Interstitial cystitis (IC) is associated with increased activated mast cell numbers in the bladder and impairment of the barrier function of the urothelium. We stimulated immortalized urothelial cells derived from the inflamed region of IC bladders (SR22A or SM28 abn) or from healthy bladders (PD07i or PD08i) with tryptase and measured phospholipase A2 (PLA2) activity and the resultant release of arachidonic acid and prostaglandin E2 (PGE2). Tryptase stimulation of either PD07i or SR22A resulted in similar increases in PLA2 activity and arachidonic acid release. However, tryptase stimulation of SR22A and SM28 abn did not result in a significant increase in PGE2 release when compared to the increase in PGE2 release from tryptase-stimulated PD07i and PD08i cells. Expression of mRNA for cyclooxygenase-2 (COX-2) and prostaglandin E synthase was lower and mRNA for 15-hydroxyprostaglandin dehydrogenase was higher in SR22A compared to PD07i, suggesting that both decreased synthesis and increased metabolism is responsible for the lack of a PGE2 response in tryptase stimulated SR22A cells. Since PGE2 is a cytoprotective eicosanoid, the failure to produce this metabolite in cells isolated from the IC bladder may represent an increased susceptibility to damage by pro-inflammatory stimuli.