Vitamin D metabolism during pregnancy and lactation in the rat.

The plasma concentration of the major vitamin D metabolites; 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, and 24,25-dihydroxyvitamin D were measured during pregnancy and lactation in the adult female rat. The concentrations of these metabolites were also measured in rat pups during lactation and after weaning. The plasma concentration of 1,25-dihydroxyvitamin D in the adult female increases from a control value of 26 pg/ml to 86 pg/ml during the latter stages of pregnancy, reaches a peak of 158 pg/ml during lactation, and then returns to control levels by 3 weeks postweaning. Plasma concentrations of 24,25-dihydroxyvitamin D fall dramatically during pregnancy from a control level of 3.9 ng/ml to 1.6 ng/ml remain low during lactation, and return to control levels by 3 weeks postweaning. In the neonatal rat pup at 14 days postpartum, 1,25-dihydroxyvitamin D plasma concentration is 25 pg/ml and 24,25-dihydroxyvitamin D concentration is 2.8 ng/ml. By day 25 postpartum, 1,25-dihydroxyvitamin D concentrations reached levels of 101 pg/ml, whereas 24,25-dihydroxyvitamin D concentrations fell to 1.9 ng/ml.