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

The influence of acetylsalicylic acid (ASA) (150 mg/kg/12 h) and naproxen (20 mg/kg/12 h) on bone metabolism in young male rats has been studied. The doses were chosen to provide serum concentrations comparable with ordinary anti-inflammatory steady-state levels in humans. After the rats had been prelabeled with collagen- and mineral-tracing radioisotopes the rats received the drugs by gavage twice a day for 9 and 18 days. Bone resorption was measured as loss of carbon-labeled hydroxyproline (collagen) and strontium-85 (minerals). At 9 days ASA had retarded both collagen and mineral resorption in the femur by about 10% compared with controls. The resorption of both collagen and minerals was inhibited. After 18 days' treatment there were no differences regarding bone resorption, but bone formation had decreased by about 10% in the ASA-treated animals, as measured by net increases of collagen and calcium in the femur. Naproxen did not influence bone resorption or formation significantly. The results indicate an inhibitory effect of ASA on bone resorption and formation in growing rats, whereas the effect of naproxen seems negligible.