The effect of strain on bone cell prostaglandin E2 release: a new experimental method.

A new method of investigating the mechanisms of strain-induced bone remodeling has been developed. Bone cells were subjected to cyclical strains in vitro by computer-controlled stretching of the plastic substrate on which they were cultured, enabling both physiological and pathological strains to be investigated. Physiological strains have not previously been investigated in vitro. The prostaglandin E2 (PGE2) released by the cells was found to depend on the strain magnitude. It was independent of cycle time, and 5 hours after straining had ceased, it had returned to control levels. These results are similar to the in vivo findings that bone remodeling is dependent on strain magnitude and not strain frequency, indicating that PGE2 may play an important role in strain-induced bone remodeling. The relationship between PGE2 release and strain magnitude was biphasic, with particularly high levels being released at strains that would be associated with either abnormally strenuous activity or microstructural bone damage. It is therefore possible that PGE2 stimulates the osteogenesis caused by increased functional demands, and initiates the remodeling caused by bone damage. This new method of investigating strain-induced remodeling is useful, as any cell type, any mediator, and any strain pattern or parameter can be individually studied.