Effect of endogenous angiotensin II on renal nerve activity and its arterial baroreflex regulation.

To determine the effects of physiological alterations in endogenous angiotensin II (ANG II) activity on basal renal sympathetic nerve activity and its arterial baroreflex regulation, the effect of ANG II receptor (AT1) blockade with losartan was examined in conscious rats consuming low, normal, or high sodium diet that were instrumented for the simultaneous measurement of arterial pressure and renal sympathetic nerve activity. Intravenous losartan decreased arterial pressure in low (-27 +/- 4 mmHg) and normal (-15 +/- 2 mmHg) but not in high sodium diet rats (-5 +/- 2 mmHg). When arterial pressure had been restored to the prelosartan value with methoxamine infusion, renal sympathetic nerve activity was decreased in low (-27 +/- 4%) and normal (-20 +/- 3%) but not in high sodium diet rats (-5 +/- 2%). Arterial baroreflex regulation of renal sympathetic nerve activity was shifted to a lower pressure (arterial pressure at midrange) in low (-8 +/- 2 mmHg) and normal (-7 +/- 2 mmHg) but not in high sodium diet rats (0 +/- 2 mmHg). Intracerebroventricular losartan did not significantly decrease arterial pressure but decreased renal sympathetic nerve activity in low (-28 +/- 5%) and normal (-20 +/- 4%) but not in high sodium diet rats (-2 +/- 2%). Arterial baroreflex regulation of renal sympathetic nerve activity was shifted to a lower pressure (arterial pressure at midrange) in low (-7 +/- 2 mmHg) and normal (-5 +/- 1 mmHg) but not in high sodium diet rats (0 +/- 2 mmHg). These results indicate that physiological alterations in endogenous ANG II activity tonically influence basal levels of renal sympathetic nerve activity and its arterial baroreflex regulation.