Activated human protein C prevents thrombin-induced thromboembolism in mice. Evidence that activated protein c reduces intravascular fibrin accumulation through the inhibition of additional thrombin generation.

Activated protein C (APC) is a potent physiologic anticoagulant with profibrinolytic properties, and has been shown to prevent thrombosis in different experimental models. We investigated the effect of human APC on thrombin-induced thromboembolism in mice, a model of acute intravascular fibrin deposition leading to death within minutes. APC given intravenously (i.v.) as a bolus 2 min before thrombin challenge (1,250 U/kg) reduced mortality in a dose-dependent manner despite the lack of thrombin inhibitor activity. Significant inhibition of thrombin-induced death was observed at the dose of 0.05 mg/kg, and maximal protection was obtained with 2 mg/kg (> 85% reduction in mortality rate). Histology of lung tissue revealed that APC treatment (2 mg/kg) reduced significantly vascular occlusion rate (from 89.2 to 46.6%, P < 0.01). The protective effect of APC was due to the inhibition of endogenous thrombin formation as indicated by the fact that (a) the injection of human thrombin caused a marked decrease in the coagulation factors of the intrinsic and common pathways (but not of Factor VII), suggesting the activation of blood clotting via the contact system; (b) APC pretreatment reduced markedly prothrombin consumption; (c) the lethal effect of thrombin was almost abolished when the animals were made deficient in vitamin K-dependent factors by warfarin treatment, and could be restored only by doubling the dose of thrombin, indicating that the generation of endogenous thrombin contributes significantly to death; and (d) APC failed to protect warfarin-treated animals, in which mortality is entirely due to injected thrombin, even after protein S supplementation. Other results suggest that APC protects from thrombin-induced thromboembolism by rendering the formed fibrin more susceptible to plasmin degradation rather than by reducing fibrin formation: in thrombin-treated mice, fibrinogen consumption was not inhibited by APC; and inhibition of endogenous fibrinolysis by epsilon-aminocaproic or tranexamic acid resulted in a significant reduction of the protective effect of APC. Since APC did not enhance plasma fibrinolytic activity, as assessed by the measurement of plasminogen activator (PA) or PA inhibitor (PAI) activities, PAI-1 antigen, or 125I-fibrin degrading activity, we speculate that the inhibition of additional (endogenous) thrombin formation by APC interrupts thrombin-dependent mechanisms that make fibrin clots more resistant to lysis, so that the intravascular deposited fibrin can be removed more rapidly by the endogenous fibrinolytic system.

Activation of phospholipase A2 and beta-thromboglobulin release in human platelets: comparative effects of thrombin and fluoroaluminate stimulation.

Several reports have suggested that the activity of platelet phospholipase A2 is modulated by GTP-binding protein(s) whose nature and properties need to be defined. Fluoroaluminate is known to activate G-proteins and this leads to a number of cellular responses including the activation of phospholipases. This paper demonstrates that human platelets, prelabelled with [3H]arachidonic acid, produce free arachidonic acid when stimulated with fluoroaluminate and this effect is time- and dose-dependent. The production of arachidonic acid is not inhibited by neomycin, a PI-cycle inhibitor, but is completely abolished by mepacrine, an inhibitor of both phospholipase A2 and C. At low concentration of fluoroaluminate (10 mM NaF) phospholipase A2 but not phospholipase C is activated. In addition, fluoroaluminate treatment releases beta-thromboglobulin (beta-TG) and this effect is not inhibited by acetylsalicylic acid. Under identical conditions both neomycin and mepacrine suppress the release of arachidonic acid and beta-TG induced by thrombin. Sodium nitroprusside, which increases cGMP levels in platelets, inhibits arachidonic acid liberation and beta-TG release in thrombin-stimulated platelets but has no effect in fluoroaluminate-treated platelets; cGMP was reported to suppress phospholipase C activation. These results are consistent with the hypothesis that, in thrombin-stimulated platelets, the liberation of arachidonic acid and beta-TG are strictly dependent on the activation of phospholipase C. We have also provided evidence for the existence of a phospholipase A2 activated by a G-protein which is independent from the degradation of phosphoinositides and, contrary to phospholipase C, it is not down regulated by cGMP.

