Local vasodilatation with metacholine, but not with nitroprusside, increases forearm glucose uptake

Insulin is known to increase blood flow in parallel to glucose uptake in skeletal muscle. However, it is not known if an increase in blood flow by itself is associated with an increase in glucose uptake in the absence of hyperinsulinemia. To investigate further this matter, the effect of increased blood flow on forearm glucose uptake was studied in the fasting state during intra-arterial infusions of two different vasodilators, metacholine and nitroprusside, in 19 hypertensive subjects. Both metacholine (4 microg/min) and nitroprusside (10 microg/min) increased resting forearm blood flow, measured by venous occlusion plethysmography, to a similar degree (180 % and 170 %, respectively, p<0.0001 for both). However, metacholine infusion increased the forearm glucose uptake from 2.0+/-0.9 (S.D.) during rest to 5.5+/-3.0 umol/min/100 ml tissue (p<0.0001), while no significant change in glucose uptake was seen during nitroprusside infusion (2.3+/-1.4 micromol/min/100 ml tissue). In conclusion, vasodilatation induced by metacholine, but not by nitroprusside, increased glucose uptake in the forearm of hypertensive patients. Thus, an increase in forearm blood flow does not necessarily improve glucose uptake in the forearm during the fasting state.