Effects of acetylsalicylic acid on heterotopic bone resorption and formation in rats.

The effects of acetylsalicylic acid (ASA) on bone metabolism have been studied in a bone transplantation model using radioisotopic and biochemical parameters. Isografts (femora) from infant inbred rats, extensively prelabeled with collagen and mineral-tracing radioisotopes, were transplanted to muscle pouches in young male rats. Bones from the opposite side of the donor rats served as nonimplanted reference bones. The recipients were given 150 mg/kg/12 h of ASA by gavage for 18 days. The serum concentrations obtained were comparable with the recommended anti-inflammatory levels in humans. Twenty-four hours before being killed the animals were labeled again with other collagen and mineral radioisotopes. After 18 days of medication the resorption of the transplanted bone was inhibited by about 15% in the ASA treated rats compared with controls, as measured by the losses of collagen (14C-hydroxyproline) and mineral (strontium-85). Also, the net gains of mineral and collagen in the ASA-treated transplants were reduced by about 15% and 11% respectively compared with controls during the medication period. During the last 24 h of the study the rates of mineral incorporation (calcium-47 uptake) and collagen synthesis (3H-hydroxyproline) were reduced to an even greater degree in the ASA-treated transplants. These results indicate an inhibitory effect of ASA on bone metabolism.