Intravascular Coagulation In Rabbits Research Articles

Endotoxin-Induced Intravascular Coagulation in Rabbits: Effect of Tissue Plasminogen Activator vs Urokinase on PAI Generation, Fibrin Deposits and Mortality

Endotoxin-Induced Intravascular Coagulation in Rabbits: Effect of Tissue Plasminogen Activator vs Urokinase on PAI Generation, Fibrin Deposits and Mortality

Effect of hydrogen sulfide on tissue factor-induced disseminated intravascular coagulation in rabbits

To investigate the protective effect of hydrogen sulfide (H2S) on tissue factor-induced disseminated intravascular coagulation (DIC) in rabbits and its mechanism. Thirty-two healthy rabbits were randomly divided into four groups: normal control group, NaHS control group, DIC model group, NaHS pretreatment group (each, n = 8). Ten minutes before model reproduction, rabbits in NaHS control and pretreatment groups were given 3.4 mg/kg NaHS (dissolved in normal saline to 5 mL) via ear vein, while rabbits in normal control and DIC model groups were given an equivalent volume of normal saline. Ten minutes later, rabbits in DIC model and NaHS pretreatment groups were intravenously given tissue factor (TF) 2 mL/kg (dissolved in normal saline to 30 mL, at the speed of 1 mL/min for 5 minutes, 2 mL/min for 5 minutes, and 3 mL/min for 5 minutes), and rabbits in normal control and NaHS control groups were given normal saline. 3 mL of blood was collected 10 minutes before TF injection, and 3, 5, 8, 10, 13, 15, 45, 85, 135 minutes after TF injection for determination of prothrombin time (PT), activated partial thromboplastin time (APTT), thrombin time (TT), fibrinogen content (FIB), fibrin degradation products (FDP), and platelet count (PLT). Microcirculation in the mesentery was also observed under microscope. Compared with normal control group, PT and APTT became shorter at 5 minutes after TF injection, and the rate of their change was increased [PT: -8.3 (-11.7 to -5.3)% vs. 1.3 (-2.5 to 3.8)%, P < 0.01; APTT: -19.1 (-30.4 to -9.4)% vs. -2.6 (-6.2 to 3.0)%, P < 0.05]. PT and APTT were prolonged 15 minutes after TF injection, and their changes were more significant [PT: 31.0 (25.0 to 36.9)% vs. -1.3 (-6.3 to 5.0)%, APTT: 61.3 (50.0 to 72.9)% vs. 0.0 (-10.0 to 10.0)%, both P < 0.01] in DIC model group. TT was gradually reduced after TF injection, FIB and PLT were gradually decreased, and their changes were more obvious at 15 minutes in DIC model group compared with those in normal control group [TT: -9.5 (-12.0 to -6.2)% vs. -2.0 (-4.0 to 0.7)%, FIB: -4.3 (-9.9 to -2.2)% vs. -1.0 (-5.8 to 4.3)%, PLT: -90.0 (-93.4 to -86.5)% vs. -1.0 (-3.9 to 2.6), all P < 0.01]. After TF injection, it appeared latex-like particles in FDP test board, and it was gradually increased within 3-15 minutes, and then it gradually became less marked. The rate of blood flow in mesenteric capillaries was decreased obviously within 10 minutes, and it became faster accompanying with obvious hemorrhage. PT and APTT in NaHS pretreatment group became shortened 5 minutes after TF injection, and their rate of change was significantly decreased compared with that of DIC model group [PT: -6.3 (-8.6 to 0.0)% vs. -8.3 (-11.7 to -5.3)%, APTT: -13.6 (-24.2 to -2.3)% vs. -19.1 (-30.4 to -9.4)%, both P < 0.05], and prolonged at 15 minutes, and their rate of change was significantly decreased compared with that of DIC model group [PT: 10.1 (3.8 to 15.2)% vs. 31.0 (25.0 to 36.9)%, P < 0.01; APTT: 27.8 (-15.8 to 39.7)% vs. 61.3 (50.0 to 72.9)%, P < 0.05]. TT, FIB, and PLT were reduced at 15 minutes in NaHS pretreatment group, and their rate of change was markedly decreased compared with that of DIC model group [TT: -4.5 (-7.8 to -1.3)% vs. -9.5 (-12.0 to -6.2)%, P < 0.01; FIB: -3.3 (-8.0 to 1.9)% vs. -4.3 (-9.9 to -2.2)%, P < 0.05; PLT: -58.8 (-53.0 to 64.0)% vs. -90.0 (-93.4 to -86.5)%, P < 0.01]. The rate of agglutination of latex particles in NaHS pretreatment group was decreased significantly at each time point compared with DIC model group; mesenteric capillary blood flow slowed down gradually within 10 minutes, but it was faster as compared with the DIC model group. It became faster later, but bleeding was obviously less. These results show that H2S protects against TF-induced DIC by inhibiting the activity of coagulation system and platelet aggregation.

