Abstract
The objective of this study was to determine whether vitamin D directly stimulates the shell gland to induce calcium binding protein-D28K (CaBP-D28K) in vivo, which plays an essential role in calcium transport for shell formation. White Leghorn laying hens were injected with 1, 25-dihydroxyvitamin D3 [1, 25 (OH)2D3] or saline (control) into the shell gland lumen at 3h (precalcification phase) or 8h (early calcification phase) after oviposition. The CaBP-D28K levels in the shell gland and intestine were examined by immunocytochemistry and Western blot analysis. Also, the changes in the serum calcium levels were examined. The immunoreaction products for CaBP-D28K were localized in the tubular glands of the shell gland at precalcification and calcification phases in both the 1, 25 (OH)2D3 treated and control hens. At the calcification phase the density of immunoreaction band for CaBP-D28K was greater in the 1, 25 (OH)2D3 treated hens than in the control hens, whereas difference in the densities of CaBP-D28K was not found between 1, 25 (OH)2D3 treated and control hens at the precalcification phase. No significant differences in the densities of immunoreaction products for the intestine CaBP-D28K and in the serum calcium concentrations were observed between the 1, 25 (OH)2D3 treated and control hens. These results suggest that 1, 25 (OH)2D3 directly stimulates the shell gland to induce CaBP-D28K.
