Effect of concentration of ingested ethanol on blood alcohol levels

Ranitidine increases the bioavailability of imbibed alcohol by accelerating gastric emptying

To investigate the mechanism of the increase in alcohol bioavailability by ranitidine, we determined by nuclear scan the changes in gastric emptying of a 10% ethanol solution (containing 0.3 g ethanol/kg body weight and 300 microCi of technetium-labeled diethylene triamine pentacetic acid) in 8 normal men, before and after treatment with 300 mg ranitidine orally each evening for 1 week. We compared these changes with those of ethanol bioavailability, calculated by integration of the Michaelis-Menten function over the entire alcohol curves after random i.v. and, on a separate day, oral administration of the same ethanol dose, pre- and post-ranitidine. With ranitidine, we found an acceleration of gastric emptying in 7 of 8 subjects, with 20% shortening of the time to 50% emptying (51.8 +/- 4.1 min vs 64.3 +/- 3.4, without ranitidine; P < .001 by paired t test). Despite the disappearance (from the stomach) of most of the dose by the end of the blood alcohol curves, only 83 +/- 4% reached the systemic blood vs 64 +/- 4% without ranitidine (P < .02), most likely because of a shortened exposure of alcohol dehydrogenase to optimal ethanol concentrations. As a result, after oral but not intravenous alcohol administration, ranitidine increased blood alcohol concentrations (29 +/- 4 mg/dl vs 22 +/- 3, without ranitidine; P < .02), with a corresponding decrease in first pass metabolism of ethanol from 107 +/- 16 mg/kg to 47 +/- 16 (P < .01).

Gastric metabolism of ethanol in Syrian golden hamster

First-pass metabolism (FPM) of orally ingested alcohol has been attributed to gastric alcohol dehydrogenase (ADH) activity in both humans and rats. To determine whether gastric alcohol dehydrogenase is essential for alcohol FPM, we sought a species lacking this enzyme. We found that Syrian golden hamsters have negligible gastric ADH yet alcohol FPM (265 +/- 25 mg ethanol/kg) was comparable to that of rats (251 +/- 31 mg/kg). To determine whether hamster gastric mucosal cells metabolize sufficient alcohol to account for this FPM, primary cultures were established, and these cells metabolized 1.99 +/- 0.84 mumol ethanol/10(6) cells/hr, an amount sufficient to account for the bulk of alcohol FPM. In contrast to alcohol dehydrogenase, catalase activity in hamster gastric mucosa (870 +/- 93 units/g tissue) was eightfold higher than in rat gastric mucosa (111 +/- 9 units/g tissue; P < 0.0001). FPM in hamsters treated with 3-aminotriazole was reduced from 242 +/- 24 to 130 +/- 22 mg/kg (P < 0.05) but was not reduced in rats. The results imply that catalase participates in gastric alcohol metabolism of hamsters.

Alcohol metabolism in Helicobacter pylori-infected stomach

Studies in our laboratory have revealed that Helicobacter pylori exhibits significant cytosolic alcohol dehydrogenase activity and that the enzyme is fully active at ethanol concentrations prevailing in the stomach during alcohol consumption or after alcohol is completely absorbed from the stomach and is available through blood circulation only. Moreover, even the low levels of endogenous ethanol found in the stomach can be oxidized to acetaldehyde by H. pylori alcohol dehydrogenase. The metabolic significance of the enzyme remains as yet unresolved. Under microaerobic conditions, however, the enzyme could be of importance in the energy metabolism of the organism. In the presence of excess ethanol, H. pylori alcohol dehydrogenase produces significant amounts of acetaldehyde. Acetaldehyde is a toxic and reactive compound and could theoretically be a pathogenetic factor in H. pylori-associated gastric injury. Preliminary studies have indicated that acetaldehyde inhibits gastric mucosal regeneration and forms stable adducts with mucosal proteins. Both of these mechanisms could cause gastric injury. The role of H. pylori-related acetaldehyde formation in vivo, however, needs to be established in future studies. In antral human gastric mucosa, H. pylori infection is associated with a significant decrease in alcohol dehydrogenase activity. Similarly, in specific pathogen-free mice with a prolonged infection, gastric alcohol dehydrogenase activity is decreased; however, this is not clearly reflected in the bioavailability of ethanol or the amount of its first pass metabolism.

