Nutritional edema in a rat model of protein deficiency: significance of the dietary potassium and sodium content.

The importance of the levels of dietary sodium and potassium in the etiology of gross nutritional edema in a rat model was explored. For this purpose a mineral mixture (EAM) was designed to permit changing the levels of sodium and potassium while maintaining other components of the mixture. The mixture supplied (as % of diet) 0.075 sodium and 0.270 potassium. In study 1 the EAM mixture was found to support adequate growth (approximately 6 g/d) in well-nourished rats. In study 2 the effects of feeding the diet in either agar gel or dry form were explored. The agar gel diet did not aggravate disturbances in body water balance in rats receiving low protein (0.75 and 1.0% lactalbumin) diets for 20 wk. In study 3 the effects of changes in the sodium and potassium content were evaluated with respect to development of edema and body composition. Excessive levels of sodium or potassium (each 493 mg/100 g diet) in the low protein diet (0.5% lactalbumin) increased mortality and the prevalence of gross edema. When dietary sodium and potassium were closer to the estimated requirement for the rat (0.075% and 0.270%, respectively) there was no development of visible edema in protein-restricted rats. Measurements of exchangeable body sodium, total body water and extracellular and intracellular fluid spaces in the animals indicated that fluid and electrolyte changes result largely from dietary protein restriction alone. However, these changes only proceed to a condition of visible edema where an excessive or unbalanced intake of sodium and potassium is superimposed upon protein deficiency.