1. An increase in capillary blood flow and pressure has been implicated in the pathogenesis of diabetic microangiopathy. Abnormal vascular reactivity of the resistance vasculature may play a contributory role by permitting alterations in regional haemodynamics.

2. We have studied the contractile behavior of isolated resistance arteries from normotensive patients with insulin-dependent diabetes mellitus and non-diabetic matched control subjects. Contractile responses to potassium (123 mmol/l), noradrenaline (10−8 to 3 × 10−5 mol/l) and angiotensin II (10−11 to 3 × 10−8 mol/l) were recorded. Relaxation studies were performed in maximally contracted vessels using acetylcholine (10−8 to 10−5 mol/l) and bradykinin (10−9 to 10−6 mol/l) (endothelium-dependent) and sodium nitroprusside (10−9 to 10−5 mol/l) (endothelium-independent).

3. The maximal contractile responses to potassium (P < 0.05), noradrenaline (P < 0.01) and angiotensin II (P < 0.01) were depressed in diabetic patients. Relaxation to acetylcholine was impaired (P < 0.05), but was normal with bradykinin and sodium nitroprusside.

4. These results suggest that there may be a defect in the endothelial cell acetylcholine receptor excitation-coupling in diabetes mellitus rather than a decreased ability to synthesize and release endothelium-derived relaxing factor. Impaired contraction and endothelium-dependent relaxation of resistance arteries in diabetic patients may contribute to the development of diabetic microangiopathy by causing an increase in tissue blood flow, a rise in capillary pressure and, as a result, an increase in vascular permeability.

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