Hydrogen sulfide downregulates the aortic L-arginine/nitric oxide pathway in rats

The aim of the present study was to investigate the effect of hydrogen sulfide (H2S) signaling by nitric oxide (NO) in isolated rat aortas and cultured human umbilical vein endothelial cells (HUVECs). Both administration of H2S and NaHS, as well as endogenous H2S, reduced NO formation, endothelial nitric oxide synthase (eNOS) activity, eNOS transcript abundance and L-arginine (L-Arg) transport (all P < 0.01). The kinetics analysis of eNOS activity and L-Arg transport showed that H2S reduced V-max values (all P < 0.01) without modifying K-m parameters. Use of selective NOS inhibitors verified that eNOS [vs. inducible NOS (iNOS) and neuronal NOS (nNOS)] was the specific target of H2S regulation. H2S treatment (100 mu mol/l) reduced Akt phosphorylation and decreased eNOS phosphorylation at Serl 177. H2S reduced L-Arg uptake by inhibition of a system y+ transporter and decreased the CAT-I transcript. H2S treatment reduced protein expression of eNOS but not of nNOS and iNOS. Pinacidil (K-ATP channel opener) exhibited the similar inhibitory effects on the L-Arg/NOS/NO pathway. Glibenclamide (KATP channel inhibitor) partly blocked the inhibitory effect of H2S and pinacidil. An in vivo experiment revealed that H2S downregulated the vascular L-Arg/eNOS/NO pathway after intraperitoneal injection of NaHS (14 mu mol/kg) in rats. Taken together, our findings suggest that H2S downregulates the vascular L-Arg/NOS/NO pathway in vitro and in vivo, and the KATP channel could be involved in the regulatory mechanism of H2S.