The contribution of the stomach to ethanol oxidation in the rat

Overview of the role of alcohol dehydrogenase and aldehyde dehydrogenase and their variants in the genesis of alcohol-related pathology

Alcohol dehydrogenase (ADH) and mitochondrial aldehyde dehydrogenase (ALDH2) are responsible for metabolizing the bulk of ethanol consumed as part of the diet and their activities contribute to the rate of ethanol elimination from the blood. They are expressed at highest levels in liver, but at lower levels in many tissues. This pathway probably evolved as a detoxification mechanism for environmental alcohols. However, with the consumption of large amounts of ethanol, the oxidation of ethanol can become a major energy source and, particularly in the liver, interferes with the metabolism of other nutrients. Polymorphic variants of the genes for these enzymes encode enzymes with altered kinetic properties. The pathophysiological effects of these variants may be mediated by accumulation of acetaldehyde; high-activity ADH variants are predicted to increase the rate of acetaldehyde generation, while the low-activity ALDH2 variant is associated with an inability to metabolize this compound. The effects of acetaldehyde may be expressed either in the cells generating it, or by delivery of acetaldehyde to various tissues by the bloodstream or even saliva. Inheritance of the high-activity ADH β2, encoded by theADH2*2gene, and the inactiveALDH2*2gene product have been conclusively associated with reduced risk of alcoholism. This association is influenced by gene–environment interactions, such as religion and national origin. The variants have also been studied for association with alcoholic liver disease, cancer, fetal alcohol syndrome, CVD, gout, asthma and clearance of xenobiotics. The strongest correlations found to date have been those between theALDH2*2allele and cancers of the oro-pharynx and oesophagus. It will be important to replicate other interesting associations between these variants and other cancers and heart disease, and to determine the biochemical mechanisms underlying the associations.

Expression, localization and potential physiological significance of alcohol dehydrogenase in the gastrointestinal tract

ADH1 and ADH4 are the major alcohol dehydrogenases (ADH) in ethanol and retinol oxidation. ADH activity and protein expression were investigated in rat gastrointestinal tissue homogenates by enzymatic and Western blot analyses. In addition, sections of adult rat gastrointestinal tract were examined by in situ hybridization and immunohistochemistry. ADH1 and ADH4 were detected along the whole tract, changing their localization and relative content as a function of the area studied. While ADH4 was more abundant in the upper (esophagus and stomach) and lower (colorectal) regions, ADH1 was predominant in the intestine but also present in stomach. Both enzymes were detected in mucosa but, in general, ADH4 was found in outer cell layers, lining the lumen, while ADH1 was detected in the inner cell layers. Of interest were the sharp discontinuities in the expression found in the pyloric region (ADH1) and the gastroduodenal junction (ADH4), reflecting functional changes. The precise localization of ADH in the gut reveals the cell types where active alcohol oxidation occurs during ethanol ingestion, providing a molecular basis for the gastrointestinal alcohol pathology. Localization of ADH, acting as retinol dehydrogenase/retinal reductase, also indicates sites of active retinoid metabolism in the gut, essential for mucosa function and vitamin A absorption.

Effect of Helicobacter pylori infection on the activity of class I, III and IV alcohol dehydrogenase in the human stomach

BACKGROUND/AIMS

In the human stomach various alcohol dehydrogenase (ADH) isoenzymes exist. The gastric ADH activity is affected by a number of factors including also the infection of Helicobacter pylori. The objective was to investigate the activity of alcohol dehydrogenase isoenzymes of class I, III and IV in endoscopic specimens of gastric mucosa from the different parts of the stomach of men and women, considering the H. pylori infection.

METHOD

Biopsy samples of gastric mucosa were taken from the corpus and antrum of 68 patients (42 of men and 26 of women) suspected for gastric ulcer. The colonization of H. pylori was present in 22 samples of men and 13 samples of women. The activity of class I isoenzyme was measured by the fluorimetric method with a specific substrate (4-methoxy-1-naphthaldehyde) and the activity of class III and IV by the photometric method with n-octanol and m-nitrobenzaldehyde as a substrates, respectively.

RESULTS

In infected samples from the antrum and corpus of men's and women's stomachs the activity of class IV isoenzyme was decreased as compared to non-infected specimens. The activity of class III isoenzyme was decreased in the infected samples from the corpus of male patients, but the activity of class I does not significantly differ between infected and noninfected specimens from both sexes.

CONCLUSION

H. pylori infection leads to significant decrease in the activity of class IV ADH in the stomach of men and women.

Enhanced intracellular calcium promotes metabolic and secretory disturbances in rat gastric mucosa during ethanol-induced gastritis

Changes in the Ca(2+) homeostasis have been implicated in cell injury and death. However, Ca(2+) participation in ethanol-induced chronic gastric mucosal injury has not been elucidated. We have developed a model of ethanol-induced chronic gastric injury in rats, characterized by marked alterations in plasma membranes from gastric mucosa and a compensatory cell proliferation, which follows ethanol withdrawal. Therefore, the present study explored the possible role of intracellular Ca(2+) in the oxidative metabolism and in acid secretion in this experimental model. Glucose oxidation was greatly enhanced in the injured mucosa, as evaluated by CO(2) production by isolated mucosal preparations incubated with (14)C-radiolabeled glucose in different carbons. Oxygen consumption and acid secretion (aminopyrine accumulation) were also stimulated. A predominating secretory status was morphologically identified by electron microscopy in oxyntic cells of gastric mucosa from ethanol-treated rats. A coupling between secretory and metabolic effects induced by ethanol (demonstrated by an inhibitory effect of omeprazole in both parameters) was found. These ethanol-induced effects were also inhibited by addition of Ca(2+) chelators to isolated gastric mucosa samples. Lanthanum, a Ca(2+) channel blocker, inhibited ethanol-promoted increase of oxidative metabolism. In addition, a stimulated Ca(2+) uptake by mucosal minces and increased in vivo Ca(2+) levels in cytosolic and mitochondrial fractions, were also noticed. Enhanced glucose and oxygen consumptions were associated with higher ATP and NADP+ availability, whereas cytosolic NAD/NADH ratio (assessed by mucosal levels of lactate and pyruvate) was not significantly modified by the chronic ethanol administration. In conclusion, changes in Ca(2+) homeostasis, probably mainly due to increased extracellular Ca(2+) uptake, could mediate secretory and metabolic alterations found in the gastric mucosa from rats chronically treated with ethanol.

