Objective Recent studies showed that adenosine played important roles in vasodilation.This study aimed to investigate the effects of adenosine,its A1 and A2b receptor agonists on pulmonary artery hypertension (PAH) induced by chronic hypoxia in rats by continuously subcutaneous administration with an osmotic pump for 14 days,and to see if rennin angiotensin system and inducible nitric oxygen synthase (iNOS)itric oxide (NO) mediate the effects.Method Fifty-six male SD rats were randomly assigned to seven groups.Each group included eight rats.They were normoxic group,hypoxic group,adenosine-treated group [adenosine was administered at a dose of 150 μg(kg · min) under the hypoxic condition],adenosine A1 receptor agonist CPA-treated group [CPA was administered at a dose of 20 μg/(kg · min)under the hypoxic condition],CPA plus selective adenosine A1 antagonist DPCPX-treated group [CPA and DPCPX were administered simultaneously under the hypoxic condition,the dose of CPA was the same as the above,and the dose of DPCPX was 25 μg/(kg · min)],adenosine A2b receptor agonist NECA-treated group [NECA was administered at a dose of 30 μg/(kg · min) under the hypoxic condition],NECA plus selective adenosine A2b receptor antagonist MRS-treated group [NECA and MRS1754 were administered simultaneously under the hypoxic condition,the dose of NECA was the same as the above,and the dose of MRS1754 was 50 μg/(kg · min)].Osmotic pumps containing adenosine or selective adenosine A1 receptor agonist (CPA),or nonselective but potent adenosine A2b receptor agonist (NECA) were placed subcutaneously 7 days after hypoxia and continuously administered the agents for 14 days.Mean pulmonary artery pressure (mPAP) was detected after administration of the agents.Then blood samples were taken from heart for measurement of renin activity,angiotensin Ⅱ (Ang Ⅱ) and endothelin-1 (ET-1) concentration by radioimmunoassay,NO by measuring nitrate.Small pulmonary arteries were prepared for immunoreactivity staining of proliferating cell nuclear antigen (PCNA) and iNOS.Result (1) Chronic hypoxia induced PAH [mPAP:(31.38 ± 3.42)mm Hg].Adenosine or CPA or NECA administered for 14 days by subcutaneous route attenuated the mPAP [(21.17 ± 3.56) mm Hg,(22.88 ± 2.95) mm Hg,(19.81 ±2.39) mm Hg,respectively],which showed significant difference when compared with hypoxia group (P ＜0.05 respectively).(2) Plasma rennin activity and Ang Ⅱ level in hypoxia group [(2.51 ± 0.25) ng/(ml· h),(83.01 ± 9.38) pg/ml] were significantly higher than that in normoxic group (P ＜ 0.05,respectively).(3) Adenosine treatment decreased the rennin activity and Ang Ⅱ level when compared with hypoxic group(P ＜0.05,respectively) ;CPA and NECA attenuated respectively the rennin activity and Ang Ⅱ level of rats induced by chronic hypoxia (P ＜0.05,respectively).