To investigate the effects of pulsatile and nonpulsatile systemic circulation on the sympathetic nerve activity, using a left heart bypass technique, we converted systemic circulation between the pulsatile and the nonpulsatile mode in anesthetized goats and analyzed differences in periodicity and quantity of renal nerve activity (RNA). After pulsatile systemic circulation was converted to the nonpulsatile mode, the mean RNA was significantly increased from 10.7 +/- 3.6 to 13.1 +/- 3.4 microV and periodic discharges of RNA, which corresponded to pulse-related rhythm during pulsatile circulation, became obscure, whereas an 8-12 cycle/s rhythm, which was distinguished and accounted for 30 +/- 9% of total intervals during pulsatile circulation, became dominant (48 +/- 11%). These results clarified a significant increase in mean RNA after depulsation of the systemic circulation and indicated that the cardiac-related rhythm in RNA could be produced by periodic inputs from arterial baroceptors alone, whereas the 8-12 cycle/s rhythm that was present regardless of the type of circulation was the fundamental rhythm originating from the vasomotor center.