Beta-adrenergic blockade heightens the exercise-induced increase in leucine oxidation.

The purpose of this study was to assess the interaction between beta-blockade and exercise on amino acid kinetics. This was a three-way crossover experiment using beta 1-blockade, beta 1,beta 2-blockade, and a placebo control. Three 6-h L-[1-13C]leucine and L-[alpha-15N]lysine infusions were performed. The first 3 h established an isotopic steady state, and 1 h of exercise (approximately 50% of maximal O2 consumption) and 2 h of recovery followed. Plasma glucose decreased with exercise during all trials (P < 0.0001). During beta 1- and beta 1,beta 2-blockade, plasma free fatty acids were reduced during rest and exercise (P < 0.001). Leucine and lysine rates of appearance were unaffected by beta-blockade during rest but were decreased with placebo exercise. Leucine oxidation increased with beta-blockade (P < 0.01) and exercise (P < 0.001). There was a statistical interaction between both treatments (P < 0.004). In conclusion, leucine oxidation increased with exercise, further increased with beta 1-blockade, and was additionally heightened with beta 1,beta 2-blockade. This cumulative response indicates that leucine oxidation was regulated through beta 1- and beta 2-receptors.