Abstract
Blood, lymph, and cerebrospinal fluid contain a beta globulin termed plasminogen which is a precursor of the proteolytic enzyme plasmin. This enzyme's affinity for fibrin is thought to be pronounced hence it has been implicated in the elimination of intra and extravascular fibrin deposits. By its ability to destroy fibrin it could provide a potential weapon for the prevention or treatment of thrombosis. Unfortunately, it is not yet known how this process can be utilized to the best advantage.
The activators of plasminogen are considered the second most significant components of the enzyme system. There are many. Several pharmacological agents act as exogenous activators as do the bacterial products streptokinase (1) staphylokinase (2) and endotoxin (3). Endogenous activator is present in urine (4), as urokinase, and in tissues, as tissue activator (5).
Despite a great deal of investigation on several aspects of plasminogen activation, particularly on its mode of activation (6), its inhibition by both natural and synthetic inhibitors (7), and its elimination by the liver (8), the information on the origin of the endogenous plasminogen activators responsible for the spontaneous lysis of blood clots is limited. Spontaneous lysis takes place at rates that vary greatly suggesting that the concentation of circulating activator is subject to marked fluctuations.
Evidence for a possible vascular origin was previously postulated by Mole (9) and subsequently provided by Kwaan et al. (10). Information gained from the present experiments suggests that considerable quantities of this material also come from the intestine. In view of its profound systemic effect we have to assume that in contrast to previously described endogenous activators, which are eliminated by the liver (8), this material traverses the liver under certain circumstances.
Methods and Materials. Three groups of mongrel dogs weighing between 15 and 20 kg were studied.
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