Effect of pentobarbital anesthesia on renal sympathetic nerve activity in the rabbit

The effects of pentobarbital (PB) anesthesia on arterial pressure, heart rate, and renal nerve activity (RNA) were studied in chronically instrumented intact rabbits and rabbits with sinoaortic baroreceptor denervation (SAD). In intact rabbits, PB caused an initial decrease in mean arterial pressure from 82 +/- 2 to 42 +/- 5 mm Hg, which then returned to the control level within 5 min. RNA increased by 144 +/- 19% in response to hypotension induced by PB then also returned to the control level within 5 min. Heart rate increased by 56 +/- 10 from 244 +/- 11 beats/min and remained elevated for 60 min. Sensitivities of baroreflex control of heart rate and RNA were markedly impaired by PB anesthesia. In SAD rabbits, PB caused hypotension (-46 +/- 5 mm Hg), which lasted for 15 min. RNA decreased initially by 80 +/- 5%, then gradually returned toward the control level. However, at 45 min after injection of PB, RNA was still depressed significantly. Tachycardia induced by PB was abolished by SAD, i.e. heart rate actually decreased by 53 +/- 10 beats/min. These results suggest that in intact rabbits steady-state effects of PB were: no change in mean arterial pressure or RNA, and tachycardia, all due to baroreflex compensation. However, in the absence of baroreflex compensation, PB elicited hypotension, bradycardia, and a decrease in RNA.