Prevention of ethanol-induced gastric damage by the imidazobenzodiazepines Ro 15-4513 and Ro 15-3505 in rats

Drugs acting at the GABAA receptor attenuate ethanol-induced gastric mucosal damage in vitro

1. Benzodiazepines (BZ) have been reported to protect against ethanol-induced gastric damage in rats in both in vivo and in vitro models. However, the effects of some drugs in the new in vitro model do not agree with results reported previously in in vivo studies. 2. Therefore, the aim of the present study was to modify the new in vitro model to a model that more closely resembles the in vivo model and, using the new in vitro model, to reassess the gastroprotective effects of some BZ and to assess the effects of some new compounds. 3. The rat stomach was isolated from the whole animal and kept in aerated Krebs' solution at 37 degrees C in an organ bath. Gastric mucosal damage was induced by instillation of 1 mL of 100% ethanol into the stomach. Drugs or their vehicle were administered inside the bath 15 min before ethanol instillation into the stomach. One hour after the instillation of ethanol, the stomach was removed from the organ bath, opened along the greater curvature and then examined for gastric mucosal damage. 4. The results indicate that, compared with vehicle pretreatment, ethanol-induced gastric mucosal damage was significantly reduced in a dose-dependent manner by pretreatment with clonazepam, a drug that acts as an agonist at central BZ sites of the GABAA receptor, and Ro 15-4513, a partial inverse agonist at BZ sites of the GABAA receptor. Flumazenil (an antagonist of central BZ sites of the GABAA receptor) did not affect gastric mucosal lesions provoked by ethanol. However, flumazenil significantly reversed the mucosal protective effects of clonazepam and Ro 15-4513. 5. CGS 9896 (a partial agonist at BZ sites of the GABAA receptor, with anxiolytic and anticonvulsant but no sedative effects) did not offer any protection against ethanol-induced gastric mucosal damage. Ro 5-3663, an atypical BZ that binds to the picrotoxin site of the GABAA receptor and reported to be a potent convulsant and only a weak antagonist of GABA, did not show any protection against the development of lesions. 6. The results suggest local gastric mediation of the effects of ethanol, as well as the gastric protective effects of BZ, through an action at local central-type BZ sites of the GABAA receptor located in the rat stomach.

Benzodiazepines protect against ethanol-induced gastric mucosal damage in vitro

The protective effects of drugs acting at the benzodiazepine receptors against ethanol-induced gastric damage were investigated using a newly developed in vitro model of the ethanol-induced gastric damage. The rat stomachs were isolated from the whole animal and kept in Kreb's solution at 37 degrees C. Gastric damage was induced by administration of 1 mL of 50% V/V ethanol into the isolated rat stomach. Administration of the benzodiazepine agonist, clonazepam (25, 50, 100 microg), or the partial benzodiazepine inverse agonist Ro15-4513 (50 or 100 microg), significantly protected against ethanol-induced gastric damage when these agents were administered 15 min before ethanol. The protective effects of these drugs were blocked by the benzodiazepine receptor antagonist flumazenil (200-400 microg). Flumazenil alone was found to aggravate ethanol-induced gastric damage (200-400 microg). The results of this study give evidence for the involvement of central-type benzodiazepine receptors located in the stomach in the protective action of benzodiazepines against ethanol-induced gastric damage.

A new in vitro model for ethanol-induced gastric mucosal damage

A new in vitro model for ethanol-induced gastric damage is described. The stomach was dissected from the rat, a polyethylene cannula introduced into the remnants of the esophagus, and the pyloric end tied off. With the cardiac and pyloric regions of the stomach secured by thread to a vertical glass rod or tube, the whole was suspended in an organ bath containing aerated Krebs solution. Fifteen minutes later, ethanol was introduced via the esophageal cannula. After an additional 60 min, the stomach was removed from the Krebs solution, opened along the mid line, and the lesions studied. Comparisons were made with a conventional in vivo model. Results show that the lesion number, length, and total lesion area obtained by the in vitro model were comparable to those obtained in the older in vivo model. Histopathologically, lesions induced by both models were also comparable. Clonazepam, a drug previously used in the in vivo model, was tested in this model. Results indicate that clonazpam protected against ethanol-induced gastric damage in vitro. The new model provides a method to study the action of drugs on the stomach alone and to exclude in indirect actions of drugs via other sites in the body.

Ro 15-4513 potentiates, instead of antagonizes, ethanol-induced sleep in mice exposed to small platform stress

The effects of ethanol and the benzodiazepine receptor ligand ethyl-8-azido-5,6-dihydro-5-methyl-6-oxo-4H-imidazo-[1,5a] [1,4] benzodiazepine-3-carboxylate (Ro 15-4513), were examined in NMRI mice exposed to small platform stress. This model contains several factors of stress, like rapid eye movement (REM) sleep deprivation, isolation, immobilization, falling into water and soaking. In control mice, ethanol exerted an anxiolytic effect in the plus-maze, but did not further enhance the anxiolytic-like effects induced by small platform stress. Ro 15-4513 antagonized ethanol-induced sleep in control animals, but enhanced the hypnotic and lethal actions of ethanol in small platform stressed mice. Small platform stress did not alter the characteristics (KD and Bmax) of [3H]Ro 15-4513 binding to cerebellar membranes. Muscimol-stimulated 36Cl- uptake into brain microsacs was significantly reduced in cortex from small platform stressed animals. Ethanol had no effect on 36Cl- uptake into brain microsacs from cortex or cerebellum. It is proposed that small platform stress alters the activity of the gamma-aminobutyric acid (GABA)A receptor-chloride ionophore complex, causing changes in the interaction between ethanol and Ro 15-4513.

Drugs acting at central benzodiazepine receptors attenuate ethanol-induced gastric lesions in rats

The characteristics of the receptors involved in the protective action of benzodiazepines against ethanol-induced gastric lesions were investigated by studying the effect of benzodiazepine ligands on such lesions in both intact and unilaterally vagotomized rats. Clonazepam [5-(2-chlorophenyl)-1,3-dihydro-7-nitro-2H-1,4-benzodiazepine-2-one] a specific central-type receptor agonist (0.625-2.5 mg/kg p.o. or i.p.) and CGS 9896 [2-(4-chlorophenyl)-2,5-dihydropyrazolo(4,3-c)quinoline-3(3H)-one] a non-sedative partial agonist with anxiolytic properties (2.5-10 mg/kg p.o.) significantly reduced the gastric damage induced by ethanol (10 ml/kg of a 50% solution v/v p.o.) in non-vagotomized rats but Ro 5-4864 [7-chloro-5-(4-chlorophenyl)-1,3-dihydro-1-methyl-2H-1,4-benzodiazepine- 2 -one] a pure peripheral-type receptor agonist (5-20 mg/kg p.o.) failed to affect this damage. The protective action of clonazepam and CGS 9896 against ethanol-induced gastric lesions was blocked, dose dependently, by the central-type receptor antagonist, flumazenil [ethyl 8-fluoro-5,6-5-methyl-6-oxo-4H-imidazo(1,4)f1p4odiazepine-3-carbox ylate] (1.25-20 mg/kg i.p.). In the unilaterally vagotomized rat, ethanol produced lesions in the right (vagotomized) and the left (non-vagotomized) halves of the gastric mucosa to nearly the same extent, while clonazepam and CGS 9896 uniformly decreased the lesions in both halves. It is concluded that central-type benzodiazepine receptors located in the stomach, specifically those mediating the anxiolytic effect of benzodiazepines, are involved in the protective action of benzodiazepines against ethanol-induced gastric lesions.