title: Microvascular oxygen pressures in muscles comprised of different fiber types: Impact of dietary nitrate supplementation.
abstract: Nitrate (NO3(-)) supplementation via beetroot juice (BR) preferentially improves vascular conductance and O2 delivery to contracting skeletal muscles comprised predominantly of type IIb + d/x (i.e. highly glycolytic) fibers following its reduction to nitrite and nitric oxide (NO). To address the mechanistic basis for NO3(-) to improve metabolic control we tested the hypothesis that BR supplementation would elevate microvascular PO2 (PO2mv) in fast twitch but not slow twitch muscle. Twelve young adult male Sprague-Dawley rats were administered BR ([NO3(-)] 1 mmol/kg/day, n = 6) or water (control, n = 6) for 5 days. PO2mv (phosphorescence quenching) was measured at rest and during 180 s of electrically-induced 1-Hz twitch contractions (6-8 V) of the soleus (9% type IIb +d/x) and mixed portion of the gastrocnemius (MG, 91% type IIb + d/x) muscles. In the MG, but not the soleus, BR elevated contracting steady state PO2mv by ~43% (control: 14 ± 1, BR: 19 ± 2 mmHg (P < 0.05)). This higher PO2mv represents a greater blood-myocyte O2 driving force during muscle contractions thus providing a potential mechanism by which NO3(-) supplementation via BR improves metabolic control in fast twitch muscle. Recruitment of higher order type II muscle fibers is thought to play a role in the development of the VO2 slow component which is inextricably linked to the fatigue process. These data therefore provide a putative mechanism for the BR-induced improvements in high-intensity exercise performance seen in humans.
authors.affiliation: Department of Anatomy and Physiology, Kansas State University, Manhattan, KS 66506, USA.
authors.forename: Scott K
authors.initials: SK
authors.lastname: Ferguson
authors.affiliation: Department of Anatomy and Physiology, Kansas State University, Manhattan, KS 66506, USA.
authors.forename: Clark T
authors.initials: CT
authors.lastname: Holdsworth
authors.affiliation: Department of Anatomy and Physiology, Kansas State University, Manhattan, KS 66506, USA.
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Wright
authors.affiliation: Department of Anatomy and Physiology, Kansas State University, Manhattan, KS 66506, USA.
authors.forename: Alex J
authors.initials: AJ
authors.lastname: Fees
authors.affiliation: Department of Community and Family Medicine, Department of Medicine, Duke University, Durham, NC 27710, USA.
authors.forename: Jason D
authors.initials: JD
authors.lastname: Allen
authors.affiliation: Sport and Health Sciences, University of Exeter, St. Luke's Campus, Exeter EX12LU, UK.
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Jones
authors.affiliation: Department of Anatomy and Physiology, Kansas State University, Manhattan, KS 66506, USA; Department of Kinesiology, Kansas State University, Manhattan, KS 66506, USA.
authors.forename: Timothy I
authors.initials: TI
authors.lastname: Musch
authors.affiliation: Department of Anatomy and Physiology, Kansas State University, Manhattan, KS 66506, USA; Department of Kinesiology, Kansas State University, Manhattan, KS 66506, USA. Electronic address: poole@vet.ksu.edu.
authors.forename: David C
authors.initials: DC
authors.lastname: Poole
mesh_terms: D000818:Animals; D019587:Dietary Supplements; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D018656:Muscle Fibers, Fast-Twitch / Q000187:drug effects; D018657:Muscle Fibers, Slow-Twitch / Q000187:drug effects; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism*; D009566:Nitrates / Q000097:blood / Q000494:pharmacology*; D010100:Oxygen / Q000378:metabolism*; D017207:Rats, Sprague-Dawley
chemical_list: D009566:Nitrates; D010100:Oxygen
keywords: Blood flow; Exercise; Metabolic control; Nitric oxide; Nitrite; Oxygen flux