U50488h Improves Endothelial Function In Hypoxic Pulmonary Hypertension Rats

BackgroundPulmonary hypertension is a serious clinical disease. Because of its highdegree of malignancy, it is now known as ‘cancer of cardiovascular disease’,and is characterized by the progressive increase of pulmonary vascularresistance and pulmonary vascular remodeling. In addition, due to its highmortality and high cost, pulmonary hypertension has become an urgent problemto be studied and resolved. So far there has been no magic cure for pulmonaryhypertension, and the goal of treatment is to delay or prevent progression of thedisease. Among various types of pulmonary hypertension (PH), hypoxicpulmonary hypertension (HPH) occurs mainly in patients with cardiopulmonarydisease and residents and soldiers living at high altitudes. In our country, thereare about60to80million population living at an altitude of2500m. Making anintensive study of the prevention and treatment of HPH lays a solid foundationfor the health of residents and strengthens fighting power of troops. Therefore ithas aroused great interest from researchers. Its precise mechanism is unclear.Therefore, deeply investigating the pathogenesis of HPH and seeking effective control strategy are of great significance.AimsThis present study was designed to determine whether U50488H improvesendothelial function of HPH rats and to investigate its precise mechanism. Inaddition, the study was aimed to observe whether U50488H reduces apoptosisof PMVECs exposed to hypoxia.MethodsMale Sprague-Dawley (SD) rats (180~200g) were randomized and rats weresubjected to hypoxia for8h every day in a homemade automodulating cabin for2w to form the rat model of HPH. After the experiment, right ventricularpressure (RVP) was measured by inserting a polyethylene microcatheter fromright external carotid vein to right ventricle. After finishing the experiment,hearts, blood and pulmonary were harvested and the pulmonary artery wasisolated. The effect of U50488H on endothelial function, nitric oxide (NO)content and superoxide production, gp91phoxexpression, and endothelial nitricoxide synthase (eNOS)/inducible NOS (iNOS) activity/expression wasmeasured.Primary culture of rat pulmonary microvascular endothelial cells (PMVECs)was exposed to stimulated hypoxia for12h. U50488H pretreatment wasperformed to observe the effect of U50488H on PMVECs apoptosis.ResultsThe effect of U50488H on endothelial function of HPH ratsAdministration of U50488H abolished HPH induced elevation of RVP andRVHI of rats. Concentration-dependent vasorelaxation in response to Ach wasblunted in pulmonary artery segments isolated from HPH rats. However,vasorelaxation in response to the endothelium-independent vasodilator (NaNO2) did not change among these vessels. Peritoneal injection of U50488H enhancedACh-induced vasorelaxation. Besides, administration of U50488H reversedHPH induced attenuation of NO content in rats exposed to chronic hypoxia for2w. These data indicated that U50488H improves endothelial function andelevates NO contents.The effect of U50488H on NO productionThe activity of eNOS was enhanced, but the activity of iNOS was atteunatedin the pulmonary artery of chronic hypoxic rats treated with U50488H. Inaddition, U50488H resulted in a significant increase in endothelial nitric oxide(NO) synthase (eNOS) phosphorylation in pulmonary artery of HPH rats.However, administration of U50488H did not alter Akt phosphorylation. Thesedata indicated that U50488H increased the phosphorylation level of eNOS in anAkt-independent manner.The effect of U50488H on NO destructionU50488H resulted in a significant increase in total antioxidant capacity inpulmonary artery of HPH rats. In addition, U50488H markedly bluntedHPH-induced elevation of gp91phoxexpression in pulmonary artery, and theseeffects were blocked by nor-BNI, a selective κ-opioid receptor antagonist. Thesedata indicate that U50488H prevents NO destruction by elevating totalantioxidant capacity of pulmonary artery and decreasing gp91phoxoverexpression.The effect of U50488H on hypoxia-stimulated PMVECs apoptosisU50488H significantly reduced apoptosis of PMVECs exposed to hypoxia.And this effect was block nor-BNI (a selective κ-opioid receptor antagonist),which indicated that this effect was mediated by κ-opioid receptor. In addition,the effect of U50488H on hypoxia-stimulated PMVECs apoptosis was blocked by L-NAME (an eNOS inhibitor). These results indicate that U50488H exertsantiapoptotic role on PMVECs and this effect is related to NO pathway.ConclusionsThe present study, for the first time, demonstrates that activation ofκ-opioid receptor with U50488H exerts its antioxidative/nitrative effect viapromoteing NO production and preventing NO destruction and ultimatelyimproves endothelial function in HPH rats. U50488H enhances ACh-inducedvasorelaxation and this effect is closely related to U50488H-induced elevationof NO content. On the one hand, U50488H stimulates bioactive NO productionby preservation of eNOS activity and enhancement of eNOS phosphorylation;on the other hand, U50488H prevents NO destruction by elevating totalantioxidant capacity of pulmonary artery and decreasing gp91phoxoverexpression.The present study demonstrates for the first time that activation of κ-opioidreceptor with U50488H significantly reduces stimulated hypoxia-inducedapoptosis of PMVECs and this effect is mediated by κ-opioid receptor.Additionally, this effect is closely related to NO pathway.