Ontogeny of vitamin D action on the morphology and calcium transport properties of the chick embryonic yolk sac.
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.
Clark
N B
NB
Department of Physiology and Neurobiology, University of Connecticut.
Murphy
M J
MJ
Lee
S K
SK
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*
D002132:Calcium Radioisotopes; D007444:Inulin; D002117:Calcitriol; D002118:Calcium