Effects of parathyroid hormone on osteoclasts in vivo

Summary Young rats were treated with high doses of parathyroid hormone (PTH). Osteoclasts from these animals revealed characteristic alterations in comparison to control cells: a) The cytoplasm contained large vacuoles with phagocytosed cells, some of which resembled osteoblasts or osteocytes. The vacuoles were interpreted as lysosomes because the engulfed cells often appeared partly digested and the vacuoles contained acid phosphatase as demonstrated histochemically, b) lipid droplets were present in the cytoplasm and usually located close to the endoplasmic reticulum and/or in regions with many free ribosomes, c) the Golgi complex was more frequently separated from the nuclei than in control cells, d) small coated cytoplasmic bodies were numerous in the peripheral cytoplasm, e) the membranes of the endoplasmic reticulum were fused in some places, f) cytoplasmic regions with numerous free ribosomes were frequent, g) large ring-shaped granules occurred in some mitochondria. Energy dispersive X-ray analysis of these granules provided evidence that they contained calcium and probably phosphorus, h) in some osteoclasts the mitochondria were enlarged. — The findings are consistent with an increased activity of osteoclasts and in particular a stimulation of the lysosomal system in these cells.This research was supported by grants no. 512-819, 512-1545 and 512-1912 from the Danish Research Council. The observations were reported in part at the annual meeting of the Scandinavian Society for Electron Microscopy in Aarhus 1972 (Lucht, 1973). — The authors thank Mr. K. Ibe for cooperation in the energy dispersive X-ray analysis, which was carried out at the JEOL (Europe) S. A. Application Center, Paris.