Role of the renal sympathetic nerves in the development and maintenance of hypertension in the spontaneously hypertensive rat

Neurogenic factors and, in particular, enhanced renal sympathetic tone, have been implicated in the pathogenesis of hypertension in the spontaneously hypertensive rat of the Okamoto strain. To examine the hypothesis that the renal sympathetic nerves contribute to the development and maintenance of hypertension by causing urinary sodium retention, 7-wk-old (early hypertensive) and 18-wk-old (established hypertensive) male spontaneously hypertensive rats were subjected to bilateral renal denervation and compared with sham-operated controls. In 7-wk-old animals renal denervation delayed the onset and slowed the rate of development of hypertension. These alterations were associated with a significantly greater fractional excretion of sodium (percentage of sodium intake excreted) during the first 3 wk after denervation. Blood pressure 2 wk after surgery was 169+/-3.5 (sham) vs. 150+/-2.4 mm Hg (denervated) (P < 0.001), corresponding to fractional sodium excretions of 65+/-1.3% (sham) vs. 80+/-2.3% (denervated) (P < 0.001). By the 5th wk after surgery, at which time an increase in renal norepinephrine content of denervated animals suggested reinnervation, blood pressures in the two groups converged (sham, 199+/-6.5 mm Hg vs. denervated 180+/-3.5 mm Hg, NS) and there was no difference in sodium excretion (sham, 77+/-2.5% vs. denervated 79+/-2.3%). Plasma and kidney renin activity of denervated animals did not differ significantly from that of sham-operated controls. In 18-wk-old rats renal denervation did not alter blood pressure or urinary sodium excretion. These data indicate that the renal sympathetic nerves contribute to the development of hypertension in the spontaneously hypertensive rat in part by causing enhanced sodium retention. Once hypertension is established the renal nerves do not play a significant role in the maintenance of increased blood pressure.