Experiments on rats have confirmed that Nattokinase is absorbed from the intestinal tract, and the absorbed Nattokinase decomposes plasma fibrinogen.

＜References＞
Fujita M , Hong K, Ito Y, Misawa S, Takeuchi N, Kariya K, et al. 　
Transport of nattokinase across the rat intestinal tract. 
Biol. Pharm. Bull. 1995;18(9):1194-6．

（Abstract）
Intraduodenal administration of nattokinase (NK) at a dose of 80mg/kg, resulted in the degradation of fibrinogen in plasma suggesting transport of NK across the intestinal tract in normal rats. The action of NK on the cleavage of fibrinogen in the plasma from blood samples drawn at intervals after intraduodenal administration of the enzyme was investigated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting analysis with an anti-fibrinogen γ chain antibody. The 270kDa fragment carrying antigenic sites for the binding of the anti-fibrinogen γ chain antibody appeared within 0.5h and was then degraded gradually to a 105kDa fragment via a 200kDa fragment. This suggests that fibrinogen was degraded to a 105kDa fragment via several intermediates (270 and 200kDa). In parallel with the degradation process, plasma recalcification times were remarkably prolonged. NK was also detected in the plasma from blood samples drawn 3 and 5 hours after administration of the enzyme by SDS-PAGE and Western blotting analysis with an anti-NK antibody. The results indicate that NK is absorbed from the rat intestinal tract and that NK cleaves fibrinogen in plasma after intraduodenal administration of the enzyme.