STIMULATING EFFECT ON TISSUE-TYPE PLASMINOGEN-ACTIVATOR - A NEW AND SENSITIVE INDICATOR OF DENATURED FIBRINOGEN

A high clottability and a short thrombin clotting time have routinely been considered as evidence of genuineness of the fibrinogen molecule. Since denatured fibrinogen stimulates the t-PA-catalysed conversion o f plasminogen to plasmin, it was of interest to study the sensitivity of t-PA-stimulation as evidence of fibrinogen denaturation. Therefore, fibrinogen was intentionally exposed to various denaturating conditio ns (freeze-drying, heating, EDTA, alkali), and the clottability, the t hrombin,clotting time and the t-PA-stimulating effect were recorded. W e found that the clottability was a poor indicator of fibrinogen denat uration, whereas the t-PA-stimulating effect could detect even mild fi brinogen denaturation. The thrombin clotting time was shortened after freeze-drying or heating at 47 degrees C, in spite of what might have been expected. Thus, denaturation is not necessarily accompanied by a prolonged clotting time. In some instances therefore, the t-PA-stimula tion is an even more sensitive and reliable indicator of fibrinogen de naturation than is the thrombin clotting time. Consequently, this para meter should be combined with the thrombin clotting time to characteri se preparations of fibrinogen.