title: Ontogeny of vitamin D action on the morphology and calcium transport properties of the chick embryonic yolk sac.
abstract: The ontogeny of the calcium transport properties and hormonal modulation of the yolk sac membrane in amniote embryos is presently poorly understood. We investigated the role of 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) on plasma calcium values, yolk sac morphology and the ability of the yolk sac membrane to transport 45Ca from yolk to embryo. 1,25-(OH)2D3 treatment caused significant hypercalcaemia in 9-, 12- and 15-day embryos. Additionally, this hormone caused a hypertrophy of the endodermal cell layer that comprises the bulk of the yolk sac membrane. Both of these effects were the most dramatic in the 15-day embryo, the oldest age tested. 45Ca added to the yolk was transported into the blood rapidly across the yolk sac membrane. 1,25-(OH)2D3 significantly enhanced this transport in all age groups. [14C]Inulin was also taken across the yolk sac membrane, but at a slower rate than 45Ca; this transport was unaffected by 1,25-(OH)2D3. Thus, the yolk sac responds to 1,25-(OH)2D3 treatment both morphologically and functionally. The mechanism for transport appears to be a specific one, rather than a simple enhancement of non-specific endocytosis.
authors.affiliation: Department of Physiology and Neurobiology, University of Connecticut.
authors.forename: N B
authors.initials: NB
authors.lastname: Clark
authors.forename: M J
authors.initials: MJ
authors.lastname: Murphy
authors.forename: S K
authors.initials: SK
authors.lastname: Lee
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002117:Calcitriol / Q000494:pharmacology*; D002118:Calcium / Q000097:blood / Q000378:metabolism*; D002132:Calcium Radioisotopes; D002642:Chick Embryo; D007444:Inulin / Q000378:metabolism; D013997:Time Factors; D015017:Yolk Sac / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*
chemical_list: D002132:Calcium Radioisotopes; D007444:Inulin; D002117:Calcitriol; D002118:Calcium