title: Mixed muscle and hepatic derived plasma protein metabolism is differentially regulated in older and younger men following resistance exercise.
abstract: 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 (DeltaFSR-M: 0.044%/h), whereas FSR-M in the younger men was not elevated until 180 min POST-EX (DeltaFSR-M: 0.030%/h). FSR-A and FSR-F increased at all POST-EX periods in the older men (DeltaFSR-A = 10 min: 1.90%/day; 60 min: 2.72%/day; 180 min: 2.78%/day; DeltaFSR-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.
authors.affiliation: Department of Internal Medicine, Division of Endocrinology and Metabolism, University of Texas Medical Branch, 301 University Blvd., Galveston, TX 77555-1060, USA. melmoore@utmb.edu
authors.forename: M
authors.initials: M
authors.lastname: Sheffield-Moore
authors.forename: D
authors.initials: D
authors.lastname: Paddon-Jones
authors.forename: A P
authors.initials: AP
authors.lastname: Sanford
authors.forename: J I
authors.initials: JI
authors.lastname: Rosenblatt
authors.forename: A G
authors.initials: AG
authors.lastname: Matlock
authors.forename: M G
authors.initials: MG
authors.lastname: Cree
authors.forename: R R
authors.initials: RR
authors.lastname: Wolfe
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D000418:Albumins / Q000032:analysis*; D001798:Blood Proteins / Q000032:analysis; D005080:Exercise Test; D005340:Fibrinogen / Q000032:analysis*; D005786:Gene Expression Regulation / Q000502:physiology; D006801:Humans; D008099:Liver / Q000378:metabolism*; D008297:Male; D008657:Metabolic Clearance Rate; D009124:Muscle Proteins / Q000097:blood*; D018482:Muscle, Skeletal / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*
chemical_list: D000418:Albumins; D001798:Blood Proteins; D009124:Muscle Proteins; D005340:Fibrinogen