AJP - Gastrointestinal and Liver Physiology, Vol 255, Issue 5 640-G646, Copyright © 1988 by American Physiological Society
Alpha 2-receptors mediate catecholamine-stimulated acid secretion in Amphiuma jejunum
C. F. Hinton and J. F. White
Department of Physiology, Emory University, Atlanta, Georgia 30322.
The receptors mediating adrenergic stimulation of acid secretion by
Amphiuma jejunum were characterized in this study using alpha- and
beta-adrenergic agonists and antagonists. Isolated segments of jejunum were
mounted in Ussing chambers and bathed in Cl- -free (SO4(2-] medium.
Shortcircuit current (Isc) and acid secretion (JH) were recorded, the
latter by measuring the rate of alkalinization of the serosal medium. The
beta-adrenergic receptor antagonist, propranolol (10(-4) M), had no effect
on the Isc and JH stimulated by norepinephrine (NE). The alpha 2-adrenergic
agonists, clonidine and UK-14,304, mimicked the effect of NE, with
effective concentrations providing 50% maximal delta Isc of 2.0 X 10(-7)
and 9.0 X 10(-8) M, respectively. NE added subsequently produced no greater
stimulation. In contrast, the alpha 1-adrenergic agonists, phenylephrine
and methoxamine, produced little stimulation of JH and Isc; NE added
subsequently stimulated the Isc. The alpha 1-adrenergic antagonist prazosin
had no effect on the NE-induced Isc or JH, whereas the alpha 2-adrenergic
antagonist yohimbine inhibited the NE-stimulated Isc with a half-maximal
effective concentration of 3.5 X 10(-7) M. Yohimbine (10(-4) M) reduced the
NE-stimulated Isc by 88%, whereas the spontaneous Isc was reduced by only
12%. These results demonstrate that alpha 2-adrenergic receptors on the
basolateral membrane of Amphiuma enterocytes mediate NE-enhanced, but not
spontaneous, intestinal acid secretion.
