Calcium and inorganic phosphate transport in embryonic chick intestine: triiodothyronine enhances the genomic action of 1,25-dihydroxycholecalciferol.
The influence of triiodothyronine (T3) on the induction of intestinal calcium and inorganic phosphate (Pi) transport by 1,25-dihydroxycholecalciferol (1,25-(OH)2D3) was studied in 48 h cultures of embryonic chick jejunum. While T3 alone had no effect on calcium uptake by gut segments cultured on d 20 of embryonic development, the thyroid hormone amplified the effect of 1,25-(OH)2D3 on calcium transport and effectively shifted the dose-response curve to lower 1,25-(OH)2D3 concentrations. T3 had a dual effect on Pi uptake by cultured jejunum: It induced transport activity even in the absence of the steroid hormone, and, in addition, synergistically raised 1,25-(OH)2D3-related Pi uptake. In d 17 embryonic small intestine, which does not respond to 1,25-(OH)2D3 by a significant increase in Pi transport, T3 permitted the induction of Pi transport by the sterol. In general, the thyroid hormone enhanced the responsiveness of cultured embryonic intestine toward 1,25-(OH)2D3 by two orders of magnitude, resulting in facilitated induction of calcium and Pi transport by the sterol and, in particular, modulated the stage-specific expression of 1,25-(OH)2D3 action on intestinal Pi transport.
Cross
H S
HS
Department of General and Experimental Pathology, University of Vienna Medical School, Austria.
Peterlik
M
M
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002117:Calcitriol / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D002642:Chick Embryo; D004305:Dose-Response Relationship, Drug; D007583:Jejunum / Q000196:embryology / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism*; D014284:Triiodothyronine / Q000494:pharmacology*
D010710:Phosphates; D014284:Triiodothyronine; D002117:Calcitriol; D002118:Calcium