Effects of ischemic and hypoxic hypoxia on VO2 and lactic acid output during tetanic contractions.
We measured O2 uptake (VO2), CO2 output (VCO2), and net lactic acid output (L) during a 30-min period of repetitive 1/s isotonic tetanic contractions of the dog gastrocnemius-plantaris muscle group. The conditions were modest ischemic hypoxia (ischemia), hypoxia hypoxia (hypoxia), and free-flow normoxia (control). The major goal was to assess the effects of these perturbations on L during contractions. Ischemia and hypoxia were initiated just before the start of the contractions and at minute 7 of contractions in separate groups of experiments. Whenever applied, both ischemia and hypoxia reduced VO2 compared with the control values. When ischemia was initiated at the start of contractions, L was reduced transiently compared with the controls. When ischemia began at minute 7, L was increased modestly but transiently compared with the controls. When hypoxia was initiated at the start of contractions, L was increased during the entire period of contractions. The L pattern was the same as in the controls, rising to a maximal value at 3 min and declining steadily to a lower value at 30 min. When hypoxia began at minute 7, L declined initially at a slower rate than it did in the controls and was thereby elevated above the controls from 9 to 30 min. Ischemia was associated with a more rapid reduction in mechanical performance than hypoxia. The data suggest that the mechanisms of the decreased mechanical performance and VO2 are different for ischemia and hypoxia.
Stainsby
W N
WN
Department of Physiology, College of Medicine, University of Florida, Gainesville 32610.
Brechue
W F
WF
O'Drobinak
D M
DM
Barclay
J K
JK
D000818:Animals; D002245:Carbon Dioxide / Q000378:metabolism*; D004285:Dogs; D000860:Hypoxia / Q000378:metabolism* / Q000503:physiopathology; D007511:Ischemia / Q000378:metabolism* / Q000503:physiopathology; D007773:Lactates / Q000096:biosynthesis*; D009119:Muscle Contraction / Q000502:physiology*; D009132:Muscles / Q000098:blood supply* / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism*
D007773:Lactates; D002245:Carbon Dioxide; D010100:Oxygen