Alcohol metabolism: role in toxicity and carcinogenesis

This article contains the proceedings of a symposium at the 2002 RSA Meeting in San Francisco, organized and co-chaired by Thomas M. Badger, Paul Shih-Jiun Yin, and Helmut Seitz. The presentations were (1) First-pass metabolism of ethanol: Basic and clinical aspects, by Charles Lieber; (2) Intracellular CYP2E1 transport, oxidative stress, cytokine release, and ALD, by Magnus Ingelman-Sundberg; (3) Pulsatile ethanol metabolism in intragastric infusion models: Potential role in toxic outcomes, by Thomas M. Badger and Martin J.J. Ronis; (4) Free radicals, adducts, and autoantibodies resulting from ethanol metabolism: Role in ethanol-associated toxicity, by Emanuele Albano; and (5) Gastrointestinal metabolism of ethanol and its possible role in carcinogenesis, by Helmut Seitz.

ALCOHOL: its metabolism and interaction with nutrients

In the past, alcoholic liver disease was attributed exclusively to dietary deficiencies, but experimental and judicious clinical studies have now established alcohol's hepatotoxicity. Despite an adequate diet, it can contribute to the entire spectrum of liver diseases, mainly by generating oxidative stress through its microsomal metabolism via cytochrome P4502E1 (CYP2E1). It also interferes with nutrient activation, resulting in changes in nutritional requirements. This is exemplified by methionine, one of the essential amino acids for humans, which needs to be activated to S-adenosylmethionine (SAMe), a process impaired by liver disease. Thus, SAMe rather than methionine is the compound that must be supplemented in the presence of significant liver disease. In baboons, SAMe attenuated mitochondrial lesions and replenished glutathione; it also significantly reduced mortality in patients with Child A or B cirrhosis. Similarly, decreased phosphatidylethanolamine methyltransferase activity is associated with alcoholic liver disease, resulting in phosphatidylcholine depletion and serious consequences for the integrity of membranes. This can be offset by polyenylphosphatidylcholine (PPC), a mixture of polyunsaturated phosphatidylcholines comprising dilinoleoylphosphatidylcholine (DLPC), which has high bioavailability. PPC (and DLPC) opposes major toxic effects of alcohol, with down-regulation of CYP2E1 and reduction of oxidative stress, deactivation of hepatic stellate cells, and increased collagenase activity, which in baboons, results in prevention of ethanol-induced septal fibrosis and cirrhosis. Corresponding clinical trials are ongoing.

Gastritis in the alcoholic: relationship to gastric alcohol metabolism and Helicobacter pylori

Chronic gastritis is common in the alcoholic. It is characterized by histological inflammation of the gastric mucosa and is associated with variable symptomatology. Its etiology is still the subject of debate. Recently, a new alcohol dehydrogenase isoenzyme, called sigma ADH, absent from the liver but predominant in the upper GI tract, has been fully characterized, its gene cloned, and it appears to play a major role in gastric ethanol metabolism. Indeed, it has now been established, both in vivo in experimental animals and in vitro in cultured human gastric cells, that alcohol is metabolized in the gastric mucosa, resulting in the production of acetaldehyde, a toxic metabolite. In addition, Helicobacter pylori infection is common in the alcoholic, resulting in the breakdown of urea to ammonia, another toxic product. A number of studies carried out over the last 40 years revealed that antibiotic treatment eradicates ammonia production and results in histological and symptomatic improvement in the majority of patients with alcoholic gastritis. Non-invasive tests for the detection of H. pylori are now available which will facilitate the large scale studies needed to confirm whether, in H. pylori -positive patients, antibiotics should become routine treatment for alcoholic gastritis.

Gastric ethanol metabolism and gastritis: interactions with other drugs, Helicobacter pylori, and antibiotic therapy (1957-1997)--a review

The stomach provides some protection against the penetration of ethanol into the body by contributing to the metabolism of ethanol. The latter is attenuated by various drugs and, although the magnitude of this effect is still the subject of debate, patients should be warned of the corresponding possible increase in blood alcohol levels. Furthermore, oxidation of ethanol generates acetaldehyde, a toxic metabolite. In addition, chronic alcohol abuse seems to favor colonization by Helicobacter pylori, which produces ammonia that also contributes to the commonly associated chronic gastritis. Because antibiotics were shown over the last 4 decades to effectively eliminate gastric ammonia, they should be considered for the routine treatment of such chronic gastritis in the way they are now being used for ulcer therapy.

First-pass metabolism of ethanol is negligible in rat gastric mucosa

Controversy exists concerning whether first-pass metabolism of imbibed ethanol occurs in the gastric mucosa or liver. We assessed ethanol metabolism in rat gastric mucosa by determining to what extent intact [14C]ethanol in body water plus hepatic metabolism could account for [14C]ethanol absorbed from the pylorus-ligated stomach. Intact [14C]ethanol in systemic body water accounted for 84 +/- 1.9% of the [14C]ethanol absorbed from the stomach over a 30-min period. Assuming a 15 ml/min hepatic blood flow, the predicted hepatic metabolism of [14C]ethanol over the 30 min of the study was 18% of the dose. The sum of intact [14C]ethanol and predicted hepatic metabolism accounted for 100% of the ethanol absorbed from the stomach. We conclude that negligible metabolism of ethanol occurred in the gastric mucosa.

Experimental liver fibrosis induced in rats receiving high doses of alcohol and alternating between regular and vitamin-depleted diets

Liver fibrosis was induced in rats by simulating human alcoholic eating and drinking patterns. Alcohol addiction was established by gradually increasing the ethanol concentration in the drinking water; salts were added at the terminal stage. The hepatocytes of rats receiving alcohol concentrations exceeding 50% (v/v) (similar to vodka) exhibited alcoholic hyaline (Mallory bodies). Alcoholic liver fibrosis was induced by alternating between regular and autoclaved (vitamin-depleted) diets, simulating the irregular eating habits of human alcoholics. In the livers of rats receiving 70% (v/v) ethanol (comparable to absinthe) with 25% saline and fed the alternating diets, pericellular fibrosis was induced. No significant difference in calorie intake between control and alcohol rats was detected except when rats underwent drinking bouts (heavy drinking phase). This indicates that neither a high-fat diet nor a choline-depleted diet is necessary to induce the alcoholic fibrosis seen in human alcoholics.

