Modulation Of The Tension Of The Isolated Coronary Artery By Hydrogen Sulfide In Porcine

Objective:Hydrogen sulfide (H2S) is a novel gaseous transmitter and generated endogenously in mammalian tissue by sulfur amino acid metabolism. In the cardiovascular system, the myocardial cells, vascular smooth muscle cells and vascular endothelial cells as well may generate H2S. Recent research showed that H2S may play a variety of biological effect in the cardiovascular system by acting at different targets, such as regulating vascular tone, adjusting the blood pressure, protecting the myocardium, inhibiting the proliferation of the smooth muscle cells. In heart, the coronary tone may directly modulate the myocardial oxygen supply, the reduced coronary flow will cause the imbalance of oxygen supply and demand in cardiomyocytes, finally lead to myocardial ischemia. Therefore, expansion of coronary artery and improve coronary blood flow is an effective way of protecting myocardium from damage in the early stage of myocardial ischemia and hypoxia. In the isolated perfused rat heart, the inhibition of the myocardial systolic and diastolic function by H2S did not result in a decreased, coronary flow, suggesting that H2S may dilate coronary artery to counteract the depression of coronary flow by myocardial. Peritoneal injection of NaHS (H2S donor) can significantly expand coronary arteries, improve myocardial perfusion and prevent myocardial injury. Different from the other two endogenous gaseous signaling molecule, nitric oxide (NO) and carbon monoxide (CO), H2S can directly open the ATP sensitive potassium channels (KATP channels). However, H2S has a close and complicated relation with NO and CO in synthesis, metabolism, biological targets, signal transduction and biological effects. NO is synthesized from endothelial cells, and modulate coronary tone by cGMP pathway. Furthermore, adenosine, which is respectively produced by myocardial metabolism, may facilitate the effect of the KATP channels agonist. As the only endogenous opener of KATP so far, no results were reported about the relationship between H2S and adenosine. The present study intended to assess the regulation effect of H2S on isolated porcine coronary artery tone, explore its possible mechanism and the relationship between H2S and two vasodilation factors, adenosine and NO.Methods:(1) Modulation of H2S on the tension of the isolated coronary arteries:The porcine coronary artery rings were mounted in the organ bath. To observe the vascular relaxation by accumulatively applied NaHS (H2S donor, 100,200,400,800μmol/L). The effects of NaHS were also studied in endothelium-intact or endothelium-denuded coronary arteries pretreated with different tool drugs. The curve were recorded by RM-6240 bio-signal acquisition and processing system. (2) To test the activity of cystathionine y-lyase (CSE) with or without the presence of NOS inhibitor NG-nitro-L-arginine methyl ester (L-NAME,100μmol/L). The coronary arteries were incubated with 10 ml K-H solution or that containing L-NAME (100μmol/L) for 30 min, the CSE activity were observed according to the method reported by Stipanuk and his colleagues.Results:(1) Exogenous H2S (NaHS,100,200,400 and 800μmol/L) dose-dependently induced vascular relaxation in U46619 (300nmol/L) or 20K/BayK-precontracted coronary arteries. The effect of NaHS was attenuated in endothelium-denuded porcine coronary arteries. (2) Pretreatment with L-type calcium channels agonist Bay K 8644 (1μmol/L) or NOS inhibitor L-NAME (100μmol/L) significantly inhibited NaHS-induced vasorelaxation (P<0.05). KATP channel blocker glibenclamide (Gli,10μmol/L) attenuated the relaxation induced by NaHS at 400μmol/L, but had no effect on the dilatation induced by the other dose. Mitochondrial KATP channel blocker 5-hydroxydecanoate (5-HD,100μmol/L) pretreatment showed no effect on the relaxation induced by NaHS. However, soluble guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo-[4,3a]quinoxalin-1-one (ODQ,10μmol/L) enhanced relaxation effect of NaHS (P<0.05). (3) Gli (10μmol/L) 30-min incubation markedly decreased the effect of NaHS in 20K/BayK precontration (P<0.05). (4) Addition of voltage-dependent potassium channels (Kv channels) 4-aminopyridine (4-AP,2 mmol/L) had no influence on relaxation effect of NaHS. (5) Adenosine (Ado,50μmol/L) augmented the effect of NaHS, and could be inhibited by the antagonist of A2 receptor ZM241385 (100 nmol/L) (P<0.05). ZM241385 incuation did not affect the vasorelaxation. (6) The CSE activity was slightly decreased after L-NAME (100μmol/L) pretreatment.Conclusions:NaHS (100,200,400 and 800μmol/L) can induce an endothelium-dependent relaxation in a concentration-dependent manner in porcine coronary arteries. The opening of KATP channels and further closing or directly closing the calcium channels in vascular smooth muscles may contribute to the vasorelaxation effect of NaHS. The mitochondrial KATP channels, Kv channels or cGMP pathways may not be involved. Adenosine and NO may facilitate the effect of NaHS on vasodilation.