Significant increase of blood alcohol by cimetidine after repetitive drinking of small alcohol doses

To assess effects of repetitive alcohol drinking and pre-existing first-pass metabolism on the cimetidine-induced increase in blood alcohol concentrations, 20 healthy men (aged 20 to 40) of varied ethnicity and consuming less than 60 g alcohol per week underwent baseline quantitation of first-pass metabolism of alcohol. This was followed by oral administration of 0.6 g/kg ethanol given postprandially in 3 to 4 drinks spread over 135 min, before and after cimetidine (400 mg twice a day for 7 days). Blood alcohol concentrations were determined by breath analysis. First-pass metabolism was quantified by applying Michaelis-Menten kinetics to blood alcohol curves after intravenous or oral administration of equal alcohol doses. At baseline, 15 subjects had a substantial first-pass metabolism (over one sixth of the dose); their alcohol levels increased with repeated doses with a mean peak of 27 +/- 3 mg/dl before and 39 +/- 5 after cimetidine (P < 0.01), an effect much greater and longer than after a single alcohol dose. Three subjects exceeded 50 mg/dl, the legal limit for driving in several countries. By contrast, in the five subjects with minimal first-pass metabolism, cimetidine did not increase alcohol levels. Thus, under conditions mimicking social drinking, cimetidine increased blood alcohol to concentrations known to impair psychomotor skills and they persisted at those levels over prolonged periods of time. In a minority of subjects, no such interaction was found, but their first-pass metabolism at baseline was absent or minimal and thus no inhibition by the drug was to be expected.

Changes in blood alcohol levels as a function of alcohol concentration and repeated alcohol exposure in adult female rats: potential risk factors for alcohol-induced fetal brain injury

Fetal alcohol syndrome and alcohol-related birth defects are the result of heavy maternal alcohol consumption during gestation. The magnitude of deficit manifested by the offspring is invariably a consequence of several risk factors that may result in high peak blood alcohol concentrations (BACs), such as the duration, timing, or pattern of alcohol consumption. In addition, the alcohol content of the consumed beverage may play a role in determining offspring developmental consequences. Because higher BACs are positively correlated with risk and severity of brain injury early in postnatal life, initially it was important to determine how BAC is influenced by alcohol concentration and whether that influence is constant over repeated alcohol treatments. Groups of female Sprague-Dawley rats received daily intragastric intubations of 5 g/kg alcohol in one of several concentrations: 45% (v/v), 30% (v/v), 22.5% (v/v), or 15% (v/v) for a duration of 18 consecutive days. Blood samples were taken at various times postintubation on days 3, 8, 13, and 18 of treatment, and analyzed by headspace gas chromatography. Multivariate analyses of peak BAC, average BAC, and time to reach peak BAC revealed some noteworthy results. First, peak BAC and average BAC were significantly lower in the 45% group, compared with the other concentration groups, whereas this group also took a longer time to reach peak BAC than the other three groups. Second, peak BAC and average BAC were higher on the last day of treatment than any of the other treatment days. These results suggest that alcohol concentration and repeated alcohol exposure can influence BAC and, as such, are important risk factors to be considered in the appraisal of alcohol-induced fetal brain injuries.

