Studies of eicosanoid production in the air pouch model of synovial inflammation

The time course of the inflammatory reaction in the rat air pouch model of synovial inflammation has been investigated at different stages of development of the lining structure using immune (pertussis vaccine) and non-immune (carrageenan) irritants. Exudate volumes and leucocyte numbers were greater with carrageenan than with pertussis vaccine but with both irritants much greater reactions were obtained when the irritant was injected at a time when the air pouch architecture most closely resembled synovium (i.e. 6 days). The time course of fluid accumulation following carrageenan in 6 day pouches was not interrupted when exudate was aspirated from the pouch six days after carrageenan injection. In the 6 day old air pouch PGE2 and 6-oxo-PGF1 alpha concentration peaked at 6 hours and 24 hours respectively. With carrageenan and pertussis vaccine stimulation, LTB4 concentrations were maximal at 3-6 hours with both irritants and low concentrations were still present at 13 days. The presence of a lining structure was found to influence concentrations of PGE2 in the air pouch. Pre-treatment with colchicine or 5-fluorouracil to reduce cell accumulation was not found to effect the modified PGE2 response. Our findings suggest that the presence of a synovial like lining structure may induce changes in composition in respect to cellular content and in putative mediator concentrations. We conclude that it is important in elucidating the mechanisms involved in arthritic inflammation to study injury in a cavity lined by macrophages and fibroblasts.