ARS | Publication request: PREGNANCY AND LACTATION INCREASE VITAMIN D-DEPENDENT INTESTINAL MEMBRANE CALCIUM ATPASE AND CALCIUM BINDING PROTEIN MRNA EXPRESSION

Submitted to: Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 1, 1998
Publication Date: N/A

Interpretive Summary: Milk fever is a disease affecting about 6-8% of dairy cattle and results from a failure of the body to maintain normal blood calcium levels at the time the cow calves and begins to produce calcium-rich milk. Two proteins are thought necessary for efficient intestinal absorption of calcium in the diet. These proteins are calcium binding protein and calcium ATPase pump. Using pregnant and lactating rats to model the changes a cow would go through at calving, it was discovered that the messenger RNA that allows production of these proteins increases 2- to 3-fold just before the end of pregnancy in rat tissues and remains elevated while the rats are lactating. It appears from these results that a vitamin D compound is responsible, in part, for the increase in these proteins at the end of pregnancy. Future experiments will focus on pharmacologic intervention to increase these proteins in cattle using vitamin D to prevent milk fever, which would have a significant financial impact on dairy farmers.

Technical Abstract: The calcium demands of pregnancy and lactation are known to upregulate intestinal calcium absorption. Intestinal epithelial cells contain calcium ATPases and calcium binding proteins which are believed to play important roles in intestinal calcium transport. However, the possible role of these two proteins in the upregulation of intestinal calcium absorption observed in pregnancy and lactation is unknown. In this study, intestinal calcium ATPase (PMCA1), calcium binding protein (9K) (CaBP-9K) and vitamin D receptor (VDR) mRNA levels were determined by Northern analysis at different stages of pregnancy and early lactation in rats. Intestinal calcium ATPase and calcium binding protein mRNA levels did not differ significantly among non-pregnant rats and rats pregnant for 7 to 14 days. However, at 21 days gestation both calcium ATPase and calcium binding protein mRNA levels increased 2-3 fold. Calcium ATPase and calcium binding protein mRNA remained elevated at 7 days of lactation. Plasma 1,25-dihydroxyvitamin D3 (1,25-D3) concentration exhibited a similar pattern, rising markedly at 21 days gestation and remaining elevated in lactation. VDR mRNA levels did not change during the entire experiment. However, intestinal VDR content increased 2-fold in late pregnancy and lactation. These data suggest that transcription of calcium absorption factors is increased in late gestation and early lactation, perhaps mediated by increased plasma 1,25-dihydroxyvitamin D3 concentrations, and that the effects of gestation and lactation on VDR concentrations are probably post-transcriptional.