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Osteocalcin is vitamin D-dependent during the perinatal period in the rat
J Verhaeghe1, M Thomasset, F A Van Assche
1Laboratorium voor Experimentele Geneeskunde en Endocrinologie, Katholieke Universiteit Leuven, Belgium.
Insights
This study investigated vitamin D-dependent bone proteins in fetal and neonatal rats on standard or low calcium-phosphorus diets. Osteocalcin, a key bone protein, showed vitamin D dependence during development.
Area of Science:
- Endocrinology
- Developmental Biology
- Nutritional Science
Background:
- Vitamin D is crucial for calcium homeostasis and bone metabolism.
- Perinatal development involves significant changes in bone mineralization and protein expression.
- The roles of vitamin D-dependent proteins like calbindin D-28K and osteocalcin during this period require further elucidation.
Purpose of the Study:
- To investigate the vitamin D-dependence of renal calbindin D-28K and osteocalcin during rat perinatal development.
- To compare these protein levels in fetuses and neonates fed standard versus calcium-phosphorus restricted diets.
Main Methods:
- Studied rat fetuses (days 18, 21) and neonates (days 2, 12, 17, 22) on high or low calcium-phosphorus diets.
- Measured body weight, plasma calcium, 1,25(OH)2D, plasma and femoral osteocalcin, and femoral calcium content.
- Analyzed renal calbindin D-28K concentrations.
Main Results:
- Plasma 1,25(OH)2D concentrations were significantly higher in low Ca-P diet rats throughout perinatal life.
- Renal calbindin D-28K levels peaked at day 12 and were similar between diet groups.
- Plasma and femoral osteocalcin levels were higher in low Ca-P diet rats, indicating vitamin D dependence, while femoral calcium decreased in late neonates on the low Ca-P diet.
Conclusions:
- Osteocalcin exhibits vitamin D dependence in fetal and neonatal rats.
- Dietary calcium and phosphorus restriction leads to increased 1,25(OH)2D and osteocalcin levels during perinatal development.
- While calbindin D-28K levels peak similarly, osteocalcin's regulation highlights vitamin D's critical role in bone health during early life.
Abstract:
The vitamin D-dependence of renal calbindin D-28K and osteocalcin during the perinatal period was studied in fetuses (days 18 and 21) and neonates (days 2, 12, 17 and 22) of rats fed either a standard diet (0.85% Ca-0.7% P; "high Ca-P diet" rats) or a mildly Ca-P restricted diet (0.2% Ca-0.2% P; "low Ca-P diet" rats). Body weight and plasma calcium levels were identical in both groups. Plasma 1,25(OH)2D concentrations were markedly higher in the low Ca-P diet rats at all stages of fetal and neonatal life (in 22-day-old neonates: 536 +/- 58 pg/ml versus 126 +/- 12 pg/ml). 1,25(OH)2D concentrations increased between day 18 and 21 of fetal life, remained constant between day 21 of fetal and day 12 of neonatal life, and increased sharply between day 12 and 17 in both groups; after day 17, 1,25(OH)2D concentrations increased further in pups fed the low Ca-P diet. Renal calbindin D-28K reached peak concentrations on day 12 of neonatal life; calbindin D-28K levels were similar in the high and low Ca-P diet rats at all stages of perinatal development. Plasma osteocalcin levels increased steadily during the perinatal period; at most stages of perinatal life, and already from the fetal period was osteocalcin higher in the low Ca-P diet rats than in the high Ca-P diet rats (in 22-day-old pups: 1106 +/- 47 ng/ml versus 429 +/- 14 ng/ml). Femoral osteocalcin concentrations were also increased in fetal and early neonatal (days 2 and 12) low Ca-P diet rats, while the femoral calcium content and concentration of these rats were decreased in the late neonatal period (days 12, 17 and 22). These studies indicate that osteocalcin is vitamin D-dependent in the fetal and neonatal rat.