Antiplasmin activity has been determined by means of the plasmin specific trlpeptlde substrate H-D-Vai-L-Leu-L-Lys-p-nltroanlllde (S-2251)It Is concluded that the method mainly measures the antiplasmin described by Collen and coworkers ( Thromb. Res. 7, 245, 1975), although α2-macroglobulln may interfere to a small extent. Different categories of patients with tendency to thrombosis and Increased fibrinolysis have been studied During normal mlddlesized operations antiplasmin decreased slightly, but increased postoperatively. Antiplasmin likewise decreased during deliveries, and Increased In th PuerperiumPatients with acute deep vein thrombosis had normal antiplasmin activity at the time for diagnosis, but antiplasmin Increased later during the course of eventsStreptokinase treated patients showed a pronounced and rapid drop In antiplasmin activity, which was normalized as soon as the streptokinase administration was InterruptedPatients with liver cirrhosis had lower antiplasmin activity than normals , and so had patients with disseminated Intravascular coagulation.

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The physiologically important α₂-antiplasmin has been measured by aid of a chromogenic tripeptide substrate. Low values in patients’ plasmas are found in situations with increased fibrinolysis such as streptokinase therapy and liver cirrhosis, whereas high values are found postoperatively, postpartum and after an acute thrombosis.

alpha 2-Antiplasmin and alpha 2-macroglobulin have been studied during the menstrual cycle, pregnancy and parturition in healthy women, and during use of various types of contraception in both healthy and diabetic women, and compared with a reference group of healthy men and women. alpha 2-Antiplasmin showed a slight sex difference, with higher values in women. The luteal phase of the menstrual cycle showed slightly higher values than the other phases. alpha 2-Antiplasmin increased during pregnancy, decreased (probably due to consumption) during labor and increased again in the puerperium. Treatment with neither combined contraceptive pills nor low dose progestogen pills gave any changes in alpha 2-antiplasmin. alpha 2-Macroglobulin showed low values during menstruation. The increase during pregnancy and treatment with combined contraceptive pills is in accordance with earlier findings. It is concluded that synthesis and metabolism of alpha 2-antiplasmin are under hormonal influence. The role of alpha 2-antiplasmin in the decreased fibrinolysis in pregnancy is discussed.