Effect of Sodium Restriction on Renal Hypertension and on Renin Activity in the Rat

Control rats and rats with experimental renal hypertension due to unilateral stenosis of one renal artery received a standard diet (0.23% sodium) and a sodium-deficient diet (0.004% sodium), alternately, during which time blood pressure and plasma renin activity were determined. At the end of the experiment, renin content of the kidneys was measured. In normotensive control rats, the sodium-deficient diet did not affect blood pressure, but plasma renin activity and renin content of the kidneys increased. In rats with renal hypertension, restriction of sodium supply was followed by a fall in blood pressure to normotensive levels, provided that an intact contralateral kidney was present. Similarly, sodium-deficient diet prevented the development of hypertension if given immediately after placing the clip on one renal artery. Restriction of sodium supply provoked a marked increase in plasma renin activity, whereas renin content of the ischemic kidney was only slightly, but significantly, higher than in rats with normal sodium intake. Contrary to this, in unilaterally nephrectomized rats with renal hypertension, neither hypertension nor plasma renin activity or renin content of the kidneys was affected by sodium-deficient diet. In control rats with unilateral nephrectomy, plasma renin activity was only half that of intact rats, and restriction of sodium provoked no more than an increase up to normal values of intact rats. Sodium loss by the contralateral kidney may contribute to both the antihypertensive effect of a sodium-deficient diet and the increase in plasma renin activity.