Hepatic glutathione after ethanol administration in rat: effects of cimetidine and omeprazole

As a fraction of ingested ethanol (EtOH) is metabolized by gastric mucosa, different amounts of alcohol reach the liver, when the same dose is administered by oral or intravenous route. In previous experiments, we demonstrated that the decrease of hepatic reduced glutathione (GSH) is less pronounced and is followed by a quicker recovery after oral than after intraperitoneal administration of the same amount of EtOH. Therefore, the time-course of hepatic GSH concentration seems to be an indirect assay of EtOH metabolism by the liver. On the basis of these findings, any condition causing a reduced function of gastric alcohol dehydrogenase (ADH) should show up as a more severe depletion of hepatic GSH. In the same rat experimental model we determined the effects of cimetidine and omeprazole administration on gastric ADH activity and on the time-course of hepatic GSH after EtOH load. Cimetidine was shown to inhibit gastric ADH with a Ki of 0.167 +/- 0.009 mmol l-1; accordingly, the pretreatment with this drug (20 mg kg-1 b.w. per day for 1 week) determined, after oral EtOH load, a marked reduction of hepatic GSH, likewise after intraperitoneal administration. Omeprazole exerted only a marginal inhibition on gastric ADH and this drug (0.3 mg kg-1 b.w. per day for 1 week) did not modify the time-course of hepatic GSH concentrations after EtOH load. This study indicates that the inhibition of gastric ADH, when associated with EtOH intake, induces depletion of the hepatic GSH concentration and, therefore, possible liver damage.

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.

Helicobacter infection and gastric ethanol metabolism

The organism frequently colonizing the stomach of patients suffering from chronic active gastritis and peptic ulcer disease--Helicobacter pylori--possesses marked alcohol dehydrogenase (ADH) activity. Consequently, Helicobacter infection may contribute to the capacity of the stomach to metabolize ethanol and lead to increased acetaldehyde production. To study this hypothesis, we first determined ADH activity in a variety of H. pylori strains originally isolated from human gastric mucosal biopsies. ADH activity was also measured in endoscopic gastric mucosal specimens obtained from H. pylori-positive and -negative patients. Furthermore, we used a mouse model of Helicobacter infection to determine whether infected animals exhibit more gastric ethanol metabolism than noninfected controls. Most of the 32 H. pylori strains studied possessed clear ADH activity and produced acetaldehyde. In humans, gastric ADH activity of corpus mucosa did not differ between H. pylori-positive and -negative subjects, whereas in antral biopsies ADH activity was significantly lower in infected patients. In mice, gastric ADH activity was similar or even lower in infected animals than in controls, depending on the duration of infection, despite the fact that the infectious agent used--Helicobacter felis--showed ADH activity in vitro. In accordance with this, Helicobacter infection tended to decrease rather than increase gastric ethanol metabolism in mice. In humans, it remains to be established whether the observed decrease in antral ADH activity associated with H. pylori infection can lead to reduced gastric first-pass metabolism of ethanol.

Hepatic glutathione determination after ethanol administration in rat: evidence of the first-pass metabolism of ethanol

As a fraction of ingested ethanol is metabolized by gastric mucosa, different amounts of alcohol should reach the liver when the same dose is administered by oral or intravenous route. Therefore, we investigated the time-course of hepatic reduced glutathione (GSH) concentrations after intra-peritoneal or intra-gastric load of the same amount of ethanol in the rat. The test was also performed in fasted and Cimetidine-treated rats. The oral ethanol administration was followed by a less pronounced decrease and by a quicker recovery of hepatic content of GSH than after intraperitoneal route. In the fasted rat, basal hepatic GSH significantly decreased; after alcohol administration the decrease of hepatic GSH was more severe and prolonged than in the fed rat. Cimetidine was shown to be a potent inhibitor of gastric ADH. Pre-treatment with Cimetidine did not change the basal levels of hepatic GSH, but after oral ethanol load, the decrease of the hepatic GSH content was significantly (p < 0.005) more pronounced than in controls. This study demonstrates the beneficial effects of gastric ethanol metabolism on the liver. The reduced gastric ethanol metabolism, induced by fasting or by Cimetidine resulted in a decreased content and delayed recovery of liver GSH content.

H2-antagonists and alcohol. Do they interact?

