Heterogeneity and lability of endogenous digitalis-like substances
in the plasma of the toad, bufo marinus.
Butler, Vincent P, Jr., Jennifer F Morris, Toshifumi Akizawa, Motomi
Matsukawa, Paula Keating, Ann Hardart, and Inna Furman.
Department of Medicine, Columbia University, College of Physicians
& Surgeons, New York NY 10032 and the Department of Analytical
Chemistry, Pharmaceutical Sciences, Setsunan University, Osaka 573
-01, Japan
APStracts 3:0057R, 1996.
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+-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.
Received 31 January 1995; accepted in final form 11 February
1996.
APS Manuscript Number R78-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 13 March 96