Thromboxane synthase inhibitors, thromboxane receptor antagonists and dual blockers in thrombotic disorders.

Thromboxane A2 (TXA2) plays a pivotal role in platelet activation and is involved in the development of thrombosis. Thromboxane synthase inhibitors suppress TXA2 formation and increase the synthesis of the antiaggregatory prostaglandins PGI2 and PGD2; however, accumulated PGH2 may interact with the platelet and vessel wall TXA2 receptor, thus reducing the antiplatelet effects of this class of drug. TXA2 receptor antagonists block the activity of both TXA2 and PGH2 on platelets and the vessel wall. Very recently, drugs possessing both thromboxane synthase-inhibitory and thromboxane receptor-antagonist properties have been developed. Paolo Gresele and colleagues explain here why these drugs can be more efficacious than traditional antiplatelet agents and review the available experimental studies involving these drugs.

Safety and efficacy of ximelagatran: meta-analysis of the controlled randomized trials for the prophylaxis or treatment of venous thromboembolism.

BACKGROUND: Ximelagatran has been approved in Europe for VTE prophylaxis in orthopedic surgery at fixed doses and without laboratory monitoring. Aim of the study was to evaluate safety and efficacy of ximelagatran in a meta-analysis of prophylaxis and/or treatment randomized controlled trials. METHODS: Absolute risk of events for ximelagatran and OR for its comparison with LMWH and coumarins were calculated. Subgroup analysis was performed for ximelagatran regimen, comparator agent, type of surgery, starting time of prophylaxis. RESULTS: Twelve studies and 16,992 patients were meta-analysed. Ximelagatran showed an absolute risk of major VTE of 4.04% and 1.69% and of major bleedings of 1.68% and 1.03% in prophylaxis and treatment trials, respectively. In prophylaxis trials, a significant excess mortality (OR: 2.5; 95% CI: 1.02 - 6.13) and an excess in major bleedings (OR: 1.41; 95% CI: 0.93 - 2.14) was found in the whole ximelagatran group. No evidence of treatment effect for major VTE was seen in the comparison with LMWH (OR: 1.01; 95% CI: 0.52 - 1.97). The cohort of patients treated with 24 mg b.i.d. showed similar results. An increase in the absolute risk of bleeding (from 1.04% to 3.03%) was found between post and preoperative administration of ximelagatran. Major VTE risk was increased when ximelagatran was compared to b.i.d. LMWH. CONCLUSIONS: Ximelagatran can be considered for its potential advantages for prevention and treatment of VTE. Future efforts are needed by researchers to prospectively investigate the best postoperatively starting time and by clinicians to monitor overall mortality in prophylactic use.

Impedance plethysmography in the diagnosis of asymptomatic deep vein thrombosis in hip surgery. A venography-controlled study.

We prospectively evaluated the accuracy of computerized impedance plethysmography (CIP) in the diagnosis of asymptomatic deep vein thrombosis (DVT) in 246 consecutive high-risk patients scheduled for hip surgery, with bilateral venography used for comparison. The CIP was performed as a surveillance program every third day. If the CIP remained negative, bilateral venography was performed on postoperative day 10 +/- 1 or on day of treatment 14 +/- 1 in nonoperated-on patients. If the CIP became positive, venography was performed within 24 hours. The sensitivity and specificity of CIP for proximal and distal DVT were 19% (confidence interval [CI], 13% to 24%) and 91% (CI, 87% to 94%), respectively. The positive and negative predictive values were 52% (CI, 38% to 65%) and 70% (CI, 65% to 74%), respectively. The sensitivity and specificity of CIP for proximal DVT were 24% (CI, 13% to 34%) and 90% (CI, 87% to 94%), respectively; the positive and negative predictive values were 31% (CI, 20% to 51%) and 87% (CI, 83% to 90%), respectively. We conclude that, because of its low sensitivity, CIP cannot be used in the surveillance of DVT in high-risk patients or for outcome measurements in clinical trials on DVT prophylaxis.

