AJP - Renal Physiology, Vol 248, Issue 4 507-F512, Copyright © 1985 by American Physiological Society
Evidence that aldosterone influences transport in target tissues by dissimilar mechanisms
D. Hirsch, P. Pace, H. J. Binder and J. P. Hayslett
The present study was performed to answer the question: Is the action of
aldosterone on electrolyte transport and electrical properties similar in
all target tissues? Studies were performed in vivo in control animals and
rats with secondary hyperaldosteronism, caused by a sodium-free diet, to
compare the effects of hyperaldosteronism on distal colon with
hormone-induced changes in proximal colon. In distal colon aldosterone
increased net sodium absorption and potassium secretion approximately
threefold. Transmural potential difference increased from -15 +/- 2 to -83
+/- 3 mV (lumen negative) and ISC rose from 167 +/- 26 to 1,023 +/- 17
microA X cm-2. These aldosterone-induced responses were completely
inhibited by 0.1 mM amiloride. In contrast, in proximal colon potential
difference was unchanged or increased slightly in experimental animals and
ISC increased only 28% above control, although increases in net sodium and
potassium transport were similar to changes observed in distal colon.
Amiloride did not reduce sodium absorption in proximal colon of animals
with hyperaldosteronism; ISC was decreased by 43%. These studies
demonstrate that rat proximal colon is an aldosterone-sensitive tissue, but
that the mechanism by which aldosterone influences sodium transport is not
identical in distal and proximal portions of colon.
