Effects of High Doses of Vitamin D3 and 1,25-Dihydroxyvitamin D3in Lactating Rats on Milk Composition and Calcium Homeostasis of the Suckling Pups*

Abstract

Changes in serum Ca and phosphorus and in kidney Ca were determined in lactating rats and their suckling pups after the mothers received high doses of vitamin D₃ or 1,25- dihydroxyvitamin D3 [1,25-(OH)₂D₃]. High dietary vitamin D₃ intake (300 IU/g diet) or daily oral doses of vitamin D₃ (1 μg/g BW) to vitamin D-replete (+D) lactating rats for 8 or 12 days caused significant increases in serum Ca in the mothers (1–2 mg/dl) and in their suckling pups (1.5 mg/dl). Daily oral doses of 1,25-(OH)₂D₃ (2 ng/g BW) to +D lactating rats caused a similar increase in serum Ca in the mothers, but did not affect the serum Ca of the pups. The administration of a high dose of 1,25-(OH)₂D₃ to vitamin D-deficient lactating rats or high doses of vitamin D₃ to +D rats, caused no change in milk Ca, Mg, or phosphorus. Milk from +D rats given high doses of [³H]vitamin D₃ (1 μg/g BW) contained mostly [³H]vitamin D₃ (85%) and a small amount of [³H]25-hydroxyvitamin D₃ (6%). The results indicate that high doses of vitamin D₃, but not 1,25-(OH)₂D₃, given to +D lactating rats can cause hypercalcemia in the suckling pups. The hypercalcemic effect on the pups observed after vitamin D₃ treatment of the mother is probably a result of transport of toxic amounts of primarily vitamin D₃ into the milk and is not due to altered mineral composition of the milk.