The VEGF content of medium supernatant (as determined by ELISA). Stimulation of immortalized chondrocytes (a) and articular cartilage explants (b) with PMA (μg per 1 ml of medium) or SIN-1 (μM). The level of VEGF protein is increased after stimulation with PMA or SIN-1. Results are shown as mean ± standard error of the mean for five separate experiments. * p < 0.05 versus Con. Con, control; PMA, phorbol myristate acetate; SIN-1, 3-morpholino-sydnonimine hydrochloride; VEGF, vascular endothelial growth factor.