title: Effects of acute and chronic exercise on skeletal muscle glucose transport in aged rats.
abstract: The purpose of this study was to investigate the effects of acute and chronic exercise on skeletal muscle glucose transport in aged rats by using an isolated sarcolemmal membrane preparation. In 24-mo-old female Fischer 344 rats, a maximum dose of insulin increased glucose transport from 43 +/- 6 to 82 +/- 6 pmol.mg protein-1.15 s-1. A 45-min bout of exhaustive treadmill running increased glucose transport to the same maximum level (88 +/- 5 pmol.mg protein-1.15 s-1). Eight weeks of progressive exercise training resulted in a 65% increase in succinic dehydrogenase activity in hindlimb muscles and a 55% increase in total cellular GLUT-4 content. Despite these biochemical adaptations, there was no change in either basal or maximum insulin-stimulated glucose transport between control (43 +/- 6 and 82 +/- 6 pmol.mg protein-1.15 s-1, respectively) and trained (42 +/- 2 and 82 +/- 8 pmol.mg protein-1.15 s-1, respectively) animals. When hindlimb muscle succinate dehydrogenase activity and GLUT-4 content were compared for both the combined sedentary and trained groups, a significant correlation (r = 0.68) was obtained. This study demonstrates that the skeletal muscle glucose transport system of 24-mo-old rats is fully stimulated by acute exercise and that, although GLUT-4 levels are increased in aged animals after exercise training, this does not result in an enhancement of maximal insulin-stimulated glucose transport. Thus increases in GLUT-4 are not sufficient to improve muscle insulin responsiveness with training.
authors.affiliation: Department of Physiological Science, University of California, Los Angeles 90024, USA.
authors.forename: J F
authors.initials: JF
authors.lastname: Youngren
authors.forename: R J
authors.initials: RJ
authors.lastname: Barnard
mesh_terms: D000375:Aging / Q000378:metabolism*; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D015153:Blotting, Western; D005260:Female; D005947:Glucose / Q000378:metabolism*; D051275:Glucose Transporter Type 4; D007328:Insulin / Q000494:pharmacology; D008566:Membranes / Q000201:enzymology / Q000378:metabolism; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D009124:Muscle Proteins; D018482:Muscle, Skeletal / Q000378:metabolism*; D010805:Physical Conditioning, Animal; D005082:Physical Exertion / Q000502:physiology*; D051381:Rats; D011916:Rats, Inbred F344; D012508:Sarcolemma / Q000201:enzymology / Q000378:metabolism
chemical_list: D001786:Blood Glucose; D051275:Glucose Transporter Type 4; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; C495694:Slc2a4 protein, rat; D005947:Glucose