(4) Adenosine administration for 14days attenuated the wall thickness induced by chronic hypoxia (P ＜ 0.05).CPA showed no effect on wall thickness,but NECA significantly attenuated the wall thickness (P ＜ 0.05).(5) The number of iNOS staining positive cells in small pulmonary artery was higher in hypoxia group than in that in normoxic rats (23.75 ± 7.91 vs.8.00 ± 2.20,P ＜ 0.05).Adenosine or CPA,or NECA administration increased respectively the iNOS expression in rats treated with chronic hypoxia.Chronic hypoxia caused significant decrease of nitric oxide level.Adenosine treatment increased the nitric oxide level in rats treated with chronic hypoxia.CPA and NECA also increased respectively the nitric oxide level in rats treated with chronic hypoxia.Chronic hypoxia caused significant increase of ET-1 level.The ET-1 level in rats treated with adenosine,CPA or NCEA respectively were lower than that in chronic hypoxia rats (P ＜ 0.05).(6)Adenosine treatment partially attenuated the number of PCNA-positively stained cells.NECA treatment also attenuated the PCNA expression,but CPA showed no effect.Conclusion Adenosine and its agonists CPA,NECA administered continually by subcutaneous route attenuate mPAP of rats induced by chronic hypoxia.CPA attenuates mPAP through reduction of RA/Ang Ⅱ activity and balance of NO/ET-1 level.NECA attenuates mPAP by inhibiting PCNA expression and proliferation of mooth muscle of pulmonary artery.%目的 探讨外源性腺苷治疗低氧肺动脉高压的作用和机制.方法 将56只SD大鼠按随机数字表随机分为7组,每组8只,分别为常氧组、低氧组、腺苷处理组[在低氧条件下予以腺苷处理,腺苷剂量150 μg/(kg·min)]、腺苷A1受体激动剂CPA处理组[低氧条件下予以CPA处理,CPA剂量20 μg/(kg·min)]、CPA+选择性腺苷A1受体拮抗剂DPCPX处理组[低氧条件下同时予CPA和DPCPX处理,CPA剂量同前,DPCPX剂量25μ/(kg·min)]、腺苷A2b受体激动剂NECA处理组[低氧条件下予以NECA处理,NECA剂量30 μg/(kg·min)]、NECA+选择性腺苷A2b受体拮抗剂MRS处理组[低氧条件下予以NECA和MRS1754联合处理,NECA同前,MRS1754剂量50 μg/(kg· min)].给药14 d后测量平均肺动脉压力(mPAP),然后取血用放射免疫法测血浆肾素活性(RA)、血管紧张素Ⅱ(AngⅡ)、内皮素1水平,比色法测定一氧化氮(NO)浓度,取肺动脉作免疫组化染色测定肺动脉增殖细胞核抗原(PCNA)和诱导型一氧化氮合酶(iNOS)的蛋白表达.结果 (1)腺苷处理组和CPA、NECA处理组mPAP[分别为(21.17 ±3.56)mm Hg(1 mm Hg =0.133 kPa)、(22.88 ±2.95)mm Hg、(19.81±2.39)mmHg]均低于低氧组大鼠mPAP(31.38±3.42) mm Hg,差异有统计学意义(P均＜0.05)；(2)低氧组血浆RA和AngⅡ水平分别为(2.51±0.25) ng/(ml·h)和(83.01±9.38) pg/ml,高于常氧组(P均＜0.05).腺苷、CPA和NECA处理后血浆RA和AngⅡ水平均低于低氧组(P均＜0.05)；(3)腺苷处理后肺动脉血管壁厚度低于低氧组(P ＜0.05)；CPA处理对低氧所致肺动脉血管壁厚度无影响,NECA处理则降低低氧所致肺动脉血管壁厚度,与低氧组比较差异有统计学意义(P＜0.05)；(4)低氧组肺动脉血管iNOS阳性细胞数明显高于常氧组(23.75±7.91 vs.8.00±2.20,P＜0.05)；腺苷、CPA和NECA处理后iNOS表达进一步增高(P均＜0.05)；腺苷处理后血浆NO水平高于低氧组(P＜0.05),CPA处理后其水平高于低氧组,且高于腺苷处理组和常氧组(均P＜0.05),NECA处理组其水平高于低氧组,但仍低于常氧组(均P＜0.05)；低氧组血浆内皮素1水平明显高于常氧组(P＜0.05),腺苷、CPA、NECA处理后其水平均低于低氧组(P均＜0.05)；(5)腺苷部分降低肺动脉PCNA细胞表达,NECA亦可以降低肺动脉PCNA细胞表达,而CPA对其无影响.结论 外周持续给予腺苷、A1和A2b受体激动剂均能降低低氧性肺动脉高压,选择性A1受体激动剂通过降低RA-AngⅡ系统活性和纠正NO和内皮素1平衡降低mPAP.A2b受体激动剂能抑制低氧性肺动脉PCNA表达,改善肺动脉结构,降低mPAP,同时对RA-AngⅡ系统、iNOS-NO及内皮素1等均有调节作用.
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