Effect of glyceryl trinitrate on distensibility of peripheral muscular arteries in humans is not mediated by prostaglandins.

STUDY OBJECTIVE: Vasodilator prostaglandins have been claimed to be responsible for the coronary haemodynamic and venodilator effects of glyceryl trinitrate, although conflicting results have been reported. The aim of this study was to evaluate whether vasodilator prostaglandins play a role in the effect of glyceryl trinitrate on the distensibility of peripheral muscular arteries in healthy humans. DESIGN: A non-invasive technique, impedance plethysmography, was applied to the assessment of the effects of sublingual glyceryl trinitrate on the compliance of the forearm and digital arteries. The subjects studied received placebo (on two separate occasions), indomethacin (100 mg orally), or ibuprofen (800 mg orally) 1 h before glyceryl trinitrate (0.3 mg sublingual) on four occasions separated from each other by at least 48 h. Blood pressure and heart rate were measured by standard techniques; changes in peripheral arterial compliance were evaluated by impedance plethysmography of the forearm and finger. The study was double blind, cross over, placebo controlled, and randomised. SUBJECTS: 12 healthy male volunteers were enrolled in the study. All subjects were fasting for at least 10 h and had abstained from smoking and from methylxanthine or alcohol containing beverages. MEASUREMENTS AND MAIN RESULTS: Glyceryl trinitrate increased heart rate by 11.6(SEM 1.6) beats.min-1 (p less than 0.0005) and diastolic blood pressure by 8.7(1) mm Hg (p less than 0.01), and decreased systolic blood pressure by 8.7(1.5) mm Hg (p less than 0.01) in placebo treated volunteers; the amplitude of the plethysmograph c wave in the forearm and in the finger was also augmented, by 120(11)% and 78(13)% respectively, indicating an increase in arterial compliance. The results obtained in the two placebo sessions did not differ, indicating good reproducibility of the system. Pretreatment with either indomethacin or ibuprofen did not modify the effects of glyceryl trinitrate on heart rate, blood pressure, and arterial compliance in the forearm and the finger. Both indomethacin and ibuprofen suppressed prostaglandin synthesis, as shown by the striking inhibition of serum TxA2 concentration, by 97.2(1.5)% and 93.7(3.0)%, respectively. CONCLUSIONS: Sublingual glyceryl trinitrate, in doses used clinically, induces a reproducible increase in peripheral arterial compliance in healthy volunteers; prostaglandins do not play any significant role in this effect.

Protein kinase C inhibitors enhance G-protein induced phospholipase A2 activation in intact human platelets.

Washed intact human platelets were prelabelled with [3H]arachidonic acid ([3H]AA) and stimulated with thrombin or with AlF4-, a known unspecific activator of G-proteins. Both stimuli induced the liberation of [3H]AA, the release of beta-thromboglobulin (beta-TG) and platelet aggregation. PMA did not induce liberation of [3H]AA although it induced beta-TG release and aggregation; preincubation with PMA did not modify significantly the amounts of [3H]AA and beta-TG released by thrombin or AlF4-. Different inhibitors of PKC (staurosporine, H-7 and calphostin C) increased the release of [3H]AA and inhibited beta-TG release and aggregation induced by AlF4- but they had no effect when platelets were stimulated with thrombin (0.5 U/ml). Calphostin C was able to release [3H]AA by itself without inducing aggregation of beta-TG release. Okadaic acid (a serine/threonine phosphoprotein phosphatase inhibitor) greatly inhibited the release of [3H]AA, beta-TG and aggregation in AlF4--stimulated platelets. These results indicate the presence of a G-protein mediated mechanism for the activation of a platelet phospholipase A2 which is negatively affected by a protein kinase, sensible to putative inhibitors of protein kinase C, and it is activated by a protein phosphatase, sensible to okadaic acid.

