Archer S L, Hampl V, Nelson D P, Sidney E, Peterson D A, Weir E K
Minneapolis Veterans Affairs Medical Center, MN 55417, USA.
Circ Res. 1995 Jul;77(1):174-81. doi: 10.1161/01.res.77.1.174.
Dithionite is a powerful reducing agent used to deoxygenate hemoglobin and create anaerobic conditions in vitro. Recently, dithionite has been used as a convenient means of creating "hypoxia" in experiments studying the O2 sensor in the pulmonary circulation and carotid body. We evaluated the hypothesis that hypoxia created by hypoxic ventilation and that created by dithionite have different effects on the pulmonary circulation. In vitro, dithionite (10(-5) to 10(-3) mol/L), added to oxygenated Krebs' solution, rapidly created superoxide anion in a dose-dependent manner. Dithionite consumed O2 in parallel with the generation of superoxide radical, with both processes peaking within seconds. Anoxia was sustained only if resupply of O2 was prevented. In isolated rat lungs (whether perfused with autologous blood or Krebs' solution), hypoxic ventilation alone lowered perfusate PO2 from approximately 140 to 40 mm Hg and decreased lung levels of activated oxygen species (AOS), measured by luminol-enhanced chemiluminescence, before the onset of hypoxic pulmonary vasoconstriction. Constrictor responses to angiotensin II and KCl were not impaired by intermittent hypoxic challenges, and lung weight did not increase. In contrast, dithionite impaired constrictor responses of the Krebs' solution-perfused lungs to all vasoconstrictors tested and increased lung weight. When given as a bolus (5 x 10(-3) mol/L) into the pulmonary artery during normoxic ventilation, dithionite caused no vasoconstriction and only briefly lowered PO2 (because of constant resupply of O2 from the alveoli). When superimposed on hypoxic ventilation, dithionite further lowered PO2 from approximately 40 to approximately 0 mm Hg and caused additional constriction. Unlike hypoxic ventilation, dithionite increased AOS production. Antioxidant enzymes diminished dithionite-induced radical production and diminished the loss of vascular reactivity and lung edema. In conclusion, unlike hypoxic ventilation, dithionite causes edema and loss of vascular reactivity in the lung by generating superoxide anion and hydrogen peroxide. Hypoxia elicited by dithionite is not equivalent to authentic hypoxia because of the obligatory associated generation of AOS. Dithionite usage should not be substituted for authentic hypoxia in studies of O2 sensing.
连二亚硫酸盐是一种强还原剂，用于使血红蛋白脱氧并在体外创造无氧条件。最近，连二亚硫酸盐已被用作在研究肺循环和颈动脉体中氧传感器的实验中创造“缺氧”的便捷手段。我们评估了以下假设：低氧通气造成的缺氧和连二亚硫酸盐造成的缺氧对肺循环有不同影响。在体外，将连二亚硫酸盐（10⁻⁵至10⁻³mol/L）添加到含氧的 Krebs 溶液中，会以剂量依赖的方式迅速产生超氧阴离子。连二亚硫酸盐在消耗氧气的同时产生超氧自由基，这两个过程在数秒内达到峰值。只有在防止氧气重新供应的情况下，缺氧状态才能持续。在离体大鼠肺中（无论用自体血液还是 Krebs 溶液灌注），仅低氧通气就能在低氧性肺血管收缩开始前，将灌注液的氧分压从约140mmHg降至40mmHg，并降低通过鲁米诺增强化学发光测量的肺中活性氧物质（AOS）水平。间歇性低氧刺激不会损害对血管紧张素 II 和氯化钾的收缩反应，肺重量也不会增加。相比之下，连二亚硫酸盐会损害用 Krebs 溶液灌注的肺对所有测试血管收缩剂的收缩反应，并增加肺重量。在常氧通气期间，以大剂量（5×10⁻³mol/L）注入肺动脉时，连二亚硫酸盐不会引起血管收缩，只会短暂降低氧分压（因为肺泡持续供应氧气）。当叠加在低氧通气上时，连二亚硫酸盐会使氧分压从约40mmHg进一步降至约0mmHg，并引起额外的收缩。与低氧通气不同，连二亚硫酸盐会增加AOS的产生。抗氧化酶可减少连二亚硫酸盐诱导的自由基产生，并减少血管反应性丧失和肺水肿。总之，与低氧通气不同，连二亚硫酸盐通过产生超氧阴离子和过氧化氢导致肺水肿和血管反应性丧失。由于必然会伴随产生AOS，连二亚硫酸盐引起的缺氧不等同于真正的缺氧。在氧传感研究中，不应使用连二亚硫酸盐替代真正的缺氧。
