Adiponectin improves diastolic functions of isolated pulmonary artery of intermittent hypoxia pulmonary hypertension rats and its mechanism

AIM To investigate the effect of recombinant human globular adiponectin (gAd) on isolated pulmonary artery of intermittent hypoxic pulmonary hypertension (HPH) rats and the underlying mechanisms. METHODS Twenty four male Sprague Dawley (SD) rats were divided randomly into three groups: control group, 2-week HPH (HPH2W) group and 4-week HPH (HPH4W) group. Rats in control group were fed in normal environments and rats in hypoxia groups became HPH models using intermittent hypobaric hypoxia method. After establishing the hypoxia models, mean pulmonary artery pressure (mPAP) and mean right ventricular pressure (mRVP) were measured using right cardiac catheter. Weight ratio of right ventricle and left ventricle+ventricular septum (RV/LV+S) and the weight ratio of right ventricle and body weight (RV/BW) were also measured and the gAd and NO concentrations in blood serum were detected using ELISA detection kit. Microstructure changes of pulmonary small artery were observed after H/E staining on the inferior lobe of the right lung. Left and right pulmonary artery trunks of the rat were taken to make vascular circles. Isolated perfusion experiment was then carried out and the vascular diastolic function induced by acetylcholine and sodium nitroprussiate under varied concentrations was observed. The pulmonary artery trunks were removed from the lungs in HPH4W group and were incubated by grouping (HPH4W group: incubated in Krebs fluid; HPH4W+gAd group: incubated in gAd 2 μg/ml, HPH4W+gAd+L-NAME group: incubated in gAd 2 μg/ml+L-NAME 0.5 mmol/L). After incubation, the author observed the vascular diastolic functions induced by acetylcholine and sodium nitroprussiate under varied concentrations. The perfusate was then collected, which acted on the vascular circle and detected NO product. The author took the pulmonary arterial vessels in the HPH4W group, divided them into groups according to the above method, incubated them and then conducted Western blot to detect the expressions and phosphorylation levels of AMPK, Akt and eNOS. RESULTS Compared with those in control group, mPAP, mRVP, RV/LV+S and RV/BW all significantly increased (P<0.05) and serum levels of gAd and NO decreased (P<0.05). Under light microscope, smooth muscle and elastic fiber layer of pulmonary artery proliferated, the wall of the vessels thickened and lumen of the vessels was narrow. Compared with those in control group, vascular diastolic functions of the pulmonary artery in HPH rats induced by acetylcholine decreased significantly (P<0.05). The maximal diastolic rate in control group was 69.94%, 48.79% in HPH2W group and only 42.09% in HPH4W group. After gAd incubation in vitro, the diastolic function dependent on vascular circle endothelium increased significantly, the maximal diastolic rate reached 46.35% in HPH4W group and the vascular circle diastolic function in L-NAME group was obviously blocked. The reflection of vasodilation of rats induced by sodium nitroprussiate in all three groups was good with no statistically significant difference. Through gAd incubation, the phosphorylation levels of AMPK, Akt and eNOS of the vascular circle tissue and the NO product of perfusate all increased (P<0.05). L-NAME blocked the gAd effect of increasing eNOS phosphorylation and NO level. CONCLUSION gAd has a direct protective effect on the vascular diastolic function dependent on the pulmonary artery endothelium in intermittent hypoxia pulmonary hypertension rats. The signal channels of AMPK/Akt/eNOS/NO may be the molecular mechanism through which gAd exerts the protective effect on the pulmonary artery.