Evidence that cytosolic phospholipase A2 is down-regulated by protein kinase C in intact human platelets stimulated with fluoroaluminate.

We reported that protein kinase C (PKC) inhibitors increase the release of arachidonic acid induced by fluoroaluminate (AlF4-), an unspecific G-protein activator, in intact human platelets. Now we demonstrate that this effect is independent of the extracellular Ca2+ concentration and that AlF4(-)-induced release of AA is abolished by BAPTA, an intracellular Ca2+ chelator, even in the presence of GF 109203X, a specific and potent PKC inhibitor. This compound also blocks the liberation of the secretory phospholipase A2 in the extracellular medium, indicating that this enzyme is not involved in the potentiation of arachidonic acid by PKC inhibitors. On the other hand, the latter effect is completely abolished by treatment of platelets with AACOCF3, a specific inhibitor of cytosolic phospholipase A2 (cPLA2). These observations indicate that cPLA2 is responsible for the AlF4(-)-induced release of arachidonic acid by a mechanism that is down-regulated by PKC.

Effects of gemfibrozil on insulin sensitivity and on haemostatic variables in hypertriglyceridemic patients.

In order to assess the efficacy of gemfibrozil on lipid and haemostatic parameters in patients with plurimetabolic syndrome, a multicenter double-blind placebo controlled, parallel study was carried out in 56 patients with primary hypertriglyceridemia and glucose intolerance. These patients had elevated PAI activity and antigen and t-PA antigen levels at rest and after venous occlusion. Gemfibrozil reduced plasma triglyceride levels (P<0.001), whereas it increased free fatty acids (P<0.05) and high density lipoprotein cholesterol levels (P<0.05). In those patients reaching normalization of plasma triglyceride levels (triglyceride reduction > or =50%) (n=15), insulin levels (P<0.05) as well as the insulin resistance index were reduced by gemfibrozil treatment, suggesting an improvement of the insulin resistance index in this patient subgroup. Gemfibrozil treatment did not affect plasma fibrinolysis or fibrinogen levels, despite marked reduction of plasma triglycerides and improvement of the insulin sensitivity associated with triglyceride normalization.

The comparative effects of recombinant hirudin (CGP 39393) and standard heparin on thrombus growth in rabbits.

The aim of this study was to compare the ability of standard heparin and recombinant (r-)hirudin, a specific inhibitor of thrombin, to inhibit thrombus growth in a rabbit jugular vein model. Doses of standard heparin and r-hirudin equivalent in prolonging the aPTT were first identified. The ability of these doses to inhibit 125I-fibrin accretion onto preexisting thrombi was then evaluated. 0.5 and 0.75 mg/kg of standard heparin and 0.8 and 1.25 mg/kg of r-hirudin infused over 3 h produced a mean prolongation of the aPTT of 1.5 and 2 times, respectively. In saline treated rabbits 62 +/- 7 micrograms of 125I-fibrin were accreted on the pre-formed thrombi. The lower doses of standard heparin and r-hirudin produced a 125I-fibrin accretion of 44 +/- 5 and 25 +/- 4 micrograms, respectively (p less than 0.01). The two higher doses of standard heparin and r-hirudin produced a 125I-fibrin accretion of 34 +/- 4 and 17 +/- 3 micrograms, respectively (p less than 0.01). The increase in the dose of standard heparin up to 2.5 mg/kg produced a 125I-fibrin accretion of 26 +/- 3 micrograms a 58% reduction when compared with saline. The increase in the dose of r-hirudin up to 5 mg/kg produced a 125I-fibrin accretion of 12 +/- 2 micrograms, an 81% reduction when compared with saline. No further inhibition was observed when the doses of both agents were further increased. We conclude that doses of standard heparin and r-hirudin equivalent in prolonging the aPTT have a different effect on thrombus growth inhibition, r-hirudin being twice as effective as standard heparin. Exclusive inhibition of thrombin without any other inhibiting effect on blood coagulation appears to be sufficient to inhibit thrombus growth. Our results seem to be promising in view of a clinical evaluation of r-hirudin.

