Leucine-Enriched Essential Amino Acids Augment Mixed Protein Synthesis, But Not Collagen Protein Synthesis, in Rat Skeletal Muscle after Downhill Running

Abstract

Mixed and collagen protein synthesis is elevated for as many as 3 days following exercise. Immediately after exercise, enhanced amino acid availability increases synthesis of mixed muscle protein, but not muscle collagen protein. However, the potential for synergic effects of amino acid ingestion with exercise on both mixed and collagen protein synthesis remains unclear. We investigated muscle collagen protein synthesis in rats following post-exercise ingestion of leucine-enriched essential amino acids. We determined fractional protein synthesis rates (FSR) at different time points following exercise. Mixed protein and collagen protein FSRs in skeletal muscle were determined by measuring protein-bound enrichments of hydroxyproline and proline, and by measuring the intracellular enrichment of proline, using injections of flooding d₃-proline doses. A leucine-enriched mixture of essential amino acids (or distilled water as a control) was administrated 30 min or 1 day post-exercise. The collagen protein synthesis in the vastus lateralis was elevated for 2 days after exercise. Although amino acid administration did not increase muscle collagen protein synthesis, it did lead to augmented mixed muscle protein synthesis 1 day following exercise. Thus, contrary to the regulation of mixed muscle protein synthesis, muscle collagen protein synthesis is not affected by amino acid availability after damage-inducing exercise.

Keywords: Leucine-enriched essential amino acids; downhill running; mammalian target of rapamycin; mixed muscle protein synthesis; muscle collagen protein synthesis.

Figure 1

Rates of mixed protein synthesis for the vastus lateralis muscle after downhill running exercise. Mixed protein synthesis was measured in exercised groups with administration of water (open bars) before exercise, 1 h, 4 h, 1 day, 2 days, 4 days, and 7 days, and in exercised groups with administration of LEAA (filled bars) 1 h and 1 day after downhill running exercise. Values are means ± SEM, with n below each bar. #, p < 0.05; ***, p < 0.001 vs. sedentary group.

Figure 2

Rates of collagen protein synthesis for the vastus lateralis muscle after downhill running exercise. Collagen protein synthesis was measured in exercised groups with administration of water (open bars) before exercise, 1 h, 4 h, 1 day, 2 days, 4 days, and 7 days, and in exercised groups with administration of LEAA (filled bars) 1 h and 1 day after downhill running exercise. Data are means ± SEM, with n below each bar. **, p < 0.01 vs. sedentary group.