Alterations in Viscosity and Filterability of Whole Blood and Blood Cell Subpopulations in Diabetic Cats

Capillary closure and venous dilatation occur early in diabetic retinopathy, and altered blood rheology may play a role. For example previous studies have shown leukocytes are less deformable, are more activated, and occlude retinal capillaries more often in diabetic subjects. The purpose of this study was to determine if rheologic changes developed in diabetic eats, a model in which we have documented retinal capillary basement membrane thickening, microaneurysms, and intraretinal hemorrhage characteristic of early diabetic retinopathy. Viscosity of blood, plasma and purified erythrocyte suspensions was measured by rotational viscometry and plasma fibrinogen content was deterarmed by heat precipitation. Filterability of blood and purified erythrocyte, mononuclear leukocyte, and granulocyte suspensions was determined at constant flow, measuring the increase in pressure over 2 min relative to the pressure generated by buffer alone. Viscosity of whole blood and plasma, but not erythrocytes, was significantly elevated ( P < 0·005) in the diabetic cats over normals at all shear rates studied (450, 225 and 90 sec -1). Furthermore, fibrinogen levels were significantly elevated in diabetic cats compared to normals ( P < 0·004), and were positively correlated with the viscosity of whole blood and plasma. The filterability of mononuclear leukocytes and whole blood in diabetic cats was decreased 56% and 74% when compared to normals, P > 0·0006 and P < 0·025, respectively. In contrast, the filterability of granulocytes and erythrocytes was not significantly different between the two groups. These results suggest that the rheologic alterations in diabetes are numerous, and involve both cellular and plasma protein changes. The changes in the fibrinogen levels, plasma and whole blood viscosity, and mononuclear cell filterability may play important roles in the genesis of diabetic microangiopathy.