Hydrogen sulfide (H₂S), a new endogenous mediator, produces both vasorelaxation and vasoconstriction. This study was designed to examine whether cAMP mediates the vasoconstrictive effect of H₂S. We found that NaHS at a concentration range of 10-100 µM (yields approximately 3-30 µM H₂S) concentration-dependently reversed the vasodilation caused by isoprenaline and salbutamol, two -adrenoceptor agonists, and forskolin, a selective adenylyl cyclase activator, in phenylephrine-precontracted rat aortic rings. Pretreatment with NaHS (10-100 µM) for 5 min also significantly attenuated the vasorelaxant effect of salbutamol and forskolin. More importantly, NaHS (5-100 µM) significantly reversed forskolin-induced cAMP accumulation in vascular smooth muscle cells. However, NaHS produced significant, but weaker, vasoconstriction in the presence of NG-nitro-L-arginine methyl ester (100 µM), a nitric oxide synthase inhibitor, or in endothelium-denuded aortic rings. Blockade of ATP-sensitive potassium channels with glibenclamide (10 µM), failed to attenuate the vasoconstriction induced by H₂S. Taken together, we demonstrated for the first time that the vasoconstrictive effect of H2S involves the adenyly cyclase/cAMP pathway. .