Inhibition of proteoglycan loss in bovine chondrocytes. (a) Cartilage explants were incubated in the absence and presence of IL-1α and the drugs tadalafil, zaprinast, or vardenafil at concentrations of 50 μmol/l. The tissues were weighed, extracted with guanidinium hydrochloride, and the amount of proteoglycans was determined after 5 days. The data were related to controls without IL-1α as 100%. The error bars represent the standard deviation of three determinations; *P < 0.05. (b) Effect of inhibitor tadalafil (○), zaprinast (□), or vardenafil (△) on proteoglycan synthesis. Bovine chondrocytes were cultured in alginate beads and incubated with increasing concentrations of the inhibitors in the presence of [35S]sulphate. After 24 hours the radioactivity incorporated into [35S]proteoglycans was determined.