AJP - Gastrointestinal and Liver Physiology, Vol 251, Issue 3 405-G412, Copyright © 1986 by American Physiological Society
Adrenergic agents stimulate and cholinergic agents inhibit H+ secretion by amphibian jejunum
J. F. White and R. Britanisky
In vitro segments of Amphiuma jejunum secrete H+ spontaneously. This study
explored the effect of cholinergic and adrenergic agents on H+ secretion.
Segments of mucosa were short-circuited and exposed on their mucosal
surface to HCO3- -buffered medium while the pH of the unbuffered serosal
medium was held by the pH-stat technique. Methacholine added to the serosal
medium nearly abolished the spontaneous short-circuit current (Isc) and
serosal alkalinization (JHCO3-) with an EC50 of 3.7 X 10(-7) M. Subsequent
addition of norepinephrine (NE) to the serosal medium caused a
dose-dependent increase in Isc and JHCO3. For three catecholamines the
order of potency was epinephrine greater than NE greater than
isoproterenol. The spontaneous Isc was significantly reduced (P less than
0.05) by the gastric H+-K+-ATPase inhibitor omeprazole, while the
NE-induced Isc was unaltered by the inhibitor. Replacement of medium Na+
with choline abolished the response to NE. The NE-induced Isc was also
reduced by methacholine. Acetazolamide inhibited the spontaneous and
NE-induced Isc and JHCO3. In summary, cholinergic and adrenergic agents
have opposing effects on intestinal H+-HCO3- transport. Jejunal acid
secretion may be controlled in part by these antagonistic influences.
Adrenergically activated acid secretion occurs by a different mechanism
than spontaneous acid secretion.
