AJP - Renal Physiology, Vol 249, Issue 6 923-F932, Copyright © 1985 by American Physiological Society
Binding of aldosterone metabolites in isolated tubular segments
N. Farman, P. Pradelles and J. P. Bonvalet
High-performance liquid chromatography (HPLC) analysis was performed on
tissue extracts from whole kidney cortex (after in vivo injection or in
vitro incubation with [3H]-aldosterone ([3H]A], from products bound to
aldosterone receptors in cytoplasmic and nuclear fractions, and from the
convoluted (PCT) and straight (PR) portion of the proximal tubule and
cortical collecting tubule (CCT) isolated by micro-dissection after in
vitro incubation with [3H]A (10 and 80 nM). After in vitro incubation of
whole tissue, about 10% of the radioactivity corresponded to three groups
of metabolites, two polar ones, which eluted earlier than aldosterone, and
one less polar, which eluted later than aldosterone. When HPLC analysis was
performed on bound products, after removal of free [3H]A, only one group of
polar metabolites was detected (about 8% of the radioactivity) in addition
to native [3H]A in the cytoplasmic and nuclear fractions. The binding of
polar metabolites was nonspecific (nondisplaceable) and did not vary with
incubation time and aldosterone concentration. In isolated tubules, in
addition to [3H]A, an early peak of polar metabolites, corresponding to
that observed in bound fractions, was present in PCT (10%) and in PR and
CCT (20-25%). Other metabolites were not found in isolated tubules. We
conclude the following: 1) The kidney is able to form at least three groups
of aldosterone metabolites in small amounts. 2) Only one of them (more
polar) was detected, as a nonspecifically bound product, in cellular
fractions containing hormone-receptor complexes after removal of free
[3H]A. Other metabolites were removed with free [3H]A. 3) These polar
metabolites were found in both mineralocorticoid target segments such as
CCT and in classically nontarget segments such as the proximal tubule. 4)
The nonspecificity of the binding of polar metabolites and the absence of
selective localization along the nephron suggest that they have no major
mineralocorticoid action.
