The fibrinolysin-antifibrinolysin system in serum; mechanism of its endocrine control.

EARLIER studies have indicated that fibrinolysin (FL), a proteolyticenzyme, appears in blood as a result of the activation of its inactive precursor, profibrinolysin (PFL), by certain stimuli such as the antigen-antibody reaction (Ungar and Mist, 1949). Evidence was presented that the rate of inactivation of fibrinolysin by its inhibitor, antifibrinolysin (AFL), is accelerated by hormones from the pituitary gland and the adrenal cortex. This action appears to be mediated by the spleen since it is absent in splenectomized animals and can be reproduced by a substance present in the spleen, splenin A (Ungar, 1945). In contrast to this accelerating effect of splenin A, a retarding influence was shown by another substance found in the spleen and bone marrow, splenin B (Ungar and Damgaard, 1951). The present paper deals mainly with endocrine factors which retard the fibrinolysin-antifibrinolysin (FL-AFL) reaction. In view of the close correlation