Influence of acid-secretion blockers on gastric and hepatic alcohol dehydrogenase in rat

Human skeletal muscle lactate dehydrogenase activity in the presence of some alcohol dehydrogenase inhibitors

Methanol, ethylene glycol and other alcohol intoxications are complicated by severe acidosis which could be caused by formation of metabolic acids and additionally lactic acid production. An increasing nicotinamide adenine dinucleotide reduced/nicotinamide adenine dinucleotide oxidized (NADH/NAD) ratio during alcohol biotransformation is responsible for the induction of lactic acidosis. The main purpose of the present paper was to evaluate the effect of 4-methylpyrazole, cimetidine, ethylenediaminetetraacetic acid disodium salt, ethanol and methanol on lactate dehydrogenase (E.C. 1.1.1.27) activity and to discuss this issue. The activity of the enzyme was determined spectrophotometrically, in vitro using human enzyme skeletal muscle homogenates. 4-Methylpyrazole, cimetidine and ethylenediaminetetraacetic acid disodium salt at concentrations 0.01, 0.1, 1.0 mM and 12.5, 25.0, 50.0 mM of ethanol and methanol were studied. Our results showed that cimetidine increased lactate dehydrogenase activity as compared to the control at all tested concentrations. Such activity was noted for 4-methylpyrazole at 0.1 mM and higher concentration. By contrast, no significant effect on lactate dehydrogenase activity in the presence of ethylenediaminetetraacetic acid disodium salt, methanol and ethanol was observed.

Pharmacokinetics of ethanol: a review of the methodology

This paper reviews current concepts on tools for studying the pharmacokinetics of alcohol. It has been known that ethanol metabolism occurs mainly in the liver via alcohol dehydrogenase and an accessory microsomal pathway. The contribution of each pathway has been examined by administration of metabolic inhibitors. The role of gastric alcohol dehydrogenase in the first-pass effects of ethanol has been speculative and may be relatively low. Some pharmacokinetic approaches with mathematical models have elucidated the role of gastric alcohol dehydorgenase, hepatic alcohol dehydrogenase and cytochrome P450 2E1 in ethanol elimination. The scale-up of ethanol elimination kinetics has enabled extrapolation from animal models to human kinetics. The clarification of the pharmacokinetics of ethanol is very important for estimating the effects of ethanol on biological events.

Alcohol levels are increased in social drinkers receiving ranitidine

OBJECTIVE

Ranitidine increases blood alcohol concentrations by decreasing the first pass metabolism of ethanol. The effect of ranitidine on alcohol levels has been found to be variable when using large doses of alcohol or conditions in which its first pass metabolism is known to be minimal. Despite a consensus that the drug increases alcohol levels after small doses of ethanol, this effect has been considered inconsequential, because of the low alcohol levels. However, social drinking comprises repetitive consumption of small doses of alcohol and the ranitidine effect could thereby be potentiated.

METHODS

To study this factor, alcohol levels were determined by breath analysis in nine men (social drinkers), after four drinks of 0.15 g/kg ethanol given postprandially every 45 min, before and after ranitidine (150 mg b.i.d. for 7 days).

RESULTS

Their blood alcohol increased with repeated doses, reaching peak values of 24+/-3 mg/dl before ranitidine and 33+/-2 after ranitidine (p = 0.04). In seven of the nine subjects blood alcohol exceeded 25 mg/dl, a level at which impairment of judgment and of finely tuned skills occurs and which exceeds legal limits of driving in some European countries. Moreover, the high levels persisted for a longer time with than without the drug. These effects were associated with a 62% decrease in first pass metabolism.

CONCLUSION

Under conditions mimicking social drinking, ranitidine increases blood alcohol to levels known to impair psychomotor skills needed for driving.

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).

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.

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.