Bone pathology in hypervitaminosis D an experimental study in young pigs.

Five groups of 4 weanling pigs were fed a diet with 1.2% calcium and 1.0% phosphorus for 8 weeks with vitamin D3 at 1, 5, 25, 125 and 625 times the recommended levels, respectively. Hypercalcemia and hypophosphatasemia developed rapidly and persisted in Group 5 and developed more slowly but steadily in Group 4. Increasing levels of vitamin D3 influenced progressively and negatively the activity of resorbing osteocytes with osteopetrosis in Groups 2 and 3 and with osteonecrosis in Group 5. Atrophy of osteoblasts further contributed to the osteopenia in Group 5. Cartilage growth activity was arrested in Group 5. The negative effect on the resorbing osteocytes, which finally lead to death of the cells, was ascribed directly to vitamin D3 toxicosis since hypoparathyroidism and hypercalcitonism, both resulting from hypercalcemia, are not known to induce osteonecrosis. Since hypercalemia was finally as severe in Group 4 as in Group 5 and since there was soft tissue calcinosis only in Group 5, the calcinosis was always considered dystrophic, an interpretation supported by the observation that degenerative histologic changes preceded soft tissue calcinosis.