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

Abstract

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.

Reversal of two-kidney one clip renovascular hypertension in the rat.

“…Our results refute the suggestion that the blood pressure fall induced by any of these procedures is mediated by increased sodium excretion. The degree of sodium retention induced by surgical correction of hypertension demonstrated here is approximately equal to the negative sodium balance that we have previously demonstrated during the development of hypertension in this model, 1 suggesting that the sodium retention represented correction of sodium depletion produced by pressure natriuresis through the nonischemic kidney. The fall in urine volume (table 1) is attributable to relief of pressure diuresis.…”

“…Balance procedures were carried out according to a previously described method. 1 Rats were allowed to familiarize themselves with the cages for 5 to 7 days before balances were begun. Balances were then analyzed for at least 4 days before any definitive procedure was carried out.…”

“…The presence of a contralateral nonischemic kidney appears to be of critical importance to the pathogenesis of hypertension. When contralateral nephrectomy is performed (one-kidney, one clip hypertension), plasma and renal renin levels are normal or reduced, 1 and sodium balance is positive. 1 In the two-kidney, one clip model, on the other hand, renin levels are elevated during the early phases of hypertension, although renin may then fall.…”

“…When contralateral nephrectomy is performed (one-kidney, one clip hypertension), plasma and renal renin levels are normal or reduced, 1 and sodium balance is positive. 1 In the two-kidney, one clip model, on the other hand, renin levels are elevated during the early phases of hypertension, although renin may then fall. 8 "" In addition, there is little or no blood pressure response to renin-angiotensin blockade with the competitive 1 "* Sodium balance is usually negative in the early phase of hypertension, presumably as a result of perfusion pressure natriuresis by the nonischemic kidney, 2 although importance has been attached to transient sodium retention observed during the development of hypertension.…”

Salt and hypertension--future directions.

“…12 Future studies aimed at defining the mechanisms whereby excess salt can raise blood pressure should use better-defined and simpler models in which more of the variables can be controlled. One such model in dogs and rats is the sensitivity to salt that is conferred by physical reduction of renal mass from 65% to 80% of normal size.…”