Antagonism by salvianolic acid B of lipopolysaccharide-induced disseminated intravascular coagulation in rabbits.

The aim of the present study was to investigate the effects of salvianolic acid B on lipopolysaccharide (LPS)-induced disseminated intravascular coagulation (DIC) in rabbits. Continuous infusion of LPS was used to induce a DIC model in rabbits. Treatment with salvianolic acid B (1, 3 or 6 mg/kg) was started simultaneously with LPS infusion (0.5 mg/kg LPS in 60 mL saline; 10 mL/h over a period of 6 h) through the contralateral marginal ear vein. Activated partial thromboplastin time (APTT), prothrombin time (PT), platelet count and fibrinogen concentration were determined, as were plasma levels of fibrin-fibrinogen degradation products (FDP), alanine aminotransferase (ALT), blood urea nitrogen (BUN), protein C activity, antithrombin III (ATIII) and tumour necrosis factor (TNF)-α concentration. The gradual impairment of haemostatic parameters was induced by continuous infusion of LPS. There were marked increases in APTT, PT, BUN, ALT and plasma TNF-α and marked decreases in the platelet count, fibrinogen, FDP, protein C and ATIII. The intravenous administration of 1, 3 or 6 mg/kg salvianolic acid B attenuated the increases in APTT, PT, BUN, ALT and plasma TNF-α and the decreases in fibrinogen, platelet, FDP, protein C and ATIII induced by LPS infusion. These observations indicate that salvianolic acid B has an effect against LPS-induced DIC in rabbits.

Crocetin administration ameliorates endotoxin-induced disseminated intravascular coagulation in rabbits

Disseminated intravascular coagulation (DIC), a life-threatening secondary complication in several diseases, is characterized by large amounts of thrombin that lead to fibrin deposition and microthrombus formation throughout the microcirculation. Recent in-vitro studies suggest that crocin, crocetin or safranal, carotenoid constituents of the spice Crocus sativus L. (saffron), have antithrombotic properties, especially anti-Xa activity. The present study was designed to evaluate the effect of crocetin on thrombosis procedure using a rabbit model of bacterial endotoxin-induced DIC. Crocetin administration (3 mg/kg), 30 min before the beginning of endotoxin infusion, improved DIC-related haemostatic indices such as platelet blood counts (P≤ 0.05), blood plasma fibrinogen and protein C concentration (P≤ 0.05). In addition, it ameliorated DIC-associated disease and fibrin deposition in the glomeruli (P≤ 0.05). These results indicate that crocetin reveals a preventive antithrombotic role in vivo and prescribe further investigation on the possibility of developing crocetin-based DIC treatment modalities.

