Quantitative and qualitative assessment of plasma von Willebrand factor variations, as induced by forearm venous stasis in patients with diabetic microangiopathy.

Plasma von Willebrand factor was studied for quantitative and qualitative assessment in basal conditions and after release from the endothelium, as elicited by venous stasis of the forearm, in 8 healthy subjects and 8 patients with diabetic microangiopathy. von Willebrand factor was measured as factor VIII-related antigen (VIII R:Ag) and ristocetin co-factor (VIII R:Co). Its molecular size distribution was evaluated by bidimensional immunoelectrophoresis. The patients had higher basal levels of VIII R:Ag (171 +/- 45% vs 64 +/- 11% of plasma pooled from 20 healthy donors, p less than 0.05) and VIII R:Co (144 +/- 11% vs 88 +/- 8%, p less than 0.01). After stasis, both moieties increased significantly in the 2 groups, remaining higher in the patients (VIII R:Ag = 292 +/- 74% vs 89 +/- 18%, p = 0.01; VIII R:Co = 216 +/- 25% vs 116 +/- 10%, p less than 0.01). No differences in the molecular size distribution were observed between patients and controls, nor within the 2 groups before and after stasis. It is concluded that, in diabetic microangiopathy, the endothelial cells synthesize and store increased amounts of structurally normal von Willebrand factor.