There are conflicting data on the existence of significant first-pass metabolism of alcohol (ethanol) in the human stomach and its inhibition by histamine H2-receptor antagonists. Alcohol is predominantly metabolised in the liver by the microsomal alcohol oxidising system, alcohol dehydrogenase (ADH) and a catalase enzyme. Histochemical and kinetic studies have revealed several ADH isoenzymes in the gastric mucosa with different kinetic properties. After small oral doses of alcohol first-pass metabolism in the stomach occurs, as shown by reduced area under the plasma concentration-time curve (AUC) compared with intravenous or intraduodenal administration. The activity of gastric ADH is reduced in women, the elderly, Asian individuals, the fasting state, chronic alcoholism and after gastrectomy. The effect is only present with small (< or = 0.3 g/kg) alcohol doses and with a high alcohol concentration. In a number of studies, cimetidine in therapeutic doses over 7 days produced a significant increase in the AUC and in the peak plasma concentration after administration of alcohol 0.15 and 0.30 g/kg. This was related to an inhibition of gastric ADH activity, as shown by in vitro studies. Ranitidine inhibited gastric ADH to a similar extent on a molar basis, but its effect on alcohol levels in vivo was less constant in various studies. Nizatidine also reduced gastric alcohol first-pass metabolism, but famotidine and roxatidine did not show this effect. In other studies, H2-receptor antagonists did not change AUC and peak alcohol concentration. The controversy is not easy to resolve, since a number of the positive studies did not use a placebo-controlled, randomised, crossover design, while some of the negative studies did not exclude habitual alcohol consumers and included Oriental volunteers, although both groups have been shown to lack significant gastric ADH activity. In this case, when first-pass metabolism of alcohol does not exist, this by definition cannot be abolished by H2-antagonists. The inclusion of oral and intravenous dosage data of alcohol is mandatory to positively identify first-pass metabolism in any individuals. The significance of the effect of H2-antagonists on blood alcohol concentrations is minor. It only occurs in young, male, nonalcoholic, non-Asian individuals, and alcohol must be given in a small (social) dose, in a high concentration, and after meals. An increase in alcohol levels in predisposed patients during treatment with some H2-antagonists cannot be excluded, although the likelihood is small. Furthermore, carefully designed studies are needed to clarify fully the significance of this interaction.

Alcohol and the liver: 1994 update

This article reviews current concepts on the pathogenesis and treatment of alcoholic liver disease. It has been known that the hepatotoxicity of ethanol results from alcohol dehydrogenase-mediated excessive generation of hepatic nicotinamide adenine dinucleotide, reduced form, and acetaldehyde. It is now recognized that acetaldehyde is also produced by an accessory (but inducible) microsomal pathway that additionally generates oxygen radicals and activates many xenobiotics to toxic metabolites, thereby explaining the increased vulnerability of heavy drinkers to industrial solvents, anesthetics, commonly used drugs, over-the-counter medications, and carcinogens. The contribution of gastric alcohol dehydrogenase to the first-pass metabolism of ethanol and alcohol-drug interactions is discussed. Roles for hepatitis C, cytokines, sex, genetics, and age are now emerging. Alcohol also alters the degradation of key nutrients, thereby promoting deficiencies as well as toxic interactions with vitamin A and beta carotene. Conversely, nutritional deficits may affect the toxicity of ethanol and acetaldehyde, as illustrated by the depletion in glutathione, ameliorated by S-adenosyl-L-methionine. Other "supernutrients" include polyunsaturated lecithin, shown to correct the alcohol-induced hepatic phosphatidylcholine depletion and to prevent alcoholic cirrhosis in nonhuman primates. Thus, a better understanding of the pathology induced by ethanol is now generating improved prospects for therapy.

