Pearce William J, Williams James M, White Charles R, Lincoln Thomas M
Department of Physiology, Center for Perinatal Biology, Loma Linda Univ. School of Medicine, Loma Linda, CA 92350, USA.
J Appl Physiol (1985). 2009 Jul;107(1):192-9. doi: 10.1152/japplphysiol.00233.2009. Epub 2009 Apr 30.
A broad variety of evidence obtained largely in pulmonary vasculature suggests that chronic hypoxia modulates vasoreactivity to nitric oxide (NO). The present study explores the general hypothesis that chronic hypoxia also modulates cerebrovascular reactivity to NO, and does so by modulating the activity of soluble guanylate cyclase (sGC), the primary target for NO in vascular smooth muscle. Pregnant and nonpregnant ewes were maintained at either sea level or at 3,820 m for the final 110 days of gestation, at which time middle cerebral arteries from term fetal lambs and nonpregnant adults were harvested. In both fetal and adult arteries, NO-induced vasodilatation was attenuated by chronic hypoxia and completely inhibited by 10 microM 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), a selective inhibitor of sGC. sGC abundance (in ng sGC/mg protein) measured via Western immunoblots was approximately 10-fold greater in fetal (17.6 +/- 1.6) than adult (1.7 +/- 0.3) arteries but was not affected by chronic hypoxia. The specific activity of sGC (in pmol cGMP.microg sGC(-1).min(-1)) was similar in fetal (255 +/- 64) and adult (280 +/- 75) arteries and was inhibited by chronic hypoxia in both fetal (120 +/- 10) and adult (132 +/- 26) arteries. Rates of cGMP degradation (in pmol cGMP.mg protein(-1).min(-1)) were similar in fetal (159 +/- 59) and adult (134 +/- 36) arteries but were not significantly depressed by chronic hypoxia in either fetal (115 +/- 25) or adult (108 +/- 25) arteries. The cGMP analog 8-(p-chlorophenylthio)-cGMP was a more potent vasorelaxant in fetal (pD(2) = 4.7 +/- 0.1) than adult (pD(2) = 4.3 +/- 0.1) arteries, but its ability to promote vasodilatation was not affected by chronic hypoxia in either age group. Together, these results reveal that hypoxic inhibition of NO-induced vasodilatation is attributable largely to attenuation of the specific activity of sGC and does not involve significant changes in sGC abundance, cGMP-phosphodiesterase activity, or the vasorelaxant activity of protein kinase G.
大量在肺血管系统中获得的各种各样的证据表明，慢性缺氧会调节对一氧化氮（NO）的血管反应性。本研究探讨了一个总体假设，即慢性缺氧也会调节脑血管对NO的反应性，并且是通过调节可溶性鸟苷酸环化酶（sGC）的活性来实现的，sGC是血管平滑肌中NO的主要作用靶点。在妊娠的最后110天，将怀孕和未怀孕的母羊分别饲养在海平面或海拔3820米处，此时采集足月胎羊和未怀孕成年羊的大脑中动脉。在胎儿和成年动脉中，慢性缺氧都会减弱NO诱导的血管舒张，并且会被10 microM 1H-[1,2,4]恶二唑并[4,3-a]喹喔啉-1-酮（ODQ，一种sGC的选择性抑制剂）完全抑制。通过蛋白质免疫印迹法测得的sGC丰度（以ng sGC/mg蛋白质计）在胎儿动脉（17.6±1.6）中比成年动脉（1.7±0.3）中大约高10倍，但不受慢性缺氧的影响。sGC的比活性（以pmol cGMP·μg sGC⁻¹·min⁻¹计）在胎儿动脉（255±64）和成年动脉（280±75）中相似，并且在胎儿动脉（120±10）和成年动脉（132±26）中都会被慢性缺氧所抑制。cGMP降解速率（以pmol cGMP·mg蛋白质⁻¹·min⁻¹计）在胎儿动脉（159±59）和成年动脉（134±36）中相似，但在胎儿动脉（115±25）或成年动脉（108±25）中都不会被慢性缺氧显著降低。cGMP类似物8-（对氯苯硫基）-cGMP在胎儿动脉（pD₂ = 4.7±0.1）中比成年动脉（pD₂ = 4.3±0.1）中是一种更有效的血管舒张剂，但其促进血管舒张的能力在两个年龄组中都不受慢性缺氧的影响。总之，这些结果表明，缺氧对NO诱导的血管舒张的抑制主要归因于sGC比活性的减弱，并且不涉及sGC丰度、cGMP磷酸二酯酶活性或蛋白激酶G的血管舒张活性的显著变化。
