Activation of the contact system in ascites from patients with gastrointestinal cancer.

Our observations indicates that the plasma contact system is activated in ascites from patients with gastrointestinal cancer: Factor XII is activated, plasma kallikrein is present in complex with the protease inhibitor alpha 2-macroglobulin, and the plasma kallikrein substrate high molecular weight kininogen, is highly degraded. Contact activation seems to take place in spite of a high level of inhibition. Activation of the contact system generates mediators, which may play a role in the accumulation of ascites.