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

Metabolic turnover of fibrinogen and plasminogen were studied in thirty insulin-treated diabetics and ten non-diabetic controls. 131-iodine labelled fibrinogen and 125-iodine labelled plasminogen were injected intravenously and the plasma clearance of the two proteins measured simultaneously over a period of 8 days. The diabetics were selected to represent three grades of severity of diabetic retinopathy assessed by ophthalmoscopy and fluorescein angiography; ten patients had no significant retinopathy, ten background and ten 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 less than 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-1 day-1) than controls (14.0 mg kg-1 day-1; P less than 0.025) and higher in patients with background retinopathy (24.1 mg kg-1 day-1) and proliferative retinopathy (22.4 mg kg-1 day-1) than diabetics without retinopathy (16.3 mg kg-1 day-1; P = 0.05). Fibrin(ogen) degradation products were detectable in all diabetics but in only one-third of controls. Plasminogen metabolism was normal in all groups of diabetics. It is concluded that fibrinogen metabolism is increased in diabetes and bears a relationship to diabetic retinopathy but is not accompanied by significant alterations of plasminogen metabolism.