Butler V P, Morris J F, Akizawa T, Matsukawa M, Keating P, Hardart A, Furman I
Department of Medicine, Columbia University College of Physicians & Surgeons, New York, New York 10032, USA.
Am J Physiol. 1996 Aug;271(2 Pt 2):R325-32. doi: 10.1152/ajpregu.1996.271.2.R325.
Three major groups of endogenous digitalis-like substances (EDLS) have been identified in the plasma of the toad, Bufo marinus. One group of compounds, present in fresh plasma, is composed of chromatographically homogeneous polar conjugates, principally bufadienolide 3-sulfates, which exhibit relatively weak Na(+)-K(+)-adenosinetriphosphatase (ATPase) inhibitory activity. A second and larger group of compounds, also found in fresh plasma, includes chromatographically heterogeneous conjugates, which are effective inhibitors of Na(+)-K(+)-ATPase; these compounds possess properties similar to those of bufotoxins. The third group of EDLS consists of free unconjugated bufadienolides, which are also effective Na(+)-K(+)-ATPase inhibitors. These unconjugated bufadienolides are present in relatively low concentrations in fresh toad plasma, but appreciable quantities are enzymatically generated from conjugates (believed to consist principally of bufotoxins) during the in vitro incubation of plasma. We suggest that the extent to which circulating polar EDLS are enzymatically deconjugated in vivo may be important in the regulation of the digitalis-sensitive Na(+)-K(+)-ATPase of toad brain, the only known digitalis-sensitive Na(+)-K(+)-ATPase in the toad.
在海蟾蜍（Bufo marinus）的血浆中已鉴定出三类主要的内源性洋地黄样物质（EDLS）。一类存在于新鲜血浆中的化合物，由色谱纯的极性共轭物组成，主要是蟾蜍二烯羟酸内酯3 - 硫酸盐，它们表现出相对较弱的钠钾腺苷三磷酸酶（ATP酶）抑制活性。在新鲜血浆中还发现的第二类且数量更多的化合物，包括色谱异质共轭物，它们是钠钾ATP酶的有效抑制剂；这些化合物具有与蟾毒素相似的性质。第三类EDLS由游离的非共轭蟾蜍二烯羟酸内酯组成，它们也是有效的钠钾ATP酶抑制剂。这些非共轭蟾蜍二烯羟酸内酯在新鲜蟾蜍血浆中的浓度相对较低，但在血浆体外孵育过程中，会从共轭物（据信主要由蟾毒素组成）中酶促生成可观的量。我们认为，循环中的极性EDLS在体内被酶促去共轭的程度，可能对蟾蜍脑中对洋地黄敏感的钠钾ATP酶（蟾蜍中唯一已知的对洋地黄敏感的钠钾ATP酶）的调节很重要。
