Changes in renal sympathetic nerve activity during experimental septic and endotoxin shock in conscious rats

Changes in postganglionic renal sympathetic nerve activity, arterial pressure, and heart rate were measured in conscious rats during intravenous infusion of live E. coli bacteria (10(9)/h) or bolus injection of E. coli endotoxin (20 mg/kg). Bacteria infusion was associated with a marked and parallel increase in heart rate and sympathetic activity with only minor changes in mean arterial pressure. The early response to bolus injection of endotoxin was a short-lasting decrease in mean arterial pressure combined with a marked increase in sympathetic activity and heart rate, probably due to baroreceptor unloading. However, when mean arterial pressure returned to pre-endotoxin levels, sympathetic activity and heart rate remained markedly elevated, indicating a partly nonreflexogenic increase in central sympathetic outflow. This study using direct nerve recordings of sympathetic activity in conscious animals confirms earlier clinical observations of an increased activity of the sympathetic nervous system in septic shock.