Twenty male Wistar rats were studied in normoxia or hypoxia (F(I)02 = 0.12) at rest and during exercise to exhaustion (24 ± 10 min.). Diaphragm, intercostal, and plantaris muscles were analyzed for metabolite levels. At rest, hypoxia (PaO2 = 47 mmHg) had no effect on muscle metabolites. During hypoxic exercise (HEX) PaCO2 averaged 21.6 mmHg, PaO2 61 mmHg and pHa 7.17. Arterial lactate rose from 2.9 to 16mM and liver glycogen fell from 308-155 μmoles/g. In all 3 muscles the increase in lactate was less than in blood, i.e., from 1.0 to 8.5, from 1.0 to 7.5 and from 1.6 to 6.0 μmoles/g in plantaris, diaphragm and intercostal respectively. ATP and CP were unchanged in all three muscles. Glycogen fell to 44, 58 and 20% of control for diaphragm, intercostal and plantaris respectively. G-6-P increased 166 and 113% in diaphragm and intercostal, but was unchanged in plantaris. We previously showed that normoxic exercise of any severity or duration (i.e., 3 min at 106% VO2 max/38 min at 84% max) did not deplete diaphragm glycogen; we attributed this to an allosteric inhibition of phosphorylase by the exercise-induced increase in G-6-P. In HEX glycogen depletion in diaphragm is less than in plantaris but is not completely prevented, suggesting that inhibition of phosphorylase by G-6-P is overridden in HEX, possibly by catecholamines.
|Original language||English (US)|
|Pages (from-to)||No. 3469|
|State||Published - 1985|
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