Structural analysis of endogenous digitalis and studies on the role of it in electrolytes and blood pressure control. In particular, studies on a novel substance, marinobufagenin with double hydrogen.

海蟾毒配基（MBG）和端蟾毒配基（TCB）对钠钾腺苷三磷酸酶（Na，K-ATPase）的抑制作用强于哇巴因。我们发现这些蟾蜍二烯内酯在人体血液中循环，通过使用多个步骤的液相色谱（LC）和质谱（LC/MS），核磁共振（NMR）分析结构。TCB比MBG多两个氢原子，血药浓度几乎是MBG的2倍，两者之间有高度相关性。由于TCB的浓度远高于MBG，因此认为TCB是洋地黄的主要内源性成分。这是第一份报告，以显示在哺乳动物样品中存在的TCB。此外，比较了正常受试者和终末期肾衰竭患者的浓度，患者血浆中的浓度几乎是正常受试者的两倍。因此，TCB和MBG可能都是电解质的生理调节剂，从而调节血压。因此，我们制备了TCB的单克隆抗体，但不幸的是，它也与MBG交叉反应，并建立了酶联免疫吸附测定法（ELISA）。由于该ELISA系统受血浆成分的干扰，仅适用于尿液样品的测定。用该酶联免疫吸附试验检测了钠负荷对大鼠的影响，发现高盐饮食大鼠的TCB/MBG排泄量高于正常饮食大鼠。

Inhibition of sodium-potassium adenosine triphosphatase (Na,K-ATPase) by marinobufagenin (MBG) or telocinobufagin (TCB) are more potent than that of ouabain. We found that those bufadienolides are circulating in human blood, upon analyzing the structure by using multiple steps of liquid chromatography (LC) and mass-spectrometry (LC/MS), nuclear magnetic resonance (NMR). TCB has two more hydrogen than MBG.Plasma concentration of TCB was almost double of MBG, the correlation among them was highly significant. Therefore, we thought that the TCB is hydrolysed to MBG.Since the concentration of TCB is much higher than MBG, TCB was thought to be the cardinal endogenous digitalis. This is the first report to show the existence of TCB in mammalian samples. Furthermore, the concentration was compared in normal subjects and patients with terminal renal failure, and it was almost twice higher in the patient plasma as compared to it in normal subjects. Therefore, both TCB and MBG may be functioning as the physiological regulator of electrolytes and consequently blood pressure.Then, we made monoclonal antibody for TCB, but unfortunately it cross-reacted with MBG too, and enzyme-linked immunosorbent assay (ELISA) was developed. Because this ELISA system was interfered with constituents of plasma, it was useful only for measurement of urine samples. By using this ELISA, effects of sodium-loading was tested in rats, we found that rats with high salt diet excreted more TCB/MBG than in rats with normal diet.