Renal Sympathetic Neuroeffector Function in Renovascular and Angiotensin II–Dependent Hypertension in Rabbits

Abstract

We tested the hypotheses that the gains of specific renal sympathetic neuroeffector mechanisms are altered in secondary hypertension and that the nature of these alterations depends on the precise experimental setting of the kidney. Rabbits were sham operated, or made comparably hypertensive (mean arterial pressure increased 17% to 24%) by clipping the left or right renal artery or by chronic infusion of angiotensin II (20 to 50 ng kg −1 min −1 SC). Four to 6 weeks later, under pentobarbital anesthesia, the left renal nerves were sectioned and electrically stimulated at low (0 to 2 Hz) and high (4 to 8 Hz) frequencies. Neurally evoked reductions in total renal blood flow, cortical perfusion, urine flow, and sodium excretion and increases in renal norepinephrine spillover were not significantly greater in kidneys of hypertensive rabbits than normotensive controls. Neurally evoked increases in renal renin release and the slope of the relationship between renin release and norepinephrine spillover were less in kidneys of hypertensive rabbits than normotensive controls. Low-frequency renal nerve stimulation reduced medullary perfusion, which was negatively correlated with renal norepinephrine spillover in kidneys from all 3 groups of hypertensive rabbits but not normotensive controls. Two-hertz stimulation reduced medullary perfusion by 19% in hypertensive rabbits but not in normotensive rabbits. Thus, of all of the renal sympathetic neuroeffector mechanisms studied, only neural control of medullary perfusion was enhanced in these models of secondary hypertension. This effect appears to be mediated postjunctionally, not through enhanced neural norepinephrine release, and may contribute to the development and/or maintenance of hypertension in these models.