Competence of 1.ALPHA.,25-dihydroxyvitamin D3 receptor system in embryonic chick intestine.

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Abstract
The competence of the duodenal [1.alpha.,25-dihydroxyvitamin D3] receptor system in embryonic chicks was studied in the reconstituted cytosol-chromatin system. The sucrose density gradient centrifugation following incubation of duodenal cytosol with 1.alpha.,25-dihydroxy-[3H]-vitamin D3 revealed that a cytosol 1.alpha.,25-dihydroxyvitamin D3 receptor existed in the duodenum of 18-day-old embryos. In the duodenum of 14-day-old embryos the cytosol 1.alpha.,25-dihydroxyvitamin D3 receptor was not detected. In the reconstituted cytosol-chromatin system duodenal cytosol of 18-day-old embryos stimulated the association of 1.alpha.,25-dihydroxy-[3H]-vitamin D3 with chromatin of the vitamin D-deficient chick duodenum. The association of 1.alpha.,25-dihydroxy-[3H]-vitamin D3 was saturable and temperature dependent. In a system where duodenal chromatin of 18-day-old embryos was reconstituted with cytosols, 1.alpha.,25-dihydroxy-[3H]-vitamin D3 associated specifically with the chromatin in the presence of duodenal cytosol obtained from 18-day-old embryos or vitamin D-deficient chicks. No significant association of 1.alpha.,25-dihydroxy-[3H]-vitamin D3 with duodenal chromatin of 18-day-old embryos occurred in the absence of duodenal cytosol. The intestinal 1.alpha.,25-dihydroxyvitamin D3 receptor system in embryonic chicks is apparently competent for the intracellular transfer of 1.alpha.,25-dihydroxyvitamin D3 before hatching.