Effects Of Iptakalim On The Mrna And Protein Expression Of Enos In Pulmonary Tissue Of Chronic Hypoxic Rats

Objective: Hypoxic pulmonary hypertension (HPH) has been demonstrated to be the key event in the process from chronic obstructive pulmonary disease (COPD) to chronic cor pulmonale. Previous study had found that the novel ATP-sensitive potassium (K_ATP) channel opener Iptakalim (IPT) could prevent pulmonary hypertension in chronic hypoxic rats, so the aim of this study was to investigate if any difference exists in mRNA and protein expression of endothelial nitric oxide synthase (eNOS) in pulmonary tissue between chronic hypoxic and normal rats, and to examine if any changes of eNOS mRNA and protein expression occurred after long-term treatment of IPT on chronic hypoxic rats. This study will provide new insight of the molecular biology and theoretical basis about the treatment of HPH.Methods:Sixty Sprague-Dawley (SD) male rats were randomly divided into control group (saline, 5 ml·kg^-1·d^-1,ig), hypoxic group (saline, 5 ml·kg^-1·d^-1,ig), low dose IPT group (0.75 mg·kg^-1·d^-1,ig), and high dose IPT group (1.5 mg·kg^-1·d^-1,ig). Except the control group, the other three groups were put into hypoxic and normobaric chamber (10%±0.5%O2,8 h/day and 6 day/week) to establish chronic hypoxic model. After four weeks, the mean pulmonary arterial pressure (mPAP), RV/(LV+S) and the concentration of NO in the plasma were measured. Reverse transcription polymerase chain reaction (RT-PCR) was performed to analyze the mRNA expression of eNOS in pulmonary tissue. Western-blot was performed to analyze the protein expression of eNOS in pulmonary tissue. Results:(1) The levels of mPAP were significantly higher in the hypoxic group (32.12±3.77mmHg) than those in control group (18.90±1.30 mmHg) (P<0.05), low dose IPT (21.64±2.29 mmHg) and high dose IPT (20.17±2.19 mmHg) decreased the levels of mPAP significantly (P<0.05). (2)The levels of RV/(LV+S) were significantly higher in the hypoxic group (0.339±0.018) than those in control group (0.256±0.007) (P<0.05), both low dose IPT (0.285±0.013) and high dose IPT (0.274±0.011) decreased the levels of RV/(LV+S) significantly (P<0.05). (3)The levels of NO in the plasma were significantly lower in the hypoxic group (21.22±2.54μmol·L^-1) than those in control group (31.84±7.41μmol·L^-1) (P<0.05), low dose IPT (31.18±4.54μmol·L^-1) and high dose IPT (34.81±6.54μmol·L^-1) increased the levels of NO in the plasma significantly (P<0.05). (4)The mRNA expression of eNOS in the hypoxic group (0.063±0.005) was significantly lower than those in the control group (0.295±0.025) (P<0.05). Low dose IPT (0.288±0.009) and high dose IPT (0.309±0.013) increased the expression of eNOS significantly (P<0.05). (5)The protein expression of eNOS in the hypoxic group (0.379±0.108) was significantly lower than those in the control group (1.231±0.120) (P<0.05). Low dose IPT (0.801±0.147) and high dose IPT (1.227±0.179) increased the expression of eNOS significantly (P<0.05).Conclusion: The results indicate that eNOS of pulmonary tissue could contribute to the pathogenesis of chronic hypoxia pulmonary hypertension. Chronic hypoxia would damage the function of pulmonary vascular endothelial cell, which decreased the mRNA and protein expression of eNOS and further inhibited NO production. IPT could improve the vascular endothelial dysfunction, increase the expression of eNOS and the level of NO in the plasma and reverse hypoxic pulmonary hypertension.