Nitric oxide measurements in rat mesentery reveal disrupted venulo-arteriolar communication in diabetes.

Objective: Arteriolar tone is partially controlled by diffusing mediators released by closely paired venules and is reported to depend on venular shear and venular leukocyte adherence. In healthy rat mesentery, venule-initiated arteriolar dilation and consequent enhanced capillary flow appear to be tightly regulated by nitric oxide (NO). In contrast, diabetes inhibits NO-dependent vasodilation and is associated with dysfunctional microcirculation. The objective of this study was to investigate venule-dependent NO in diabetes.

Methods: Arteriolar and venular wall concentrations of NO were measured in control and diabetic (streptozotocin-induced) rat mesentery with fluorescent diaminofluorescein-2-diacetate (DAF-2-DA); tissue NO was measured with DAF-2. Venular leukocyte adherence and microvascular shear rates were also measured.

Results: Microvascular NO in diabetic rats was found to be significantly lower (<50%) than in controls. In normal rats, arteriolar NO demonstrated a positive correlation with venular NO and venular shear, and a negative correlation with venular leukocyte adherence. Diabetes eliminated all these correlations. No correlation was present between arteriolar NO and arteriolar shear in either normal or diabetic rats.

Conclusions: Arteriolar NO appears to be enhanced by venular shear in normal but not in diabetic rats. This dysfunction could contribute to poor capillary perfusion in diabetes.