Comparative Response in Growth and Bone Status to Three Dexamethasone Treatment Regimens in Infant Piglets

The objectives of this study were 1) to determine whether a zenith in bone formation (indicated by circulating osteocalcin) existed at night in early life, and 2) to compare the effects of three different dexamethasone (DEX) treatment regimens on bone turnover, bone mineral content, and growth. Three DEX treatment regimens were tested in 8-d-old piglets (n = 8/group):1) low evening dose of DEX (0.5 mg/kg/d) as 70% in the morning and 30% in the evening for 10 d;2) tapering course of DEX (0.5, 0.3, and 0.2 mg/kg/d) as 50% in the morning and 50% in the evening for 14 d; and 3) constant dose of DEX (0.5 mg/kg/d) as 50% in the morning and 50% in the evening for 10 d. Oral water placebo groups were tested with the same time courses. At pretreatment, plasma osteocalcin was significantly higher (p < 0.05) at 0100 than at 0900 and 1700. At necropsy, measures for DEX groups were calculated as Z-scores using values from the placebo groups. The low evening DEX dose led to a significantly lower reduction in plasma osteocalcin compared with the tapered and constant dosing regimens (p < 0.05). The significant weight reduction in the DEX group occurred at d 9 in the low evening dose regimen but at d 7 in the constant dosing regimen, compared with the placebo group. Bone mineral content Z-score was reduced similarly in all DEX-treated groups across the three dosing regimens. We conclude that a plasma osteocalcin zenith at night exists in early life. A high DEX dose in the morning and low DEX dose in the evening may partially attenuate corticosteroid-induced suppression of bone formation and growth restriction.