RT Journal Article
SR Electronic
T1 Chronic ethanol feeding produces a muscarinic receptor upregulation, but not a muscarinic supersensitivity in lower esophageal sphincter muscle.
JF Journal of Pharmacology and Experimental Therapeutics
JO J Pharmacol Exp Ther
FD American Society for Pharmacology and Experimental Therapeutics
SP 601
OP 607
VO 260
IS 2
A1 A Keshavarzian
A1 J H Gordon
A1 C Willson
A1 G Urban
A1 J Z Fields
YR 1992
UL http://jpet.aspetjournals.org/content/260/2/601.abstract
AB Muscarinic acetylcholine receptors (mAChR) are important in esophageal physiology, and mAChR alterations may be involved in ethanol-induced esophageal dysfunction. We previously demonstrated that acute ethanol decreases lower esophageal sphincter pressure (LESP), whereas withdrawal from chronic ethanol results in pressure increases which are reversible by acute ethanol. To see if this increase in LESP is due to upregulation of mAChR, we evaluated both mAChR binding and dose-response curves for bethanechol and atropine-induced changes in LESP before and after acute and chronic ethanol exposure. The number of mAChR sites (Bmax) in LES (3.4 fmol/mg tissue) was lowered by acute ethanol (1.72, -50%); withdrawal from chronic ethanol raised Bmax (5.2, +54%). Acute injection of ethanol into cats in withdrawal reversed this increase in mAChR density (3.1, -10%). These changes correlated with our earlier data on ethanol-induced changes in LESP. However, the dose-response curve for bethanechol-induced pressure increases shifted to the right [ED25 (micrograms/kg); control, 8.6; withdrawal, 21.3], paralleled by an increase in the number of low-affinity agonist binding sites. Thus, 1) the withdrawal-associated increase in Bmax (up-regulation) is more likely to be a compensatory response to deficits (functional subsensitivity) distal to the receptor recognition site than to proximal deficits; 2) the increase in Bmax does not cause LESP hyperactivity; and 3) receptor binding changes do not necessarily translate into physiological changes.