title: Heterogeneity and lability of endogenous digitalis-like substances in the plasma of the toad, Bufo marinus.
abstract: 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.
authors.affiliation: Department of Medicine, Columbia University College of Physicians & Surgeons, New York, New York 10032, USA.
authors.forename: V P
authors.initials: VP
authors.lastname: Butler
authors.forename: J F
authors.initials: JF
authors.lastname: Morris
authors.forename: T
authors.initials: T
authors.lastname: Akizawa
authors.forename: M
authors.initials: M
authors.lastname: Matsukawa
authors.forename: P
authors.initials: P
authors.lastname: Keating
authors.forename: A
authors.initials: A
authors.lastname: Hardart
authors.forename: I
authors.initials: I
authors.lastname: Furman
mesh_terms: D000818:Animals; D002018:Bufanolides / Q000097:blood / Q000737:chemistry; D002024:Bufo marinus / Q000097:blood*; D002298:Cardenolides; D002851:Chromatography, High Pressure Liquid; D004077:Digoxin; D004355:Drug Stability; D004791:Enzyme Inhibitors / Q000097:blood*; D005260:Female; D012503:Saponins / Q000097:blood* / Q000737:chemistry; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors
chemical_list: D002018:Bufanolides; D002298:Cardenolides; D004791:Enzyme Inhibitors; D012503:Saponins; C034504:digoxin-like factors; D004077:Digoxin; D000254:Sodium-Potassium-Exchanging ATPase