Plasma fibrinogen and plasminogen levels in health and in ischaemic heart disease

Abstract

SYNOPSIS Plasma fibrinogen and plasminogen levels were measured in 122 male and 56 female healthy adult subjects and in 64 men with ischaemic heart disease. Plasma fibrinogen levels were found to rise markedly and progressively with age in both male and female healthy subjects; plasminogen showed only a slight rise with age. No sex differences were found for either fibrinogen or plasminogen. The correlation between plasminogen and fibrinogen levels was low, reaching the 5 Y.level of significance only in men. Patients with ischaemic heart disease were found to have significantly increased fibrinogen and plasminogen levels in the 31-45 years age group only.Plasminogen is the inactive precursor of the proteolytic enzyme plasmin which, under physiological circumstances, specifically digests fibrin and thus causes lysis of thrombi or fibrinous exudates. Conversion of plasminogen to plasmin takes place by activators which are widespread in body tissues and present in small amounts in circulating blood. Plasminogen has a close affinity for fibrinogen and fibrin and this affinity forms part of the evidence for the theory of thrombolysis put forward by Sherry, Fletcher, and Alkjaersig (1959) which suggests that the function of plasminogen is to endow fibrin with the capacity for subsequent lysis. They showed that clots of low plasminogen content lyse poorly when exposed to activator.Because of the possibility that a defect in the fibrinolytic enzyme system has a role in the causation of thrombotic disease we have studied the plasminogen content of plasma in a group of healthy controls and in patients with ischaemic heart disease. In view of the affinity of plasminogen for fibrin and previous reports that fibrinogen levels are elevated in patients with ischaemic heart disease (McDonald and Edgill, 1957; Merskey, Gordon, Lackner, Schrire, Kaplan, Sougin-Mibashan, Nossel, and Moodie, 1960;Pilgeram, 1961; Egeberg, 1962;Katz, McDonald, Davies, and Edgill, 1963) we have also studied the plasma fibrinogen in the same groups and its relationship to plasminogen levels. PLASMA FIBRINOGEN This was determined by a modification of the method of Ratnoff and Menzie (1951). Oxalated plasma, 0-25 ml., was mixed with 4-5 ml. 0-85 % saline and 0-2 ml. thrombin (100 units/ml.).After standing for 30 minutes the clots were filtered on squares of fibre glass and washed with saline. The clots were compressed in the fibre glass to remove the fluid trapped in the fibrin interstices. After further washing the fibrin the fibre glass was dried between cloths. The folded fibre glass squares with the enclosed fibrin was boiled with 2 ml. 0-2 N sodium hydroxide for 10 minutes. When cool, 6 ml. 12-5 % w/v sodium carbonate and 1 ml.Folin-Ciocalteu's reagent (diluted 1:2) were added. After 15 minutes the intensity of the colour was read at 670 miu. The fibrin content of the clot was read from a standard curve prepared from purified fibrinogen (Kabi Pharmaceuticals Ltd.). All determinations were performed in duplicate.Blood samples were obtained with the m...

The effect of age on the fibrinolytic enzyme system

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