Salt loss as a possible mechanism eliciting an acute malignant phase in renal hypertensive rats

1. The acute malignant phase of hypertension in rats with an untouched contralateral kidney is characterized by salt and fluid loss, increased fluid intake, decrease in body-weight gain, and reduced food consumption. Plasma concentrations of sodium and potassium were reduced, and plasma angiotensin II rose to about four times normal. 2. To investigate the significance of an untouched contralateral kidney for the development of the acute malignant phase in renal hypertensive rats, comparative studies were undertaken in unilaterally nephrectomized rats with stenosis of the remaining renal artery and in rats with bilateral renal artery stenosis. In addition, the effect of declamping one renal artery in rats with bilateral stenosis was studied. 3. In unilaterally nephrectomized rats, no signs of sodium and fluid loss were demonstrable, despite marked increase in blood pressure. Similarly, rats with bilateral renal artery stenosis had no acute malignant phase of hypertension. 4. In hypertensive rats with bilateral stenosis, removal of the clip from one renal artery was followed by an immediate fall in blood pressure and a subsequent gradual increase. Eleven of sixteen rats lost salt and fluid and developed an acute malignant phase. Plasma angiotensin II was high and serum urea elevated. 5. Consumption of 2% saline in addition to water as drinking fluid had a beneficial effect, since only five of fourteen rats showed signs of the acute malignant phase, which were milder than in rats on water only. 6. It is concluded that the untouched contralateral kidney is responsible for the negative salt and water balance and its consequences, which are characteristic of the acute malignant phase of experimental renal hypertension.