H.C. Hemker

Evaluation of a Coagulation Assay Determining the Activity State of Factor VII in Plasma

A coagulation assay is described that allows the measurement of the degree of activation of factor VII in circulating blood. The test is based on the use of both bovine and human brain thromboplastin, together with an artificial factor VII-deficient plasma. The latter can be prepared on a relatively large scale which makes it possible to measure factor VII activation in large series of patients. The determination of factor VII activation during incubation at 4 degrees C of plasma of women using oral contraceptives shows that the test described adequately measures factor VII activation. Differences in the time course of factor VII activation during this incubation in glass and plastic containers are found and implicate that rigorous standardization of blood sampling and test conditions is necessary. A possible mechanism that causes this critical dependence upon the test conditions is discussed.

The action of echis carinatus venom on the blood coagulation system. Demonstration of an activator of factor X

It is shown that Echis carinatus venom activates both coagulation factor II and coagulation factor X. The activation of both proenzymes by the venom is Ca++-dependent; phospholipids are not necessary. The activation of factor II by the venom is a slow process and, in the absence of factor X, the clotting activity towards fibrinogen is generated only very slowly. Because Echis carinatus venom clots plasma readily, we postulate that under conditions where the prothrombinase complex can be formed from the factor X activated by the venom it is this complex, rather than the venom itself, that is responsible for the major part of the thrombin formation.

The activity state of factor VII in plasma: two pathways for the cold promoted activation of factor VII

Summary. The apparent amount of factor VII as determined in a one‐stage test depends on the type of thromboplastin used: bovine thromboplastin only reacts with human factor VIIa whereas human thromboplastin interacts with unactivated human factor VII as well. Therefore the ratio factor VII activity as measured with bovine thromboplastin divided by the factor VII activity as assessed with human thromboplastin reflects the state of activation of factor VII in plasma. This approach was used to study the process of cold promoted factor VII activation and the involvement of different clotting factors therein. It could be shown that cold promoted activation does not occur in the absence of factors II and XII and is reduced for about 50% in factor IX deficient plasma. The other coagulation factors have a minor influence on the process. The results indicate that the cold promoted factor VII activation is the result of activation by both activated contact products and thrombin.

Measurement of Macrophage Cellular Procoagulant Activity

We developed a simple technique for the measurement of the procoagulant activity exposed on the surface of macrophages. The cells are isolated, adhered to plastic surfaces, and assayed in the same device. This approach allows us to study the microcoagulation on the surface of intact macrophages by sensitive and specific clotting tests.

Half-Life Time and Control Frequency of Vitamin K-Dependent coagulation factors

A short review about the place of coagulation factor VII in the initial phase of blood coagulation is given. A theoretical model describing the relationship between the half-life times of vitamin K-dependent coagulation factors and the control frequency of oral anti-coagulation therapy is presented. The constraints that control frequency imposes on the type of determination to be carried out are discussed.

Inhibition of blood coagulation factors by serine esterase inhibitors

The reaction mechanism of blood coagulation presumably comprises a series of proenzyme-enzyme conversiqns, In a strict sense this has only been proven for prothrombin (factor II) which has been shown upon activation to yield the serine esterase thrombin I l ] . The coagulation factors II, VII, IX and X have much in common, both in the way of synthesis (dgpendence upon vitamio K) and physicochemical plgperties [2]. It therefole is conceivable that these fqur factors are proenzymes of serine esterases, that is they are serine esterases when in their activated forms*. It has been shown that factor Xu can split organic esters and is inhibited by DFP [3]. No enzymatic properties have been found to the fgptors Vu and VIII. [18, 19] . We qet out to investigate the inhibitory action of a sel of 25 known serine esterase inhibitors on the activities of coagulation factors II, V, VII, VIII, IX and X with the purpose of finding out which of these were serine esterases. We also hoped to finfl specific inhibitors for epch factor which would qreatly facilitate furtt-rg1 research in blood coazulation.

Inhibition of activated factors II, VII, IX, and X by synthetic organic compounds directed against the active-site seryl residue

A series of 53 organic chemicals belonging to the groups of organic phosphates, sulfonyl derivatives and carbamates were screened for their activity against the coagulation factors IIa (thrombin), VIIa, IXa and Xa. Relatively specific inhibitors for the factors IIa, VIIa and Xa were found.