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-C-13]leucine and L-[alpha-N-15]lysine infusions were performed. The first 3 h established an isotopic steady state, and 1 h of exercise (similar to 50% of maximal O-2 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.