Sodium Pump Inhibitors In Blood Pressure Regulation

盐敏感型高血压占全球高血压患者的40%。尽管如此，盐敏感的分子机制还没有被很好地理解。一种理论认为内源性洋地黄样强心性类固醇(CTS)在盐敏感型高血压的发病机制中起核心作用。内源性哇巴因和华蟾素(MBG)两种CTs共存于哺乳动物组织中。MBG是对哇巴因耐药的Na/K-ATPaseα-1亚型(NKA)的选择性抑制剂，NKA是肾脏、血管平滑肌和成年心肌细胞中的主要亚型。在高盐摄入量的Dahl盐敏感大鼠(DS)中，大脑内源性哇巴因触发外周MBG，从而升高血压。在人类中，适度的氯化钠负荷会导致MBG产量增加。在过去的一年里，我们的研究集中在(I)模拟盐负荷并启动MBG刺激的血管紧张素II敏感途径的大鼠中枢高血压前期效应的药理学分析，(Ii)在实验性盐敏感型高血压中MBG水平升高对糖耐量的影响的研究，以及(Iii)在正常血压人群中等盐负荷期间MBG在血压调节和钠排出中的作用，重点是年龄和性别相关的盐敏感性差异。 (I)盐敏感型高血压的发病机制。 我们对小剂量哇巴因对DS大鼠肾上腺皮质MBG生成的中枢降压作用进行了药理学分析。海马区注射60 ng哇巴因可激活下丘脑视上核和垂体的肾素-血管紧张素系统(RAS)。这种激活引起交感神经激活，从而触发肾上腺皮质RAS，随后MBG产生增加。通过在下丘脑视上核注射抗哇巴因抗体，中枢和全身注射氯沙坦，以及通过外周肾上腺素受体阻断，在多个水平上进行了药物干预，对这一事件序列进行了分析。这些结果允许在大脑哇巴因、中枢和外周RAS、交感神经系统和外周CTS之间复杂的相互作用中建立一个等级，这是盐敏感型高血压发病的基础。 (Ii)CTS的作用已经在另外两个盐敏感型高血压的实验模型中进行了研究。已知，戒酒的人表现出肾脏钠滞留，这是晚年心血管事件的负面预后因素。我们假设，MBG是与酒精戒断相关的高血压的中介。在大鼠急性酒精戒断模型中，动物表现出肾脏钠滞留和升压反应，这可以通过体内注射抗MBG抗体来预防。以前，我们已经证明，MBG与1型糖尿病的发病机制和闭锁前期的发病机制有关。在补充盐后的高血压妊娠糖尿病大鼠中，MBG水平的升高与糖耐量的改善有关。因此，MBG在糖尿病和妊娠高血压综合征的发病机制中是一个共同的环节。 (Iii)与瑞典马尔莫隆德大学合作，在血压正常的人中研究了性别和年龄对氯化钠负荷对CTS反应的影响。在这项研究中，适量的氯化钠负荷(150 mmol/天)导致血浆MBG水平升高，血压适度升高。在男性中，血浆和尿液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，在老年女性中，这种关系正好相反。值得注意的是，在男女健康受试者中，MBG水平随着年龄的增长而下降，而血压的盐敏感性随着年龄的增长而增加。因此，不仅MBG的过量产生，而且这种激素对氯化钠负荷的反应失败，可能是与年龄相关的血压对盐敏感性增加的原因。

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.