Objective: The role of selective β₂-adrenergic stimulation in regulation of leg glucose uptake and free fatty acid (FFA) balance is inadequately explored in humans. The objective of this study was to investigate β₂-adrenergic effects on net leg glucose uptake and clearance, as well as FFA balance at rest and during exercise.

Design: The study was a randomized, placebo-controlled crossover trial, where 10 healthy men received either infusion of β₂-agonist terbutaline (0.2 to 0.4 mg) or placebo. Net leg glucose uptake and clearance, and FFA balance were determined at rest and during 8 min of knee extensor exercise using Fick's principle. Vastus lateralis muscle biopsies were collected at rest and at cessation of exercise. The primary outcome measure was net leg glucose uptake.

Results: At rest, net leg glucose uptake and clearance were 0.35 (±0.16) mmol/min and 41 (±17) mL/min (mean ± 95% CI) higher (P < 0.001) for terbutaline than placebo, corresponding to increases of 84% and 70%. During exercise, no treatment differences were observed in net leg glucose uptake, whereas clearance was 101 (±86) mL/min lower (P < 0.05) for terbutaline than placebo. At rest, terbutaline induced a net leg FFA release of 21 (±14) µmol/min, being different from placebo (P = 0.04). During exercise, net leg FFA uptake was not different between the treatments.

Conclusions: These observations indicate that β₂-agonist alters net leg glucose uptake and clearance, as well as FFA balance in humans, which is associated with myocellular β₂-adrenergic and insulin-dependent signaling. Furthermore, the study shows that exercise confounds the β₂-adrenergic effect on net leg glucose uptake and FFA balance.