Mixed muscle and hepatic derived plasma protein metabolism is differentially regulated in older and younger men following resistance exercise

• Published in: American journal of physiology: endocrinology and metabolism 2005-05, Vol.51 (5), p.E922-E929
• Main Authors: SHEFFIELD-MOORE, M, PADDON-JONES, D, SANFORD, A. P, ROSENBLATT, J. I, MATLOCK, A. G, CREE, M. G, WOLFE, R. R
• Format: Article
• Language: English
• Subjects: Age; Biological and medical sciences; Exercise; Fundamental and applied biological sciences. Psychology; Liver; Men; Metabolism; Muscular system; Plasma; Proteins; Vertebrates: endocrinology
• ISSN: 0193-1849; 1522-1555

We sought to determine whether exercise-induced muscle protein turnover alters the subsequent production of hepatically derived acute-phase plasma proteins, and whether age affects how these proteins are regulated. We measured arteriovenous (a-v) balance and the synthesis of mixed muscle protein, albumin (A) and fibrinogen (F) before exercise (REST) and from the beginning of exercise to 10, 60, and 180 min following a single bout of moderate-intensity leg extension exercise (POST-EX) in postabsorptive untrained older (n = 6) and younger (n = 6) men using L-[ring-2H5]phenylalanine (Phe). Subjects performed 6 sets of 8 repetitions of leg extension at 80% of their 1-RM (one-repetition maximum). All data are presented as the difference from REST (delta from REST at 10, 60, and 180 min POST-EX). Mixed muscle fractional synthesis rate (FSR-M) increased significantly from the beginning of exercise until 10 min POST-EX in the older men ([delta]FSR-M: 0.044%/h), whereas FSR-M in the younger men was not elevated until 180 min POST-EX ([delta]FSR-M: 0.030%/h). FSR-A and FSR-F increased at all POST-EX periods in the older men ([delta]FSR-A = 10 min: 1.90%/day; 60 min: 2.72%/day; 180 min: 2.78%/day; [delta]FSR-F = 10 min: 1.00%/day; 60 min: 3.01%/day; 180 min: 3.73%/day). No change occurred in FSR-A in the younger men, but FSR-F was elevated from the beginning of exercise until 10 and 180 min POST-EX (10 min: 3.07%/day and 180 min: 3.96%/day). Net balance of Phe was positive in the older men in the immediate POST-EX period. Our data indicate that mixed muscle and hepatic derived protein synthesis is differentially regulated in younger and older men in response to a single bout of moderate-intensity leg extension exercise. Moreover, our data suggest that with age may come a greater need to salvage or make available amino acids from exercise-induced muscle protein breakdown to mount an acute-phase response. [PUBLICATION ABSTRACT]