Reduced sodium excretory ability in young spontaneously hypertensive rats

The excretory response of spontaneously hypertensive rats (SHR) and stroke-prone SHR (SHRSP) to acute saline load was compared to that of control Wistar Kyoto rats (WKY) in pre- and early-hypertensive phases. In each of the 3 groups, half of the animals was fed a low salt diet, and the other half a normal diet. At the prehypertensive phase, sodium and water excretion and sodium-potassium ratio in the urine in SHR and SHRSP fed a normal diet were significantly less than those in WKY. The ability of SHR to excrete sodium and water, however, was improved by the elevation of blood pressure that developed between 7 and 10 weeks after their birth. While young SHR fed a normal diet had a reduced ability to excrete sodium, the young SHR fed a sodium-restricted diet did not. Salt restriction significantly delayed the appearance of high blood pressure in both SHR and SHRSP. These results suggest that in both SHR and SHRSP, and elevation of blood pressure is important to compensate for the reduced ability to excrete sodium and water.