Abstract: Objective To study the role of cAMP-PKA signal transduction pathway on vasodilatation of rataorticrings caused by SO₂ der ivatives.Methods Levels of cAMA,cGMP,6-keto-PGF 1A,TXB₂ in the isolated aor tic rings of rats were deter mined by radioimmunoassay.PKA activity was assayed by transferr ing phosphorus(32p)into the biotinylated peptide Kemptide,the most specific substrate for PKA.Results Levels of cAMP,6-keto(PGI₂)and PKA activity in isolated aorticrings were increased by SO₂ derivat ives in a dose-dependent way,which wer e independent of endothelium;No change of cGMP and TXB₂ in rings with or without endothelium were observed;cAMP/cGMP and 6-keto/TXB₂,ratios were increased significantly.Conclusion The relaxation effect on the rings caused by SO₂ der ivatives might be mediated partly by the PGI₂-cAMP-PKA signal transduction pathway.SO/SO₂,the precursors of SO₂ derivatives,might be a newcellular gas signal molecule,more studies are needed to understand its physiological role.