Aldehyde dehydrogenases of the rat colon: comparison with other tissues of the alimentary tract and the liver

Intracolonic bacteria have previously been shown to produce substantial amounts of acetaldehyde during ethanol oxidation, and it has been suggested that this acetaldehyde might be associated with alcohol-related colonic disorders, as well as other alcohol-induced organ injuries. The capacity of colonic mucosa to remove this bacterial acetaldehyde by aldehyde dehydrogenase (ALDH) is, however, poorly known. We therefore measured ALDH activities and determined ALDH isoenzyme profiles from different subcellular fractions of rat colonic mucosa. For comparison, hepatic, gastric, and small intestinal samples were studied similarly. Alcohol dehydrogenase (ADH) activities were also measured from all of these tissues. Rat colonic mucosa was found to possess detectable amounts of ALDH activity with both micromolar and millimolar acetaldehyde concentrations and in all subcellular fractions. The ALDH activities of colonic mucosa were, however, generally low when compared with the liver and stomach, and they also tended to be lower than in small intestine. Mitochondrial low K(m) ALDH2 and cytosolic ALDH with low K(m) for acetaldehyde were expressed in the colonic mucosa, whereas some cytosolic high K(m) isoenzymes found in the small intestine and stomach were not detectable in colonic samples. Cytosolic ADH activity corresponded well to ALDH activity in different tissues: in colonic mucosa, it was approximately 6 times lower than in the liver and about one-half of gastric ADH activity. ALDH activity of the colonic mucosa should, thus, be sufficient for the removal of acetaldehyde produced by colonic mucosal ADH during ethanol oxidation. It may, however, be insufficient for the removal of the acetaldehyde produced by intracolonic bacteria. This may lead to the accumulation of acetaldehyde in the colon and colonic mucosa after ingestion of ethanol that might, at least after chronic heavy alcohol consumption, contribute to the development of alcohol-related colonic morbidity, diarrhea, and cancer.

Diet composition, alcohol utilization, and dependence

Experiments were carried out in which a nutritionally balanced liquid diet previously used in this laboratory was modified as to total calorie content and high or low carbohydrate and fat concentration. Ethanol was added at 4.5% and 6.2% of diet weight and provided either 27% or 34-37% of total calories depending upon the changes in nutrient content. Measurements included 8-day food/calorie and ethanol consumption, plasma ethanol level, liver alcohol dehydrogenase (ADH) activity, and rate of audiogenic-induced withdrawal seizures. The original liquid diet with 4.5% ethanol was consumed in significantly lesser amounts than the alcohol-free diet, and essentially no body weight gain occurred, regardless if the major nonalcohol, nonprotein calorie source was fat or carbohydrate. When the calorie content of the diet was boosted through the addition of extra carbohydrate or fat (at the expense of water), appreciable weight gain was noted; in the case of the higher calorie diet boosted with more carbohydrate (maltodextrin) calories, growth was similar to that observed on the alcohol-free control diet. On this latter diet ethanol calories appeared to be utilized close to their theoretical value of 7 kcal/g. Blood alcohol levels were significantly higher on the lower calorie diets and were lowest on the high-calorie, high-carbohydrate, 4.5% ethanol diet. This diet also allowed for the lowest rate of withdrawal seizures despite an ethanol intake that was as high as on the lower calorie diets. Essentially, no differences were noted among ADH activities for the dietary treatments studied and thus, did not explain the differences observed among blood ethanol levels. When the alcohol concentration in the high-carbohydrate, high-calorie diet was raised to 6.2% from 4.5% to provide 34% of total calories, the rats responded by decreasing their food (and alcohol) intake to the same level as did the animals receiving a much lower calorie diet, but with 37% of caloric alcohol content. This suggests that at a diet alcohol concentration of 34-37%, one or more nutrient metabolites become limiting in the utilization of ethanol, resulting in food intake adjustments that maintain similar amounts of alcohol consumption.

Hepatic saturation mechanism of ethanol: application of mathematical models to ethanol outflow profiles in the perfused rat liver

The saturation mechanism of hepatic ethanol (EtOH) elimination was studied in the perfused rat liver. EtOH outflow profiles after the instantaneous administration of 3 (mg/ml) x 0.4(ml), 12 x 0.1, 24 x 0.1, and 3 x 0.1 mg (as a dose concentration x a volume) through the portal vein were analyzed by the statistical moment analysis and mathematical models (i.e., dispersion models). Results for 3 x 0.1 and 12 x 0.1 mg doses by moment analysis were similar. This demonstrated that the elimination exhibits linear kinetics. Recovery ratio and hepatic volume of distribution for 3 x 0.4 and 24 x 0.1 mg were larger than those for 3 x 0.1 and 12 x 0.1 mg doses and were similar. Kinetics after administration of 3 x 0.4 and 24 x 0.1 mg may be nonlinear. A difference in the relative dispersion (CV2) obtained by moment analysis between 3 x 0.4 and 24 x 0.1 mg doses indicated different properties of the nonlinear elimination kinetics. There were no differences in all the parameters in the one-compartment dispersion model between 3 x 0.4 and 24 x 0.1 mg doses. In the two-compartment dispersion model, there were differences in the blood volume (VB) and the forward partition rate constant (k12) between 3 x 0.4 and 24 x 0.1 mg (p < 0.05), whereas the elimination rate constant (k sigma) and the dispersion number values for these doses were similar. These findings demonstrated that there is difference in the no-equilibrium process between 3 x 0.4 and 24 x 0.1 mg doses. Therefore, we suggest that the continuous EtOH input into the liver causes the saturation of enzyme pathways and the change of the nonequilibrium process.

Metabolism of ethanol in rat gastric cells and its inhibition by cimetidine

BACKGROUND/AIMS

Several studies have shown that the stomach has sufficient alcohol dehydrogenase activity to metabolize a significant amount of alcohol and that cimetidine depresses this alcohol dehydrogenase activity. However, both gastric metabolism of ethanol and its inhibition by cimetidine remain controversial. Given the difficulty in assessing gastric metabolism of ethanol in vivo, this subject was investigated in vitro.

METHODS

Cultured rat gastric epithelial cells were incubated with 200 mmol/L [1-14C]ethanol for 90 minutes with and without cimetidine (0.1-1 mmol/L) or omeprazole (1 mmol/L). The quantity of ethanol oxidized by gastric cells was measured by the amount of acetate produced using ion exchange chromatography.

RESULTS

The majority of cells at confluency had typical features of mucous cells. The gastric cells metabolized significant amounts of ethanol, sufficient to account for in vivo first-pass metabolism of ethanol in rats. Cimetidine, but not omeprazole, reduced ethanol metabolism by 39.9% +/- 4.9% (P < 0.01), an inhibition comparable with that previously reported for first-pass metabolism in vivo.

CONCLUSIONS

Gastric cells in tissue culture are capable of significant ethanol oxidation, the in vitro rates are sufficient to account for first-pass metabolism of ethanol in vivo, and cimetidine inhibits ethanol metabolism in tissue culture, an effect that parallels its decrease of first-pass metabolism in vivo.

