induced dyskinesias in the rat. The antidyskinetic action of DHLA given i.p. to the guinea-pig could be antagonized by aspirin or eicosa-5,8,11,14-tetraynoic acid (100 mg kg-1 i.p. daily, starting 2 days before a 5 day treatment with DHLA). Aspirin (25-100 mg kg-1, i.p.) dose-dependently antagonized the antidyskinetic activity of 5 and 20 micrograms DHLA given bilaterally into the striatum (2 days). DHLA (100 mg kg-1 i.p.) given daily for 10 days or approximately 200 mg kg-1 DHLA (daily for 10-14 days given in the diet) administration to the rat failed to modify the stereotyped behaviour induced by apomorphine, 0.5 or 2 mg kg-1 s.c., to induce catalepsy, or to modify the cataleptic effects of haloperidol 0.25 or 1 mg kg-1 i.p.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of interleukin-4 and interleukin-10 on leucocyte migration and nitric oxide production in the mouse.

1. The effect of systemic treatment of mice with murine recombinant interleukin-4 (IL-4) or interleukin-10 (IL-10) on neutrophil infiltration into a specific tissue site and nitric oxide (NO) production from peritoneal macrophages was investigated. 2. Intravenously (i.v.) administered IL-4 (0.01-10 micrograms per mouse, approximately 0.3-300 micrograms kg-1, i.v.) and IL-10 (0.01-1 micrograms per mouse, approximately 0.3-30 micrograms kg-1, i.v.) dose-dependently inhibited neutrophil accumulation into a 6-day-old murine air-pouch induced by local application of interleukin-1 beta (IL-1 beta, 5 ng), with approximate ED50s of 0.35 and 0.90 micrograms, respectively. Neither IL-4 (1 micrograms, 30 micrograms kg-1, i.v.) nor IL-10 (1 micrograms, 30 micrograms kg-1, i.v.) prevented leucocyte accumulation in the mouse air-pouches when interleukin-8 (IL-8, 1 micrograms) was used as chemoattractant. Similarly, neither cytokine had any effect on the in vitro up-regulation of CD11b antigen on the surface of murine circulating neutrophils. 3. Treatment of mice with lipopolysaccharide (LPS, 0.3 mg kg-1, i.p.) caused an increase in the formation of NO (measured as nitrite accumulation) in the supernatant of peritoneal macrophages ex vivo. Pretreatment of mice with IL-4 (0.01-1 micrograms i.v., 20 min before LPS), but not with IL-10 (1 micrograms i.v., 20 min before LPS), caused a dose-dependent reduction in this LPS-stimulated formation of nitrite by peritoneal macrophages ex vivo. 4. Activation of murine macrophages with LPS (1 microgram ml-1 for 24 h) in vitro caused a significant increase in nitrite release in the supernatant of these cells.(ABSTRACT TRUNCATED AT 250 WORDS)     

Respiratory effects of baclofen and 3-aminopropylphosphinic acid in guinea-pigs.

1. The effects of the GABAB receptor agonists, baclofen and 3-aminopropylphosphinic acid (3-APPi) given by the subcutaneous or intracerebroventricular (i.c.v.) route were examined on minute ventilation (V), tidal volume (VT) and respiratory rate (f) due to room air and carbon dioxide (CO2)-enriched gas hyperventilation in conscious guinea-pigs. 2. Baclofen (0.3-10 mg kg-1, s.c.) produced a dose-dependent inhibition of V and f due to room air and CO2 inhalation. The maximum inhibition of room air breathing V was 85% +/- 3 and f was 74% +/- 3 at 10 mg kg-1, s.c. The maximum effects on CO2-induced hyperventilation were 68% +/- 9 and 51% +/- 6, for V and f respectively. Only the highest dose of baclofen studied (10 mg kg-1) produced a significant inhibition of VT due to room air breathing (46% +/- 6) and CO2 breathing (38% +/- 11). 3. 3-APPi (0.3-100 mg kg-1, s.c.) did not affect V, VT or f due to room air breathing or CO2 inhalation at any dose tested. Also, i.c.v. administration of 3-APPi (100 micrograms) did not affect ventilatory responses due to room air breathing or CO2 inhalation. 4. Pretreatment with the GABAB antagonist, CGP 35348 3-aminopropyl-(diethoxymethyl) phosphinic acid (3-30 mg kg-1, s.c.) blocked the respiratory depressant effects of baclofen (3 mg kg-1, s.c.) in a dose-related fashion. 5. Intracerebroventricular (i.c.v.) administration of CGP 35348 (50 micrograms) blocked the respiratory depressant effects of baclofen.(ABSTRACT TRUNCATED AT 250 WORDS)     

The profiles of interaction of yohimbine with anxiolytic and putative anxiolytic agents to modify 5-HT release in the frontal cortex of freely-moving rats.

