Alcohol dehydrogenase activity in the uremic rat

Influence of epinephrine on alcohol dehydrogenase activity in rat hepatocyte culture

The effects of epinephrine on alcohol dehydrogenase activity and on rates of ethanol elimination were determined in rat hepatocyte culture. Continuous exposure of the hepatocytes to epinephrine (10 microM) in combination with dexamethasone (0.1 microM) enhanced alcohol dehydrogenase activity on days 4-7 of culture, whereas neither hormone alone had an effect. The increased alcohol dehydrogenase activity was associated with an increased rate of ethanol elimination. Acute addition of 10 microM epinephrine to hepatocytes maintained in culture with 0.1 microM dexamethasone did not change alcohol dehydrogenase activity, but resulted in an immediate marked, but transitory, increase in ethanol elimination within the first 5 min after the addition of the hormone. Prazosin, an alpha 1-adrenergic blocker, and antimycin, an inhibitor of mitochondrial respiration, were powerful inhibitors of the transient increase in ethanol elimination, whereas 4-methylpyrazole was only partially inhibitory. These observations indicate that epinephrine has a chronic effect in increasing alcohol dehydrogenase activity and ethanol elimination and, also, an acute transient effect of increasing ethanol elimination which is not limited by alcohol dehydrogenase activity.

Ethanol metabolism

Alcohol is metabolized by two pathways in humans: the ADH pathway which accounts for the bulk of the metabolism, and the MEOS pathway which contributes to the increased rate of ethanol elimination at high blood alcohol levels. The increased rate of elimination which results from chronic alcohol consumption is due to an increase in MEOS activity. The activities of these pathways are influenced by environmental factors such as smoking, diet, and endocrine factors. In addition, individuals inherit different types of ADH isoenzymes which have different kinetic properties. