Arterial baroreflexes are not essential in mediating sympathoadrenal activation in conscious endotoxic rats

We examined the contributions of arterial baroreceptor reflexes in mediating sympathoadrenal activation during endotoxicosis. Conscious rats with chronic sinoaortic denervation (SAD) or sham-operation (SHAM) were subject to endotoxin treatment (5 mg/kg, i.v.). Hemodynamic responses, renal sympathetic nerve activity (RSNA) and plasma catecholamines were assessed at different times post endotoxin infusion. In both SAD and sham groups, intravenous endotoxin injection induced a rapid and significant sympathoadrenal activation, as indicated by a parallel elevation of RSNA and plasma catecholamines. Such activation peaked 15-30 min following endotoxin and was sustained throughout the 2-3 h protocol. The early response of the sympathoadrenal system to endotoxin is more profound in SAD rats compared to sham rats. We propose that the afferent neural input from arterial baroreceptors is not essential in mediating sympathoadrenal activation during sepsis. The elimination of feedback buffering mechanisms with SAD may account for the augmented sympathetic response seen in SAD animals.