Turnover of antiplasmin, the fast-acting plasmin inhibitor of plasma.

Human antiplasmin, the fast-acting plasmin inhibitor in plasma, was purified to homogeneity and labeled with 125I. This material, which was indistinguishable from antiplasmin in plasma with respect to several physicochemical and functional properties, was injected intravenously and its turnover measured in control subjects and in patients undergoing thrombolytic therapy. In eight control subjects (four healthy persons and four patients with atherosclerosis), the following turnover characteristics were obtained: plasma radioactivity half-life 2.64 +/- 0.32 days, fractional catabolic rate 0.53 +/- 0.09 of the plasma pool per day, intravascular fraction 0.51 +/- 0.05, and synthetic (catabolic) rate 1.4 +/- 0.27 mg/kg/day. The half-life of the plasmin-antiplasmin complex in plasma, measured from the disappearance rate of labeled antiplasmin, plasmin or plasmin-antiplasmin complex during thrombolytic therapy was approximately 0.5 days.