This study was aimed to investigate the role of eicosapentaenoic acid monoacylglyceride (MAG-EPA) and 17,18-epoxyeicosatetraenoic acid (17,18-EpETE) on the regulation of contractile reactivity and nuclear protein expression in 72-h-cultured and TNF-α-treated guinea pig tracheal rings. Tension measurements performed on native tissues demonstrated that the cytochrome P-450 epoxygenase (CYP450)-dependent EPA metabolite, 17,18-EpETE, displayed a higher potency than MAG-EPA in inhibiting U-46619-induced tone. Calphostin C (a PKC inhibitor), whether in association or not with MAG-EPA or 17,18-EpETE, had no further effect, while 17,18-EpETE and Y-27632 (a Rho kinase inhibitor) yielded additive effects. Of note, MAG-EPA and 17,18-EpETE pre-treatments normalized the contractile responses to broncho-constrictive agents in 72-h-cultured trachea. The enhanced expression of TNF-α, P-p65-nuclear factor kappaB (NF)-κB, c-fos and c-Jun in 72-h-cultured tissues likely contributed to the hyperresponsiveness. β-Escin-permeabilized preparations demonstrated that 17,18-EpETE abolished Ca(2+) hypersensitivity, suggesting a blunting of PKC and/or Rho kinase activation. Lastly, activation of NF-κB and activating protein-1 (AP-1) signalling by exogenous TNF-α markedly increased the contractile response to MCh, through an increase in 17-kDa PKC-potentiated inhibitory protein of PP1 (CPI-17) phosphorylation and IκBα degradation. Dual incubation of 17,18-EpETE with calphostin C or Y-27632 induced cumulative inhibitory effects on MCh responses in TNF-α-incubated tracheal rings. 17,18-EpETE also reduced the detection level of P-p65-NF-κB and AP-1 subunits. The present data provide evidence that MAG-EPA, through its bioactive metabolite, represents a prospective pharmacological target in respiratory diseases.