Influences of chemical sympathectomy, demedullation, and hindlimb suspension on the V(O2)max of rats

The contributions of catecholamines from the adrenal medulla to the reduction in maximal oxygen consumption is investigated in chemically sympathectomized rats. The rats are injected with saline and chemically sympathectomized, and approximately half of the rats are surgically demedullated. The subjects undergo head-down suspension for two weeks and are examined in terms of submaximal mechanical efficiency, treadmill run time, and maximal oxygen consumption. Rats with adrenal medullas and injected with saline demonstrate reduced levels of maximal O consumption, whereas chemically sympathectomized rats with adrenal medullas showed no significant reduction. Reduced levels of maximal O consumption is also noted in the sympathectomized demedullated rats. The paper concludes that circulating epinephrine enhances the attenuation of the decrease in the maximal O consumption caused by chemical sympathectomy.