Calcium metabolism in glucocorticoid-treated pony foals

Pony foals were injected intramuscularly with 0, 0.5, or 5.0 mg dexamethasone per 100 kg body weight daily for up to 11 months. True absorption of dietary calcium was inhibited by treatment at 18 days (57% versus 14% of intake; P less than .01) and 10 months (72% versus 55% versus 43%: P less than .01), but not at 2 or 7 months, and was independent of age and treatment related decreases in intestinal calcium binding protein activities. Uninary excretion of calcium was increased by treatment through 7 months but decreased at 10 months. Treatment for 18 days resulted in total calcium excretions equivalent to 127% of dietary intake. All animals were in positive calcium balance thereafter. Endogenous fecal calcium excretion was not affected by treatment, age, or sex, averaging 18.0 mg per kg body weight per day. At 2 months, rates of calcium deposition into bone were 13.02, 7.01 and 6.83 g per 100 kg per day in ponies treated with 0, 0.5 and 5.0 mg per 100 kg, respectively. Corresponding rates of calcium removal from bone were 5.41, 1.88, and 2.69 g per 100 kg per day. These rates remained significantly inhibited in the treated ponies at 7 and 10 months. The net effect of dexamethasone treatment was an inhibition of bone turnover: calcium removal was suppressed more than inhibition of bone turnover: calcium removal was suppressed more than calcium deposition.