Plasminogen activator inhibitor: a regulator of ancrod-induced fibrin deposition in rabbits

Plasma levels of a fast-acting plasminogen activator inhibitor (PAI), which neutralizes both tissue plasminogen activator (t-PA) and urokinase, are markedly increased in endotoxin-treated rabbits. The ability of this inhibitor to prevent the fibrinolysis that occurs after a thrombogenic stimulus was investigated in a rabbit model. Normal and endotoxin-treated male New Zealand rabbits were infused with ancrod, an enzyme that causes noncrosslinked fibrin formation in vivo. Ancrod stimulated t-PA activity by 90% in normal rabbits and caused hypofibrinogenemia but did not increase PAI levels or induce fibrin deposition in target organs. Rabbits injected with endotoxin (10 micrograms/kg) showed an increase in PAI from less than 1 to 32 U/mL 4 hours later. When ancrod was infused at this time, 90% of the rabbits developed renal fibrin thrombi. Fibrin deposition was recorded in 40% of the rabbits that received a lower dose of endotoxin (1.0 microgram/kg) and had a PAI level of 14 U/ml at the time of ancrod infusion 4 hours later. Fibrin deposition did not occur in the endotoxin-treated rabbits that received normal saline. These data suggest that high levels of PAI inhibit fibrinolysis in vivo, thereby promoting fibrin clot deposition following a thrombogenic stimulus.

Clotting of fibrinogen. 2. Calorimetry of the reversal of the effect of calcium on clotting with thrombin and with ancrod

When clotting is effected by thrombin in the presence of calcium, the endotherm for the D nodules of fibrinogen broadens significantly and then becomes narrow again, while increasing in size. Clotting effected by the snake venom enzyme Ancrod, which releases only the A fibrinopeptides from the E nodule, shows only the broadening of the D endotherm. Accordingly, significant interactions of the D nodules of fibrinogen become possible only when the B fibrinopeptides of the E nodule are released on clotting. When calcium present during clotting is removed from the fibrin clot with ethylenediaminetetraacetic acid, the endotherm for the D nodules of fibrin shows nearly complete reversal if clotting was effected with Ancrod but appears to be divided into two endotherms if clotting was effected with thrombin. At neutral pH, new endotherms were observed for fibrinogen in the temperature range 105-140 degrees C.

Therapeutic defibrinogenation in peripheral vascular disease

Despite considerable uncontrolled clinical data implying a beneficial effect of defibrinogenation in peripheral vascular disease, this is not supported by double blind placebo controlled trials. A hypothetical explanation for this discrepancy is developed from experimental studies suggesting that in the absence of adequate shear forces defibrinogenation might induce occlusion of the impaired microcirculation and therefore can lead to an aggravation of tissue hypoxia.

The effect of cycloheximide, heparin and ancrod on mice given Ehrlich ascites tumour cells intravenously

Mice injected intra-venously with Ehrlich ascites tumour cells showed a fatal susceptibility to normally-tolerated doses of cycloheximide when the latter was given at the following times after the tumour cells--2 h, 24 h, 48 h, and 72 h. When the interval between tumour cell injection and cycloheximide challenge was extended to 1 week or 3 weeks (at which latter time mice have clinical "metastatic" neoplasia), no such susceptibility was shown. In the case of the 2 h interval between tumour cells and cycloheximide (and also when cycloheximide was given 2 h before tumour cells), the lethal syndrome was prevented by heparin treatment and also by Ancrod defibrination. This strongly suggests that heparin is effective by virtue of its anticoagulant properties, and that fibrinogen-to-fibrin conversion is an essential step in the pathogenesis. Neither heparin nor Ancrod confer any protection when used in the syndrome consequent upon cycloheximide challenge 24 h after tumour cell injection, which indicates that, in this case, the conversion of fibrinogen to fibrin is not an essential step in determining the fatal outcome.

