title: Oxidative stress does not modulate metabolic rate or skeletal muscle sympathetic activity with primary aging in adult humans.
abstract: Support of resting metabolic rate (RMR) by the beta-adrenergic receptors of the sympathetic nervous system is attenuated with age and contributes to declines in RMR. This may be mediated by an age-associated increase in oxidative stress that can suppress beta-adrenergic responsiveness and/or modulate sympathetic activity. To address these issues, RMR was determined in 12 young (23 +/- 1 yr, mean +/- SE) and 21 older (68 +/- 3 yr) adults before and during systemic infusion of ascorbic acid [bolus, 0.06 g/kg fat free mass (FFM); drip, 0.02]. Ascorbic acid increased plasma concentrations similarly in young (72 +/- 5 to 1107 +/- 114 micro mol/liter) and older (70 +/- 6 to 1022 +/- 63 micro mol/liter) adults, and reduced (P = 0.001) plasma concentrations of isoprostanes (young, -82.8 +/- 47; older, -107 +/- 29 pg/ml). Baseline RMR(FFM) was lower (5719 +/- 215 vs. 6703 +/- 328 kJ/d; P = 0.001) and muscle sympathetic nerve activity (MSNA) was greater (MSNA, 28 +/- 2 vs. 23 +/- 3 bursts/min; P < 0.05) in older compared with young. However, neither RMR(FFM) (young, +117 +/- 63; older, +163 +/- 48 kJ/d; P = 0.14) or MSNA (young, 0 +/- 2; older, -1 +/- 1 bursts/min; P = 0.71) changed in either age group during ascorbic acid infusion compared with saline control. These results indicate that increased oxidative stress: 1) is not a mechanism contributing to decreases in RMR with primary aging; and 2) does not modulate MSNA in healthy adult humans.
authors.affiliation: Department of Integrative Physiology, University of Colorado, Boulder, Colorado 80309-0354, USA. Christopher.Bell@Colorado.edu
authors.forename: Christopher
authors.initials: C
authors.lastname: Bell
authors.forename: Pamela P
authors.initials: PP
authors.lastname: Jones
authors.forename: Douglas R
authors.initials: DR
authors.lastname: Seals
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000378:metabolism*; D000975:Antioxidants / Q000008:administration & dosage / Q000378:metabolism; D001205:Ascorbic Acid / Q000008:administration & dosage / Q000097:blood; D001481:Basal Metabolism / Q000187:drug effects / Q000502:physiology*; D001794:Blood Pressure / Q000502:physiology; D001823:Body Composition; D002149:Energy Intake / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000294:innervation* / Q000378:metabolism*; D018384:Oxidative Stress / Q000187:drug effects / Q000502:physiology*; D013564:Sympathetic Nervous System / Q000502:physiology*
chemical_list: D000975:Antioxidants; D001205:Ascorbic Acid