Picotamide protects mice from death in a pulmonary embolism model by a mechanism independent from thromboxane suppression.

We have previously characterized the new antiplatelet agent picotamide as a dual thromboxane synthase inhibitor/thromboxane A2 receptor antagonist in human platelets. We have now studied the antithrombotic activity of this drug in a simple animal model of lung platelet thromboembolism in the mouse. Picotamide, given i.p. 1 hr before the thrombotic challenge, protected mice from death caused by the i.v. injection of collagen plus epinephrine in a dose-dependent way; the dose reducing mortality by 50% was 277 mg/kg while for aspirin it was 300 mg/kg. Picotamide was also able to reduce the mortality provoked by the i.v. injection of the stable TxA2 mimetic U46619; BM 13.505, a pure TxA2-receptor blocker, was also effective while aspirin was totally inactive. Picotamide, finally, reduced the lethal consequences of the i.v. injection of a 12.5% suspension of hardened rat red blood cells, a model in which platelets are not involved; aspirin was totally ineffective in this model while nicardipine, a calcium channel blocker, was active. Picotamide did not inhibit the formation of TxB2 in serum at any of the doses tested (100 to 750 mg/kg i.p.) while it did enhance significantly PGI2-synthesis from mice aortae and, even more, from mice lungs. The i.v. administration of picotamide (250 mg/kg 2 min before the thrombotic challenge) lead to a strong inhibition of serum TxB2 (-84.6%) and was associated with a higher antithrombotic effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Treatment of intermittent claudication with mesoglycan--a placebo-controlled, double-blind study.

OBJECTIVE: To assess the effect of treatment with mesoglycan, a sulphated polysaccharide compound, on the walking capacity of patients with stage II peripheral arterial disease. METHODS: Non-diabetic outpatients with intermittent claudication, duplex ultrasound evidence of peripheral atherosclerosis, ankle/arm index <0.80, systolic ankle pressure >50 mmHg, and absolute walking distance (AWD) between 100 and 300 m (standardised treadmill test) were eligible. After a 5-week run-in on single-blind placebo, patients were randomised to double-blind treatment with mesoglycan, 30 mg/day intramuscularly for 3 weeks followed by 100 mg/day orally for 20 weeks, or matching placebo. All patients received low-dose aspirin and lifestyle instructions. Clinical response was defined as an AWD increase at Week 23 >50% over baseline. Health-related quality of life and ischaemic events were assessed as secondary efficacy variables. RESULTS: 242 patients were randomised and 237 were assessed for clinical response. Patients achieving clinical response were 59/118 with mesoglycan (50.0%) and 31/119 with placebo (26.1%; p <0.001). Geometric mean AWD increased from 192 to 298 m with mesoglycan, and from 192 to 238 m with placebo (p <0.001). Pain-free walking distance showed a non-significant increase with mesoglycan (p = 0.057). Changes in quality of life scores were in favour of mesoglycan. The rate of ischaemic events was 1/120 on mesoglycan and 6/122 on placebo (p = 0.053). The rate of non-ischaemic adverse events leading to treatment discontinuation was 7/120 and 4/122, respectively. CONCLUSION: Treatment with mesoglycan improves the walking capacity of patients with intermittent claudication, and might confer additional antithrombotic protection over that of aspirin.

