SODIUM PUMP INHIBITORS IN BLOOD PRESSURE REGULATION

我们之前的研究表明，在哺乳动物组织中共存的两种内源性Na配体，K atp酶（NKA），或强心类固醇（CS），瓦巴因样化合物（OLC）和marinobufagenin (MBG)，对NaCl负荷和血浆容量扩张有反应，在引起释放增加的有效刺激方面有所不同，其靶点（NKA的α -3和α -1亚型）也不同。我们首次证明了生理上实际浓度的MBG在高亲和（纳摩尔）结合位点水平上抑制肾脏NKA。在α -1 NKA基因突变的达尔盐敏感大鼠（DS）中，高NaCl摄入量诱导OLC排泄短暂增加，而血浆和尿MBG的进行性增加与血压升高并行。急性给药MBG抗体（而非乌阿班抗体）对高血压DS有降压作用。代偿性左心室肥厚的发展（服用8% NaCl饮食4周）和高血压8周后过渡到心力衰竭，分别与心肌α -1 NKA的上调和下调有关。心肌α -1 NKA的上调与NKA对MBG的敏感性增加有关。在子痫前期，如快速发展的体积依赖性和钠敏感性高血压，血浆MBG水平比正常妊娠增加了4倍。从子痫前期血浆中纯化的MBG免疫反应物质在纳摩尔浓度范围内抑制来自人肠系膜动脉的NKA。在对MBG和OLC血管收缩作用机制的研究过程中，我们首次发现心血管组织中蛋白激酶C （PKC）对NKA的异构体特异性磷酸化增加了NKA对CS的敏感性。这一机制可能在CS本身的作用以及CS与其他激素相互作用对心血管重构的影响中起重要作用。相反，抗高血压化合物环氨酸对PKC的抑制，在体外减弱了MBG的NKA抑制剂活性。这一机制可以解释环汀在Dahl高血压中的夸大疗效，其中MBG升高并有助于血管张力增强。总之，我们的研究结果表明，α -1 NKA的内源性配体MBG水平升高有助于实验和临床NaCl敏感性高血压的血管收缩。PKC对α -1 NKA的磷酸化可能是CS与其他血管活性激素在血管收缩和心血管重构中的相互作用的基础，并且是内源性CS受到刺激的高血压状态下治疗干预的靶点。-高血压，达尔大鼠，氯化钠，钠，K atp酶，异构体，抑制剂，蛋白激酶C

SUMMARY OF WORK Our previous studies demonstrated that two endogenous ligands of Na,K ATPase (NKA), or cardiotonic steroids (CS), ouabain- like compound (OLC) and marinobufagenin (MBG), coexisting in mammalian tissues, are responsive to NaCl loading and plasma volume expansion, differ with respect to effective stimuli that evoke an increased release, and differ in their targets (alpha-3 and alpha-1 isoforms of NKA). For the first time we demonstrated that MBG in the the physiologically realistic concentrations inhibits renal NKA at the level of high-affiniy (nanomolar) binding sites. In the Dahl salt sensitive rats (DS) with mutated alpha-1 NKA gene, high NaCl intake induced transient increase in OLC excretion, whereas progressive increase in plasma and urinary MBG paralleled blood pressure elevation. Acute administration of MBG antibody (but not ouabain antibody) to hypertensive DS exhibited antihypertensive effect. The development of compensatory left ventricular hypertrophy (4 weeks on an 8% NaCl diet) and transition to heart failure after 8 weeks of hypertension in DS, was associated with an upregulation and downregulation of alpha-1 NKA in myocardium, respectively. Upregulation of myocardial alpha-1 NKA was associated with increased NKA sensitivity to MBG. In preeclampsia, e.g. rapidly developing, volume dependent and Na sensitive hypertension, plasma levels of MBG were increased four-fold as compared to that in normotensive pregnancy. MBG immunoreactive material purified from preeclamptic plasma caused inhibition of NKA from human mesenteric arteries at nanomolar range of concentrations. In the course of studies of mechanisms of vasoconstrictor action of MBG and OLC, we have shown for the first time, that the isoform-specific phosphorylation of NKA by protein kinase C (PKC) in cardiovascular tissues increased sensitivity of NKA to CS. This mechanism may play an important role in the action of CS, per se, and in interaction of CS and other hormones on cardiovascular remodeling. Conversely, inhibition of PKC by an antihypertensive compound, cicletanine, in vitro attenuated NKA inhibitor activity of MBG. This mechanism may explain the exaggerated efficacy of cicletanine in Dahl hypertension, where MBG is elevated and contributed to enhanced vascular tone. In summary, our results demonstrate that elevated levels of an endogenous ligand of alpha-1 NKA, MBG, contribute to vasoconstriction in experimental and clinical NaCl sensitive hypertension. Phosphorylation of alpha-1 NKA by PKC is likely to underlie the interaction of CS and other vasoactive hormones on vasoconstriction and cardiovascular remodeling, and represents a target for therapeutic intervention in the hypertensive states where endogenous CS are stimulated. - Hypertension, Dahl rats, sodium chloride, Na,K ATPase, isoforms, inhibitors, protein kinase C