Cyclic AMP levels in alveolar bone of orthodontically-treated cats

Specific biochemical changes in mechanically stressed bone were studied in cats, orthodontically treated for periods of time ranging from 1 hr to 28 days. Alveolar bone samples were obtained from compression and tension sites surrounding tipping maxillary and mandibular canines. The samples were extracted with water, boiled, homogenized and the supernatants were assayed for cyclic AMP by a protein-binding method. It was found that cyclic AMP levels in treated sites initially decreased, then increased after 1–2 days and remained elevated to the end of the experimental period. It was suggested that the initial decrease in cyclic AMP at the compression sites was due to periodontal ligament cell-necrosis, while at the tension sites the decrease was due to a rapid increase in the cell population. The elevation in the level of cyclic AMP observed 2 weeks after the initiation of treatment was probably due to increased bone remodelling activity by a maturing cell population with a slow rate of growth. The level of cyclic AMP in bone after application of orthodontic forces may be the result of increased phosphodiesterase activity, and/or the involvement of a relatively small number of cells. It is concluded that mechanical forces can act as a first messenger and facilitate bone formation and resorption by activation of the cyclic nucleotide system.