Effects of uremia and vitamin D on bone and the ultrastructure of thyroid parafollicular cells and parathyroid chief cells in the rat.

Abstract

The tibial metaphysis in uremic rats administered vitamin D had long thin trabeculae lined by fusiform osteoblasts and a few osteoclasts. In vitamin D-treated sham-operated rats metaphyseal trabeculae were reduced greatly in length and covered with numerous osteoclasts and cuboidal osteoblasts. Cortical bone in the diaphyses in both groups had increased osteoblastic and osteoclastic activity. Serum calcium, phosphorus and blood urea nitrogen were significantly greater in uremic rats given vitamin D compared to sham-operated rats administered vitamin D. Thyroid parafollicular cells in vitamin D-treated uremic rats had evidence of increased secretory activity with prominent Golgi apparatuses, well developed rough endoplasmic reticulum, and depletion of mature secretory granules. Parafollicular cells in sham-operated rats given vitamin D had less prominent rough endoplasmic reticulum and Golgi apparatuses and were depleted only partially of secretory granules. Parathyroid chief cells in both groups receiving vitamin D appeared to be less active than in uremic rats given placebo. Uremic rats administered placebo had metaphyseal trabecular bone of intermediate length lined with plump osteoblasts and frequent osteoclasts. Serum calcium was significantly lower than in vitamin D-treated uremic rats. Parathyroid chief cells were interpreted to be relatively active with complex interdigitations of plasma membranes and well developed Golgi apparatuses. Thyroid parafollicular cells were fully granulated and had poorly developed organelles. It was suggested that the altered response of metaphyseal bone to vitamin D in uremic rats was due to an elevated serum phosphorus and increased calcitonin release.