Date of Award


Degree Type


Degree Name

Doctor of Philosophy



Major Professor

Roy E. Beauchene

Committee Members

Jane R. Savage, Bernadine Meyer, Mary Rose Gram


The effects of age and acid stress on bone and renal responses in rats were investigated. Albino, male weanling rats and male 10-month old retired breeder rats were maintained on a commercial laboratory chow until they were 4 months and 16 months of age, respectively, and then transferred to semi-synthetic experimental diets, containing either 500 mg or 100 mg calcium per 100 g diet, with or without 2% ammonium chloride as an acid stress. The rats remained on the experimental diets 9 months, that is, until the "young" animals were 13 months and the "old" ones were 25 months of age. Prior to sacrifice, 72-hour urine collections were made on all rats for the determinations of urine volume, pH, titratable acid, ammonium, calcium and phosphorus excretions. At the time of sacrifice, blood samples were taken for determination of serum calcium and phosphorus concentrations, kidneys were weighed and their phosphate-dependent glutaminase activities and concentrations of proteins were measured. The right tibias were removed for determination of their dry and fat-free weights, and they were also analyzed for their percent ash, calcium and phosphorus.

As measured in this study, neither organic nor inorganic phases of tibias were affected by dietary treatments in either age group of rats, but tibias of old animals weighed significantly less and their tibia fat content was significantly higher than that of younger animals. Serum phosphorus levels were significantly higher in young rats. Acid-stressed animals showed significant decreases in urinary pH and significant increases in urinary titratable acid, ammonium, calcium and phosphorus excretions, with age-associated decrements in those urinary responses in old rats. The urinary responses were affected by the level of calcium in the diet in both age groups. Renal hypertrophy was observed in acid-stressed animals, as well as significantly increased phosphate-dependent glutaminase activities; however those changes were not age-associated. Concentrations of kidney protein were significantly lower in old rats than in younger animals, regardless of dietary treatments. The effects of incorporating sodium and potassium bicarbonate into the diets containing ammonium chloride were most pronounced in old animals fed the low calcium diet as evidenced by significant decrements in the urinary responses. The data indicated that animals in both age groups adapted to the acid stress and decreased level of calcium in the diet.

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