Summary
A study was carried out in order to evaluate the Astrup and Mullertz fibrin plate
method for estimating plasminogen activators.
Choice of a suitable fibrinogen substrate was found to be the most important factor
in setting up a workable assay. Many preparations contained a large proportion of
non-clottable protein and plates made from these fibrinogens were usually unreliable.
In addition, plasminogen content varied appreciably between preparations so that sensitivity
of the method required careful calibration with each new batch of fibrinogen.
The effect of additives in the fibrin plate was considered and it was found that calcium
chloride alone was sufficient to ensure a stabilised plate which could be stored at
4° C for some time. The addition of tranexamic acid (AMCHA) was found to be a slightly
more convenient way of estimating direct proteolytic activity, compared with the traditional
heated plate. However neither method distinguished completely between proteolysis
and plasminogen activation.
In order to improve the precision of the method, the use of an analysis of variance
technique has been studied. This technique provides information on the dose-response
curves of test and unknown substances, and in addition produces an approximately threefold
increase in precision over single plate tests.