Ancrod: normalization of fibrinolytic enzyme abnormalities in patients with systemic lupus erythematosus and lupus nephritis

Ancrod is a thrombinlike enzyme from Malayan pit viper (Agkistrodon rhodostoma) venom that has a selective enzyme substrate specificity for fibrinogen. Unlike thrombin, it splits only fibrinopeptide A from the fibrinogen molecule and does not activate factor XIII. Simultaneously with the occurrence of hypofibrinogenemia there is a reduction of plasma plasminogen and a rise in fibrin degradation products, suggesting secondary recruitment of the fibrinolytic enzyme system. Ancrod was given to 18 patients with systemic lupus erythematosus and glomerular and vascular microthrombi. Before treatment vascular plasminogen activator (VPA) was low or unmeasurable in 14, an inhibitor of urokinase-induced plasminogen activation (IPA) was elevated in 18, and an inhibitor of plasmin (PI) was elevated in five. Ancrod treatment resulted in prompt normalization of IPA levels in 13 patients; they were classified as fibrinolysis responders. In five patients IPA levels remained elevated throughout treatment with ancrod; they were classified as fibrinolysis nonresponders. In these five the PI level was elevated before treatment and decreased slowly toward the normal range during ancrod administration. The PI did not appear related to the nonspecific serine protease inhibitors, and was shown to be identical with alpha 2-antiplasmin. In the fibrinolysis responders serial histologic studies showed a striking decrease of disappearance of microvascular thrombosis; in the fibrinolysis nonresponders microvascular thrombosis persisted. The action of ancrod is discussed.

Ancrod in systemic lupus erythematosus with thrombosis. Clinical and fibrinolysis effects

A patient with systemic lupus erythematosus had severe hypertension, rapidly worsening renal failure, and multiple successive thrombotic cerebrovascular and retinal lesions develop. In a kidney biopsy specimen luminal thrombi were demonstrated in arteries and arterioles, without vasculitic or inflammatory changes. The patient's plasma was markedly deficient in both prostacyclin stimulating factor (PSF) and vascular plasminogen activator (VPA), and also contained a potent inhibitor of in vitro urokinase-induced fibrinolysis. Treatment with ancrod resulted in striking reversal of the progressive renal damage and clinical recovery from the thrombotic cerebrovascular and retinal lesions. This clinical improvement was associated with improved renal histologic appearance, correction of the PSF and VPA deficiencies, and disappearance of the urokinase inhibitor. Possible mechanisms of action of ancrod are discussed.

The effect of blood viscosity on blood flow in the experimental saphenous flap model

A study has been made of the effect of lowering blood viscosity with ancrod (Arvin) on blood flow in an experimental island skin flap. Blood flow was measured directly using an electromagnetic flowmeter. It was observed that blood flow into the flap increased significantly (p less than 0.02) as a result of lowering blood viscosity.

Fibronectin: blood turnover in normal animals and during intravascular coagulation

Plasma fibronectin (FN) binds fibrin in vitro by both noncovalent and covalent bonds and is decreased in DIC. In rabbits, conventionally purified 125I-FN had a complex blood clearance with a late t1/2 of 71 hr. A large portion was apparently altered, as evinced by rapid clearance and an intravascular/total body ratio (C1) of 0.28-0.51. 3H-labeled FN, made in vivo by injection of 3H amino acids, had a t1/2 of 73 hr. Crosstransfusion of 131I-FN and 3H-FN into a second set of animals gave similar t1/2s and C1s of 0.74-0.82, indicating the altered 125I-FN was biologically screened in the first animals. Other animals were given 125I-fibrinogen and "screened" 131I-FN. Intravenous thrombin (50-60 U/kg/1 hr) caused a 25%-50% decrease in both 125I-fibrinogen and 131I-FN. Ancrod injection reduced fibrinogen by greater than 90% but had no effect on 131I-FN. 131I-FN levels did not change when thrombin was given after ancrod. No cross-linked FN-fibrinogen alpha-chain was found in the plasma, nor was the thrombin-induced fall in FN affected by spermidine blockade. These experiments demonstrate that FN and fibrin bind in vivo during defibrination and are rapidly cleared from the blood. The abnormal fibrin resulting from ancrod either does not bind FN in vivo or does so reversibly.

