Plasminogen assay in rabbit, rat and mouse plasma using the chromogenic substrate S-2251

An amidolytic assay has been developed for measuring plasminogen in rabbit, rat and mouse plasma using the synthetic substrate S-2251. The assay includes an acidification step to make plasminogen more readily activatable; the conditions required for optimal activation of plasminogen by urokinase were found to vary in the 3 animal species studied. Compared with human plasma, rat, mouse and rabbit plasma (in decreasing order) all had higher plasminogen activity. A close correlation was found between amidolytic and caseinolytic assay of plasminogen in all species studied. The method described may be of significant help in the study of the fibrinolytic system of laboratory animals.