Effects of dietary calcium level, acid stress, and age on renal, serum, and bone responses of rats.

The effects of age and acid stress on renal, serum, and bone responses in 13- and 25-month-old rats, which were fed two levels of dietary calcium, 100 and 500 mg/100 g of diet, for 9 months, with and without dietary ammonium chloride (2%), were investigated. Acid-stressed animals showed significant decreases in urinary pH and significant increases in urinary total acid, calcium and phosphorus excretions, kidney weights, and phosphate-dependent glutaminase activities. Renal responses were affected by the level of calcium in the diet and the age of the animal. Acid stress tended to decrease serum calcium and phosphorus. Serum phosphorus was decreased in old animals, while serum calcium was unaffected by age. Tibia ash weights of old animals were significantly less and their fat content was significantly higher than that of young animals. However, neither acid stress nor the level of calcium in the diet significantly affected bone analysis in either age group. J. Nutr. 105: 1039-1047, 1975.