1. The interaction of yohimbine with anxiolytic and putative anxiolytic agents to modify 5-hydroxytryptamine (5-HT) release in the frontal cortex of the freely-moving rat was assessed using the microdialysis technique. 2. The alpha 2-adrenoceptor antagonist, yohimbine (5.0 mg kg-1, i.p.) increased maximally the extracellular levels of 5-HT in the rat frontal cortex by approximately 230% of the basal levels. 3. The alpha 2-adrenoceptor agonist, clonidine (30-100 micrograms kg-1, i.p.) decreased dose-dependently the extracellular levels of 5-HT in the rat frontal cortex by approximately 0-60% of the basal levels. A 5 min pretreatment with clonidine (50 micrograms kg-1, i.p.) prevented the yohimbine-induced increase in the extracellular 5-HT levels. 4. The benzodiazepine receptor agonist, diazepam (2.5 mg kg-1, i.p.) and the 5-HT3 receptor antagonist, ondansetron (100 micrograms kg-1, i.p.) (5 min pretreatment) completely prevented the yohimbine (5.0 mg kg-1, i.p.)-induced increases in the extracellular levels of 5-HT. The 5-HT1A receptor agonist, 8-OH-DPAT (0.32 mg kg-1, s.c.) partially antagonized the yohimbine response. 5. A 5 min pretreatment with the 5-HT3/5-HT4 receptor ligand R(+)-zacopride (10 micrograms kg-1, i.p.) reversed the yohimbine (5.0 mg kg-1, i.p.)-induced increase in the extracellular levels of 5-HT to approximately 30% below the basal levels. A 5 min pretreatment with S(-)-zacopride (100 micrograms kg-1, i.p.) failed to modify the response to yohimbine.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mediation of endothelin-1-induced inhibition of platelet aggregation via the ETB receptor.

1. The effects of FR139317 (ETA antagonist) or PD145065 (non-selective ETA/ETB antagonist) on endothelin-1 (ET-1)-induced changes in blood pressure and inhibition of ex vivo platelet aggregation were investigated in the anaesthetized rabbit. 2. ET-1 (1 nmol kg-1, i.a. bolus) caused a sustained increase in mean arterial pressure (MAP) (peak increase 47 +/- 5 mmHg, n = 8). Intravenous infusion of FR139317 at 0.2 (n = 4) or 0.6 mg kg-1 min-1 (n = 4) inhibited the ET-1 pressor response by 83 or 89%, respectively. Infusion of PD145065 at 0.2 (n = 4) or 0.6 mg kg-1 min-1 (n = 4) inhibited the ET-1-induced increase in MAP by 79 or 75%, respectively. 3. The transient depressor response (-16 +/- 3 mmHg) which preceded the rise in blood pressure induced by ET-1 (1 nmol kg-1, i.a., n = 8) was enhanced by an intravenous infusion of FR139317 (0.6 mg kg-1 min-1) to -35 +/- 5 mmHg (P < 0.05, n = 4). This enhancement was abolished by indomethacin (5 mg kg-1, i.v.) pretreatment (-17 +/- 1 mmHg, n = 4). PD145065 (0.2 mg kg-1 min-1, i.v.) attenuated the ET-1-induced fall in blood pressure to -9 +/- 1 mmHg (n = 4), while a higher dose of this antagonist (0.6 mg kg-1 min-1, i.v.) completely abolished the ET-1-mediated depressor response. 4. ET-1 (1 nmol kg-1, n = 8) inhibited ex vivo platelet aggregation by 96% at 5 min after injection of the peptide.(ABSTRACT TRUNCATED AT 250 WORDS)     

Role of neuronal and vascular Ca(2+)-channels in the ACTH-induced reversal of haemorrhagic shock.

1. In a rat model of volume-controlled haemorrhagic shock causing the death of all control (saline-treated) animals within 30 min, the intravenous (i.v.) bolus injection of ACTH-(1-24) at a dose of 160 micrograms kg-1 produced an impressive and sustained restoration of arterial pressure, pulse pressure and respiratory function, with 100% survival at the end of the observation period (2 h). 2. Both intracerebroventricular (i.c.v., 0.015-0.06 microgram kg-1) and i.v. (5 micrograms kg-1) pretreatment with the N-calcium channel blocker, omega-conotoxin GVIA, and i.v. (but not i.c.v.) pretreatment with the L-calcium channel blocker, nicardipine (125-500 micrograms kg-1) dose-dependently prevented the ACTH-induced shock reversal. 3. These results further indicate that the effect of ACTH in haemorrhagic shock may involve a neuronal link and the eventual restoration of vascular tone mediated by N- and L-type calcium channels, respectively.     

CGP 35348, a new GABAB antagonist, prevents antinociception and muscle-relaxant effect induced by baclofen.

1. CGP 35348, a new GABAB antagonist, was examined on antinociception induced by (+/-)-baclofen by use of the hot plate and writhing tests in mice and the paw pressure test in rats. CGP 35348 was also studied in mice on (+/-)-baclofen-induced impairment of rota-rod performance. 2. CGP 35348, injected either i.p. (60-100 mg kg-1 in mouse) or intracerebroventricularly (i.c.v.) (0.5-2.5 micrograms per mouse; 25 micrograms per rat) prevented (+/-)-baclofen-induced antinociception. 3. CGP 35348 did not modify oxotremorine- and morphine-induced antinociception in mice and rats. 4. CGP 35348 (2.5 micrograms i.c.v. per mouse) also prevented (+/-)-baclofen-induced impairment of the rota-rod test. 5. Two other GABAB antagonists, phaclofen (50 micrograms i.c.v. per mouse) and 2-OH-saclofen (2.5 micrograms-10 micrograms i.c.v. per mouse) did not modify (+/-)-baclofen-induced antinociception. 7. These results suggest that, at present, CGP 35348 is the only compound able to antagonize (+/-)-baclofen-induced antinociception.