Norepinephrine increases canine skeletal muscle VO2 during recovery

The purpose of this study was to investigate the effect of norepinephrine on the rate of O2 uptake (VO2) of the denervated canine gastrocnemius-plantaris muscle group in situ. In seven experiments, VO2 and developed tension were measured without and with norepinephrine infusion during rest, during contractions at 1.0 Hz, and during recovery. In six additional experiments with two consecutive rest-contraction-recovery periods, no norepinephrine was given during the second sequence. During rest, VO2 was increased by norepinephrine. Changes in VO2 during contractions were small, but the arteriovenous O2 content difference was significantly greater during norepinephrine infusion. The most significant finding was that net recovery VO2 was increased 40% by norepinephrine infusion. The ratio of net recovery VO2 to the VO2 during the preceding contraction period was significantly increased from 0.78 +/- 0.07 (mean +/- SEM) to 1.23 +/- 0.07 (mean +/- SEM) by norepinephrine infusion. This increase in net recovery VO2 could be due to either a direct metabolic effect of norepinephrine during recovery or to hypoxia during the preceding contractions. In either case, the data indicated that norepinephrine can produce large increases in muscle recovery VO2; this supports the notion that catecholamines may make a significant contribution to post-exercise recovery VO2.