Effect of hydrocortisone on osteoclasts generated in cat bone marrow cultures

Summary The generation of osteoclasts in cultures of cat bone marrow was completely inhibited for 4 weeks with 10⁻⁶M hydrocortisone (HC) and partially inhibited with 10⁻⁷ to 10⁻⁹M in a dose-dependent fashion. This effect was completely reversible when cultures were exposed for only 2 weeks to 10⁻⁹ or 10⁻⁸M HC. However, cultures in which higher concentrations (10⁻⁷ to 10⁻⁵M) were maintained for the same period did not show complete recovery in terms of numbers of osteoclasts and number of nuclei per cell after withdrawal of HC, suggesting that precursor cells of osteoclasts were also damaged by HC. To study the effects of HC on osteoclasts already present in the cultures, 10⁻⁶M was added to 4-week-old untreated cultures. The number of osteoclasts decreased rapidly and a gross morphological response was also apparent (rounding of the cells leading to detachment from the substratum and inhibition of cell fusion), indicating that the generation as well as the survival of osteoclasts in vitro are sensitive to HC. The morphological changes observed under optical and electron microscopy correspond to those of the reported inactive form of osteoclasts, and suggest that their function may also be altered by HC.