Fibrinolytic enzyme system and pregnancy

The effect of pregnancy on the components of the fibrinolytic enzyme system was determined by serial observations on 10 healthy women during normal pregnancy, labour, and the puerperium. The plasminogen level was substantially increased in the third trimester; the increase occurred pari passu with a pronounced increase in fibrinogen concentration. After allowing for the expansion of plasma volume in pregnancy a twofold increase in the absolute amounts of circulating fibrinogen and plasminogen was found. In late pregnancy and during labour the level of plasminogen activator was greatly decreased, whereas a normal or increased level was present in the first week of the puerperium. No alteration in the levels of inhibitors of plasminogen activation by urokinase was found during normal pregnancy. The thrombin time and platelet count remained unchanged during pregnancy and labour but the platelet count rose significantly during the first week of the puerperium.The haemostatic mechanism in pregnancy appears to be altered towards an enhanced capacity to form fibrin and a diminished ability to lyse fibrin. These changes may be a physiological development to ensure the integrity of the foetal and maternal circulations and provide rapid and effective haemostasis in the uterus during and after placental separation. Nevertheless, the changes may also establish a vulnerable state for intravascular fibrin deposition.

Fibrin degradation products in normal and abnormal pregnancy and parturition

The levels of fibrin, fibrinogen degradation products (F.D.P.) in the serum were investigated in normal pregnancy and parturition, after caesarean section, and in patients with abruptio placentae, eclampsia, intrauterine death, and post-partum haemorrhage. No significant change occurred during normal pregnancy, but a highly significant increase was found during labour and again during the first week after normal delivery. After caesarean section the levels of F.D.P. were increased two to four hours after operation, and substantially higher levels were found three to eight days after operation than after normal delivery. High levels of F.D.P. were associated with abruptio placentae and eclampsia, and increased levels after intrauterine death and post-partum haemorrhage.An excess of F.D.P. with diminished or normal systemic fibrinolytic activity suggests that local intravascular fibrin deposition and fibrinolysis occur in normal parturition and in these complications of pregnancy. The very high levels of F.D.P. found in abruptio placentae will be important in the pathogenesis of the defective haemostasis that may accompany this complication.

B. The fibrinolytic mechanism. The mechanism of fibrinolysis

In recent years, stimulated by the production by the pharmaceutical industry of fibrinolytic agents suitable for therapeutic use in man, there has been a great increase in interest in the components and functions in health and disease of the fibrinolytic enzyme system. Development of knowledge of fibrinolysis Spontaneous lytic activity of blood clots It has been known for many years that human blood possesses fibrinolytic activity. Hunter (1794) records that in 'animals killed by lightning or by electricity’ or in animals 'who are run very hard, and killed in such a state’ the blood does not clot. This phenomenon was partly explained by Morawitz (1906) who found that the blood from victims of sudden death contained no fibrinogen and could destroy the fibrinogen and fibrin of normal blood. Denis (1838) observed that the blood clots obtained in wet cupping redissolved in less than 24 h. Green (1887) noted that when fibrin prepared from ox blood had dissolved when incubated in saline it could not be clotted again by thrombin. Dastre (1893), during the course of phlebotomy in dogs, observed a reduction in fibrin yield, which he attributed to destruction of fibrin, a process which he named ‘fibrinolysis’; and Hedin (1904) found spontaneous proteolytic activity in the globulin fraction of ox blood. The main outline of present-day knowledge of spontaneous fibrinolytic activity in the blood was finally achieved when Macfarlane (1937) showed that in man, fibrinolytic activity in the blood could be provoked by surgical operation.

Action of a pyrimido-pyrimidine compound on platelet behaviour in vitro

A pyrimido-pyrimidine compound (RA433) was found in vitro to be a significantly more potent inhibitor of platelet behaviour than the previously available pyrimido-pyrimidine compound RA8-dipyridamole. In a turbidimetric system RA433 inhibits platelet aggregation induced by adenosine diphosphate, collagen, and noradrenaline; further, in a glass-bead-column technique it is a powerful inhiitor of platelet adhesiveness.

Effects of three cobra venoms on blood coagulation, platelet aggregation, and fibrinolysis

The effects of the venoms of Naja melanoleuca, Naja nigricollis, and Ophiophagus hannah on blood coagulation, platelet aggregation, and fibrinolysis were studied in vitro. All three venoms were shown to be anticoagulant. This action appeared to be due to an effect on both the extrinsic and blood thromboplastin mechanisms. Platelet aggregation in Chandler's tubes and adenosine diphosphate reactivity were inhibited by the three venoms, although in the case of Ophiophagus hannah venom they were inhibited only with intermediate concentrations. The three venoms possessed proteolytic properties, but when incorporated into purified caseinolytic systems and euglobulin clot lysis systems inhibition of plasmin activity was observed.

Effect of gaboon viper (Bitis gabonica) venom on blood coagulation, platelets, and the fibrinolytic enzyme system

The action of the venom of the gaboon viper (Bitis gabonica) on blood coagulation, platelets, and the fibrinolytic enzyme system was studied. The results confirm that the venom of Bitis gabonica has a marked anticoagulant action in vitro. The venom appears to impair clot formation by a direct proteolytic action on fibrinogen, releasing soluble breakdown products.

Plasminogen-activator-producing tumour

In a patient with giant-cell carcinoma of the lung a secondary tumour deposit in the arm was incised and bled for three weeks. Investigations showed the tumour to be rich in plasminogen activator. Haemostasis in the tumour was achieved with aminocaproic acid therapy. For a period the plasminogen-activator properties were retained in cell culture of the tumour.

Cryoprecipitate therapy in haemophilia

This paper describes experience over an 18-month period of a new preparation of factor VIII, cryoprecipitate, prepared by the Regional Blood Transfusion Service from human plasma. This relatively simple and inexpensive method selectively extracts the factor VIII leaving behind the other blood products for use in other ways.

Replacement therapy in the treatment of haemophilia has been generally regarded as inadequate due to the difficulty in obtaining potent antihaemophilic globulin in sufficient amounts, and cryoprecipitate represents a useful advance.

Bleeding episodes in 25 patients with factor VIII deficiency have been treated with cryoprecipitate on 41 occasions and an assessment of the haemostatic effect of this material has been made in treating haemarthrosis, muscle haematomata and the management of major and minor surgical operations. Routine follow-up over a 6 month period was undertaken to determine the incidence of side effects. Two cases of hepatitis were found, possibly resulting from cryoprecipitate therapy. However, both patients had also received blood or fresh frozen plasma and the source of the hepatitis virus must remain in doubt. No factor VIII inhibitors were found despite repeated courses of therapy in several patients.

The advantages and disadvantages of cryoprecipitate are set out and its encouraging place in the management of haemophilic bleeding assessed.

Idiopathic gangrene in African children

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