Daidzin, an antioxidant isoflavonoid, decreases blood alcohol levels and shortens sleep time induced by ethanol intoxication

The extract from an edible vine, Pueraria lebata, has been reported to be efficacious in lessening alcohol intoxication. In this study, we have tested the efficacy of one of the major components, daidzin, from this plant extract. When ethanol (40% solution, 3 g/kg body weight) was given to fasted rats intragastrically, blood alcohol concentration (BAC) peaked at 30 min after alcohol ingestion and reached 1.77 +/- 0.14 mg/ml (mean values +/- SD, n = 6). If daidzin (30 mg/kg) was mixed with the ethanol solution and given to animals intragastrically, BAC was found to peak at 90 min after alcohol ingestion and reached only 1.20 +/- 0.30 mg/ml (n = 6) (p < 0.05 vs. controls). The ability of daidzin to delay and decrease peak BAC level after ethanol ingestion was also observed in fed animals. In both fasted and fed rats given alcohol without daidzin, BAC quickly declined after reaching its peak at 30 min. By contrast, BAC levels receded more slowly if daidzin was also fed to the animals. Daidzin showed a chronic effect. Rats fed daidzin for 7 days before ethanol challenge, but not on the day of challenge, also produced lower and later peak BAC levels. Interestingly, daidzin, whether fed to rats only once or chronically for 7 days, did not significantly alter activities of either alcohol dehydrogenase or mitochondrial aldehyde dehydrogenase in the liver. Further experiments demonstrated that daidzin shortened sleep time for rats receiving ethanol intragastrically (7 g/kg) but not intraperitoneally (2 g/kg). To test whether daidzin delayed stomach-emptying, [14C]polyethylene glycol was mixed with ethanol and fed to rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Bioavailability of ethanol is reduced in several commonly used liquid diets

Liquid diets are often used as a vehicle for chronically treating laboratory animals with ethanol. However, a recent report suggested that one or more components of these diets may bind ethanol which could result in a decrease in the bioavailability of ethanol. Consequently, we compared the blood ethanol concentration vs. time curves obtained following the intragastric (i.g.) administration of ethanol dissolved in water or in one of three liquid diets (Bioserv AIN-76, Sustacal, or Carnation Slender) using the long-sleep (LS) and short-sleep (SS) mouse lines. The initial rates of absorption were generally the same for the water-ethanol and diet-ethanol groups, but the diets generally produced lower peak levels and the areas under the ethanol concentration-time curves were less for all of the liquid diets than for the control, ethanol-water solution. In vitro dialysis experiments indicated that the Bioserv diet binds ethanol in a saturable manner. Therefore, it may be that the slower release of ethanol, which should occur as a result of binding, serves to increase the role of first pass metabolism in regulating ethanol concentrations following oral administration. Because the effects of the diets were seen even after pyrazole treatment, it may be that the lower blood ethanol levels arise because metabolism by gastric ADH, rather than hepatic ADH, is responsible for a major portion of ethanol metabolism as ethanol is slowly released by the diets. If so, the observation that the diet/water differences were uniformly greater in the LS mice may indicate that LS-SS differences in gastric ADH exist.(ABSTRACT TRUNCATED AT 250 WORDS)

First-pass metabolism of ethanol is predominantly gastric

Oral consumption of alcohol results in much lower blood alcohol concentrations (BACs) than does the same dose administered intravenously, suggesting significant first-pass metabolism (FPM). The questions remain, however, (1) whether this difference truly represents FPM or simply reflects slower absorption of alcohol, and (2) if there is FPM, is it mainly of gastric or hepatic origin. To study this, rats were given the same dose alcohol (1 g/kg) by either intragastric intubation or by intravenous, intraportal, and intraduodenal infusions at a rate that mimicked the loss of alcohol from the stomach. Higher BAC levels after intravenous than intragastric alcohol indicated true FPM. Higher levels after intraportal or intraduodenal infusions (in fact, comparable to those obtained with the intravenous route) demonstrated negligible FPM when the route of delivery bypassed the stomach, yet included the liver. Furthermore, rats that had developed portosystemic shunts after ligation of the portal ven exhibited blood alcohol curves and FPM equivalent to those of sham-operated controls, indicating that FPM is not dependent on first-pass flow through the liver, but reflects gastric metabolism. The absence of significant hepatic FPM is attributable to the saturation of hepatic alcohol dehydrogenase by recirculating alcohol, resulting in no appreciable increase in metabolism secondary to newly absorbed alcohol. Finally, the in vivo gastric metabolism of alcohol in pylorus-ligated rats was demonstrated by significantly lower BACs when alcohol was administered intragastrically than when an amount identical to that lost from the ligated stomach was given intraportally. Thus, the lower BACs with oral as opposed to intravenous alcohol are not simply a consequence of slow absorption, but result from FPM occurring predominantly in the stomach.

Human gastric alcohol dehydrogenase activity: effect of age, sex, and alcoholism

As various isoenzymes of gastric alcohol dehydrogenase exist and as the effect of sex and age on these enzymes is unknown, this study measured the activity of gastric alcohol dehydrogenase at high and low ethanol concentrations in endoscopic biopsy specimens from a total of 290 patients of various ages and from 10 patients with chronic alcoholism. Gastric alcohol dehydrogenase was also detected by immunohistological tests in biopsy specimens from 40 patients by the use of a polyclonal rabbit antibody against class I alcohol dehydrogenase. A significant correlation was found between the immunohistological reaction assessed by the intensity of the colour reaction in the biopsy specimen and the activity of alcohol dehydrogenase measured at 580 mM ethanol. While alcohol dehydrogenase activity measured at 16 mM ethanol was not significantly affected by age and sex, both factors influenced alcohol dehydrogenase activity measured at 580 mM ethanol. Young women below 50 years of age had significantly lower alcohol dehydrogenase activities in the gastric corpus and antrum when compared with age matched controls (SEM) (6.4 (0.7) v 8.8 (0.6) nmol/min/mg protein; p < 0.001 and 6.0 (1.3) v 9.5 (1.3) nmol/min/mg protein; p < 0.001). Over 50 years of age this sex difference was no longer detectable, as high Km gastric alcohol dehydrogenase activity decreases with age only in men and not in women. In addition, extremely low alcohol dehydrogenase activities have been found in gastric biopsy specimens from young male alcoholics (2.2 (0.5) nmol/min/mg protein), which returned to normal after two to three weeks of abstinence. The activity of alcohol dehydrogenase in the human stomach measured at 580 mM ethanol is decreased in young women, in elderly men, and in the subject with alcoholism. This decrease in alcohol dehydrogenase activity may contribute to the reduced first pass metabolism of ethanol associated with raised ethanol blood concentrations seen in these people.

