Acute hyperglycaemia in the forearm induces vasodilation that is not modified by hyperinsulinaemia

Objective: To evaluate whether acute elevations of local plasma glucose con centrations could influence forearm blood flow (FBF) and how this interacts with local hyperinsulinaemia in healthy volunteers. Methods: Using the perfused forearm technique, in random order, glucose 20% or saline 0.9% as a control was infused in three dose steps (0.3, 1.0, and 3.0 ml/min) for 5 min each in eight healthy men. The infusion experiments were repeated, in random order, during local hyperinsulinaemia by intra-art erial infusion of insulin 0.05 mU/kg/min. The ratio of FBF of the infused o ver the FBF in the control arm (FR) was measured at 15-sec intervals during the infusions. Results: Glucose infusion increased the FR dose-dependently by 172% +/- 39% (M +/- SE) at the highest dose (P < 0.01). During hyperinsulinaemia the gl ucose-induced increase in FR was significantly (P < 0.01) less, 96% +/- 26% , however, when changes in FR or forearm vascular resistance were related t o the plasma glucose concentrations both glucose infusions were equipotent. The saline infusions induced small increases in FR of 27 +/- 5% (P < 0.01) and 24 +/- 11% (P > 0.05), without or with insulin respectively. The chang es in FR during the saline infusions were much smaller than during the gluc ose infusions (P < 0.01). During the glucose infusions small but significan t increases in FBF and venous plasma glucose in the non-infused forearm app eared, indicating carry-over effect and the possibility of a very low thres hold for glucose-induced vascular effects. Conclusions: High, local levels of glucose in the forearm have a vasodilato r effect on resistance vessels in skeletal muscle of the forearm that is no t modified by local hyperinsulinaemia. Indications were found that the thre shold for this glucose-induced vasodilation may be remarkably low, but this needs to be studied more formally.