Effect of dietary protein on electrolyte excretion in the mouse

Abstract

Consuming either high or low protein content significantly affects kidney function. Ingesting a low protein (LP) diet impairs the kidney's ability to concentrate the urine and induces water diuresis whereas a high protein (HP) diet increases GFR, enhances the concentrating mechanism, and on the long-term, enlarges the kidney. Physicians prescribe LP diets for patients with chronic renal disease. HP diets have proven useful for treating obesity. Given the principle role of the kidney to control electrolyte homeostasis, the effect of dietary protein on electrolyte excretion requires investigation. Our purpose was to determine the effects of HP and LP diets on Na, K, and Ca excretion. Three groups of mice (n=4 each group) were placed in metabolic cages for 20 days and consumed 40%, 20%, or 6% casein (HP, normal-NP, LP, respectively) and water ad libitum. The protocol contained three periods. Mice consumed NP diet for the first five days. Two groups then consumed either HP or LP diet for the next ten days and returned to the NP diet for the final five days. Daily measurements included body weight, food and water intake, urine volume and osmolality, urine Na, K, and Ca levels. Data below show the average excretion (mEq/day) during the 10-day experimental period. No differences existed in the control period, i.e., the first five days. We conclude that LP diet increases Na, K, and Ca excretion whereas HP diet increases Ca excretion. LP diet induced water diuresis which likely caused high electrolyte excretion rates. HP diet produced osmotic diuresis and likely stimulated Na and K transport, but not Ca.