Characterization of N,N'-bis(3-picolyl)-4-methoxy-isophtalamide (picotamide) as a dual thromboxane synthase inhibitor/thromboxane A2 receptor antagonist in human platelets.

Picotamide (G137 or N,N'-bis[3-picolyl]-4-methoxy-isophtalamide), a drug which has shown platelet inhibitory effects in vitro and ex vivo, was investigated for its mechanism of action on human platelets in vitro. This compound suppresses the aggregation of human platelets induced by arachidonic acid (IC50: 1.8 x 10(-5) M), low-dose collagen (IC50: 3.5 x 10(-4) M), U46619 (IC50: 1 1.4 x 10(-4) M) and by authentic TxA2 (IC50: 1 x 10(-4) M), without affecting the aggregation induced by A23187 or primary aggregation by ADP. Picotamide inhibits dose-dependently TxA2 synthesis by platelets (IC50: 1.5 x 10(-4) M) and enhances the formation of PGE2. Picotamide-treated platelets also favour the formation of PGI2 by aspirinated endothelial cells; in addition, the drug appears to exert a direct stimulatory effect on PGI2-synthesis, at least at high concentrations. Finally, in platelet-rich plasma stimulated with arachidonic acid, picotamide increases intraplatelet cAMP while no effects on cAMP are detected in unstimulated platelets. In conclusion, picotamide is a dual thromboxane-synthase inhibitor/thromboxane-receptor antagonist in human platelets and introduces a new class of agents potentially useful in antithrombotic therapy.

Distribution and occlusiveness of thrombi in patients with surveillance detected deep vein thrombosis after hip surgery.

Venous thromboembolism is a leading cause of in-hospital postoperative morbidity and mortality. Postoperative deep vein thrombosis (DVT) is usually asymptomatic. A number of studies have consistently shown that the non invasive diagnostic methods are inaccurate in the screening of asymptomatic DVT. Failure of non invasive diagnostic methods to detect thrombi in asymptomatic patients has been suggested to be due to the features of thrombi in these patients. The aim of this study was to assess the distribution and the occlusiveness of thrombi in a series of 321 asymptomatic hip surgery patients with adequate bilateral venography of the lower limbs. Venography was performed 10 +/- 1 days after hip surgery. DVT was found in 180 limbs (28.0%). The distribution of thrombi was as follows: 26 (14.4%) isolated proximal thrombi, 55 (30.6%) proximal and distal thrombi, 99 (55.0%) isolated calf thrombi. We found that 14 of the 81 proximal trombi (17.3%) involved the superficial femoral vein either as exclusive location or in association with calf veins. An involvement of common femoral, superficial femoral and popliteal vein was observed in 37 (45.7%), 39 (48.1%) and 44 (54.3%) cases of the 91 proximal DVT. These thrombi were non occlusive in 25 (67.6%), 22 (56.4%) and 26 (59.1%) limbs, respectively. An involvement of at least one peroneal, anterior tibial and posterior tibial veins was observed in 118, 13 and 89 cases of the 220 distal thrombi. These thrombi were non occlusive in 61 (51.7%), 10 (76.9%) and 30 (33.7%) of the cases. We conclude that the majority of thrombi found in asymptomatic hip surgery patients are non occlusive. In view of this, non invasive diagnostic methods based upon venous flow measurement will be unlikely to improve the diagnosis of asymptomatic DVT. The high incidence of isolated superficial femoral vein thrombosis necessitates that real-time B-mode ultrasonography should be performed examining the entire proximal venous system.

Affects of hirudin and heparin on the binding of new fibrin to the thrombus in t-PA treated rabbits.

