Effect of changes in blood flow, norepinephrine, and pH on oxygen uptake by resting skeletal muscle.

The purpose of this study was to examine the effects of norepinephrine infusion alone and during alkalosis on oxygen uptake in the dog gastrocnemius-plantaris muscle group under conditions of constant muscle blood flow. The animals were not cold acclimatized. Blood flow was pump controlled, alkalosis was produced by hyperventilation, and norepinephrine was infused intravenously at a rate of 1--1.5 micrograms/kg per minute. Alkalosis had no effect either alone or in combination with changes in blood flow. Similarly, changing blood flow from a low (0.10 +/- 0.02 mL/g muscle per minute (mean +/- SE)) to a high (0.34 +/- 0.04 mL/g muscle per minute) rate did not alter resting oxygen uptake. Norepinphrine caused an average increase of about 30% in resting muscle oxygen uptake which was sustained for the 15-min sampling period during a low flow-norepinephrine infusion and during the low and high blood flow-norepinephrine-alkalosis sampling periods. Norepinephrine infusion during the period of high muscle blood flow without alkalosis resulted in a transient increase followed by a decrease in muscle oxygen uptake. The data demonstrated that infusion of norepinephrine increased skeletal muscle oxygen uptake in "non-cold-acclimatized" dogs at low constant muscle blood flow. Further, without alkalosis, the norepinephrine effect at high flow was transient.