A large spectrum of methods has been used in both routine and scientific studies of the hemostatic system. The particular interest of the investigators has been focused on methods simultaneously evaluating clotting and fibrinolysis processes. The aim of the present study was to develop an optical method for overall evaluation of clot formation and lysis (CL-test) that could be used in drug screening. The CL-test was performed in citrate plasma diluted with Tris-buffered saline. Thrombin was applied for plasma clotting (0.5 IU/ml), while tissue plasminogen activator (60 ng/ml) was used for fibrinolysis activation. Clot formation and lysis were monitored in thermostatic conditions (37 degrees C) as a continuous record of transmittance change. By means of own computer program, kinetic parameters of the processes studied and plasma overall clot formation and fibrinolysis potential, expressed as the area under the clotgeneration and fibrinolysis curves, were calculated. The CL-test was developed and checked by evaluation of the effect, on clot formation and lysis, of various concentrations of acetylsalicylic acid (a drug that affects hemostasis), aprotinin (fibrinolysis activator) and venoruton (fibrinolysis inhibitor). The obtained results confirmed that the test we propose for monitoring clot formation, stabilization and lysis is sensitive and enables precise estimation of the processes studied. In our opinion, it can be a useful tool in drug screening investigations.

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Nitric oxide (NO) is a potent vasodilator and inhibitor of platelet activation. Its donors, organic nitrates, are still a main group of drugs administered in ischaemic heart disease. The aim of this study was to investigate the effect of a new NO-donor analogue, 1-(3-piperidinepropionyl)-4-(2-nitrooxy-3-piperidinepropyl) piperazine trihydrochloride (NO-P), on platelet activity. Its influence on the main mechanisms of human platelet activation (adhesion, shape change, secretion and aggregation) was evaluated with the use of a pharmacological model produced on the basis of known platelet activation measuring methods and our computer program. Our experiments revealed that the new NO derivative of piperazine favourably influences platelet activity, and decreases adhesion (spontaneous and induced by ADP) and aggregation. NO-P shows the same direction of action as nitroglycerin (used as a model compound), and is even stronger in the case of ADP-induced and collageninduced aggregation. These findings broaden the possibility of using NO-P in cardiovascular diseases. Furthermore, our computer program, used to evaluate kinetic parameters of platelet aggregation, shape change, and the adhesion measuring method, provides a simple and accessible experimental model. This model can be useful in in-vitro screening studies, estimating the influence of new compounds (potential drugs) on platelet activity. Blood

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