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Manuscript received 10 July 1998. Initial reviews completed 26 August 1998. Revision accepted 5 October 1998.
Laboratoire de Nutrition et Sécurité Alimentaire, Institut National de la Recherche Agronomique, 78 352 Jouy-en-Josas cedex, France and * Département de Physiologie Gravitationnelle, Institut de Médecine Aérospatiale du Service de Santé des Armées, 91 223 Brétigny-sur-Orge cedex, France
Studies on calcium nutrition in appropriate large animal models can be directly relevant to humans. We have examined the effect of dietary Ca deficiency on various bone and bone-related variables, including plasma markers, histomorphometry, mineral content and breaking strength in pigs. Three groups of eight 38-d-old female pigs were fed adequate (0.9%; control), low (0.4%; LCa) or very low (0.1%; VLCa) Ca diets for 32 d. Plasma Ca significantly decreased over time only in the VLCa-deficient pigs. The concentrations of the parathyroid hormones (PTH) and calcitriol increased as Ca deficiency developed, and the plasma PTH and calcitriol levels varied inversely with dietary Ca. The total bone ash contents, bending moments, trabecular bone volume and the mineral apposition rate all decreased as the calcium intake decreased. The osteoclast surface areas were greater than those of controls in both Ca-deficient groups, whereas the osteoblast surface areas were greater only in the VLCa group. The plasma osteoblast-related markers (alkaline phosphatase, carboxy-terminal propeptide of type I procollagen and osteocalcin) were either greater or unaffected in the Ca-deficient pigs. The results indicate that deficient bone mineralization combined with an increased bone resorption led to bone loss and fragility. The differences in the changes in bone cells (number and activity) between LCa and VLCa groups might be due to differences (time and extent) of circulating PTH and calcitriol. The defective mineralization in both Ca-depleted groups resulted mainly from the lack of Ca because their osteoblast activity was either maintained or stimulated. The results also underline the progressive sensitivity of pigs to Ca supply and the usefulness of this model.
Key words: low calcium intake, pigs, calcium metabolism, osteoblast function, bone remodeling.
The Journal of Nutrition Vol. 129 No. 1 January 1999,
pp. 188-193
Copyright ©1999 by the American Society for Nutritional Sciences
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