Successful treatment by defibrination with ancrod in a patient with hyperacute renal allograft failure and a deficiency of plasma prostacyclin stimulating factor

Hyperacute and renal allograft failure, whether due to rejection or other mechanisms, such as perfusion injury, is usually associated with extensive intraglomerular fibrin deposition and allograft loss. Defibrination with ancrod was used to treat a patient with hyperacute renal allograft failure and extensive glomerular fibrin deposition and necrosis. The patient's plasma had normal fibrinolytic activity but a complete absence of the ability to generate prostacyclin-like activity from rat aortic endothelium "in vitro". Treatment was associated with complete recovery of renal function, disappearance of glomerular fibrin, and restoration toward normal of glomerular structure.

Defibrination with ancrod: effect on reticuloendothelial clearance of circulating immune complexes

Defibrination with ancrod has been shown to be a successful form of treatment for certain types of experimental glomerulonephritis. The effect of ancrod on reticuloendothelial function has received little attention. In the present studies the blood clearance and reticuloendothelial uptake of injected preformed BSA-anti-BSA complexes were studied in defibrinated and control mice. 3 h after their injection, the blood levels and the hepatic and splenic uptakes were significantly different in experimental and control groups. It may be concluded that the reticuloendothelial clearance of injected immune complexes is not impaired by defibrination.

Fibrinogen New Orleans: hereditary dysfibrinogenemia with an A alpha chain abnormality

An abnormal fibrinogen (Fibrinogen New Orleans, or FNO) has been found in a 30 year-old woman, her mother and daughter, but not her father. The propositus suffered mild bleeding, but not thrombo-embolism or abnormal wound healing. Plasma and purified fibrinogen from the propositus caused a prolongation in the clotting time of normal plasma. FNO had increased anodal migration when studied by immunoelectrophoresis. We have been able to follow the release of fibrinopeptides A and B using sensitive SDS-PAGE. In FNO, release of the A peptide was markedly delayed, whereas the cleavage of B peptide was much less delayed, compared to that of A peptide.

Subcutaneous ancrod therapy in peripheral arterial disease: improvement in blood viscosity and nutritional blood flow

Nine patients with extensive peripheral arterial disease were treated with subcutaneous injections of ancrod (Arvin) for 10 to 21 days. Reduction in plasma fibrinogen was associated with a sustained reduction in plasma and blood viscosity, and a sustained increase in nutritional skin blood flow, measured by a Xenon-133 clearance technique (P less than 0.001). These findings may be relevant to the therapeutic effect of ancrod in ischemic rest pain.

Regulation of fibrinogen biosynthesis: effect of fibrin degradation products, low-molecular-weight peptides of fibrinogenolysis, and fibrinopeptides A and B

Fibrinogen synthesis in rabbits was evaluated following intravenous infusions of stage 3 degradation products of homologous fibrinogen or fibrin, prepared in vitro. Fibrinogen production was measured by determining the rate of appearance of 75SeM into circulating fibrinogen. Fibrinogen synthesis increased threefold after the administration of stage 3 FDP (D and E), dialyzed to remove LMW digestion fragments, In contrast, the fdp obtained by plasminolysis of crosslinked thrombin clots or of noncrosslinked ancrod or thrombin clots failed to enhance basal fibrinogen production. Accelerated fibrinogen production was not accompanied by alterations in haptoglobin concentration or by increased incorporation of 75SeM into haptoglobin. Fibrinogen synthesis was not increased after infusions of FPA and FPB.

