EVALUATION OF THE ROLE OF 2ND MESSENGER SYSTEMS IN TUMOR NECROSIS FACTOR-STIMULATED RESORPTION OF FETAL-RAT LIMB BONES

Tumor necrosis factor (TNF) actions in target tissues are mediated by various signalling pathways. The effect of TNF to stimulate resorption in fetal rat limb bones is not inhibited by indomethacin. The current studies were designed to assess the role of cyclic AMP (cAMP) and cal cium as second messengers in this prostaglandin-independent action of TNF on bone resorption. TNF alone failed to increase cyclic AMP in fet al rat limb bones after either brief (15 min) or long-term (72 h) trea tment. TNF-stimulated resorption in fetal rat limb bones was enhanced by the phosphodiesterase inhibitor isobutylmethylxanthine (IBMX). In s hort term incubations, the combination of TNF + IBMX did not elicit in creases in cAMP in the limb bones. In 72 h cultures, addition of IBMX revealed a dose-dependent effect of TNF to increase cAMP. TNF produced a significant increase in inositol phosphate turnover in limb bones, with a greater response at 5 min than at 1 or 20 min. The calcium chan nel blocker nitrendipine inhibited TNF-stimulated resorption in the fe tal rat limb bones. TNF-stimulated resorption was attenuated by pretre atment with pertussis toxin (PTx). PTx did not inhibit the effect of T NF to increase inositol phosphate turnover. TNF did not increase cAMP, intracellular calcium, or inositol phosphates in the UMR-106 cells. T he data suggest the following: (a) cyclic nucleotides may play a role in TNF-stimulated resorption, although an increase in CAMP is not a di rect rapid effect of TNF per se; (b) inositol phosphates could also pl ay a signalling role in the action of TNF; (c) a pertussis toxin-sensi tive step is required for TNF action on bone resorption.