Effect of vitamin D deficiency on mouse mammary gland and milk

Lactational performance, milk composition, mammary calcium pools and serum calcium were examined in vitamin D-deficient lactating mice to determine whether the mammary gland is a target organ for vitamin D. CD1 mice were fed vitamin D-deficient or control diets containing 1.2% calcium and 0.5% phosphorus 8-12 weeks prior to breeding. Plasma calcium levels were within normal limits in all mice. Vitamin D deficiency was verified by lack of detectable serum 25-hydroxycholecalciferol. Deficient mice had fewer pups per litter than controls (7.1 +/- 0.5 vs. 8.4 +/- 0.3; P less than 0.05). Pups from vitamin D-deficient and repleted mothers grew at the same rate. Mammary tissue intracellular and extracellular calcium pools, measured by an efflux technique, did not differ in the two groups. Milk samples were collected by suction after injection of 0.1 IU of oxytocin i.p. or anaerobically by a surgical technique. Although protein, Na, K, ionized calcium and pH did not differ, milk from vitamin D-deficient mice had lower lactose (114.6 vs. 135.9 mM; P less than 0.02) and slightly lower calcium (66.8 vs. 75.4 mM; P less than 0.1) concentrations than controls. The data do not demonstrate any direct effects of vitamin D on mammary gland calcium metabolism.