Sensitization of stabilized fibrin to urea dispersion by undiluted plasma and serum

Clots obtained from normal native platelet-poor plasma are dispersed by the addition of 5 M urea. Clots from plasma diluted greater than 1/4 and clots from undiluted plasma, thoroughly washed, are not dispersed by urea, but are rendered susceptible to its dispersing action by prior incubation in normal undiluted plasma or serum. The same phenomenon was observed by incubating the otherwise unsoluble clots in normal plasma or serum fractions precipitated at 33% saturation with (NH4)2SO4. The serum fraction does not interfere with the incorporation of putrescine into casein, although it conditions the urea-dispersing action on stable clots.