Effects of acetylsalicylic acid and naproxen on the synthesis and mineralization of collagen in the rat femur.

The influence of acetylsalicylic acid (ASA) and naproxen on the biochemical properties of intact growing femora in young male rats was studied. The medication periods were 9 and 18 days. At an ASA dose of 150 mg/kg/12 h the rate of collagen synthesis and the rate of mineral incorporation decreased and were impaired by about 10% compared with controls after 18 days. The dry weights and contents of collagen and calcium were not influenced after 9 days, but were reduced by 4%-7% after 18 days. A higher solubility of collagen (7%) was also found at the end of the study. In rats that received ASA at 100 mg/kg/12 h no significant differences were observed. A naproxen dose of 20 mg/kg/12 h reduced the rate of mineral deposition after 18 days, but had no other detectable effects on bone. The results indicate that ASA inhibits bone formation.