Complement and coagulation: causative considerations in contrast catastrophies

Earlier studies suggest that adverse reactions to injected radiographic contrast media are idiosyncratic. In an attempt to gain a better understanding of pathophysiologic events underlying these reactions, rabbit models injected with lethal dose ranges of a cholangiographic contrast material were studied. These animals showed activation of both the complement and coagulation systems. Externally applied heat potentiated complement consumption and increased mortality. Depleting complement components C3-C9 by cobra venom factor did not prevent activation of coagulation or diminish mortality. However, depleting fibrinogen diminished complement activation and markedly diminished mortality. Heparin, administered at several hourly intervals after contrast challenge, also diminished mortality. These studies suggest that the adverse effects of contrast media in this model system are mediated chiefly by the coagulation system, and that complement, if it participates deleteriously, must involve components up to, but not including, C3. A logical role for the inhibitor of C1 esterase in adverse contrast reactions is considered.

Treatment of severe foot ischaemia by defibrination with ancrod: a randomized blind study

Forty-two patients, mean age 68 years, with severe leg ischaemia were randomly treated with placebo or by controlled defibrination with ancrod for 3 weeks. Plasma fibrinogen concentration was kept at about 20% of normal in the ancrod treated group. The two groups proved to be well matched regarding factors which could affect the degree of ischaemia. Objective measurements showed a significant rise in ankle and toe systolic blood pressure in the ancrod group lasting for 3 months. There was no rise in distal blood pressure in the control group. In the ancrod treated group the toe and ankle systolic pressures rose about 8 mmHg, but this was not accompanied by an improvement in the clinical course.

The effects of ancrod, the coagulating enzyme from the venom of Malayan pit viper (A. rhodostoma) on prothrombin and fibrinogen metabolism and fibrinopeptide A release in man

The action of ancrod on fibrinogen and prothrombin metabolism was studied in six healthy individuals by the use of 131I-fibrinogen and 125I-prothrombin and by measurement of blood levels of fibrinopeptide A. Two untreated healthy controls were studied at the same time. Rapid defibrinogenation occurred during the initial 3 hr ancrod infusion, and fibrinogen levels were maintained near zero throughout the study. Large quantities of non-thrombin-clottable TCA-precipitable 131I material could be demonstrated in the circulation, reaching a maximum 3 to 6 hr after ancrod infusion and clearing with a half-life of 6 hr. Gel filtration of 6 hr plasmas demonstrated the presence of complexes larger than fibrinogen, as well as degradation products of fibrinogen-fibrin. Prothrombin concentration and metabolism were unchanged by ancrod treatment. Fibrinopeptide A levels in the ancrod group were greather than 4,000 ng/ml during the initial defibrinogenation, declined to greater than 80 ng/ml, and then increased to high levels after 3 days. These studies provide explanations of previous observations concerning the specificity of ancrod and demonstrate that rapid clotting of fibrinogen and dissolution of fibrin can occur in vivo without recruitment of the classic coagulation mechanism.

The role of fibrin formation in the pathogenesis of bacteremic shock in the primate

In this study, an attempt was made to elucidate further the role of intravascular fibrin formation in the pathogenesis of sepsis in the primate. It was found that injected live Escherichia coli caused death in primates within four to 11 hours as a result of microcirculatory failure and acidosis. Pretreatment with Arvin did not prolong the survival rate, probably because of an overloading of the reticuloendothelial system with fibrin degradation products. This study does not support an obligatory role for intravascular coagulation or fibrin formation in primate sepsis and coincides with an earlier report (6) from this laboratory on cats. Vascular damage and malfunction, secondary to mediators released by platelets, leukocytes, red cells or Hageman factor, are not ruled out.

Partial perfusion in awake neonatal lambs: a comparison of three methods

A comparison of the effects of extended partial perfusion of conscious lambs was made between the use of a silicone-tube membrane oxygenator and a bubble oxygenator (Infant Temptrol). The survival time of the lambs was markedly shortened with the bubble oxygenator, although much longer than had been anticipated. A serious problem was uncontrollable bleeding from the cannulation wounds with a rapidly declining PCV. In a third group of experiments the suitability of Ancrod (Arvin-extract of the venom from the Malayan Pit Viper) as an anticoagulant for extended perfusion with a membrane oxygenator was assessed. In our hands bleeding from the cannulation wounds was marked and difficult to control. The fall in the haematocrit which accompanied the bubble and the arvin series was rapid and appeared to be greater than may have been expected from the loss alone. The decline in several of the plasma components appeared to be due largely to the fall in the haematocrit. Successful perfusion of conscious lambs for up to 96 hours was possible with a silicone-tube membrane oxygenator with Heparin anticoagulation.

