The metabolism of fibrinogen and plasminogen related to diabetic retinopathy in man

Abstract

Metabolic turnover of fibrinogen and plasminogen were studied in 30 insulin-treated diabetics and 10 non-diabetic controls. 131I labeled fibrinogen and 125I labeled plasminogen were injected i.v. and the plasma clearance of the 2 proteins measured simultaneously over a period of 8 days. The diabetics were selected to represent 3 grades of severity of diabetic retinopathy assessed by ophthalmoscopy and fluorescein angiography; 10 patients had no significant retinopathy, 10 background and 10 proliferative retinopathy. Subjects were matched as closely as possible for body weight, age and duration of diabetes. Plasma fibrinogen concentrations were higher in diabetics (3.24 g/l) than controls (2.65 g/l; P < 0.025); the patients with the severest retinopathy had the highest fibrinogen concentrations (3.75 g/l). As a direct consequence of the elevation of plasma fibrinogen the catabolic rate was higher in diabetics (20.9 mg/kg per day) than controls (14.0 mg/kg per day; P < 0.025), and higher in patients with background retinopathy (24.1 mg/kg per day) and proliferative retinopathy (22.4 mg/kg per day) than diabetics without retinopathy (16.3 mg/kg per day; P = 0.05). Fibrin(ogen) degradation products were detectable in all diabetics but in only 1/3 of controls. Plasminogen metabolism was normal in all groups of diabetics. Evidently fibrinogen metabolism is increased in diabetes and bears a relationship to diabetic retinopathy but is not accompanied by significant alterations of plasminogen metabolism.