AJP - Endocrinology and Metabolism, Vol 268, Issue 5 E910-E916, Copyright © 1995 by American Physiological Society

ARTICLES

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

L. S. Lamont, A. J. McCullough and S. C. Kalhan
Exercise Science Program, University of Rhode Island, Kingston, Rhode Island 02881, USA.

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.

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