Renal sympathetic nerve activity and the exaggerated natriuresis of the spontaneous hypertensive rat.

To evaluate the role of altered efferent renal sympathetic nerve activity in the exaggerated natriuresis of the spontaneous hypertensive rat (SHR), we measured efferent renal sympathetic nerve activity in anesthetized age- and sex-matched SHR and normotensive Wistar Kyoto (WKY) control rats during control and intravenous saline volume expansion. Mean arterial pressure was 40-60 mm Hg higher in SHR than in WKY. During volume expansion, the increment in urinary flow rate (17.5 +/- 3.1 vs 42.8 +/- 8.0 microliters/100 g/min) and sodium excretion (8.1 +/- 1.5 vs 15.2 +/- 2.3 muEq/min) were greater in SHR than in WKY. During control, efferent renal sympathetic nerve activity was 12.2 +/- 0.4 Hz in WKY and 12.0 +/- 0.5 Hz in SHR and fell equally during volume expansion to 5.0 +/- 0.6 Hz in WKY and to 4.0 +/- 0.8 Hz in SHR. Thus, these studies demonstrate that the exaggerated natriuresis of SHR as compared to WKY cannot be attributed to differences in reflex withdrawal of renal sympathetic nerve activity.