Ethanol metabolism in deermice: role of extrahepatic alcohol dehydrogenase

The relative contributions to ethanol metabolism of extrahepatic alcohol dehydrogenase (ADH) and of liver microsomes were assessed in deermice, which lack hepatic low Km ADH (ADH-). In vitro kinetic studies showed the existence of high Km (> 1 M) ADH activity in the liver and kidney, and an enzyme with intermediate Km in the gastric mucosa (Km = 133 mM), whereas the low Km ADH was missing. With deuterated ethanol, ADH- deermice showed a significant exchange of reducing equivalents that had been equated with ethanol metabolism by others, whereas we found a poor correlation between the rate of exchange and the rate of metabolism. In vitro studies with subcellular fractions, isolated hepatocytes, and tissue slices revealed that neither liver, nor kidney, nor stomach from ADH- deermice contributed to exchange of reducing equivalents. These findings clearly indicated that the ADHs with high or intermediate Km of the tissues studied are not responsible for the exchange. Furthermore, gastrectomized ADH- deermice still showed an exchange of reducing equivalents, thereby dissociating exchange from gastric ADH activity. Moreover, pretreatment with cimetidine (50 mg/kg body weight), an inhibitor of gastric ADH, did not alter the rate of total ethanol elimination when ethanol was given intraperitoneally. In conclusion, when ethanol was given parenterally, the microsomal ethanol-oxidizing system rather than gastric ADH is a major pathway of ethanol oxidation in ADH- deermice, whereas both pathways contribute significantly to the metabolism of orally administered ethanol.

Review article: lack of clinical significance of the interaction between H2-receptor antagonists and ethanol

It has been proposed that an appreciable fraction of ingested ethanol is metabolized in the gastric mucosa and that inhibition of this metabolism by H2-receptor antagonists produces clinically important increases in blood ethanol. This paper reviews available data concerning gastric metabolism of ethanol and the influence of H2-antagonists on ethanol metabolism. It concludes that very little, if any, metabolism of ethanol is likely to occur in the gastric mucosa, and the interaction between H2-antagonists and ethanol is clinically insignificant.

Pharmacology of gastric acid inhibition

Gastric acid secretion is precisely regulated by neural (acetylcholine), hormonal (gastrin), and paracrine (histamine; somatostatin) mechanisms. The stimulatory effect of acetylcholine and gastrin is mediated via increase in cytosolic calcium, whereas that of histamine is mediated via activation of adenylate cyclase and generation of cAMP. Potentiation between histamine and either gastrin or acetylcholine may reflect postreceptor interaction between the distinct pathways and/or the ability of gastrin and acetylcholine to release histamine from mucosal ECL cells. The prime inhibitor of acid secretion is somatostatin. Its inhibitory paracrine effect is mediated predominantly by receptors coupled via guanine nucleotide binding proteins to inhibition of adenylate cyclase activity. All the pathways converge on and modulate the activity of the luminal enzyme, H+,K(+)-ATPase, the proton pump of the parietal cell. Precise information on the mechanisms involved in gastric acid secretion and the identification of specific receptor subtypes has led to the development of potent drugs capable of inhibiting acid secretion. These include competitive antagonists that interact with stimulatory receptors (e.g. muscarinic M1-receptor antagonists and histamine H2-receptor antagonists) as well as non-competitive inhibitors of H+,K(+)-ATPase (e.g. omeprazole). The histamine H2-receptor antagonists (cimetidine, ranitidine, famotidine, nizatidine and roxatidine acetate) continue as first-line therapy for peptic ulcer disease and are effective in preventing relapse. Although they are generally well tolerated, histamine H2-receptor antagonists may cause untoward CNS, cardiac and endocrine effects, as well as interfering with the absorption, metabolism and elimination of various drugs. The dominance of the histamine H2-receptor antagonists is now being challenged by omeprazole. Omeprazole reaches the parietal cell via the bloodstream, diffuses through the cytoplasm and becomes activated and trapped as a sulfenamide in the acidic canaliculus of the parietal cell. Here, it covalently binds to H+,K(+)-ATPase, the hydrogen pump of the parietal cell, thereby irreversibly blocking acid secretion in response to all modes of stimulation. The main potential drawback to its use is its extreme potency which sometimes leads to virtual anacidity, gastrin cell hyperplasia, hypergastrinaemia and, in rats, to the development of carcinoid tumours. The cholinergic receptor on the parietal cell has recently been identified as an M3 subtype and that on postganglionic intramural neurones of the submucosal plexus as an M1 subtype.(ABSTRACT TRUNCATED AT 400 WORDS)

The intramucosal distribution of gastric alcohol dehydrogenase and aldehyde dehydrogenase activity in rats

Using qualitative and microquantitative histo-chemical techniques, alcohol dehydrogenase and aldehyde dehydrogenase activity was studied in the gastric mucosa of male and female rats. Alcohol dehydrogenase was demonstrated by staining reactions with maximum activity in surface and neck cells and with clearly weaker activity also in parietal cells. Aldehyde dehydrogenase could be detected in surface and neck cells, and also to a comparable degree in the parietal cells. Quantitative analyses of microdissected samples yielded high values for alcohol dehydrogenase activity exclusively in the superficial part of the gastric mucosa, whereas low-Km aldehyde dehydrogenase activity showed a decreasing gradient from the surface to the deeper parts of the mucosa. Sex differences could not be confirmed.

A gastric alcohol dehydrogenase in the baboon: purification and properties of a 'high-Km' enzyme, consistent with a role in 'first pass' alcohol metabolism

The major isozyme of alcohol dehydrogenase in baboon stomach, ADH3, has been purified to homogeneity and characterized with a range of alcohol and aldehyde substrates. Using kcat/Km values as an indication of substrate efficacy, medium-chain length aliphatic alcohols and aldehydes were identified as the preferred substrates. ADH3 showed 'high-Km' properties with respect to ethanol, and is expected to significantly contribute to 'first-pass' metabolism of alcohol. The enzyme exhibited more than two orders of magnitude higher turnover of substrate than the baboon liver 'low-Km' ADH, and may play a role in the rapid metabolism of a wide range of ingested alcohols in the diet.

