GUT PROTEOLYSIS CONTRIBUTES ESSENTIAL AMINO-ACIDS DURING EXERCISE

Arteriovenous difference and tracer dilution techniques were utilized to determine the effect of exercise on whole body, gut, liver, and spl anchnic leucine kinetics. Five postabsorptive dogs were infused with [ 1-C-13]leucine and studied during rest, 90 min of moderate-intensity t readmill exercise (1st 45 min, early; last 45 min, late exercise), and 90 min of recovery. The whole body leucine rate of appearance (R(a); mu mol . min-1 . kg-1) increased from rest (3.33 +/- 0.11) during earl y (3.68 +/- 0.14) and late (4.24 +/- 0.27, P < 0.05) exercise and was 3.41 +/- 0.19 during recovery. Gut R(a) increased from rest (0.64 +/- 0.08) during early (0.99 +/- 0.12) and late (1.30 +/- 0.20, P < 0.05) exercise and was 0.77 +/- 0.16 during recovery. Liver leucine R(a) did not significantly change (P > 0.05). The whole body leucine rate of d isappearance (R(d)) paralleled whole body leucine R(a) throughout. Leu cine R(d) across the gut, liver, and splanchnic bed, however, did not significantly change (P > 0.05), indicating an increase in leucine upt ake outside of these regions. Because active skeletal muscle is likely the principal consumer of these amino acids, the data suggest that gu t protein-derived amino acids are utilized for the attenuation net mus cle protein catabolism during and immediately following exercise.