Corticotropin-releasing factor (CRF) plays a central role in controlling stress-related activity of the hypothalamic-pituitary-adrenal axis. Four CRF-related peptides have been found in mammals: CRF and urocortins (Ucns) 1-3. Ucns bound to CRF₂ receptors have a physiological role in the cardiovascular system. We previously found that both Ucn1 and 2 induced accumulation of intracellular cAMP via CRF₂ receptor binding and significantly increased interleukin (IL)-6 secretion by A7r5 aortic smooth muscle cells. In the present study, we investigated Ucn effects on IL-6 gene expression and IL-6 synthesis in A7r5 aortic smooth muscle cells. Ucn1 and 2 stimulated IL-6 gene transcription and IL-6 secretion via CRF₂ receptors. Indomethacin, a COX inhibitor, suppressed IL-6 gene transcription and IL-6 secretion by Ucn1 or 2. NS-398, a COX-2 inhibitor, suppressed IL-6 induction to the same extent as indomethacin. These results suggest that the COX-2 pathway is involved down-stream in regulation of Ucn-increased IL-6 gene expression and IL-6 secretion. In addition, COX-2 expression levels were increased at 6 h with the combination of Ucn1 and IL-1 compared with single peptide activation. Ucn1 showed a potent stimulatory effect on IL-6 output, whereas IL-1 alone had no significant effects. However, when Ucn1 was simultaneously used with IL-1, it markedly potentiated the increments in IL-6 output and promoter activity produced by Ucn1. Taken together, these findings indicate that the COX-2 pathway plays a major role in increasing IL-6 levels stimulated by Ucn and IL-1 in A7r5 cells.