SODIUM PUMP INHIBITORS IN BLOOD PRESSURE REGULATION

综上所述，我们以前的研究表明，在哺乳动物组织中共存的两种内源性配基Na，K-ATPase(NKA)或强心性类固醇(CS)，哇巴因类化合物(OLC)和马利诺蟾毒配基(MBG)，对盐负荷和血浆容量膨胀做出反应，在引起增加释放的有效刺激方面不同，并且它们的靶点不同(NKA的α-3和α-1亚型)。我们首次证明了生理浓度的MBG在高亲和力(纳摩尔)结合部位水平上抑制肾脏NKA。在突变了α-1 NKA基因的Dahl盐敏感大鼠(DS)中，高盐摄入导致OLC排泄一过性增加，而血浆和尿液MBG的进行性增加与血压升高平行。急性给予抗高血压DS的MBG抗体(而不是哇巴因抗体)具有降压作用。DS的代偿性左心室肥厚(8%食盐饮食4周)和高血压8周后向心力衰竭的转变分别与心肌中α-1 NKA的上调和下调有关。心肌α-1 NKA的上调与NKA对MBG的敏感性增加相关。在快速发展、容量依赖和钠敏感型高血压等先兆子痫患者中，血浆MBG水平较正常妊娠时升高4倍。从子痫前期血浆中纯化的MBG免疫活性物质在纳摩尔浓度范围内对人肠系膜动脉NKA产生抑制作用。在研究MBG和OLC的血管收缩作用机制的过程中，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与其他激素在心血管重塑中的相互作用中发挥重要作用。相反，体外用抗高血压化合物cicletanine抑制PKC可减弱MBG的NKA抑制剂活性。这一机制可能解释了西来坦对Dahl高血压的夸大疗效，在Dahl高血压中，MBG升高并有助于增强血管张力。综上所述，我们的结果表明，内源性α-1 NKA配体MBG水平的升高有助于实验性和临床氯化钠敏感型高血压的血管收缩。PKC对α-1 NKA的磷酸化可能是CS和其他血管活性激素在血管收缩和心血管重构中相互作用的基础，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，Dahl大鼠，氯化钠，Na，K-ATPase，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