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Three‐Fold Induction of Renal 25‐Hydroxyvitamin D 3 ‐24‐Hydroxylase Activity and Increased Serum 24,25‐Dihydroxyvitamin D 3 Levels Are Correlated with the Healing Process After Chick Tibial Fracture
Author(s) -
Seo EunGyoung,
Norman Anthony W.
Publication year - 1997
Publication title -
journal of bone and mineral research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.882
H-Index - 241
eISSN - 1523-4681
pISSN - 0884-0431
DOI - 10.1359/jbmr.1997.12.4.598
Subject(s) - medicine , endocrinology , bone healing , vitamin d and neurology , chemistry , tibial fracture , tibia , surgery
To investigate the possible biological actions of 24,25‐dihydroxyvitamin D 3 (24,25(OH) 2 D 3 ), a tibial fracture‐healing model was established in White Leghorn chicks. Three‐week‐old White Leghorn chicks fed a vitamin D 3 –replete diet were divided into four groups (control, anesthetized, sham, and fractured). On varying days after tibial fracture (F) or sham manipulation (S), renal 25(OH)D 3 ‐1α‐hydroxylase and 25(OH)D 3 ‐24‐hydroxylase (24‐hydroxylase) activities and serum Ca 2+ concentrations were measured. Metofane anesthesia was found to have no effect on the activity of either of the hydroxylases; the activities of the hydroxylases in the control, anesthetized, and sham‐operated birds were similar. By 10 days after tibial fracture, the renal 24‐hydroxylase activity increased more than 3‐fold in F (1.33 ± 0.07 pmol/mg of protein) as compared with S (0.42 ± 0.03 pmol/mg of protein) ( p < 0.0001). A time‐dependent study of the renal 24‐hydroxylase activity during the fracture repair process revealed a slow increase from the first day after fracture, a higher activity at 8 days, which peaked at 10–11 days, which is consistent with the formation of the callus. The 24‐hydroxylase activity then returned to the same level as the sham group 14 days after fracture. There was no significant difference in serum Ca 2+ levels between the F and S groups over the 3‐week postfracture period. Serum levels of vitamin D 3 metabolites were also measured during the fracture healing process: a 3.4× increase of the 24,25(OH) 2 D 3 level in the fractured group (3.64 ± 1.16 nM) was observed as compared with the control groups (1.08 ± 0.49 nM) at 10 days after fracture ( p = 0.068). No significant differences were observed in the plasma levels of 25(OH)D 3 or 1α,25(OH) 2 D 3 between the group with a fracture and the controls. Exposure of primary chick kidney cells in culture to serum obtained from chicks with a tibial fracture for 20 h resulted in an ∼40% increase in the activity of the 24‐hydroxylase as compared with cells exposed to serum from control birds. These results suggest that 24,25(OH) 2 D 3 is involved in the early process of fracture repair and that there is some form of physiological communication between the fractured bone and the kidney so as to increase the renal 24‐hydroxylase and the circulating concentration of this metabolite.