title: A 31P-NMR study of tissue respiration in working dog muscle during reduced O2 delivery conditions.
abstract: To investigate the role of tissue oxygenation as one of the control factors regulating tissue respiration, 31P-nuclear magnetic resonance spectroscopy (31P-NMR) was used to estimate muscle metabolites in isolated working muscle during varied tissue oxygenation conditions. O2 delivery (muscle blood flow x arterial O2 content) was varied to isolated in situ working dog gastrocnemius (n = 6) by decreases in arterial PO2 (hypoxemia; H) and by decreases in muscle blood flow (ischemia; I). O2 uptake (VO2) was measured at rest and during work at two or three stimulation intensities (isometric twitch contractions at 3, 5, and occasionally 7 Hz) during three separate conditions: normal O2 delivery (C) and reduced O2 delivery during H and I, with blood flow controlled by pump perfusion. Biochemical metabolites were measured during the last 2 min of each 3-min work period by use of 31P-NMR, and arterial and venous blood samples were drawn and muscle blood flow measured during the last 30 s of each work period. Muscle [ATP] did not fall below resting values at any work intensity, even during O2-limited highly fatiguing work, and was never different among the three conditions. Muscle O2 delivery and VO2 were significantly less (P < 0.05) at the highest work intensities for both I and H than for C but were not different between H and I. As VO2 increased with stimulation intensity, a larger change in any of the proposed regulators of tissue respiration (ADP, P(i), ATP/ADP.P(i), and phosphocreatine) was required during H and I than during C to elicit a given VO2, but requirements were similar for H and I.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Medicine, University of California, San Diego, La Jolla 92093-0623.
authors.forename: M C
authors.initials: MC
authors.lastname: Hogan
authors.forename: S
authors.initials: S
authors.lastname: Nioka
authors.forename: W F
authors.initials: WF
authors.lastname: Brechue
authors.forename: B
authors.initials: B
authors.lastname: Chance
mesh_terms: D000693:Anaerobiosis; D000818:Animals; D002245:Carbon Dioxide / Q000097:blood; D004285:Dogs; D004734:Energy Metabolism / Q000502:physiology; D005221:Fatigue / Q000378:metabolism; D005260:Female; D006863:Hydrogen-Ion Concentration; D007537:Isometric Contraction / Q000502:physiology; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D009132:Muscles / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology*; D010710:Phosphates / Q000378:metabolism; D005082:Physical Exertion / Q000502:physiology*; D011659:Pulmonary Gas Exchange / Q000502:physiology
chemical_list: D010710:Phosphates; D002245:Carbon Dioxide