Physiology & Experimental Medicine Program, Hospital for Sick Children Research Institute, Toronto, Ontario, Canada.
Am J Physiol Heart Circ Physiol. 2012 Jun 15;302(12):H2599-611. doi: 10.1152/ajpheart.01180.2011. Epub 2012 Apr 13.
Sustained therapeutic hypercapnia prevents pulmonary hypertension in experimental animals, but its rescue effects on established disease have not been studied. Therapies that inhibit Rho-kinase (ROCK) and/or augment nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) signaling can reverse or prevent progression of chronic pulmonary hypertension. Our objective in the present study was to determine whether sustained rescue treatment with inhaled CO(2) (therapeutic hypercapnia) would improve structural and functional changes of chronic hypoxic pulmonary hypertension. Spontaneously breathing pups were exposed to normoxia (21% O(2)) or hypoxia (13% O(2)) from postnatal days 1-21 with or without 7% CO(2) (Pa(CO(2)) elevated by ∼25 mmHg) or 10% CO(2) (Pa(CO(2)) elevated by ∼40 mmHg) from days 14 to 21. Compared with hypoxia alone, animals exposed to hypoxia and 10% CO(2) had significantly (P < 0.05) decreased pulmonary vascular resistance, right-ventricular systolic pressure, right-ventricular hypertrophy, and medial wall thickness of pulmonary resistance arteries as well as decreased lung phosphodiesterase (PDE) V, RhoA, and ROCK activity. Rescue treatment with 10% CO(2), or treatment with a ROCK inhibitor (15 mg/kg ip Y-27632 twice daily from days 14 to 21), also increased pulmonary arterial endothelial nitric oxide synthase and lung NO content. In contrast, cGMP content and cGMP-dependent protein kinase (PKG) activity were increased by exposure to 10% CO(2), but not by ROCK inhibition with Y-27632. In vitro exposure of pulmonary artery smooth muscle cells to hypercapnia suppressed serum-induced ROCK activity, which was prevented by inhibition of PKG with Rp-8-Br-PET-cGMPS. We conclude that sustained hypercapnia dose-dependently inhibited ROCK activity, augmented NO-cGMP-PKG signaling, and led to partial improvements in the hemodynamic and structural abnormalities of chronic hypoxic PHT in juvenile rats. Increased PKG content and activity appears to play a major upstream role in CO(2)-induced suppression of ROCK activity in pulmonary arterial smooth muscle.
持续的治疗性高碳酸血症可预防实验动物的肺动脉高压，但尚未研究其对已建立的疾病的挽救作用。抑制 Rho-激酶（ROCK）和/或增强一氧化氮（NO）-环鸟苷酸（cGMP）信号的治疗方法可以逆转或预防慢性肺动脉高压的进展。本研究的目的是确定持续吸入 CO₂（治疗性高碳酸血症）的挽救治疗是否会改善慢性低氧性肺动脉高压的结构和功能变化。自主呼吸的幼崽从出生后第 1 天到第 21 天在 21% O₂（常氧）或 13% O₂（缺氧）中暴露，从第 14 天到第 21 天用 7% CO₂（PaCO₂升高约 25 mmHg）或 10% CO₂（PaCO₂升高约 40 mmHg）。与单纯缺氧相比，暴露于缺氧和 10% CO₂的动物的肺血管阻力、右心室收缩压、右心室肥厚和肺阻力血管的中膜厚度以及肺磷酸二酯酶（PDE）V、RhoA 和 ROCK 活性显著降低（P < 0.05）。用 10% CO₂进行挽救性治疗，或用 ROCK 抑制剂（从第 14 天到第 21 天每天两次腹腔注射 15 mg/kg Y-27632）治疗，也增加了肺动脉内皮型一氧化氮合酶和肺 NO 含量。相比之下，暴露于 10% CO₂可增加 cGMP 含量和 cGMP 依赖性蛋白激酶（PKG）活性，但 ROCK 抑制用 Y-27632 治疗则没有。体外将肺动脉平滑肌细胞暴露于高碳酸血症可抑制血清诱导的 ROCK 活性，而用 Rp-8-Br-PET-cGMPS 抑制 PKG 则可防止该活性。我们得出结论，持续的高碳酸血症剂量依赖性地抑制了 ROCK 活性，增强了 NO-cGMP-PKG 信号通路，并导致幼年大鼠慢性低氧性 PHT 的血流动力学和结构异常得到部分改善。增加的 PKG 含量和活性似乎在 CO₂诱导的肺动脉平滑肌中 ROCK 活性抑制中起主要的上游作用。