The effect of fibrinolytic enzyme FII a from Agkistrodon acutus venom on disseminated intravascular coagulation in rabbits

A novel fibrinolytic enzyme, FII(a), was isolated from Agkistrodon acutus venom, which can degrade fibrin/fibrinogen and dissolve thrombus without activating plasminogen or influencing the activities of tissue plasminogen activator (t-PA) and plasminogen activator inhibitor type-1 (PAI-1). In this study, we evaluated the effect of FII(a) on lipopolysaccharide (LPS)-induced experimental disseminated intravascular coagulation (DIC) in rabbits, through the continuous infusion of 100-microg/kg/h LPS for a period of 6 h. Seven groups were established: LPS control, FII(a) (0.1, 0.3, and 0.6 mg/kg/h, respectively), heparin control (100 IU/kg/h), heparin + FII(a) (heparin 100 IU/kg/h associated with FII(a) 0.3 mg/kg/h), and a saline control group. A continuous injection of LPS induced a gradual impairment in hemostatic parameters, kidney fibrin deposition, and a high mortality rate. The intravenous administration of FII(a) improved the concentration of fibrinogen, the activities of protein C, plasminogen, t-PA, antithrombin III (ATIII), and PAI-1. Kidney fibrin deposition and the mortality also decreased. In the in vitro experiments, FII(a) can degrade fibrin/fibrinogen and high-dose FII(a) enhanced the activity of protein C. These findings suggest that the effects of FII(a) on LPS-induced DIC were from fibrinogen degradation and enhanced protein C activity. The simultaneous administration of FII(a) and heparin further improved all the hemostatic parameters, including decreased kidney fibrin deposition, and none of the rabbits died within 24 h, which indicates that the effects were mediated by degradation of fibrin/fibrinogen together with thrombin inhibition. We conclude that FII(a) may be useful in the treatment of DIC.

Effect of some new thioglycosides on endotoxin-induced disseminated intravascular coagulation in rabbits

Disseminated intravascular coagulation (DIC) is a systemic thrombohemorrhagic disorder seen in association with many clinical situations, e.g. sepsis, malignancy, obstetrical complications and intravascular hemolysis. In our model, disseminated intravascular coagulation was induced in rabbits by two consecutive intravenous bolus injections of endotoxin from Escherichia coli, 80 and 40 μg/kg. The control group was treated with 0.9% saline. The activity of thioglycosides was compared to unfractionated heparin (UFH) and efegatran with and without administration of endotoxin. Drugs were administered in the following doses: heparin 50 and 100 IU/kg/h i.v. infusion; efegatran 0.25 and 0.5 mg/kg/h i.v. infusion; GYKI 39521 (RGH-1875) as well as GYKI 39541 (RGH-1962) 12.5 and 25 mg/kg per os. Thioglycosides did not modify coagulation parameters in this model [prothrombin time (PT), activated partial thromboplastin time (APTT), thrombin time (TT)] as compared with endotoxin/vehicle group. The changes in TFPI level after administration of thioglycosides and heparin were similar in the mentioned model to those without endotoxin. Endotoxin-induced changes of leukocyte count were not affected by GYKI 39521 and GYKI 39541 treatment in our model. Diminution of fibrinogen level and platelet count was prevented by GYKI 39521 and GYKI 39541. Fibrin degradation products and fibrinolysis were significantly decreased by GYKI 39521 and GYKI 39541. The thioglycosides may have a lower risk of bleeding in the treatment of disseminated intravascular coagulation than heparin.

Effects of low molecular weight heparin, alone or combined with antithrombin III, on mortality, fibrin deposits and hemostatic parameters in endotoxin-induced disseminated intravascular coagulation in rabbits.

The effect of low molecular weight heparin (LMWH) with or without antithrombin III (AT III) has been studied in a rabbit model of disseminated intravascular coagulation (DIC) induced by continuous infusion of 100 microg/kg/hr of Escherichia coli endotoxin for 6 hr. LMWH (5 and 10 IU/kg/hr/6 hr), alone or in combination with AT III (20 U/kg/hr/6 hr), or saline were administered simultaneously with endotoxin. Hemostatic markers at 0, 2, and 6 hr as well as kidney fibrin deposits and the mortality rate at 24 hr were determined. Rabbits receiving only endotoxin showed an impairment in hemostasis, as well as high kidney fibrin deposits and a high mortality rate. LMWH alone did not exert any effect. The simultaneous infusion of LMWH and AT III exerted a beneficial effect on the hemostatic markers and reduced the kidney fibrin deposits as well as the mortality rate in a LMWH dose-dependent manner. Fibrinogen and protein C consumption were significantly higher and renal fibrin deposits more intense in the rabbits that had died in the first 24 hr. There was also a significant positive correlation between kidney fibrin deposits and platelets, fibrinogen, and protein C consumption, taking the whole rabbit population. It is concluded that the simultaneous infusion of LMWH and AT III is useful in this DIC model and would make it possible to reduce significantly the AT III doses used when AT III is given alone.

