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

To evaluate whether acute elevations of local plasma glucose concentrations could influence forearm blood flow (FBF) and how this interacts with local hyperinsulinaemia in healthy volunteers.

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-arterial infusion of insulin 0.05 mU/kg/min. The ratio of FBF of the infused over the FBF in the control arm (FR) was measured at 15-sec intervals during the infusions.

Glucose infusion increased the FR dose-dependently by 172%+/-39% (M+/-SE) at the highest dose (P < 0.01). During hyperinsulinaemia the glucose-induced increase in FR was significantly (P < 0.01) less, 96%+/-26%, however, when changes in FR or forearm vascular resistance were related to 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 changes in FR during the saline infusions were much smaller than during the glucose infusions (P < 0.01). During the glucose infusions small but significant increases in FBF and venous plasma glucose in the non-infused forearm appeared, indicating carry-over effect and the possibility of a very low threshold for glucose-induced vascular effects.

High, local levels of glucose in the forearm have a vasodilator effect on resistance vessels in skeletal muscle of the forearm that is not modified by local hyperinsulinaemia. Indications were found that the threshold for this glucose-induced vasodilation may be remarkably low, but this needs to be studied more formally.