title: Regulation of free radical outflow from an isolated muscle bed in exercising humans.
abstract: Incremental knee extensor (KE) exercise performed at 25, 70, and 100% of single-leg maximal work rate (WR(MAX)) was combined with ex vivo electron paramagnetic resonance (EPR) spectroscopic detection of alpha-phenyl-tert-butylnitrone (PBN) adducts, lipid hydroperoxides (LH), and associated parameters in five males. Blood samples were taken from the femoral arterial and venous circulation that, when combined with measured changes in femoral venous blood flow, permitted a direct examination of oxidant exchange across a functionally isolated contracting muscle bed. KE exercise progressively increased the net outflow of LH and PBN adducts (100% > 70% > 25% WR(MAX), P < 0.05) consistent with the generation of secondary, lipid-derived oxygen (O(2))-centered alkoxyl and carbon-centered alkyl radicals. Radical outflow appeared to be more intimately associated with predicted decreases in intracellular Po(2) (iPo(2)) as opposed to measured increases in leg O(2) uptake, with greater outflow recorded between 25 and 70% WR(MAX) (P < 0.05 vs. 70-100% WR(MAX)). This bias was confirmed when radical venoarterial concentration differences were expressed relative to changes in the convective components of O(2) extraction and flow (25-70% WR(MAX) P < 0.05 vs. 70-100% WR(MAX), P > 0.05). Exercise also resulted in a net outflow of other potentially related redox-reactive parameters, including hydrogen ions, norepinephrine, myoglobin, lactate dehydrogenase, and uric acid, whereas exchange of lipid/lipoproteins, ascorbic acid, and selected lipid-soluble anti-oxidants was unremarkable. These findings provide direct evidence for an exercise intensity-dependent increase in free radical outflow across an active muscle bed that was associated with an increase in sarcolemmal membrane permeability. In addition to increased mitochondrial electron flux subsequent to an increase in O(2) extraction and flow, exercise-induced free radical generation may also be regulated by changes in iPo(2), hydrogen ion generation, norepinephrine autoxidation, peroxidation of damaged tissue, and xanthine oxidase activation.
authors.affiliation: Depts. of Anesthesiology and Surgery, Colorado Center for Altitude Medicine and Physiology, University of Colorado Health Sciences Center, PO Box 6508, Mail Stop F524, Aurora, CO 80111, USA. damian.bailey@btinternet.com
authors.forename: Damian M
authors.initials: DM
authors.lastname: Bailey
authors.forename: Ian S
authors.initials: IS
authors.lastname: Young
authors.forename: Jane
authors.initials: J
authors.lastname: McEneny
authors.forename: Lesley
authors.initials: L
authors.lastname: Lawrenson
authors.forename: Jeannie
authors.initials: J
authors.lastname: Kim
authors.forename: Jeremy
authors.initials: J
authors.lastname: Barden
authors.forename: Russell S
authors.initials: RS
authors.lastname: Richardson
mesh_terms: D000328:Adult; D000368:Aged; D000975:Antioxidants / Q000378:metabolism; D001783:Blood Flow Velocity / Q000502:physiology; D002245:Carbon Dioxide / Q000097:blood; D002395:Catecholamines / Q000097:blood; D004578:Electron Spin Resonance Spectroscopy; D015444:Exercise / Q000502:physiology*; D005609:Free Radicals / Q000378:metabolism; D006801:Humans; D015227:Lipid Peroxidation / Q000502:physiology*; D008077:Lipoproteins, LDL / Q000097:blood; D008297:Male; D008875:Middle Aged; D008928:Mitochondria / Q000378:metabolism; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000378:metabolism*; D010084:Oxidation-Reduction; D018384:Oxidative Stress / Q000502:physiology; D010100:Oxygen / Q000097:blood
chemical_list: D000975:Antioxidants; D002395:Catecholamines; D005609:Free Radicals; D008077:Lipoproteins, LDL; D002245:Carbon Dioxide; D010100:Oxygen