Sodium Pump Inhibitors In Blood Pressure Regulation

盐敏感性高血压占全球高血压患者的40%。尽管如此，盐敏感性的分子机制还没有得到很好的理解。一种理论认为内源性洋地黄样强心类固醇（CTS）在盐敏感性高血压的发病机制中起核心作用。两种CTS，内源性哇巴因和海蟾毒配基（MBG），共存于哺乳动物组织。MBG作为哇巴因抗性Na/K-ATP酶（NKA）α-1亚型的选择性抑制剂，NKA是肾脏、血管平滑肌和成人心肌细胞中的主要亚型。在Dahl盐敏感大鼠（DS）的高NaCl摄入量，脑内源性哇巴因触发外周MBG，这提高了血压。在人类中，中等NaCl负荷导致MBG产生增加。在过去的一年里，我们的研究集中在（i）低浓度哇巴因在大鼠中的中枢促高血压作用的药理学分析，其模拟盐负荷并启动MBG刺激的血管紧张素II敏感性通路，（ii）在实验性盐敏感性高血压中升高的MBG水平对葡萄糖耐量的影响的研究，和（iii）研究MBG在血压调节和尿钠排泄中的作用，在中度NaCl负荷的正常血压的人，集中在盐敏感性的年龄和性别相关的差异。 (i)NaCl敏感性高血压的发病机制 我们进行了药理学分析的中枢促高血压作用的低剂量哇巴因对肾上腺皮质MBG生产在DS大鼠。海马内给予60 ng哇巴因可诱导下丘脑视上核和垂体中的肾素-血管紧张素系统（RAS）激活。这种激活引起交感神经激活，触发肾上腺皮质RAS，随后增加MBG的生产。通过在下丘脑视上核给予抗哇巴因抗体、氯沙坦的中枢和全身给药以及通过外周肾上腺素受体阻滞，在多个水平上通过药理学干预分析了该事件序列。结果允许建立脑哇巴因，中枢和外周RAS，交感神经系统和外周CTS之间的复杂相互作用的层次结构，这是盐敏感性高血压的发病基础。 (ii)CTS的作用已经在另外两个NaCl敏感性高血压的实验模型中进行了研究。众所周知，解毒的酗酒者表现出肾钠潴留，这是晚年心血管事件的负面预后因素。我们假设MBG是与乙醇戒断相关的高血压的介导剂。在大鼠急性乙醇戒断模型中，动物表现出肾钠潴留和升压反应，这可通过体内施用抗MBG抗体来预防。以前，我们已经证明，MBG是牵连在1型糖尿病的发病机制和先兆子痫的发病机制。在高血压妊娠糖尿病大鼠补充NaCl后，MBG水平升高与葡萄糖耐量的改善有关。因此，MBG是糖尿病和妊娠高血压发病机制中的共同环节。 (iii)与马尔莫的隆德大学（瑞典）合作，在血压正常的人中研究了性别和年龄对CTS对NaCl负荷的反应的影响。在这项研究中，中度（150 mmol/天）NaCl负荷导致血浆MBG水平增加，血压中度升高。在男性中，血浆和尿MBG水平与收缩压相关，基线MBG水平预测血压的盐敏感性。然而，在老年妇女中，这种关系则相反。值得注意的是，在男性和女性的健康受试者中，MBG水平随年龄的增长而下降，而血压的盐敏感性随年龄的增长而增加。因此，不仅MBG的过量产生，而且这种激素对NaCl负荷的响应失败可能是与年龄相关的血压盐敏感性增加的基础。

Salt-sensitive hypertension accounts for 40% of the hypertensives worldwide. Still, molecular mechanisms of salt-sensitivity are not well understood. One theory attributes endogenous digitalis-like cardiotonic steroids (CTS) a central role in the pathogenesis of salt-sensitive hypertension. Two CTS, endogenous ouabain and marinobufagenin (MBG), coexist in mammalian tissues. MBG acts as a selective inhibitor of ouabain-resistant alpha-1 isoform of Na/K-ATPase (NKA), the main isoform in the kidney, vascular smooth muscle and adult cardiomyocytes. In Dahl salt-sensitive rats (DS) on a high NaCl intake, brain endogenous ouabain triggers peripheral MBG, which raises the blood pressure. In humans, moderate NaCl-loading causes increase in MBG production. During the past year our research focused on (i) pharmacological analysis of central pro-hypertensive effects of low ouabain concentrations in rat, which mimics salt-loading and initiates the angiotensin II-sensitive pathway of MBG stimulation, (ii) study of the impact of heightened MBG levels on glucose tolerance in experimental salt-sensitive hypertension, and (iii) studies of the role of MBG in blood pressure regulation and natriuresis during moderate NaCl-loading of normotensive humans, focusing on age- and gender-associated differences in salt-sensitivity. (i) Pathogenesis of NaCl-sensitive hypertension. We performed pharmacological analyses of central pro-hypertensive effect of low dose ouabain on adrenocortical MBG production in DS rats. Intra-hippocampal administration of 60 ng of ouabain induced activation of renin-angiotensin system (RAS) in the supraoptical nucleus of hypothalamus, and in the pituitary. This activation caused sympathoactivation, which triggered adrenocortical RAS, followed by increase in MBG production. This sequence of events has been analyzed via pharmacological interventions on several levels via administration of anti-ouabain antibody in the supraoptical nucleus of hypothalamus, central and systemic administration of losartan, and via peripheral adrenoceptor blockade. The results permitted to establish a hierarchy in the complex interactions between brain ouabain, central and peripheral RAS, and sympathetic nervous system, and peripheral CTS, which underlies the onset of salt-sensitive hypertension. (ii) The role of CTS has been studied in two other experimental models of NaCl-sensitive hypertension. It is known, that detoxified alcoholics exhibit renal sodium retention, which is a negative prognostic factor for cardiovascular events in the later life. We hypothesized, that MBG is a mediator of hypertension associated with ethanol withdrawal. In a model of acute ethanol withdrawal in rats, animals exhibited renal sodium retention and pressor response, which was prevented by in vivo administration of anti-MBG antibody. Previously, we have demonstrated, that MBG is implicated in pathogenesis of type 1 diabetes mellitus and in pathogenesis of preesclampsia. In hypertensive pregnant diabetic rats following NaCl-supplementation, elevated MBG levels were associated with an improvement of glucose tolerance. Thus, MBG is a common link in the pathogenesis of diabetes and pregnancy-induced hypertension. (iii) The impact of gender and age on CTS response to NaCl-loading has been studied in normotensive humans in collaboration with Lund University, Malmo (Sweden). In this study, a moderate (150 mmol/day) NaCl-loading resulted in an increase in plasma MBG levels, and a moderate elevation of blood pressure. In men, plasma and urine MBG levels correlated with systolic blood pressure, and baseline MBG levels predicted salt-sensitivity of the blood pressure. In aged women, however, this relationship was opposite. Notably, in healthy subjects of both sexes, levels of MBG declined with age, whereas salt-sensitivity of blood pressure is increased with age. Thus, not only excessive production of MBG, but also a failure in the response of this hormone to NaCl-loading may underlie age-associated increase in salt-sensitivity of blood pressure.