Calcium transport in small intestine during pregnancy and lactation

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Abstract
The factors involved in Ca homeostasis during the mammalian reproductive cycle and specifically in the control of active Ca transport in the intestine were not thoroughly investigated. For this reason Ca transport in the intestine was measured in vitamin D-replete and vitamin D-deficient rats during pregnancy and lactation using the everted gut sac technique. In addition the changes in the plasma concentrations of Ca and 1,25-dihydroxyvitamin D were measured and correlated with transport. During the later stages of pregnancy and during lactation, the Ca concentration in the plasma is reduced 10-30%. In turn, in the vitamin D-replete rat, the 1,25-dihydroxyvitamin D concentration in the plasma increases from a control value of 26 pg/ml to 158 pg/ml at day 14 of lactation. Ca transport in the intestine increases late in pregnancy, peaks during lactation, and then falls to control values by 3 wk postweaning in both vitamin D-replete and D-deficient animals. These findings strengthen the established relationship between 1,25-dihydroxyvitamin D and active Ca transport in the intestine, and suggest that some factor(s) independent of vitamin D is stimulating intestinal Ca transport during the reproductive cycle.