1. These studies were designed to investigate the effects of high dietary K+ on electrolyte and water balance in young spontaneously hypertensive rats (SHR) and to relate these effects to changes in blood pressure.
2. The high K+ diet reduced blood pressure by approximately 10 mmHg during the development of hypertension. Blood pressure, however, plateaued at the same maximum level as control by age 13 weeks.
3. Rats fed the high K+ diet showed a significant increase in water intake and urine volume throughout the treatment period but no change in plasma volume or extracellular fluid volume occurred.
4. A slight natriuresis was also observed in rats on the high K+ diet, but this was not of sufficient magnitude to decrease total body Na+.
5. These results confirm previous findings that K+ causes a diuresis and a natriuresis, but demonstrate that the diuretic action of K+ cannot explain its antihypertensive properties in young SHR.