Effect of vitamin D3 metabolites on calcium and phosphorus metabolism in chick embryos.

The biochemical nature of the physiological defect found in chick embryos from hens supported on 1,25-dihydroxyvitamin D3 as their sole source of vitamin D is described. Vitamin D-deficient hens (44-wk-old) were divided into six groups of five and dosed daily for 19 wk with either 2.0 micrograms of 25-hydroxyvitamin D3, 2.0 micrograms of 24,24-difluoro-25-hydroxy-vitamin D3, 0.4 micrograms of 1,25-dihydroxyvitamin D3, 2.0 micrograms of 24,25-dihydroxyvitamin D3, 0.4 micrograms of 1,25-dihydroxyvitamin D3 plus 2.0 micrograms of 24,25-dihydroxyvitamin D3, or vehicle only. Normal embryonic development was found in eggs from hens given 25-hydroxyvitamin D3 or 24,24-difluoro-25-hydroxyvitamin D3, whereas embryos from hens given 1,25-dihydroxyvitamin D3, 24,25-dihydroxyvitamin D3, or their combination were abnormal and failed to hatch. Embryos from hens fed 1,25-dihydroxyvitamin D3 and/or 24,25-dihydroxyvitamin D3 had vitamin D deficiency: low bone ash, low plasma calcium, low total body calcium, and extremely high plasma phosphorus. Because the shell is the major source of calcium for the developing embryo, calcium transport from the shell to the embryos across the chorioallantoic membrane apparently fails, giving rise to the observed defects in embryonic development.