Salt and water intake and sodium and potassium excretion in spontaneously hypertensive rats

1. Total fluid and saline intakes were greater in spontaneously hypertensive rats (SHR) than in normotensive rats (NTR). 2. Total fluid and saline intake were significantly elevated in prehypertensive SHR, 5 weeks old, compared with age-matched NTR, and the intakes fell with age in both strains but remained considerably greater in SHR. 3. In SHR, in which the blood pressure was maintained at normotensive levels by treatment with hydralazine, the saline and fluid intakes remained elevated above those of NTR. 4. SHR and NTR fed low sodium diet with water alone to drink have similar excretion rates of sodium, suggesting that their ability to conserve sodium was normal. 5. Measurement of sodium excretion after three different levels of sodium loading, on normal or low sodium diets, also failed to demonstrate an abnormality of renal function in SHR. 6. These results demonstrate that the fluid and saline intakes of SHR are elevated compared with NTR and this difference is independent of the hypertension in SHR and is not secondary to enhanced renal sodium loss.