Absence of Insulin-Induced Vasodilation of Internal Carotid Artery in Type 2 Diabetes

Background: Impaired cerebrovascular reserve could contribute to the increased risk of strokes in type 2 diabetes. We have shown a vasodilatory effect of insulin on the internal carotid artery in healthy subjects. As absence of this effect could be responsible for the impairment of cerebral blood flow reserve demonstrated in this population, we have now investigated the effect of insulin on the internal carotid artery of type 2 diabetics. Methods: Internal carotid artery diameter was continuously monitored, using a 7.5-MHz transducer linked to an Acuson XP10 ultrasonograph, during the infusion of 125 mL of 10% dextrose with 3 units of regular insulin and 5 mmol of potassium chloride, over 1 h. Results: The internal carotid artery diameter increased progressively from 5.4 ± 1 to 6 ± 1 mm at 60 min in controls (p < 0.05), an increase of 10% over baseline, while there was no dilatation in type 2 diabetes group; 6.6 ± 1 mm at baseline and at 60 min. The response in type 2 diabetics was significantly impaired compared to controls. Glucose levels were maintained at 114-131 mg/dL in type 2 diabetics and at 73-124 mg/dL in controls. There was no change in MABP or heart rate during the infusion. Conclusions: We conclude that insulin-induced dilation of internal carotid artery is absent in type 2 diabetes and that lack of this beneficial effect may contribute to the increased risk and the mortality and morbidity associated with stroke in this population.