Oxygen consumption in muscle stimulated by noradrenaline at various rates of oxygen delivery

Oxygen consumption and blood flow were measured in the resting autoperfused gracilis anticus muscle of anesthetized cold-acclimated rats at different rates of oxygen delivery (the product of blood flow rate and arterial O2 content) before and during systemic infusion of noradrenaline. Within normal range of O2 delivery (above 16-18 microliters O2 . g-1 . min-1) the unstimulated metabolic rate of the muscle was independent of O2 delivery. On the other hand, during infusion of noradrenaline the muscle O2 consumption increased with O2 delivery ranging from 4.5 to 33.9 microliters O2 . g-1 . min-1. Data indicate that the O2 delivery is not a limiting factor of the unstimulated rat muscle metabolic rate, but it plays an important role in the control of muscle thermogenesis induced by noradrenaline.