Effects of KC 2450 on the lower esophageal sphincter in vivo and in vitro

Abstract

The effect of KC 2450 (racemic 3,5-cis-3-methylamino-2,3,4,5-tetrahydro-1-benzoxepine-5-ol hydrochloride) on lower esophageal sphincter pressure in pentobarbital-anesthetized dogs was determined and compared to the effect of metoclopramide. The ED 20 value (i.e. the dose that increased lower esophageal sphincter pressure 20 mm Hg) was 0.72 (0.45–1.04) mg/kg i.v. for KC 2450, significantly different from 2.18 (1.30–3.42) mg/kg i.v. for metoclopramide (P<0.01). The superior potency of KC 2450 over metoclopramide also was demonstrated at a dose of 2 mg/kg i.v.; KC 2450 produced an increase in sphincter pressure of 43.2±4.4 mm Hg and metoclopramide produced an increase in sphincter pressure of only 28.5±5.4 mm Hg (P<0.05). Intraduodenally administered KC 2450 increased lower esophageal sphincter pressure at a threshold dose of 2 mg/kg with 10 mg/kg producing an increase in pressure of 53.2±9.9 mm Hg. KC 2450-induced increases in sphincter pressure were not affected by bilateral cervical vagotomy or ketanserin, but were eliminated by atropine and reduced by neuronal blockade using tetrodotoxin (TTX). KC 2450 effects also were determined in isolated circular strips of lower esophageal sphincter muscle. KC 2450 produced a concentration-related increase in canine (EC 50 = 27 μM) and opossum (EC 50 = 199 μM) sphincter muscle strip tension . The KC 2450 concentration-response curve was antagonized by atropine in canine and opossum sphincter muscle strips. Neuronal blockade of canine sphincter muscle with TTX antagonized the KC 2450 concentration-response curve in a non-competitive manner. In addition, in competitive binding experiments KC 2450 demonstrated equal affinity with acetylcholine for muscarinic receptor binding sites (IC 50 = 29 vs. 28 μM, respectively) and had no affinity for serotonin receptor binding sites. These in vivo and in vitro studies indicate that KC 2450 is a peripherally acting agent that produces direct muscle and enteric neuronal excitatory muscarinic effects on the lower esophageal sphincter.