Treatment of severe intermittent claudication by controlled defibrination

Fifteen patients with severe intermittent claudication were treated by therapeutic defibrination with subcutaneous injections of ancrod for 5 weeks. Mean plasma-fibrinogen was maintained below 50% of the initial value throughout the treatment period. This reduction in plasma-fibrinogen was accompanied by a parallel fall in whole-blood viscosity and a pronounced clinical improvement. Objective measurements showed maximum benefit on the 21st day of treatment, when the mean resting ankle/arm pressure index had increased by 37%, the post-exercise pressure index had increased by 50%, and the time taken for the pressure index to return to a resting value after a constant exercise had decreased by 33%. (The claudication-count had increased by 59%).

Improvement in experimental vascular graft patency by controlled defibrinogenation

A sensitive animal model was used to investigate treatment designed to improve vascular graft patency. A Dacron graft was inserted into the infrarenal vena cava of 30 rabbits. Half were treated with subcutaneous Arvin for 28 days after operation. This produced a significant lowering of the post operative plasma fibrinogen. The patency rate of the grafts in the treated rabbits was significantly greater than in the control rabbits.

Platelet aggregation following defibrination with ancrod

In vitro platelet aggregation was studied in dogs following defibrination with Ancrod. There was marked inhibition of aggregation immediately after defibrination. A gradual return toward normal aggregation was observed over the 96 hours study period, but aggregation was still abnormal at 96 hours after defibrination. There was an inverse and highly significant correlation between aggregation and fibrin degradation product level. Fibrinogen was not measurable after defibrination for the entire study period. Aggregation was thus independent of fibrinogen concentration in this study.

The importance of plasma fibrinogen in vascular surgery

The plasma fibrinogen concentration is directly related to blood viscosity, which in turn is inversely related to blood flow. The way in which the plasma fibrinogen level affects the clinical status of patients with peripheral vascular disease is discussed with reference to both retrospective and prospective studies of patients undergoing major arterial surgery. Animal experiments are described in which the effect of reducing the plasma fibrinogen level with oral clofibrate and parenteral Arvin (ancrod) on the patency of Dacron arterial grafts was studied.

Effect of defibrination on tumor growth and response to chemotherapy

Other investigators have demonstrated fibrin deposition in tumors. Experiments were therefore designed to test whether systemic defibrination would alter tumor growth or tumor response to chemotherapy with cyclophosphamide. Defibrination with Ancrod, a venom extract of Agkistrodon rhodostoma, did not significantly affect tumor sensitivity to chemotherapy. Similarly, defibrination plus fibrinolytic therapy with streptokinase did not affect responsiveness to cyclophosphamide. Long-term defibrination did not affect tumor growth. These results suggest three possible interpretations: (a) the coagulation system may not be important in tumor growth and response to chemotherapy; (b) adequate clearing of fibrin from the tumor was not accomplished in our experiments; or (c) other factors such as platelet deposition may be involved and platelet function was not inhibited by the therapies used in our experiments.

Comparison of the actions of thrombin and the thrombin-like venom enzymes ancrod and batroxobin

Thrombin acts on several coagulant proteins to produce products with physiologic, pharmacologic and pathologic potential. The most sensitive thrombin substrate seems to be factor VIII. Some thrombin dependent reactions studied in vitro and proposed as control reactions seem too insensitive to the action of thrombin to be of in vivo significance. The only enzymic reaction the thrombin-like venom enzymes, Ancrod and Batroxobin, have in common with thrombin is the removal of fibrinopeptide A.

