Connections between Kinin Formation and Complement
Intrinsic blood clotting, thrombolysis, plasma kinin formation and complement may be regarded as four major reactive systems which are triggered into activity when blood is exposed to noxious stimuli. The four processes do not of course rely solely on intrinsic factors, but cooperate with mechanisms available in surrounding tissues. In each of the four systems there are proteolytic enzymes, often acting in sequence, i. e. on precursors of other proteases either in their own reaction sequence or in one of the other systems. In this way, numerous functional connections inside and between systems are formed. The links between blood clotting, fibrinolysis and plasma kinin formation have been under study for many years. It is probably true to say that in vivo these reactions only rarely proceed in isolation. Only two of these connections will be mentioned here. Plasmin, a protease capable of attacking a very large number of proteins is not only responsible for the lysis of blood clots, but also intervenes in the formation of clots and kinins and in the activation of complement (Ratnoff & Naff, 1967). There is now a great deal of evidence that clotting factor XII (Hageman factor) occupies a central position as the initial step in the intrinsic sequences of blood clotting, fibrinolysis and plasma kinin formation. In recent years, evidence has been produced that factor XII or its molecular subunits may also trigger the first step in the complement sequence by catalyzing the activation of subcomponent C’1s to C’1 esterase (Donaldson, 1968a; Austen, 1971). This action of factor XII may be mediated through plasmin or plasma kallikrein.
KeywordsEllagic Acid Amino Caproic Acid Cellulose Sulphate Plasma Kallikrein Hageman Factor
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