Parathyroid Hormone Contributes to Regulating Milk Calcium Content and Modulates Neonatal Bone Formation Cooperatively with Calcium

To determine whether PTH and calcium (Ca) interact in neonatal bone formation, female lactating mice either heterozygous (PTH+/−) or homozygous (PTH−/−) for targeted deletion of the pth gene were fed either a normal (1% Ca, 0.6% phosphate) or high-Ca diet (2% Ca and 0.4% phosphate). Dietary effects on milk Ca content and Ca-regulating hormones were determined in dams, and the effects of milk content were assessed on bone turnover in 3-wk-old pups. On the normal diet, milk Ca and 1,25-dihydroxyvitamin D3 levels were lower, but milk PTH-related protein levels were higher in the PTH−/− dams compared with the PTH+/− dams. On the high-Ca diet, milk Ca levels were higher, but milk 1,25-dihydroxyvitamin D3 and PTH-related protein levels were lower in both PTH+/− and PTH−/− dams. In pups fed by PTH−/− dams compared with pups fed by PTH+/− dams on normal diets, bone mineral density, trabecular bone volume relative to tissue volume, and the number of osteoblasts were reduced in both PTH+/− (32.5 ± 1.2 vs. 39.6 ± 1....