Plasminogen II accumulates five times foster than plasminogen I at the site of a balloon de-endothelializing injury in vivo to the rabbit aorta: Comparison with other hemostatic proteins

In the rabbit blood stream, plasminogen circulates as two glycoforms, plasm inogen I (PLG-I) and plasminogen II (PLG-II), in a molar ratio of 1:2.2. To compare their relative behaviors toward a site of vascular injury, radiola beled samples of PLG-I and PLG-II were coinjected intravenously into NZW ra bbits before inducing a de-endothelializing (balloon catheter) injury to th e thoracic aorta. At various times (5 to 60 minutes) after injury, each rab bit was anesthetized and exsanguinated, the aorta was excised, and the radi oactivity per centimeters squared of aortic intima-media (IM) was measured relative to that of blood at exsanguination, The uptake of iodine 125-label ed PLG-I and iodine 131-labeled PLG-II showed that the IM was essentially s aturated by both glycoforms by 30 to 40 minutes after injury. Extrapolation of the flux rates to 1 minute after injury indicated that the uptake of PL G-II (2.4 pmol/min/cm(2)) exceeded PLG-I (0.5 pmol/min/cm(2)) almost five-f old. This result is consistent with an earlier report (Metabolism 1994;43:1 430-7) that PLG-II is released by the liver and catabolized in vivo approxi mately five times faster than PLG-I. By molar comparison, the flux of total plasminogen (ie, PLG-I plus PLG-II) into the injured aorta wall in vivo wa s 2.4 times greater than that for prothrombin. Assuming both zymogens are c onverted to their respective proteases within the wound site, then approxim ately 2 to 3 molecules of plasmin are released for each molecule of thrombi n in vivo. The possible significance of this plasmin:thrombin ratio is disc ussed in respect to the turnover of fibrin(ogen) within the site of vascula r injury.