The Effect of Calcium-Regulating Hormones and Prostaglandins on Bone Resorption by Osteoclasts Disaggregated from Neonatal Rabbit Bones*

TLDR

Osteoclastic bone resorption has only been studied in intact bone, where other cell types can influence responses to environmental agents. The study aims to evaluate how prostaglandins and calcium‑regulating hormones affect bone resorption by isolated osteoclasts. Osteoclasts were mechanically isolated from neonatal rabbit long bones, cultured on devitalized cortical bone slices for 8–24 h, and resorption pit volumes were quantified by computer‑assisted morphometry and stereophotogrammetry. Salmon calcitonin inhibited osteoclast resorption at concentrations ≥1 pg/ml, whereas PTH and 1,25‑dihydroxyvitamin D3 had no effect; paradoxically, PGI2, PGE1, and PGE2 reduced resorption in isolated cultures, implying they directly inhibit osteoclasts but may stimulate resorption through other bone cells. Endocrinology 60: 234–239, 1985.

Abstract

It has previously only been possible to assess osteoclastic bone resorption in intact bone, where other cell types may modify or mediate osteoclastic responses to environmental agents. We have recently developed techniques which enable us to measure bone resorption by osteoclasts extracted from bone and have used these techniques to assess the effects of prostaglandins (PGs) and calcium-regulating hormones on bone resorption by these cells. Osteoclasts were mechanically disaggregated from neonatal rabbit long bones and cultured on slices of devitalized cortical bone for 8 or 24 h. After this time, osteoclasts were associated with the appearance in the scanning electron microscope of characteristic resorption pits, the volume of which was calculated by computer-assisted morphometric and stereophotogrammetric techniques after removal of cells. Salmon calcitonin inhibited osteoclastic bone resorption at concentrations of 1 pg/ml and above, while PTH and 1,25-dihydroxyvitamin D3 were without significant effect. This suggests that the latter hormones do not increase bone resorption in intact bone through a direct effect on osteoclasts. PGI2, PGE1, and PGE2, all of which are known to stimulate resorption when added to intact bone, paradoxically reduced resorption in our cultures. It appears likely that PGs act as direct inhibitors of osteoclastic bone resorption but have an additional effect on other cells in bone, which are induced by PGs to cause osteoclastic stimulation. (Endocrinology60: 234–239, 1985)