Improvement in blood flow through a critical arterial stenosis by defibrination with ancrod

Using electromagnetic flow probes, cardiac output and hind limb blood flow were measured in dogs in which one hind limb had been rendered ischemic. Four dogs served as controls; seven were defibrinated by intravenous infusion of ancrod, 1 unit/kg, over a 30-minute period. In both groups, hematocrit readings remained constant, but cardiac output fell (this was attributed to barbiturate anesthesia), as did flow in the normal hind limb. In the controls after three hours, flow in the ischemic hind limb had decreased by 34%, but in the treated animals it had increased by 20%. The difference was statistically significant (P less than .001). The selective increase in blood flow in the ischemic limb may be explained by the greater reduction in blood viscosity at low shear rates achieved by defibrination.

The clotting of a snake (Crotalus viridis Helleri) plasma and its interaction with various snake venoms

The clotting of C. V. Helleri plasma is not accelerated by the factor X activator or thrombin-like enzymes from its own venom. Clotting of the plasma is accelerated by the factor Xactivator from Russell's viper venom, but not by the thrombin-like enzyme from Agkistrodon Rhodostoma venom ("Arvin"). The prothrombin activator from the Taipan venom clots C.V. Helleri plasma equally well as human plasma, but the thrombin which is produced has a marked specificity for its own fibrinogen, and clots bovine fibrinogen more slowly. C.V. Helleri plasma contains an inhibitor which progressively inactivates bovine factor Xa and thrombin, but the inhibitor is not potentiated by heparin. The slow, protracted clotting of the snake plasma either alone or when mixed with human plasma or bovine fibrinogen suggests that this inhibitor may interfere with the polymerisation of fibrin monomer.

Improvement of the flow properties of blood: a new therapeutical approach in occlusive arterial disease

The general pathophysiological basis in occlusive arterial disease is the reduced flow rate of blood in the microcirculation. Blood flow in the ischemic tissue can be increased by improving the flow properties of blood. The fibrinogen concentration of blood and the deformability of red cells are two main factors determining the flow properties of blood. Ancrod, a fibrinogen-lowering substance, improves the flow properties of blood by decreasing the viscosity of blood and plasma and by desaggregation of erythrocyte aggregates. Treatment of patients suffering from severe occlusive arterial diseases with Ancrod exhibits surprisingly good results. Disappearance of rest pains and reduction in the use of analgetic drugs has been proved statistically. In the exercising muscles a local hyperosmolarity exists, which is able to decrease the deformability of red cells thereby impairing the flow in narrow capillaries. The addition of Pentoxifyllin to blood in-vitro reduces the rigidity of red cells in hyperosmolar blood samples by increasing their cellular ATP-content. Thus the reduced flow rate of hyperosmolar blood through 8 mu-capillaries could be increased twice (p less than 0.0005) by the addition of Pentoxifyllin. These in-vitro results could be the starting point of a new idea for the treatment of patients with intermittent claudication.

Effect of platelet antiserum on the precipitation of soluble fibrin by endotoxin

Rabbits were injected with a platelet antiserum to examine the role of thrombocytopenia of the precipitation of soluble fibrin by endotoxin.dotoxin. Platelet antiserum removed more than 98% of the circulating platelets, and the resulting thrombocytopenia with platelet counts below 10,000 per mul persisted during the entire 10 hr-period of the experiment. Leukocyte counts were not significantly influenced by the platelet antiserum. Since the rabbits were treated with high doses of heparin, activation of intravascular coagulation by the antiserum did not occur. Precipitation of soluble fibrin was achieved by injection of endotoxin into rabbits with ancrod-induced circulating soluble fibrin. Thrombocytopenia did not prevent the occurrence of glomerular microclots after ancrod and endotoxin administration. On the contrary, if endotoxin was injected into antiserum- and heparin-treated rabbits with circulating soluble fibrin, glomerular microclot formation occurred even in a higher percentage than in control rabbits treated with absorbed platelet antiserum. This investigation indicates that platelet antiserum-induced thrombocytopenia does not protect against precipitation of soluble fibrin by en

