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Immunochemical measurement of the vitamin D-binding protein in rat serum
Insights
Vitamin D-binding protein (DBP) levels in rats vary significantly with age and sex. Hormonal factors, including androgens and prolactin, play a crucial role in regulating DBP concentrations.
Area of Science:
- Endocrinology
- Biochemistry
- Reproductive Biology
Background:
- Vitamin D-binding protein (DBP) is crucial for vitamin D transport.
- Understanding DBP regulation is vital for comprehending vitamin D homeostasis.
Purpose of the Study:
- To investigate the developmental and sex-specific changes in rat serum DBP levels.
- To explore the hormonal influences on DBP concentration.
Main Methods:
- Single radial immunodiffusion technique was used to measure DBP in rat serum.
- Hormonal manipulations included gonadectomy, hypophysectomy, and hormone administration.
Main Results:
- DBP levels were lowest at birth, increased significantly by adulthood, and showed a marked sex difference post-puberty (males > females).
- Gonadectomy and hypophysectomy abolished the sex difference.
- Prolactin appeared to suppress DBP, while androgens increased it to male levels.
Conclusions:
- Rat serum DBP levels are dynamically regulated by age, sex hormones, and pituitary hormones.
- Androgens promote higher DBP levels in males, while prolactin may suppress DBP.
- Free 25-hydroxyvitamin D levels are not maintained at a constant concentration despite DBP fluctuations.
Abstract:
The vitamin D-binding protein (DBP) was measured in rat serum using a single radial immunodiffusion technique. Normal serum levels at birth (74 +/- 11 mg/liter, mean +/- SD) were lower than during the last day of fetal life (130 +/- 14 mg/liter) and much lower than in adult rats. A marked sex difference in DBP occurred after puberty: male values (656 +/- 52 mg/liter) were significantly higher than female values (472 +/- 46 mg/liter). The sex difference could be abolished by either adult gonadectomy or transpharyngeal hypophysectomy. Implantation of a pituitary gland under the renal capsule in hypophysectomized male rats further decreased the DBP concentration, suggesting that PRL suppresses the DBP level. A similar decrease was also observed at the end of pregnancy and during lactation. Administration of androgens to either normal female or gonadectomized male rats increased their DBP concentration to the normal adult male level. The serum levels of total 25-hydroxyvitamin D did not fluctuate according to the concentration of DBP, indicating that the concentration of "free 25-hydroxyvitamin D" is not regulated at a constant level.