Weiler E W, Gonick H C, Prins B A, Purdy R E, Weber M A
Trace Element Laboratory, Division of Nephrology/Department of Medicine, Cedars-Sinai Medical Center, Los Angeles, CA 90048.
Am J Med Sci. 1994 Jan;307(1):27-35. doi: 10.1097/00000441-199401000-00005.
It has been demonstrated that expansion of extracellular fluid volume induces the release of a low-molecular-weight natriuretic and sodium-potassium-activated adenosine triphosphatase inhibiting hormone (NKAI). In this study, we used a highly purified hormone extracted from pooled hypertensive urines (u-NKAI). Like ouabain, this compound was found to be a potent inhibitor of the sodium-potassium-activated adenosine-triphosphatase and potassium-stimulated paranitrophenyl phosphatase enzyme systems as well as a vasoconstrictor in vitro. In contrast to ouabain, which is a competitive inhibitor of both enzyme systems with respect to potassium, u-NKAI is noncompetitive. Furthermore, u-NKAI differs from ouabain by its lack of cross-reactivity with digoxin antibodies. In addition, whereas ouabain binds to both high-affinity and low-affinity binding sites on the sodium-potassium-activated adenosine-triphosphatase enzyme in the absence of potassium, u-NKAI binds only to the low-affinity binding sites. This study demonstrates that the highly purified u-NKAI, although ouabain-like in certain respects, is not an "endogenous ouabain."
已经证明细胞外液量的增加会诱导一种低分子量利钠和抑制钠钾激活的三磷酸腺苷酶的激素（NKAI）的释放。在本研究中，我们使用了从合并的高血压患者尿液中提取的高度纯化的激素（u-NKAI）。与哇巴因一样，该化合物被发现是钠钾激活的三磷酸腺苷酶和钾刺激的对硝基苯磷酸酶系统的有效抑制剂，并且在体外是一种血管收缩剂。与哇巴因不同，哇巴因在钾方面是这两种酶系统的竞争性抑制剂，而u-NKAI是非竞争性的。此外，u-NKAI与哇巴因的不同之处在于它与地高辛抗体缺乏交叉反应性。另外，在没有钾的情况下，哇巴因会与钠钾激活的三磷酸腺苷酶上的高亲和力和低亲和力结合位点结合，而u-NKAI只与低亲和力结合位点结合。这项研究表明，高度纯化的u-NKAI虽然在某些方面与哇巴因相似，但不是“内源性哇巴因”。
