Differential effects of anesthetics on sympathetic nerve activity and arterial baroreceptor reflex in chronically instrumented rats

The effects of pentobarbital sodium, chloralose, and urethane on sympathetic nerve activity and arterial baroreceptor reflex were examined using rats chronically instrumented for recordings of blood pressure (BP), electrocardiogram and renal sympathetic nerve activity (RSNA). Pentobarbital sodium (30 mg/kg, i.v.) produced a decrease in BP with a transient decrease in heart rate (HR) and no change in RSNA. Chloralose (50 mg/kg, i.v.) also caused a decrease in BP and no change in HR and RSNA until a later increase in HR and RSNA, while urethane (800 mg/kg, i.v.) increased BP, HR, and RSNA. Baroreceptor reflex function was assessed by constructing a logistic function curve compiled from data obtained by intravenous infusion in increasing doses of phenylephrine and sodium nitroprusside. Both pentobarbital sodium and chloralose administration decreased the gain of baroreceptor reflex control of both HR and RSNA. Urethane also decreased the gain of baroreceptor reflex control of HR but elicited no change in that of RSNA. These results suggest that different intravenously administered anesthetics affect the peripheral sympathetic outflows in qualitatively and quantitatively different manners.