Gender differences in ethanol oxidation and injury in the rat stomach

A significant fraction of orally consumed ethanol is metabolized by the alcohol dehydrogenase (ADH) enzyme present in the gastric mucosa. Human studies have shown that this "first pass metabolism" of ethanol correlates quite closely with gastric ADH activity which has been demonstrated to be greater in men than women. The present study was undertaken to determine if gender influences the magnitude of ethanol-induced injury in rat gastric mucosa and whether any differences can be linked to altered levels of ADH activity. Since prostaglandins (PGs) have been shown to markedly attenuate the severity of gastric injury induced by ethanol in the rat stomach, a further goal of this study was to determine whether the efficiency of PG's protective action was in any way influenced by gender. Accordingly, both male and female rats were pretreated subcutaneously with 16,16-dimethyl PGE2 (10 micrograms/kg) or saline 30 minutes prior to administering an oral dose of 50% ethanol in saline or saline alone. They were then sacrificed 5 minutes later. In a portion of animals (n = 6 per group), samples of mucosa from the glandular stomach were obtained and kinetic activity of ADH determined. In another portion of animals (n = 6 per group), gastric tissue samples from the glandular mucosa were examined by light microscopy and the magnitude of mucosal injury quantified. Alcohol-treated females showed significantly (p less than 0.05) less superficial and more deep mucosal injury than male counterparts. Further, ADH kinetic activity in female rats was significantly less than that observed in male counterparts of similar weight (83% of males; p less than 0.04).(ABSTRACT TRUNCATED AT 250 WORDS)

Liver triglyceride concentration and body protein metabolism in ethanol-treated rats: effect of energy and nutrient supplementation

The objective of this study was to compare the metabolic effects of long-term ethanol consumption with oral (Lieber-DeCarli) and enteral feeding techniques. Enteral feeding allowed administration of greater amounts of energy and nutrients. After 21 days of treatment using the Lieber-DeCarli technique, the ethanol-treated rats had the following significant (P less than 0.05) differences from pair-fed controls: lower cumulative nitrogen balance (days 5-21; 2.8 +/- 0.1 g N vs. 3.5 +/- 0.1 g N), lower protein content of gastrocnemius muscle (289 +/- 17 mg vs. 358 +/- 11 mg) and intestinal mucosa (461 +/- 19 mg vs. 577 +/- 40 mg), higher plasma leucine concentration (147 +/- 8 mumol/L vs. 102 +/- 8 mumol/L), higher liver protein content (2222 +/- 122 mg vs. 1679 +/- 58 mg), and higher liver triglyceride concentration (38.4 +/- 2.8 mg/g vs. 8.7 +/- 1.0 mg/g). When rats received the same amount of nitrogen (1.5 g.kg-1.day-1) and ethanol (13 g.kg-1.day-1) but 16.3% more energy and nutrients by a surgically implanted gastric cannula (enterally fed), the effects of ethanol on nitrogen balance, tissue protein content, plasma leucine concentration, and liver triglyceride concentration were similar to those observed in the rats fed orally. It is concluded that the metabolic effects observed using the Lieber-DeCarli feeding technique are due to ethanol per se and not the synergism of ethanol and undernutrition as recently suggested.

First-pass gastric mucosal metabolism of ethanol is negligible in the rat

Ethanol metabolism by gastric alcohol dehydrogenase (ADH) is thought to be an important determinant of peripheral ethanol time-concentration curves (AUCs) in rats and humans. We quantitated this metabolism in rats by measuring the gastric absorption of oral ethanol (0.25 g/kg) and the gastric venous-arterial (V-A) difference of ethanol versus ethanol metabolites (acetate, acetaldehyde, and bicarbonate). Over 1 h, approximately 20% of the ethanol was absorbed from the stomach and 70% was emptied into the duodenum. The gastric V-A difference of ethanol metabolites was less than 4% of that of ethanol. Thus, gastric metabolism accounted for less than 1% (less than 4% of 20% absorbed) of the dose. This negligible metabolism was predictable from the low affinity of gastric ADH for ethanol. In contrast, gastric ADH has a high affinity for octanol, and 66% of this compound was metabolized during gastric absorption. Evidence supporting gastric metabolism of ethanol largely derives from the lower AUCs observed after oral than after intravenous administration; however, we observed increasingly higher AUCs with increasingly rapid portal vein infusions of identical ethanol doses. We conclude that gastric metabolism of ethanol is negligible in the rat, and differences in AUCs ascribed to gastric metabolism may reflect differences in ethanol absorption.

Effects of H2-receptor antagonists on gastric alcohol dehydrogenase activity

Inhibition of gastric alcohol dehydrogenase (ADH) activity by cimetidine results in elevated blood levels of ethanol after moderate consumption. To search for alternative H2-blockers lacking such an effect, we compared cimetidine, ranitidine, nizatidine, and famotidine. They inhibited rat gastric ADH noncompetitively, with a Ki for ethanol oxidation of 0.68 mM for cimetidine, 0.5 mM for ranitidine, 1 mM for nizatidine, and 4.5 mM for famotidine. These concentrations are higher than therapeutic plasma levels, but intracellular concentrations in the gastric mucosa (assessed with [3H]cimetidine and [14C]famotidine) were at least 10- and 2-fold greater than in the blood, respectively. These results suggests that, given at therapeutic doses in vivo, the degree of inhibition by cimetidine and ranitidine should be significant and comparable, that by nizatidine should be smaller, and that by famotidine should be negligible. These drugs also exerted either mixed or competitive inhibition of rat hepatic ADH, but the effects of cimetidine and famotidine were observed at concentrations unlikely to occur in vivo. Thus, in alcoholics and in social drinkers who require treatment with H2-receptor antagonists, famotidine might be preferable to the other H2 blockers tested.

Effect of concentration of ingested ethanol on blood alcohol levels

The effect of the concentration of ingested ethanol on the resulting blood alcohol concentrations (BAC) was tested in both humans and rats. In humans, when 0.3 g/kg body weight ethanol was ingested postprandially, the mean area under the blood alcohol curve (AUC) and the mean peak BAC were significantly lower with a concentrated (40% w/v) than with a dilute (4%) solution. Similarly, rats in the fed state exhibited decreasing mean AUCs with increasing concentrations (4%, 16%, and 40%) of intragastrically administered ethanol (1.0 g/kg). Pharmacokinetic analysis comparing intragastric and intraperitoneal administration of ethanol to rats indicated that the more concentrated solution resulted in less alcohol reaching the systemic circulation (4%: 0.896 +/- 0.074 g/kg: 16% 0.772 +/- 0.072 g/kg; 40%: 0.453 +/- 0.037 g/kg) and suggested that this affect could be attributed to two factors: increased gastric retention of ethanol (4%: 0.109 +/- 0.024 g/kg; 16%: 0.102 +/- 0.016 g/kg; 40%: 0.214 +/- 0.042 g/kg) and a large increase in first-pass metabolism (4%; 0.004 +/- 0.054 g/kg; 16%: 0.145 +/- 0.048 g/kg; 40%: 0.329 +/- 0.044 g/kg). In contrast to the results in the fed state, in humans fasted overnight the concentration of alcohol consumed (4%, 16%, and 40%) had no significant effect on mean AUCs. In fasted rats, mean AUCs after intragastric intubation of the two lower concentrations of ethanol (4% and 16%) were comparable to those found after intraperitoneal injection, and only the highest ethanol concentration (40%) produced a lower mean AUC.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of ranitidine, cimetidine or famotidine on low-dose post-prandial alcohol absorption

