AbstractsBiology & Animal Science

The purpose of the first study was to determine the changes in intestinal vitamin D-dependent plasma membrane calcium ATPase (PMCA1) and calcium binding protein-9K (CaBP-9K) mRNA induced by a single injection of 1,25-D3 or 1,25,28-trihydroxyvitamin D2 (1,25,28-D2) in vitamin D-deficient rats. The results indicated that a single injection of 20 ng of 1,25-D3 per rat double intestinal PMCA1 mRNA at 4, 8, 12, hours and CaBP-9K mRNA at 8, 12, and 24 hours after injection. The mRNA of PMCA1 and CaBP-9K could be increased by a larger dose of 1,25,28-D2 (20 ng). These data suggest that the up-regulation of PMCA1 and CaBP-9K mRNA may be critical to active calcium transport;In the second study, the effect of dietary calcium and/or vitamin D-deficiency on intestinal PMCA1 and CaBP-9K mRNA expression in rats was examined. The results indicate both intestinal CaATPase and CaBP-9K mRNA are down-regulated in rats fed diets containing no vitamin D. However, our data suggest that dietary calcium restriction alone did not have any effect on CaATPase and CaBP mRNA. This study demonstrates that dietary calcium itself is probably not a regulator of mRNA gene expression of PMCA1 and CaBP-9K;In the third study, intestinal PMCA1, CaBP-9K and vitamin D receptor (VDR) mRNA were determined at different stages of pregnancy and early lactation in rats. At 21 days gestation and 7 days of lactation, both PMCA1 and CaBP-9K mRNA levels increased 2-3 fold. PMCA1 and CaBP-9K mRNA remained elevated at 7 days of lactation. Interestingly, VDR mRNA levels did not change during the entire experiment. However, VDR content increased 2-fold in late pregnancy and lactation. These data suggest that the effects of gestation and lactation on PMCA1 and CaBP-9K are probably transcriptional and on VDR are post transcriptional.