Mechanisms of ethanol-drug-nutrition interactions

Mechanisms of the toxicologic manifestations of ethanol abuse are reviewed. Hepatotoxicity of ethanol results from alcohol dehydrogenase-mediated excessive hepatic generation of nicotinamide adenine dinucleotide and acetaldehyde. It is now recognized that acetaldehyde is also produced by an accessory (but inducible) pathway, the microsomal ethanol-oxidizing system, which involves a specific cytochrome P450. It generates oxygen radicals and activates many xenobiotics to toxic metabolites, thereby explaining the increased vulnerability of heavy drinkers to industrial solvents, anesthetics, commonly used drugs, over-the-counter medications and carcinogens. The contribution of gastric alcohol dehydrogenase to the first pass metabolism of ethanol and alcohol-drug interactions is now recognized. Alcohol also alters the degradation of key nutrients, thereby promoting deficiencies as well as toxic interactions with vitamin A and beta-carotene. Conversely, nutritional deficits may affect the toxicity of ethanol and acetaldehyde, as illustrated by the depletion in glutathione, ameliorated by S-adenosyl-L-methionine. Other supernutrients include polyenylphosphatidylcholine, shown to correct the alcohol-induced hepatic phosphatidylcholine depletion and to prevent alcoholic cirrhosis in non-human primates. Thus, a better understanding of the pathology induced by ethanol has now generated improved prospects for therapy.

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.

Aetiology and pathogenesis of alcoholic liver disease

Until the 1960s, liver disease of the alcoholic patient was attributed exclusively to dietary deficiencies. Since then, however, our understanding of the impact of alcoholism on nutritional status has undergone a progressive evolution. Alcohol, because of its high energy content, was at first perceived to act exclusively as 'empty calories' displacing other nutrients in the diet, and causing primary malnutrition through decreased intake of essential nutrients. With improvement in the overall nutrition of the population, the role of primary malnutrition waned and secondary malnutrition was emphasized as a result of a better understanding of maldigestion and malabsorption caused by chronic alcohol consumption and various diseases associated with chronic alcoholism. At the same time, the concept of the direct toxicity of alcohol came to the forefront as an explanation for the widespread cellular injury. Some of the hepatotoxicity was found to result from the metabolic disturbances associated with the oxidation of ethanol via the liver alcohol dehydrogenase (ADH) pathway and the redox changes produced by the generated NADH, which in turn affects the metabolism of lipids, carbohydrates, proteins and purines. Exaggeration of the redox change by the relative hypoxia which prevails physiologically in the perivenular zone contributes to the exacerbation of the ethanol-induced lesions in zone 3. In addition to ADH, ethanol can be oxidized by liver microsomes: studies over the last twenty years have culminated in the molecular elucidation of the ethanol-inducible cytochrome P450IIE1 (CYP2E1) which contributes not only to ethanol metabolism and tolerance, but also to the selective hepatic perivenular toxicity of various xenobiotics. Their activation by CYP2E1 now provides an understanding for the increased susceptibility of the heavy drinker to the toxicity of industrial solvents, anaesthetic agents, commonly prescribed drugs, 'over the counter' analgesics, chemical carcinogens and even nutritional factors such as vitamin A. Ethanol causes not only vitamin A depletion but it also enhances its hepatotoxicity. Furthermore, induction of the microsomal pathway contributes to increased acetaldehyde generation, with formation of protein adducts, resulting in antibody production, enzyme inactivation and decreased DNA repair; it is also associated with a striking impairment of the capacity of the liver to utilize oxygen. Moreover, acetaldehyde promotes glutathione depletion, free-radical mediated toxicity and lipid peroxidation. In addition, acetaldehyde affects hepatic collagen synthesis: both in vivo and in vitro (in cultured myofibroblasts and lipocytes), ethanol and its metabolite acetaldehyde were found to increase collagen accumulation and mRNA levels for collagen. This new understanding of the pathogenesis of alcoholic liver disease may eventually improve therapy with drugs and nutrients.

