Effects of acetylsalicylic acid and naproxen on the mechanical and biochemical properties of intact skin in rats.

Acetylsalicylic acid, ASA (150 mg/kg/12 h), and naproxen (20 mg/kg/12 h) were administered to young male rats for 9 and 18 days. The doses were set to provide serum concentrations comparable with anti-inflammatory steady state levels in humans. Mechanical tests were performed on skin from the back of the rats. The drugs did not affect the tensile strength of intact skin, nor were differences found in the dry weight or content and concentration of collagen in the skin. However, the rate of collagen synthesis decreased significantly during the study in the ASA treated rats. The naproxen, on the other hand, had no effect. The results may be interpreted as the ASA having an inhibitory effect both on the synthesis and degradation of collagen in skin.