Phorbol esters inhibit chondrogenesis in limb mesenchyme by mechanisms independent of PGE sub(2) or cyclic AMP

Effects of the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) on chondrogenesis and concentrations of prostaglandin E sub(2) (PGE sub(2)) and cyclic AMP (cAMP) were investigated in micromass cultures of chick limb mesenchyme derived from the distal tip of stage 25 limb buds. TPA completely inhibited chondrogenesis during the first 4 days of culture; however, a few small cartilage nodules formed by day 6. Relative to control cultures, both PGE sub(2) and cAMP concentrations were altered by TPA treatment during the 6-day period of cell culture. Concentrations of both compounds increased in control cells during the first 24 h of culture and then declined during the remaining 5 days. In TPA-treated cells both PGE sub(2) and cAMP levels increased progressively during the 6 days of cell culture, each being elevated at day 6 by twofold over control cells. The results suggest the presence of regulatory pathways important in chondrogenesis which occur independent of those initiated by PGE sub(2) and the cAMP system.