Calcium Status of the Growing Rat as Affected by Diet Acidity from Ammonium Chloride, Phosphate and Protein

Two trials of 4 and 8 weeks' duration were conducted on 64 male Long-Evans growing rats to study effect(s) of diet protein (20 and 40%), phosphate source (less or more acidic) and NH4Cl (none or 1% in water) on Ca status and acid-base balance. Treatments were arranged in a 2 X 2 X 2 factorial plan in four randomized blocks. All diets were equal in Ca (0.52%) and P (0.41%). Criteria were blood pH and bicarbonate, plasma hydroxyproline and Ca, urinary cAMP and Ca, fecal Ca, and mineral analyses and gravimetric measurement of femurs. Blood pH was lowered due to NH4Cl ingestion at 4 weeks (7.11 and 7.22, P less than 0.05) and 8 weeks (7.27 and 7.36, P less than 0.02). Protein level and phosphate source influenced blood bicarbonate. With the ingestion of more acid there were increases in urinary cAMP and Ca. Fecal Ca increased twofold with more acid. Femur specific gravity was higher with the less acidic phosphate source. In conclusion, acid phosphate, NH4Cl and protein influenced blood pH and loss of Ca via urine and feces with a resultant lowered bone density. The less acidic phosphate source reduced or prevented a lowered bone density.