Comparison of blood alcohol concentrations after beer and whiskey

To determine whether blood alcohol concentrations achieved by ingestion of various alcoholic beverages differ as a function of prandial state, healthy male volunteers, aged 24 to 48 years, were given the same amount of alcohol (0.3 g/kg) as different beverages. The alcohol was consumed in three prandial states: postprandial (1 hr after a meal, n = 10), prandial (during the meal, n = 10), and preprandial (after an overnight fast, n = 9). Each subject was tested with both beer and whiskey, and in the postprandial state also with wine and sherry, in a within-subjects design. Blood alcohol concentrations were estimated by breath analysis for 4 hr or until concentrations reached zero. Peak blood alcohol levels were higher with beer than with whiskey in the postprandial and prandial conditions (p < 0.01), whereas the opposite was true in the preprandial state (p < 0.05). Similarly, the area under the blood alcohol curve was higher with beer in the prandial state (p < 0.05), and higher with whiskey in the preprandial condition (p < 0.01). Wine and sherry yielded peak concentrations intermediate between those of beer and whiskey in the postprandial state. The results indicate that a dilute alcoholic drink can yield either higher or lower blood alcohol levels than a concentrated beverage, depending on the prandial state.

Effect of chronic alcohol feeding on hepatic iron status and ferritin uptake by rat hepatocytes

Alcohol abuse is known to cause disturbances to iron homeostasis in man and is associated with elevated serum ferritin levels. We have previously shown that ethanol metabolism in the rat hepatocyte is associated with an immediate reduction in ferritin uptake by this cell. In this study we have examined the effect of pair-feeding the Lieber-DeCarli liquid alcohol diet on ferritin uptake by rat hepatocytes. Rat liver ferritin was radiolabeled with 59Fe in vivo and isolated by conventional techniques. Rats were pair-fed the Lieber-DeCarli liquid alcoholic diet for 4-6 weeks. Hepatocytes, isolated from their livers by collagenase perfusion, were incubated with [59Fe]ferritin in L-15 medium at 37 degrees C and 4 degrees to measure ferritin uptake and binding. The in vitro effect of ethanol on these hepatocytes was also studied. Ferritin and iron parameters were measured in the sera and hepatocytes of these animals and a comparable group of normal chow-fed rats. The rate of ferritin uptake by hepatocytes from alcohol-fed rats was significantly faster than that of their pair-fed controls (0.743 +/- 0.061 vs. 0.540 +/- 0.042 ng/min/10(6) cells, p < 0.05). However, the rats on Lieber-DeCarli control diet exhibited a lower hepatocyte ferritin uptake rate than chow-fed animals (79.3 +/- 8.1% of the control values, p < 0.01). In vitro incubation of cells in 100 mM ethanol resulted in less inhibition of ferritin uptake by hepatocytes from alcoholic rats than from their pair-fed controls (11 +/- 7.1% inhibition vs. 43.6 +/- 10.7% for controls, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Daily dose of ethanol and the development and decay of acute and chronic tolerance and physical dependence in rats

Using behavioral and physiological measures, we compared the rates of development and decay of acute and chronic tolerance to ethanol (ET) and the severity of the withdrawal syndrome. Male rats were treated with 6, 9, or 12 g/kg/day ET or equicaloric dextrin maltose, delivered intragastrically. Although treatment duration varied, the total dose of ET was kept constant at 162 g/kg/rat for the three groups. The effects of a cumulative test dose of ET or equicaloric dextrin maltose, after exposure to a total of 0, 42, 83, 126, and 162 g/kg ET, and at 3, 5, and 7 days after termination of the chronic treatments, were evaluated on rectal temperature, dowel performance, and tail-flick and startle responses. After the initial five tolerance tests, chronic treatments were discontinued and rats were tested in a modified open-field apparatus and for their startle response to an auditory stimulus at 8, 12, 16, 20, 32, and 40 h later. With all measures, little tolerance developed in the 6-g/kg/day group. On the other hand, development of chronic tolerance was fastest in rats treated with the 12-g/kg/dose of ET. Chronic tolerance did not develop to ET's depressant effect on the startle response. Acute tolerance declined with chronicity of treatment in animals given the largest daily dose of ET. During withdrawal, and in contrast to the dextrin maltose-treated animals, there was impairment in all measures taken during the modified open-field test and hypersensitivity of the startle response for all three chronic ET-treated animals. Greatest behavioral impairment occurred in animals treated with 12 g/kg/day, and some impairment was still evident 40 h after the last dose of ET. Thus, the severity of the withdrawal syndrome was greatest in the group displaying the most acute and chronic tolerance.