Synthesis of tumour necrosis factor-alpha in tissue culture of rat caecum: lack of suppression by phosphodiesterase inhibitors and prostanoids.

Tumour necrosis factor-alpha (TNF) plays a pivotal role in acute and chronic inflammatory processes. It has been demonstrated that TNF is a mediator in inflammatory bowel disease. In the past different pharmacological approaches have been identified to suppress TNF synthesis in lipopolysaccharide-stimulated human mononuclear cells by cAMP-elevating agents. In the present study we examine whether TNF synthesis in the colon underlies similar regulatory mechanisms as in mononuclear cells. We therefore established a short-time organ culture of rat caecum. In this model we obtained maximal TNF formation of 159 pg/ml after a 7-h incubation period, as determined by L929 bioassay. The formation of bioactive TNF was confirmed by the application of neutralizing TNF antibody in the L929 bioassay and by immunodot blot. Lipopolysaccharide and pokeweed mitogen did not further enhance TNF synthesis. In contrast, TNF production was suppressed to 25% of control by 5 micrograms/ml hydrocortisone. Unexpectedly, the specific type IV phosphodiesterase inhibitor rolipram and cicaprost, a stable prostacyclin analogue, did not achieve significant suppression of TNF synthesis in this model. The present study defines an experimental model to investigate ex vivo TNF synthesis in rat colonic tissue. Applying this model, cAMP-elevating agents are identified as poor candidates for TNF-suppressing strategies in inflamed colon.