An in vitro bioassay for 1,25-dihydroxyvitamin D3 and other antirachitic agents

Duodenal tissue from chicken embryos (19 days in ovo) has been maintained in organ culture for 48 hours. The incubation medium and culture conditions were chosen to produce a linear relationship between calcium binding protein production and the logarithm of the dose of vitamin D3 steroid in the medium. The dose-response curves are parallel for vitamin D3 and both its major metabolites, 25-hydroxyvitamin D3 and 1,25-dihydroxyVITAMIN D3. The minimum concentration of 1,25-dihydroxyvitamin D3 capable of inducing calcium-binding-protein synthesis was 1 X 10(-9) M.