Twenty-four hour variations of von Willebrand factor and factor VIII-related antigen in diabetic retinopathy

Factor VIII/von Willebrand factor (vWF) could play a role in the pathogenesis of diabetic microangiopathy. It has been suggested that its biologic activity is controlled by hormonal and metabolic mechanisms. To verify this hypothesis, vWF was monitored over a 24 hr period in 9 insulin treated patients with diabetic retinopathy, together with factor VIII-related antigen (VIII-RAG), plasma glucose, growth hormone (GH) and prolactin. vWF levels oscillated during the 24 hr, the mean values being higher during the day than at night-time, p less than 0.01. Compared to a group of normal controls in whom blood samples were taken randomly between 9.00 and 13.00, the levels of vWF were significantly increased at 11.00, p less than 0.02, and at 13.00, p less than 0.02, but at no other time. VIII-RAG values were also higher during the day than at night-time, p less than 0.01. The mean 24 hr levels of vWF correlated with those of VIII-RAG, p less than 0.01, with the age of the patients, p less than 0.01, and with the duration of disease, p less than 0.01. The levels of plasma glucose were higher during the day, while GH and prolactin rose at night-time. No correlations were found between vWF or VIII-RAG and plasma glucose, GH or prolactin, nor between the mean 24 hr levels of all these parameters and ponderal index, daily insulin dose, degree of metabolic control, severity of retinopathy. Insulin treated diabetics with microangiopathy show circadian variations in their plasma concentrations of vWF and VIII-RAG which should be taken into account when measuring these factors for clinical or research purposes.