Plasma alcohol concentration following oral ingestion of 0.3 g/kg of alcohol (ethyl alcohol), one hour after an evening meal, was measured in four groups of 12 healthy subjects. Each group had a control study and a repeat study after 7 days dosing with either placebo or an H2-receptor antagonist (300 mg ranitidine nocte, 800 mg cimetidine nocte, or 40 mg famotidine nocte). There was no significant difference between the control and post-dosing studies in the integrated 4-h plasma alcohol concentration, peak plasma alcohol concentration, or time to reach peak alcohol concentration. This study shows that post-prandial alcohol absorption after 0.3 g/kg of alcohol is not affected by ranitidine, cimetidine or famotidine.

Human gastric alcohol dehydrogenase: its inhibition by H2-receptor antagonists, and its effect on the bioavailability of ethanol

Two types of alcohol dehydrogenase isoenzymes (differing in their affinity for ethanol, sensitivity to 4-methylpyrazole, and electrophoretic migration) have been identified in the human stomach. At the high ethanol concentrations prevailing in the gastric lumen during alcohol consumption, the sum of their activities could account for significant oxidation of ethanol. In vitro, these activities were inhibited by cimetidine and ranitidine, but not by famotidine. In vivo, therapeutic doses of cimetidine (but not of famotidine) increased blood ethanol levels when ethanol was given orally, but not when it was given intravenously, indicating a significant contribution of the gastric ADH to the bioavailability and thereby the potential toxicity of ethanol.

Mechanism of ethanol induced hepatic injury

Ethanol is hepatotoxic through redox changes produced by the NADH generated in its oxidation via the alcohol dehydrogenase pathway, which in turn affects the metabolism of lipids, carbohydrates, proteins and purines. Ethanol is also oxidized in liver microsomes by an ethanol-inducible cytochrome P-450 (P-450IIE1) which contributes to ethanol metabolism and tolerance, and activates xenobiotics to toxic radicals thereby explaining increased vulnerability of the heavy drinker to industrial solvents, anesthetic agents, commonly prescribed drugs, over-the-counter analgesics, chemical carcinogens and even nutritional factors such as vitamin A. Induction also results in energy wastage and increased production of acetaldehyde. Acetaldehyde, in turn, causes injury through the formation of protein adducts, resulting in antibody production, enzyme inactivation, decreased DNA repair, and alterations in microtubules, plasma membranes and mitochondria with a striking impairment of oxygen utilization. Acetaldehyde also causes glutathione depletion and lipid peroxidation, and stimulates hepatic collagen synthesis, thereby promoting fibrosis.

In vivo ethanol elimination in man, monkey and rat: a lack of relationship between the ethanol metabolism and the hepatic activities of alcohol and aldehyde dehydrogenases

The in vivo ethanol elimination in human subjects, monkeys and rats was investigated after an oral ethanol dosage. After 0.4 g. ethanol/kg of body weight, ethanol elimination was much slower in human subjects than in monkeys. In order to detect a rise in monkey plasma ethanol concentrations as early as observed in human subjects, ethanol had to be administered at a dose of 3 g/kg body weight. Ethanol metabolism in rats was also much faster than in human subjects. However, human liver showed higher alcohol dehydrogenase activity and higher low Km aldehyde dehydrogenase activity than rat liver. Thus, our data suggest a lack of relationship between hepatic ethanol-metabolizing activities and the in vivo ethanol elimination rate.

High levels of acetaldehyde in nonalcoholic liver injury after threonine or ethanol administration

Acetaldehyde, a product of ethanol oxidation which forms adducts with proteins, has been incriminated in the pathogenesis of alcoholic liver injury. High serum antibody titers against acetaldehyde-protein adducts have been found not only in alcoholics but also in patients with nonalcoholic liver disease, suggesting a contribution of acetaldehyde derived from sources other than exogenous ethanol. To investigate the effect of liver injury on the removal and the production of acetaldehyde, we produced fibrosis and cirrhosis (by chronic administration of carbon tetrachloride) and fatty liver (with very small doses of dimethylnitrosamine) in rats. Endogenous blood acetaldehyde levels increased by 38% in rats with severe liver injury (p less than 0.005), but not significantly in rats with fatty liver. However, an i.v. load of threonine (a physiological source of acetaldehyde), in amounts equivalent to the daily intake of this amino acid, increased blood and hepatic acetaldehyde levels in the rats with both types of liver injury more than in controls. Threonine dehydrogenase and dehydratase activities, involved in the major pathways for threonine degradation in mitochondria and cytosol, respectively, were markedly decreased in rats with liver injury with a resulting increase in hepatic threonine concentration. Moreover, the threonine aldolase activity, which splits threonine into glycine and acetaldehyde, remained unaffected or even slightly increased. Liver injury was also associated with impaired mitochondrial functions, including a 10 to 23% decrease in acetaldehyde oxidation (depending upon the severity of the lesions). As a consequence, administration of ethanol (an exogenous source of acetaldehyde) resulted in striking elevations in the levels of acetaldehyde in carbon tetrachloride-treated rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Gastric origin of the first-pass metabolism of ethanol in humans: effect of gastrectomy

The areas under the curve (AUCs) of blood ethanol concentrations are much smaller after oral than after intravenous administration of a small dose of ethanol. To study whether this difference is due to ethanol oxidation in the stomach, in the small intestine, or during first pass through the liver, we compared the AUCs after random administration of the same ethanol dose by the intravenous, oral, and intraduodenal routes to 5 abstaining alcoholics and via the two former routes to 10 subjects with Billroth II subtotal gastrectomy. In the nonoperated subjects, the AUCs after an ethanol dose (0.15 g/kg) given orally were 17% (p less than 0.01) of those achieved intravenously, in spite of the fact that greater than 99% of the dose had disappeared from the stomach at the completion of the AUC. By contrast, the AUCs after intraduodenal administration did not differ from those produced intravenously, indicating that neither the intestine nor the liver make a detectable contribution to this first-pass metabolism. Moreover, gastrectomy completely abolished the first-pass metabolism of ethanol. Gastric metabolism decreases the bioavailability of the ingested alcohol and thus attenuates its systemic toxicity. The abolition of this "protective barrier" in gastrectomized patients may increase their vulnerability to ethanol.