The aim of this study was to compare the ability of heparin and recombinant hirudin (r-hirudin) in preventing accretion of new fibrin on thrombi during and after treatment with tissue-type plasminogen activator (t-PA) and in enhancing t-PA induced fibrinolysis in a rabbit jugular vein thrombosis model. Heparin and r-hirudin were infused at doses capable of doubling aPTT. In the fibrin accretion inhibition experiments t-PA was infused over 3 h at a dose of 0.2 mg/kg along with saline or heparin, 0.75 mg/kg or r-hirudin, 1.25 mg/kg. In rabbits treated with t-PA plus saline, heparin or r-hirudin, an accumulation of 125I-fibrinogen on the thrombi of 52.5 +/- 5.1 micrograms, 49.5 +/- 5.6 micrograms and 23.5 +/- 3.5 micrograms was observed, respectively, the difference between r-hirudin and both saline and heparin being statistically significant (p less than 0.01). The inhibition of fibrin accretion on the thrombi induced by r-hirudin persists for at least 9 h after the end of the infusion. By that time r-hirudin has been cleared from the circulation and aPTT has returned to the baseline level for at least 8 h. t-PA, 0.2, 0.4, and 1 mg/kg, infused with saline produced 34 +/- 6%, 52 +/- 5% and 79 +/- 8% lysis of pre-formed thrombi, respectively. The same doses of t-PA infused with heparin, 0.75 mg/kg, produced 32 +/- 3%, 54 +/- 5% and 78 +/- 6% fibrinolysis, respectively and infused with r-hirudin, 1.25 mg/kg, 38 +/- 3%, 57 +/- 5% and 82 +/- 8%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Improvement of walking distance by defibrotide in patients with intermittent claudication--results of a randomized, placebo-controlled study (the DICLIS study). Defibrotide Intermittent CLaudication Italian Study.

Defibrotide is an antithrombotic drug which enhances prostacyclin production and activates fibrinolytic system. The aim of this study was to investigate the improvement of walking distance in patients with intermittent claudication treated with defibrotide. DICLIS was a double blind, placebo-controlled study which included patients with walking distance autonomy at a standardized treadmill test < or =350 > or =100 meters. A total of 310 patients were randomly allocated to placebo (n = 101), defibrotide 800 mg/day (n = 104) or defibrotide 1200 mg/day (n = 105). During a one year follow-up, the Absolute Walking Distance (AWD) was measured six times (0, 30, 60, 90, 180, 360 days). Similar improvement in walking distance was found in the three groups until the 90th day; thereafter placebo group showed no further increase, while AWD continued to increase in the defibrotide groups. Between the 180th and 360th day visits, AWD was significantly higher (P <0.01) in patients given defibrotide than in patients given placebo. No difference in efficacy was observed between the two dosages of defibrotide. No differences in side effects were observed among the three groups. The results of the present trial suggest that long-term administration of defibrotide improves walking distance in patients with intermittent claudication.

Post discharge clinically overt venous thromboembolism in orthopaedic surgery patients with negative venography--an overview analysis.

A high incidence of post-discharge venous thromboembolism in orthopaedic surgery patients has been recently reported drawing further attention to the unresolved issue of the optimal duration of the pharmacological prophylaxis. We performed an overview analysis in order to evaluate the incidence of late occurring clinically overt venous thromboembolism in major orthopaedic surgery patients discharged from the hospital with a negative venography and without further pharmacological prophylaxis. We selected the studies published from January 1974 to December 1995 on the prophylaxis of venous thromboembolism after major orthopaedic surgery fulfilling the following criteria: 1) adoption of pharmacological prophylaxis, 2) performing of a bilateral venography before discharge, 3) interruption of pharmacological prophylaxis at discharge in patients with negative venography, and 4) post-discharge follow-up of the patients for at least four weeks. Out of 31 identified studies, 13 fulfilled the overview criteria. The total number of evaluated patients was 4120. An adequate venography was obtained in 3469 patients (84.1%). In the 2361 patients with negative venography (68.1%), 30 episodes of symptomatic venous thromboembolism after hospital discharge were reported with a resulting cumulative incidence of 1.27% (95% C.I. 0.82-1.72) and a weighted mean incidence of 1.52% (95% C.I. 1.05-1.95). Six cases of pulmonary embolism were reported. Our overview showed a low incidence of clinically overt venous thromboembolism at follow-up in major orthopaedic surgery patients discharged with negative venography. Extending pharmacological prophylaxis in these patients does not appear to be justified. Venous thrombi leading to hospital re-admission are likely to be present but asymptomatic at the time of discharge. Future research should be directed toward improving the accuracy of non invasive diagnostic methods in order to replace venography in the screening of asymptomatic post-operative deep vein thrombosis.

