da Silva-Santos José Eduardo, Terluk Marcia Ribeiro, Assreuy Jamil
Department of Pharmacology, Universidade Federal de Santa Catarina, Florianópolis, Brazil.
Shock. 2002 Jan;17(1):70-6. doi: 10.1097/00024382-200201000-00012.
This study evaluated the involvement of nitric oxide (NO), guanylate cyclase, and potassium channels in the long-lasting vascular hyporesponsiveness to phenylephrine induced by Escherichia coli lipopolysaccharide (LPS) in vitro and in vivo. Experiments in rat aorta rings with endothelium incubated with LPS (10 microg/mL) for 12 h showed that the hyporesponsiveness depends on guanylate cyclase activity and tetraethylammonium-sensitive, but not voltage- or ATP-dependent, potassium channels. Pressor responses to phenylephrine were reduced by 50% in rats injected 8 and 24 h before with LPS (10 mg/kg, intraperitoneally). Pretreatment with NO synthase inhibitors (iNOS; Nomega-nitro-L-arginine methyl ester [L-NAME], 55 micromol/kg or aminoguanidine, 244 micromol/kg, intraperitoneally) fully prevented LPS-induced hyporesponsiveness. When administered just before phenylephrine, L-NAME (11 micromol/kg, intravenously) reversed the hyporesponsiveness in rats injected 8 h, but not in those injected 24 h before with LPS, whereas 1H-[1,2,4]-oxadiazolo-[4,3-a]-quinoxalin-1 (ODQ, 11 micromol/kg, intravenously) reversed the hyporesponsiveness in animals injected 24 h, but not in those injected 8 h before with LPS. Tetraethylammonium (360 micromol/kg, intravenously) reestablished normal responses to phenylephrine in rats injected 8 and 24 h before with LPS. Again, neither voltage- nor ATP-dependent potassium channels appears to be involved. Western blot showed that iNOS expression peaked at 8 h, decreasing to low levels 24 h after LPS injection. Therefore, NO is important in initiating LPS-induced hyporesponsiveness to vasoconstrictors, but not in maintaining it for long periods. Once NO has exerted its effects and even when iNOS expression is minimal, the long-lasting hyporesponsiveness appears to depend on a complex interplay between guanylate cyclase and potassium channel activation.
本研究评估了一氧化氮（NO）、鸟苷酸环化酶和钾通道在体外和体内大肠杆菌脂多糖（LPS）诱导的对去氧肾上腺素的长期血管低反应性中的作用。用LPS（10微克/毫升）孵育12小时的大鼠带内皮主动脉环实验表明，低反应性取决于鸟苷酸环化酶活性以及对四乙铵敏感但对电压或ATP不敏感的钾通道。在8小时和24小时前腹腔注射LPS（10毫克/千克）的大鼠中，对去氧肾上腺素的升压反应降低了50%。用一氧化氮合酶抑制剂（诱导型一氧化氮合酶；Nω-硝基-L-精氨酸甲酯 [L-NAME]，55微摩尔/千克或氨基胍，244微摩尔/千克，腹腔注射）预处理可完全预防LPS诱导的低反应性。在去氧肾上腺素给药前静脉注射L-NAME（11微摩尔/千克）可逆转8小时前注射LPS的大鼠的低反应性，但不能逆转24小时前注射LPS的大鼠的低反应性，而静脉注射1H-[1,2,4]-恶二唑并-[4,3-a]-喹喔啉-1（ODQ，11微摩尔/千克）可逆转24小时前注射LPS的动物的低反应性，但不能逆转8小时前注射LPS的动物的低反应性。静脉注射四乙铵（360微摩尔/千克）可使8小时和24小时前注射LPS的大鼠对去氧肾上腺素的反应恢复正常。同样，电压依赖性和ATP依赖性钾通道似乎均未参与其中。蛋白质印迹法显示，诱导型一氧化氮合酶表达在8小时达到峰值，LPS注射后24小时降至低水平。因此，NO在引发LPS诱导的对血管收缩剂的低反应性中很重要，但在长期维持该反应中并不重要。一旦NO发挥了作用，即使诱导型一氧化氮合酶表达最低，长期的低反应性似乎也取决于鸟苷酸环化酶和钾通道激活之间的复杂相互作用。
