Renal Nerves Promote Sodium Excretion in Angiotensin-Induced Hypertension

Abstract

To determine whether the sympathetic nervous system contributes to the hypertension induced by pathophysiological increments in plasma angiotensin II (Ang II) concentration, we determined the neurally induced changes in renal excretory function during chronic intravenous infusion of Ang II. Studies were carried out in five conscious chronically instrumented dogs subjected to unilateral renal denervation and surgical division of the urinary bladder into hemibladders to allow separate 24-hour urine collection from the denervated and innervated kidneys. After control measurements, Ang II was infused for 5 days at a rate of 4.8 pmol/kg per minute (5 ng/kg per minute); this was followed by a 5-day recovery period. Twenty-four-hour control values for mean arterial pressure (MAP) and for the ratio of denervated to innervated kidneys (DEN/INN) for urinary sodium, potassium, and creatinine excretion were 93±5 mm Hg, 1.17±0.09, 1.10±0.10, and 1.00±0.02, respectively. As expected, Ang II infusion caused sodium retention for several days before sodium balance was achieved at an elevated MAP (day 5=124±4 mm Hg). Moreover, by day 2 of Ang II-induced hypertension, there were significant reductions in the DEN/INN for sodium and potassium, which persisted for the 5 days of Ang II infusion; on day 5, the DEN/INN values for sodium and potassium were 0.71±0.10 and 0.91±0.12, respectively. In contrast, the DEN/INN for creatinine was unchanged from control levels during Ang II infusion, and measurements of renal hemodynamics indicated comparable reductions in glomerular filtration rate (≈13%) and renal plasma flow (≈25%) during Ang II infusion. This indicates that the renal nerves promoted sodium and potassium excretion during Ang II-induced hypertension by inhibiting tubular reabsorption of these electrolytes. Thus, this study provides no support for the hypothesis that increased renal sympathetic nerve activity impairs sodium excretion and contributes to Ang II-induced hypertension.