Role of extrahepatic alcohol dehydrogenase in rat ethanol metabolism

Rat alcohol dehydrogenase exhibits three isoenzymes with very different capacities of ethanol oxidation and with characteristic distribution in tissues. ADH-1 (class II isoenzyme, Km = 5 M) is especially concentrated in the most external organs: auditive, bucal, and nasal mucoses, cornea, esophagus, stomach, rectum, penis, and vagina. ADH-2 (class III isoenzyme) is present in all organs but has a poor activity with ethanol. ADH-3 (class I isoenzyme, Km = 1.4 mM) is the main liver isoenzyme, also present in lung, intestine, kidney, and sexual organs. At 33 mM ethanol and pH 7.5, total hepatic activity (3.5 +/- 0.6 units) represents 90% of the whole activity in the male rat, while the remaining 10% is distributed in many organs. The skin is the extrahepatic organ with the highest total activity (88 +/- 15 mU) followed by testis and small intestine. ADH-3 accounts for 96% of total activity (90% hepatic and 6% extrahepatic) and ADH-1 contributes with 4% (extrahepatic). However, in conditions that may be found in the digestive tract mucose after ethanol ingestion (pH 7.5, 1 M ethanol), stomach and small intestine activities represent 10% of the liver activity at 33 mM ethanol. Therefore, oral administration of ethanol will result in a higher contribution of the extrahepatic activity than will intravenous or intraperitoneal administration, because of the great ADH-1 content of the digestive tract. On the other hand, pyrazole inhibition constants at pH 7.5 for ADH-1 (33 mM) and ADH-3 (4.2 microM) are much higher than those at pH 10.0 (0.56 mM and 0.4 microM) and indicate that at the usual concentration of inhibitor only ADH-3 activity will be effectively suppressed. ADH-1 will be, therefore, responsible in part for the residual ethanol oxidation activity in pyrazole-treated rats.

The microsomal ethanol oxidizing system mediates metabolic tolerance to ethanol in deermice lacking alcohol dehydrogenase

Metabolic tolerance to ethanol has been attributed to enhanced mitochondrial reoxidation of reducing equivalents produced in the alcohol dehydrogenase (ADH) pathway or to non-ADH mechanisms. To resolve this issue, deermice lacking low Km hepatic ADH were fed for 2 weeks a liquid diet containing ethanol or isocaloric carbohydrate and hepatocytes were isolated. Ethanol (50 mM) oxidation increased (9.8 vs 4.5 nmol/min/10(6) cells in controls). To differentiate which of two non-ADH pathways (the microsomal ethanol oxidizing system (MEOS) or catalase) was responsible for the induction, four approaches were used. First, MEOS was assayed in hepatic microsomes and found to be increased (24.4 vs 6.8 nmol/min/mg protein in controls). Second, hepatocyte ethanol metabolism was measured after addition of the catalase inhibitor azide (0.1 mM) and found to be unchanged. By contrast, the competitive MEOS inhibitor, 1-butanol, depressed metabolism in a concentration-dependent manner. A third approach relied on measurement of isotope effects known to be different for MEOS and catalase. From the isotope effect values, MEOS was calculated to contribute 85% or more of total ethanol oxidation by cells from both ethanol-fed and control animals. A fourth approach involved in vivo pretreatment with pyrazole (300 mg/kg/day for 2 days), which reduced peroxidation by catalase to 13% of control values in liver homogenates while inducing MEOS activity to 152% of controls. Hepatocytes from pyrazole-treated deermice showed a 47% increase in ethanol metabolism, paralleling the MEOS induction and contrasting with the catalase suppression. These results indicate that since metabolic tolerance occurs in the absence of ADH, it is not necessarily ADH mediated, and further, that MEOS rather than catalase accounts for basal ethanol metabolism and its increase after chronic ethanol treatment.

Gastric contents alter blood alcohol levels and clearance after parenteral ethanol

Several different substances, including water, charcoal, fructose, montmorillonite clay, and liquid diets used for chronic ethanol exposure, were given intragastrically to rats, followed by a low dose of ethanol injected subcutaneously. Peak blood alcohol levels (BAL) and ethanol clearance rates were found to differ depending upon the type of gastric contents. As expected, fructose lowered peak BAL and increased ethanol clearance, and charcoal lowered peak BAL, but decreased ethanol clearance. Two liquid diets, Shorey and Sustacal, when compared to an intragastric water load, also lowered peak BAL and increased ethanol clearance of subcutaneously-administered ethanol. The difference between intragastric water and Shorey liquid diet was also seen when ethanol was administered intravenously, suggesting that absorption of ethanol from the subcutaneous site was not being affected. When sleep-inducing doses of ethanol were given subcutaneously, intragastric substances did not produce differences in sleeptimes. In in vitro studies, only charcoal was able to bind ethanol, presumably by absorption onto charcoal particles. Volume of distribution measurements were inversely related to the peak BALs measured at 60 minutes after injection, suggesting that ethanol was partitioning between the blood and stomach contents. We conclude that the presence in the stomach of various substances can lower peak BAL and increase ethanol clearance in a rapid fashion, primarily through a change in volume of distribution and possibly through a rapid change in stomach or liver metabolism of ethanol.

Effects of cimetidine on gastric alcohol dehydrogenase activity and blood ethanol levels

Chronic use of cimetidine and alcohol are commonly associated, but studies on their interactions are the subject of controversy. To investigate this question, a small ethanol dose (0.15 g/kg body wt) was randomly administered on 2 consecutive days either orally or intravenously to 6 normal volunteers, before and after 1 wk of oral administration of 400 mg of cimetidine twice daily. Although cimetidine did not change the areas under the curve of blood ethanol concentrations after intravenous administration, those after oral alcohol intake were twice as large with cimetidine than without. Similar effects were reproduced in rats after intravenous administration of cimetidine (50 mg/kg body wt). In vitro, cimetidine was a noncompetitive inhibitor of gastric alcohol dehydrogenase activity at concentrations as low as 0.01 mM, 100-fold lower than those needed to inhibit the hepatic dehydrogenase. These results indicate that gastric alcohol dehydrogenase activity governs, in part, the systemic bioavailability of ethanol. Consequently, systemic effects of alcohol may be exacerbated in patients receiving cimetidine.