Sodium, potassium and water metabolism in the rabbit: the effect of sodium depletion and repletion.

1. Dietary sodium depletion and subsequent repletion was studied in rabbits. Potassium intake was maintained constant. 2. during sodium depletion and repletion blood pressure, packed cell volume, food consumption and body weight remained at control values. 3. Decreased sodium excretion was observed in both urine and faeces during sodium depletion and the physiological control of these changes is discussed in relation to the renin-angiotensin-aldosterone system. 4. Potassium excretion during sodium depletion initially fell as a result of reduced urine volume and gradually returned to normal. Urine potassium concentration remained constant. 5. Faecal excretion of potassium rose by 63% during sodium depletion and there was a rise from a control value of 17-25% in the proportion of total potassium excretion accounted for by the faecal component. 6. Water consumption and urine volume both decreased in the initial phase of sodium depletion and then returned to control levels. 7. It is important to consider both urinary and faecal excretion of sodium and potassium when calculating balance status for either ion. Faecal excretion, as well as kidney function, shows important physiological adaptations.