Regulation of calcium-binding protein in mouse placenta and intestine

To study the developmental controls for both intestinal and placental calcium-binding protein (CaBP), we have altered mineral metabolism by feeding pregnant mice diets high in calcium and strontium. The effects of these dietary changes on CaBP content of maternal intestine and placenta and also on fetal mineral accumulation have been measured. Feeding high-calcium diets to pregnant mice decreased CaBP content in both maternal intestine and placenta (45 and 58%, respectively). Under these conditions of maternal hypercalcemia, fetal mineral accumulation was unchanged. In experiments with strontium-containing diets, CaBP content was reduced in both maternal intestine and placenta (66 and 67%, respectively), and fetal mineral accumulation was markedly reduced (70%). Administration of 1,25-dihydroxycholecalciferol [1,25(OH)2D] to the strontium-fed mice allowed the gestational rise in maternal intestinal CaBP to proceed to normal levels or above; however, the level of placental CaBP was not affected. Similarly, administration of 1,25(OH)2D to pregnant mice on a normal diet increased maternal intestinal CaBP, but had no effect upon placental CaBP. Thus, administration of 1,25(OH)2D to the mother, in amounts sufficient for a maternal intestinal response, was not a sufficient condition to increase placental production of CaBP.