Effects of low molecular weight heparin, alone or combined with antithrombin III, on mortality, fibrin deposits and hemostatic parameters in endotoxin‐induced disseminated intravascular coagulation in rabbits

Effects of low molecular weight heparin, alone or combined with antithrombin III, on mortality, fibrin deposits and hemostatic parameters in endotoxin‐induced disseminated intravascular coagulation in rabbits

Effects of low molecular weight heparin, alone or combined with antithrombin III, on mortality, fibrin deposits and hemostatic parameters in endotoxin‐induced disseminated intravascular coagulation in rabbits

Effects of low molecular weight heparin, alone or combined with antithrombin III, on mortality, fibrin deposits and hemostatic parameters in endotoxin‐induced disseminated intravascular coagulation in rabbits

Endotoxin-induced disseminated intravascular coagulation in rabbits: Effect of recombinant hirudin on hemostatic parameters, fibrin deposits, and mortality

We evaluated the effect of r-hirudin on an experimental model of disseminated intravascular coagulation (DIC) in rabbits, through the continuous infusion of 100 μg/kg/hr of Escherichia coli endotoxin for a period of 6 hours. r-Hirudin (0.05, 0.3, and 0.6 mg/kg/hr) as treatment, or saline solution as placebo, were administered simultaneously with endotoxin. Severe DIC in the endotoxin control group was shown by impairment in hemostatic parameters, kidney fibrin deposition, and a high mortality rate. Medium and high doses of r-hirudin led to an improvement in such DIC-related parameters as platelet numbers and fibrinogen and protein C concentrations. High-dose r-hirudin also reduced consumption of antithrombin III (ATIII). All doses of r-hirudin prevented decreases in tissue plasminogen activator (t-PA) and reduced the increase in plasminogen activator inhibitor-1 (PAI-1) activity observed at 2 hours after endotoxin administration. A significant reduction in kidney fibrin deposition was seen in medium- and high-dose r-hirudin groups. Additionally, the mortality rate in rabbits receiving medium- and high-dose r-hirudin was 10%, and that in rabbits receiving low-dose r-hirudin was 20%, as compared with a mortality rate of 70% in the control group. Protein C activity was significantly lower ( p < 0.001) in nonsurviving rabbits. Moreover, there was a strong positive correlation ( r = 0.68, p < 0.001) between protein C consumption and kidney fibrin deposition. We conclude that r-hirudin can be a useful drug in the clinical treatment of DIC.

The effect of immunodepletion of antithrombin III on the response of rabbits to Russell's viper venom-induced activation of factor X.

Many years ago it was shown that an infusion of tissue factor (TF) into rabbits causing only limited consumption of factor X and prothrombin resulted in extensive consumption of fibrinogen. More recently it was shown that an injection of a concentration of the factor X-activating fraction of Russell's viper venom (RVV-X) depleting rabbits of factor X resulted in only minimal consumption of both plasma prothrombin and fibrinogen. We report here experiments in which rabbits depleted of antithrombin III (ATIII) to different degrees were infused over 4 hours with a concentration of RVV-X, causing consumption of about 60% of plasma factor X. Similar minimal mean falls in plasma prothrombin and fibrinogen levels were observed in control rabbits given nonimmune goat IgG and in rabbits immunodepleted with goat anti-rabbit ATIII IgG to about 40% of normal plasma ATIII activity. However, if rabbits were immunodepleted to about 10% to 20% of normal plasma ATIII, then mean consumption of prothrombin was increased modestly and, more impressively, mean consumption of plasma fibrinogen was increased markedly. Whereas limited amounts of thrombin generated on the surface of phospholipid vesicles by factor VIIa/ TF can trigger extensive intravascular coagulation in rabbits with normal plasma ATIII levels, limited amounts of thrombin generated by reactions triggered by factor Xa formed in fluid phase did so only after plasma ATIII levels were markedly depleted. A possible reason for this difference is discussed.