Antithrombotic drugs: part II

The defibrinating agent ancrod has had limited clinical trial, but appears to give no advantages over heparin. Intravenous infusion of dextran, a glucose polymer, has been shown to have an antithrombotic effect in many experimental models of thrombosis. However, the evidence that dextran is a clinically valuable antithrombotic drug is conflicting. A number of controlled randomized studies have shown that dextran can prevent postoperative venous thromboembolism when a large volume of dextran 40 or 70 was infused rapidly during and after surgery. However, blood volume expansion during dextran treatment prohibits its use in patients with reduced cardiac reserve, and infrequent though sometimes severe, allergic reactions have been reported. Evidence that dextran is of value for the treatment of venous or arterial thromboembolism comes from uncontrolled studies and is not convincing. Many compounds have been shown to inhibit platelet function in vitro but only five of these drugs have been extensively evaluated as prophylactic or therapeutic antithrombotic agents in man. These are aspirin, sulphinpyrazone, dipyridamole, hydroxychloroquine and clofibrate. They have been evaluated mainly in patients with cerebral vascular disorders, coronary artery disease, peripheral artery ischaemia, venous thromboembolism, prosthetic heart valves, and in patients with arteriovenous shunts. The evaluation of the clinical effect of the platelet function suppressing drugs is in its early stages, but they appear to differ from each other in the spectrum of their clinical effectiveness, and they may be more effective in arterial than in venous thromboembolic disorders. Their role in the management of cerebral vascular disease and coronary artery disease is still uncertain, and should be clarified by the results of a number of multi-centre, prospective, randomized studies which are currently in progress. Three types of thrombolytic drugs have been evaluated clinically; the plasminogen activators streptokinase and urokinase, proteolytic enzymes such as plasmin, and agents which increase the level of endogenous plasminogen activator (e.g. anabolic steroids). Of these, the plasminogen activators now have a definite place in clinical practice. The plasminogen activators accelerate the lysis of recent venous thrombi and pulmonary emboli, and of arterial thrombi or emboli. Thrombolytic therapy with these agents should be considered particularly in patients with recent major pulmonary embolism, as lysis of recent emboli is rapid and substantial. It should also be considered in patients with recent extensive venous thrombosis, because total lysis of venous thrombi has been reported to result in long-term preservation of valve function, and is likely to prevent postphlebitic syndrome, though this has not been proven. However, plasminogen activator therapy carries a higher risk of bleeding than heparin treatment...

Induced fat embolism in rabbits: effects of defibrinogenation and thrombocytopenia

Fat embolism was induced in rabbits by giving an intravenous injection of radioactively labelled homologous retroperitoneal fat. One group was defibrinogenated by Arvin. A second group was made thrombocytopenic by treatment with Busulphan. After the animals had been made thrombocytopenic and had been defibrinogenated, respectively, fat embolism was induced. Macroscopic and histologic examinations were carried out, as well as recordings of wet weight and radioactivity content of the lung. There was a highly significant increase in the pulmonary wet weight of thrombocytopenic animals compared with controls. Macroscopic as well as histologic examination revealed a massive interstitial and alveolar oedema. Half of the specimens showed moderate to massive bleedings. Defibrinogenated animals did not differ from controls. Under the given circumstances, the results suggest that platelets are protective to the endothelial lining of the pulmonary capillaries during embolism. The presence or absence of fibrinogen initially does not seem to be of major importance for the pulmonary damage induced by fat injection.

[Aspects of defibrinogenation therapy]

Fibrinolysis threatment works by means of enzymatic action. It is an effective therapy for occlusive disease of the arteries at Fontaine's stages III and IV. New developments in this treatment will be of interest to phlebologists in the near future. No studies have been reported in the world literature that broaden the present indications : critical study is still required.