Cellular responses to mechanical loading in vitro.

A technique has been established in which cancellous bone biopsies may be simultaneously perfused and subjected to mechanical load bearing. Assessments of cell viability over a period of 24 h were based on the cAMP response to parathyroid hormone, intracellular lactate dehydrogenase activity, and electron micrograph morphology. Two cellular responses to mechanical loading were demonstrated similar to those that follow "osteogenic" loading in vivo, as reported previously. These were (1) a rise in intracellular G6PD in lining cells immediately after loading, and (2) an increase in RNA synthesis measured in osteocytes 6 h after loading. In vivo the osteogenic response to loading was modulated by indomethacin. In these in vitro experiments, addition of indomethacin inhibited both the loading-related G6PD and the RNA responses.