Neural control of the renal vasculature in angiotensin II-induced hypertension

1. Chronic administration of angiotensin (Ang) II causes an increase in blood pressure via a multitude of actions, including direct vasoconstriction, hypertrophy and increased sympathetic nerve activity. In the present study, we assessed whether the hypertension resulting from chronic Ang II alters the ability of the renal vasculature to respond to sympathetic activity. 2. Angiotensin II was administered for 7 weeks via an osmotic minipump at a dose of 50 ng/kg per min, i.v., to a group of six rabbits. Blood pressure, measured at 0, 1, 2 and 6 weeks after insertion of the pump, increased from 76 +/- 2 to 104 +/- 6 mmHg at the end of 6 weeks, without any significant change in heart rate. The blood pressure in the control group remained constant at 76 +/- 2 mmHg. 3. After 7 weeks, rabbits were anaesthetized and the renal nerves were stimulated at 0.5, 1, 1.5, 2, 3, 5 or 8 Hz for 3 min at their supramaximal voltage (5.5 +/- 1.0 V in the normotensive group and 6.5 +/- 1.5 V in the hypertensive group) while the renal blood flow (RBF) response was recorded. Under anaesthesia, there was no difference in mean arterial pressure between the normotensive and hypertensive animals (77 +/- 2 and 80 +/- 7 mmHg, respectively). The resting RBF under these conditions was not significantly different in the hypertensive group (30 +/- 4 vs 26 +/- 5 mL/min in the normotensive vs hypertensive group, respectively). 4. Stimulation at increasing frequencies was associated with increasing reductions in RBF (e.g. 36 +/- 8% at 2 Hz in normotensive rabbits and 48 +/- 7% at 2 Hz in hypertensive rabbits). However, there were no significant differences between RBF responses in normotensive and hypertensive rabbits. 5. We conclude that hypertension associated with chronic Ang II administration does not alter the response in RBF to electrical stimulation of the nerves.