An acid stable trypsin-plasmin inhibitor (ASTI) was found to be produced when several SH-proteases were incubated with human plasma. The maximal activity produced with bromelain was approximately 40U/ml plasma, which represented about a 10-fold increase compared with that of the normal human plasma (less than 5U/ml). On the other hand, lesser activity was observed with several serine proteases, trypsin, elastase, followed by chymotrypsin. Neither the plasma fibrinolytic enzymes including plasmin and urokinase, nor plasma kallikrein had any effect on the ASTI production in the same condition.
An increase in the ASTI acativity was also demonstrated in plasma derived from patients with acute pancreatitis (21U/ml), and the attivity was almost parallel to that of tosyl-L-arginine methylester (TAMe) hydrolyzing activity in plasma. In an experimental anaphylaxis of the rabbit, the ASTI activity in plasma also increased more than 5 times after antigen (bovine serum albumin) was injected.