Effect on gelatinases. (a) Inhibition of gelatinase liberation from bovine cartilage explants. Cartilage explants were incubated in the absence or presence of IL-1α and 25 μmol/l dibutyryl-cGMP or 10 μmol/l or 30 μmol/l vardenafil for 4 days at 37°C. The lanes marked with (-) indicate two independent control experiments with IL-1 only. The activity of gelatin-degrading enzymes released into the culture supernatant was determined by zymography. (b) Unaffected gelatinase synthesis. Unstimulated explants were incubated for 10 days in the absence and presence of 100 μmol/l zaprinast, vardenafil and tadalafil, and the gelatinase activities were again analyzed by gel zymography. MMP, matrix metalloprotease.