This paper focuses on the process of the formation of complexes between α₂-macroglobulin (α₂-M) and fibrinolytic enzymes, which play an important role in the intravascular fibrinolytic activity, and on the clearance of these complexes from the circulating blood through regulatory mechanisms, especially with reference to the mechanism involving the LDL receptor-related protein/α₂-Macroglobulin receptor (LRP/α₂-MR).
α₂-M had previously been considered as one of the plasmin inhibitors, but is now also considered as a binding protein of certain proteases and of non-proteolytic amines, peptides, and proteins.
The proteases-like tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA) showed decreased activities when they were bound to α₂-M. But under these circumstances the activities of two-chain t-PA (tct-PA), which are more promptly suppressed by Plasminogen activator inhibitor-1 (PAI-1) than are those of native single-chain t-PA, are not only preserved but also protected from this specific inhibitor. We also demonstrated in in vivo studies that the activities of tct-PA in the circulating blood showed a reverse correlation with the values of the PAI-1/α₂-M ratio, indicating that the intervention of α₂-M in the reaction between t-PA and PAT-1 enhances fibrinolysis.
The clearance of exogenous t-PA from the circulating blood showed a biphasic mode (initial phase and the terminal phase). Although the uptake of the t-PA-α₂-M complex is performed by LRP/α₂-MR, the removal of free t-PA is complicated. However, the initial phase of t-PA clearance would be mainly the responsibility of t-PA receptors (mannose and galactose receptors), and the terminal phase of that would be performed mainly by LRP/α₂-MR.
Therefore, the roles of α₂-M and LRP/α₂-MR in the entire system participating in the regulation of the plasminogen-plasmin system would be important.

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The aim of this study is to establish a microvascular thrombosis model using a hamster cheek pouch membrane suited to evaluate the thrombolytic process in vivo. Furthermore, the effect of anticoagulants such as unfractionated heparin (UFH), low molecular weight heparin (LMWH), and recombinant hirudin (r-hir) on thrombolysis induced by recombinant tissue plasminogen activator (rt-PA) was investigated in this model.
Microvascular thrombus in hamster cheek pouch membrane was produced by the irradiation of filtered light with the intravascular administration of fluorescein sodium. The thrombus, with 99% stenosis of the vascular lumen, was used for the evaluation of thrombolytic process. The thrombolytic process, induced by the administration of rt-PA (36×10⁴IU/kg·hr, 72×10⁴IU/kg·hr, 108×10⁴IU/kg·hr), was monitored through high gain camera connected to microscope and VTR. Then thrombolytic process was assessed by three parameters, % stenosis of vessel, % length of thrombus, and % area of thrombus which were calculated with computed video analyzer. Above mentioned anticoagulants were administered respectively with rt-PA and the thrombolytic process was evaluated by the same method. PT, APTT, fibrinogen, plasminogen, and α₂-PI were measured in citrated plasma.
The size of the thrombus formed in this study was increased in proportion to the irradiated area by the filtered light. Thrombus size was decreased depending on the dose of rt-PA, however there seemed to be the optimum dose for rt-PA infusion. Compared with UFH and LMWH, r-hir accelerated thrombolysis by rt-PA potently with less decrease of plasma plasminogen level.
This microvascular thrombosis model was considered to be excellent for the evaluation of thrombolytic agents in vivo, and the superiority of r-hir compared to heparins in thrombolytic therapy was suggested.

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We previously reported that the reduced normal plasma von Willebrand factor (vWF) consists of 240, 216 (220, 210), 194, 164, and 144 kDa fragments. We also described a new 200kDa reduced fragment in addition to those of normal plasma vWF in two patients with type I b von Willebrand disease (vWD). In one (T. O.) of the two families, a similar 200 kDa reduced fragment is herein reported in the proband's mother and daughter who showed abnormal laboratory findings without bleeding symptoms. This study highly suggested that they could be the heterozygotes for a mutant gene.
The abnormal 200kDa fragment reacted with both of the anti-reduced SPIII and SPII antibodies. The products of digestion by V-8 protease indicated an abnormal 80kDa fragment in addition to those of normal plasma vWF. This 80kDa fragment reacted with only the anti-reduced SPIII antibody, but not the anti-reduced SPIT antibody. These results suggested that the mutation localized on the C-terminal region of the SPIII fragment of vWF subunit.

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