Mineral and Skeletal Homeostasis Influence the Manner of Bone Loss in Metabolic Osteoporosis due to Calcium-Deprived Diet in Different Sites of Rat Vertebra and Femur

Rats fed calcium-deprived diet develop osteoporosis due to enhanced bone resorption, secondary to parathyroid overactivity
resulting from nutritional hypocalcemia.Therefore, rats provide a good experimental animal model for studying bone modelling
alterations during biochemical osteoporosis.Three-month-old Sprague-Dawley male rats were divided into 4 groups: (1) baseline,
(2) normal diet for 4 weeks, (3) calcium-deprived diet for 4 weeks, and (4) calcium-deprived diet for 4 weeks and concomitant
administration of PTH (1-34) 40 g/Kg/day. Histomorphometrical analyses were made on cortical and trabecular bone of lumbar
vertebral body as well as of mid-diaphysis and distal metaphysis of femur. In all rats fed calcium-deprived diet, despite the reduction
of trabecular number (due to themaintenance of mineral homeostasis), an intense activity of bone deposition occurs on the surface
of the few remaining trabeculae (in answering to mechanical stresses and, consequently, to maintain the skeletal homeostasis).
Different responses were detected in different sites of cortical bone, depending on their main function in answering mineral or
skeletal homeostasis. This study represents the starting point for work-in-progress researches, with the aim of defining in detail
timing and manners of evolution and recovery of biochemical osteoporosis.