Platelet activation in psoriasis.

Recent epidemiological studies have suggested that psoriasis represents a risk factor for thrombotic vascular diseases. In order to evaluate the possible role of hemostatic changes in the development of thrombotic episodes in psoriasis, some parameters of the hemostatic "balance" were investigated in 22 male psoriatic patients and compared to those of 22 male control subjects. Incidence of known risk factors for vascular diseases (diabetes, hypertension, smoking, dyslipidemia) was comparable in the two study groups. There were no statistically significant differences in platelet count, circulating platelet aggregates, platelet production of malondialdehyde (MDA), total plasma antithrombin and fibrinolytic activities. In patients with psoriasis the incidence of spontaneous platelet hyperaggregability and plasma levels of beta-thromboglobulin were significantly higher than in control subjects. Platelet regeneration time, measured as MDA recovery after aspirin ingestion, was significantly shorter in psoriatic patients. These data suggest that an in vivo platelet activation occurs in patients with psoriasis and could contribute to the development of thrombotic complications. The release of mitogenic and inflammatory substances by activated platelets may play a role in the histogenesis of psoriatic lesions.

Inhibition of spontaneous platelet aggregation by sulfinpyrazone.

In a randomized double-blind crossover study in 16 patients with enhanced in vitro spontaneous platelet aggregation, sulfinpyrazone proved to be effective in normalizing platelet aggregability within 4 days after initiation of therapy.

Thrombolytic and haemorrhagic effects of bolus doses of tissue-type plasminogen activator and a hybrid plasminogen activator with prolonged plasma half-life (K2tu-PA: CGP 42935).

K2tu-PA is a hybrid plasminogen activator linking the kringle 2 domain of tissue-type plasminogen activator (t-PA) to the catalytic protease domain of single-chain urokinase-type plasminogen activator (scu-PA). K2tu-PA, as t-PA has high affinity for fibrin and is activated by fibrin but has a longer plasma half-life (over 30 min). The aim of this study was to compare the effects of bolus doses of recombinant t-PA (rt-PA) and K2tu-PA, on: 1) lysis of performed thrombi (fibrinolysis), 2) accretion of new fibrin on pre-existing thrombi during fibrinolysis (thrombus growth), 3) thrombolysis as assessed by reduction of thrombus weight and 4) systemic plasma proteolysis and blood loss from a standard wound. A jugular vein thrombosis model and an ear bleeding model were adopted in rabbits. Saline produced 11 +/- 2% fibrinolysis. rt-PA, 0.2 mg/kg, 0.4 mg and 0.8 mg/kg produced 35 +/- 4%, 54 +/- 4% and 78 +/- 6% fibrinolysis, respectively. K2tu-PA, at the same doses, produced 39 +/- 5%, 57 +/- 6% and 83 +/- 6% fibrinolysis, respectively. Thus, no differences in the fibrinolytic activity of rt-PA and K2tu-PA were observed. Injection of saline was followed by an accretion of 56.4 +/- 5.9 micrograms of radioactive new fibrin on the thrombi. The injection of the three increasing doses of rt-PA was followed by an accretion of 54.9 +/- 5.3 micrograms, 49.1 +/- 6.1 micrograms and 47.2 +/- 4.8 micrograms.(ABSTRACT TRUNCATED AT 250 WORDS)