248 Hirudin improves fibrinolysis and mortality in endotoxin-induced intravascular coagulation in rabbits

248 Hirudin improves fibrinolysis and mortality in endotoxin-induced intravascular coagulation in rabbits

Endotoxin-Induced Intravascular Coagulation in Rabbits:Effect of Tissue Plasminogen Activator vs Urokinase on PAI Generation, Fibrin Deposits and Mortality

We have evaluated the effect of plasminogen activators (t-PA and urokinase) on an experimental model of disseminated intravascular coagulation (DIC) in rabbits by injection of 20 micrograms/kg/h of E. coli lipopolysaccharide during 6 h t-PA (0.2 mg/kg and 0.7 mg/kg), urokinase (3000 U/kg/h) and saline (control) were given simultaneously with endotoxin. Results indicated that urokinase and low dose of t-PA significantly reduced the increase of plasminogen activator inhibitor (PAI) activity observed 2 h after endotoxin (p < 0.001). High t-PA dose also diminished the PAI levels at 6 h (p < 0.001). A significant reduction of fibrin deposits in kidneys was observed din both t-PA treated groups as compared with findings in the group of rabbits infused with saline solution (p < 0.005), whereas urokinase had no significant effect on the extent of fibrin deposition. Finally, the mortality rate in the control group (70%) was reduced to 50% in rabbits receiving high doses of t-PA. In conclusion, treatment with t-PA resulted in reduced PAI generation, fibrin deposits and mortality in endotoxin-treated rabbits.

Characteristic effects of activated human protein C on tissue thromboplastin-induced disseminated intravascular coagulation in rabbits

Protein C (PC) is the zymogen of an anticoagulant serine protease and is converted to its active form (activated protein C: APC) by thrombin in the presence of thrombomodulin. APC plays an important role in regulating thrombosis and fibrinolysis by inhibiting not only blood coagulation factors Va and Villa but also type-1 plasminogen activator inhibitor (PAI-1). In the present study we examined the effects of human APC on tissue thromboplastin-induced disseminated intravascular coagulation (DIC) in rabbits and compared them with those of heparin. Both APC (300–3000U/kg) and heparin (100–300 IU/kg) inhibited the decreases in platelet count and fibrinogen level equally. APC improved the prolonged bleeding time, but heparin aggravated bleeding with potent prolongation of activated partial thromboplastin time (APTT). Furthermore, in APC-treated animals, fibrin deposition in glomeruli was less than in heparin-treated animals. This result suggests that APC accelerated local fibrinolysis by neutralizing PAI-1. From our findings, we concluded that APC can improve both coagulation and fibrinolysis in a DIC model and should be useful for the clinical remedy of DIC without having an adverse side effect like a bleeding tendency.

Studies of factor Xa/phospholipid-induced intravascular coagulation in rabbits. Effects of immunodepletion of tissue factor pathway inhibitor.

