Autoradiographic demonstration of target cells for 1,25-dihydroxycholecalciferol in the chick embryo chorioallantoic membrane, duodenum, and parathyroid glands

Abstract

Sixteen-day-old chick embryos were injected with tritiated 1,25-dihydroxycholecalciferol (1,25-DHCC) and sacrificed 2 hr later. Portions of the chorioallantoic membrane, duodenum, yolk sac, and parathyroid glands were frozen and processed for thaw-mount autoradiography. High concentration of radioactivity was found in nuclei of the chorionic epithelium; their spatial distribution suggests, although does not prove, that these nuclei correspond to “calcium-absorbing” cells. Radioactivity was also demonstrated in nuclei of the duodenal epithelial cells and the cords of parathyroid glands. No localization was found in the wall of the yolk sac after 150 days of exposure. The injection of nonradioactive 1,25-DHCC 30 min before the administration of the radiocctive hormone prevented in all cases the nuclear concentration, probably by saturating receptors. The results are interpreted as demonstrating the presence of target cells for the hormone in chorionic epithelium, duodenum, and parathyroid glands, structures all believed to be involved in calcium metabolism in the embryo.