Reduced sodium excretory ability in young spontaneously hypertensive rats.

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Abstract
The excretory response of spontaneous 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 were fed a low-salt diet, and the other half a normal diet. At the prehypertensive phase, Na and water excretion and Na-K 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 Na and water was improved by the elevation of blood pressure that developed between 7 and 10 wk after the birth. While young SHR fed a normal diet had a reduced ability to excrete Na, the young SHR fed a Na-restricted diet did not. Salt restriction significantly delayed the appearance of high blood pressure in both SHR and SHRSP. Apparently, in both SHR and SHRSP, an elevation of blood pressure is important in compensating for the reduced ability to exercise Na and water.