In earlier studies from this laboratory evidence was obtained for a physiological function of tissue factor pathway inhibitor (TFPI) as a regulator of hemostasis capable of preventing thrombotic complications that might otherwise result from exposure of blood to trace amounts of tissue factor (TF). However, it was not possible to conclude that the protective effect of TFPI stemmed solely from inhibition of factor VIIa/TF catalytic activity, since TFPI neutralizes stoichiometric amounts of factor Xa in forming an inhibited factor Xa/TFPI/factor VIIa/TF complex. Therefore, we examined the effects of immunodepletion of TFPI on the extent of coagulation initiated in rabbits by exposure to factor Xa and phospholipid in the absence of TF. In one experimental approach, factor Xa was generated endogenously with the factor X-activating fraction of Russell's viper venom (0.33 microgram/kg) in rabbits receiving an infusion of phosphatidylcholine/phosphatidylserine (PCPS) vesicles, 1 mg/kg over 2 hours. In a second approach, rabbits were injected with a complex of factor Xa (0.75 microgram/kg) and PCPS (12.5 micrograms/kg). In contrast with the observed sensitization of TFPI-depleted rabbits to TF-induced coagulation, TFPI-depleted rabbits were not sensitized to coagulation initiated by factor Xa and phospholipid in the absence of TF. These data support the conclusion that the physiological function of TFPI in regulating TF-dependent coagulation stems primarily from its ability to inhibit factor VIIa/TF catalytic activity.

The effect of two-domain tissue factor pathway inhibitor on endotoxin-induced disseminated intravascular coagulation in rabbits

Disseminated intravascular coagulation (DIC) is a common complication in sepsis, and may result from endotoxin-induced exposure of tissue factor on the surface of monocytes and endothelial cells. Tissue factor pathway inhibitor (TFPI) is a factor Xa-dependent feedback inhibitor of the tissue factor-factor VIIa complex. In the present study the effect on DIC of a two-domain TFPI analogue (2D-TFPI), consisting of the first two Kunitz domains of TFPI but lacking the third domain, was tested. DIC was induced in rabbits by two intravenous bolus injections of endotoxin from Escherichia coli (10 and 50 μg/kg) 24 h apart. Simultaneously with the last endotoxin injection an infusion of 2D-TFPI (0, 0.3, 1.0 or 3.0 mg/kg/h) was given. Blood samples were obtained at 0 h, 24 h and 31 h. At 31 h the animals were sacrificed and the kidneys were submitted to histological examination. The degree of fibrin deposition in glomeruli was scored blindly using an arbitrary scale from 0 to 3. Between 24 and 31 h the group receiving endotoxin alone showed a significant decrease in platelet count (65%), plasma fibrinogen (41%), antithrombin III (25%), and factor VIII (63%), and a significant prolongation of the aPTT (14%). Furthermore, massive fibrin deposition was detected in the renal glomeruli at 31 h. Infusions of 2D-TFPI inhibited all the endotoxininduced changes in a dose-dependent manner. In conclusion, the data demonstrate that inhibition of the TF/FVIIa complex by infusion of 2D-TFPI significantly counteracts endotoxin-induced coagulopathy in rabbits, and might thus be an attractive drug for treatment of endotoxin-induced DIC in humans.

The effect of two-domain tissue factor pathway inhibitor on endotoxin-induced disseminated intravascular coagulation in rabbits

Disseminated intravascular coagulation (DIC) is a common complication in sepsis, and may result from endotoxin-induced exposure of tissue factor on the surface of monocytes and endothelial cells. Tissue factor pathway inhibitor (TFPI) is a factor Xa-dependent feedback inhibitor of the tissue factor-factor VIIa complex. In the present study the effect on DIC of a two-domain TFPI analogue (2D-TFPI), consisting of the first two Kunitz domains of TFPI but lacking the third domain, was tested. DIC was induced in rabbits by two intravenous bolus injections of endotoxin from Escherichia coli (10 and 50 micrograms/kg) 24 h apart. Simultaneously with the last endotoxin injection an infusion of 2D-TFPI (0, 0.3, 1.0 or 3.0 mg/kg/h) was given. Blood samples were obtained at 0 h, 24 h and 31 h. At 31 h the animals were sacrificed and the kidneys were submitted to histological examination. The degree of fibrin deposition in glomeruli was scored blindly using an arbitrary scale from 0 to 3. Between 24 and 31 h the group receiving endotoxin alone showed a significant decrease in platelet count (65%), plasma fibrinogen (41%), antithrombin III (25%), and factor VIII (63%), and a significant prolongation of the aPTT (14%). Furthermore, massive fibrin deposition was detected in the renal glomeruli at 31 h. Infusions of 2D-TFPI inhibited all the endotoxin-induced changes in a dose-dependent manner. In conclusion, the data demonstrate that inhibition of the TF/FVIIa complex by infusion of 2D-TFPI significantly counteracts endotoxin-induced coagulopathy in rabbits, and might thus be an attractive drug for treatment of endotoxin-induced DIC in humans.

