抄録
Antiplasmin activities of pooled plasma of normal subjects, purified α2-macroglobulin (α2M) and purified α1-antitrypsin (α1AT) with or without heparin were measured using chromogenic substrate (S-2251) to investigate role of α2M, α1AT or heparin in fibrinolysis. Excess amount of plasmin was added to mixtures of S-2251 and diluted sample, then rate of absorbance changes (ΔA/10 seconds) was measured as soon as possible. At least, 10 seconds of reaction time were necessary to obtain reliable results. In this condition, about 30% of antiplasmin activity of normal plasma was due to α2M, while α1AT did not inhibit plasmin. Amount of plasmin neutralized by α2M reached to its maximum level, when α2M was incubated with plasmin for 30 minutes at 37°C, while amount of plasmin inhibited by α1AT was far more larger when reaction time was 360 minutes. Antiplasmin activity of plasma was accelerated by addition of large amount of heparin (10units/ml plasma), however presence of small amount of heparin (1unit/ml plasma) did not change velocity of plasma to neutralize plasmin significantly. Increase in amount of plasmin inhibited by heparinization of plasma was highest when reaction time of plasmin and heparinized plasma was 30 minutes, which was larger than that of α2M. Acceleration of the inhibitory action of plasma by heparin disappeared when plasmin and heparinized plasma were incubated for 360 minutes.
From these results, following conclusions were obtained:
(1) α2M inhibits plasmin immediately;
(2) Inhibitory action of α2M may affect assay of immediate antiplasmin using chromogenic substrate, especially when α2M markedly depletes;
(3) Large amount of heparin in plasma accelerates inhibition of plasmin by antithrombin III (ATIII);
(4) Amount of plasmin inhibited by ATIII is larger than that by α2M;
(5) Six hours are necessary for complete reaction of plasmin and ATIII without heparin.
