FLUID AND SALT INTAKE DURING THE DEVELOPMENT OF RENAL HYPERTENSION IN RATS

SUMMARY 1. In Sprague-Dawley rats, two-kidney, one-clip renal hypertension was induced, and the drinking behaviour as well as total fluid and sodium intake were studied before and for 16 days after the operation. 2. When water alone was offered as drinking fluid, the blood pressure reached values that were by about 20 mmHg higher than those in the rats which had free choice of drinking water or 2% saline. 3. In those rats which had water and 2% saline to drink, the total sodium and fluid intake rose transiently for three days, as compared with that of the sham-operated controls, and increased steeply starting from the 7th and 10th day, respectively. When a tighter stenosis of the renal artery was induced, the pressure rose more rapidly, and the total fluid and sodium intake increased continuously after the operation until the end of the experiment. 4. A positive correlation was demonstrable between the height of blood pressure and the total daily intake of fluid and sodium, respectively. 5. The relation between the total daily fluid and the total daily sodium intake followed a straight regression line. 6. The hypertensive rats which had a high total sodium intake responded to the withdrawal of the 2% saline solution, within 2 days, with increased water intake, decreased food intake, and loss of body weight, whereas the blood pressure remained high. 7. In the two-kidney, one-clip hypertension, no ‘critical level of blood pressure’ can be defined, beyond which the contralateral kidney starts to lose sodium.