The effect of a long-acting recombinant hirudin (PEG-hirudin) on experimental disseminated intravascular coagulation (DIC) in rabbits

Reproducible disseminated intravascular coagulation in rabbits was provoked by two intravenous injections 24 hours apart of endotoxin from Salmonella enteritidis.There were mild symptoms of DIC before the second injection which considerably increased thereafter. In detail there was a sharp drop of the platelet count and a considerable diminution of Antithrombin III,of Protein C,Plasminogen and Antiplasmin as well as an appearance of fibrin monomer complexes and an increase of the aPTT. When PEG-hirudin in a single dose of 1 mg/kg BW was given simultaneously with the second injection of endotoxin the following alterations were observed: The drop of the platelet count and of the activities of Antithrombin III, Protein C, Plasminogen and Antiplasmin was significantly less pronounced. The fibrin monomer complexes were lower and the aPTT was less prolonged. The thrombin time,however,as a sign of a direct action of hirudin on thrombin was considerably more prolonged than in the controls. The combined effect of these alterations strongly points in the direction of a favourable influence of PEG-hirudin on the course of DIC. It is of special interest that 6 h after the intravenous injection of PEG-hirudin its full effect on the thrombin time was still detectable. This is apparently due to a longer half-life in circulation of PEG-hirudin than of natural hirudin.

Effect of DDAVP on Endotoxin-Induced Intravascular Coagulation in Rabbits

We have evaluated the effect of 1-Deamino-8D-arginine vasopressin (DDAVP) on an experimental model of intravascular coagulation (DIC) induced in rabbits by injection of 20 micrograms kg-1 h-1 during 6 h of E. coli lipopolysaccharide. DDAVP significantly ameliorated the platelet drop and fibrinogen decrease (p less than 0.01) induced by endotoxin in control animals. A significant reduction in factor XII consumption (p less than 0.01) and a decrease in the generation of endotoxin induced PAI-1 activity in rabbits circulation was also observed (p less than 0.005). Moreover, fibrin deposition in kidneys of rabbits receiving DDAVP was significantly reduced as compared to control animals. Finally, the mortality rate in the control group was significantly higher than in DDAVP-treated rabbits (p less than 0.01). The hemostatic changes induced by DDAVP correlated with lower fibrin deposition and reduction in mortality rates.

Depletion of extrinsic pathway inhibitor (EPI) sensitizes rabbits to disseminated intravascular coagulation induced with tissue factor: evidence supporting a physiologic role for EPI as a natural anticoagulant.

Although in vitro experiments have established that extrinsic pathway inhibitor (EPI) is the only known plasma inhibitor of factor VIIa-tissue factor (TF) catalytic activity of potential physiologic significance, evidence of its function in vivo has been lacking. TF-induced intravascular coagulation may occur in patients despite normal plasma levels of EPI and, in our earlier studies, normal plasma EPI levels did not protect rabbits from intravascular coagulation induced by an infusion of purified TF (1 microgram/kg). Studies have now been carried out in which plasma EPI levels were reduced in rabbits to below 20% of the initial level by injection of anti-rabbit EPI IgG. Infusion into such animals of purified rabbit TF apoprotein (0.25 microgram/kg) reconstituted into phospholipid vesicles induced substantial disseminated intravascular coagulation. Infusion of control saline or phospholipid vesicles not containing TF was without significant effect as was infusion of TF (0.25 microgram/kg) into animals injected with nonimmune goat IgG. These data establish that EPI can dampen TF-induced intravascular coagulation in rabbits. They support the hypothesis that EPI plays a significant role in regulating coagulation resulting from the exposure of blood to trace concentrations of TF during the illnesses and minor injuries of normal existence.