ANGIOTENSIN-II ENHANCES NOREPINEPHRINE SPILLOVER DURING SYMPATHETIC ACTIVATION IN CONSCIOUS RABBITS

To investigate the potential modulating influence of angiotensin II (A NG II) on sympathetic activity in response to changes in baroreflex ac tivity, renal and total norepinephrine (NE) spillover rates were exami ned during sodium nitroprusside (SNP) and phenylephrine (PE) infusions in four groups of conscious rabbits: 1) saline (control); 2) subpress or ANG II (ANG II, 2 ng . kg(-1) . min(-1)); 3) enalaprilat (MK-422, 2 00 mu g/kg and 3.3 mu g . kg(-1) . min(-1)); and 4) MK plus ANG II (MK + ANG II). Upper plateaus of baroreflex-NE spillover curves for renal and total NE spillover were reduced in the MK group (25 and 81 ng/min ) compared with control (38 and 125 ng/min) and MK + ANG II (37 and 15 5 ng/min). To investigate the interaction of ANG II and sympathetic ac tivity during treadmill exercise, hindlimb NE spillover rate was exami ned in three groups of rabbits: 1) control, 2) MK, and 3) MK + ANG II. Exercise at 6 and 12 m/min produced similar effort-related hemodynami c responses in the three groups. At maximal exercise, hindlimb NE spil lover was reduced in the MK group (29 +/- 3 ng/min) compared with cont rol (62 +/- 17 ng/min, P < 0.05) and MK + ANG II group (51 +/- 10 ng/m in). It is concluded that endogenous ANG II enhances sympathetic activ ity during pharmacological (baroreflex) and physiological stimulation.