INTERLEUKIN-1-BETA ENHANCES THE RESPONSE OF RABBIT SYNOVIAL FIBROBLASTS IN-VITRO TO DEXAMETHASONE INJURY - IMPLICATION FOR THE ROLE OF INCREASED NUCLEAR HYPERSENSITIVE SITES AND THE NUMBER OF DEXAMETHASONE RECEPTORS

Objective. As a model system to understand the efficacy of patients wi th glucocorticoid (GC) treatment of joint inflammation of rheumatoid a rthritis, we stimulated confluent rabbit synovial fibroblasts in cultu re with interleukin 1 beta (IL-1 beta) and studied the effects of dexa methasone (Dex). Methods. Twenty-four h after IL stimulation Dex was a dded and the response of cells to Dex was estimated by [H-3]thymidine uptake, cell count and lactate dehydrogenase release. Cellular and nuc lear binding of [H-3] Dex as well as the DNase sensitivity of isolated nuclei were estimated. Results. Dex strongly inhibited the [H-3]thymi dine uptake by the stimulated cells in a dose dependent manner with Ki of lower than 10(-12) M, whereas it only slightly inhibited the unsti mulated cells. With stimulation the sensitivity of cells increased 10- fold as estimated by lactate dehydrogenase release and 85-fold by coun ting the final cell density. We found also a 5-fold increase in the DN ase I hypersensitive sites in the nuclei and a 2 to 3-fold increase in the cellular as well as the nuclear Dex binding sites following stimu lation. Conclusion. In addition to the well documented inhibition of d egradative enzyme production by the stimulated synovium, the efficacy of GC treatment of patients could be explained also on the basis of th e sensitization,of stimulated synovium to the GC mediated injury.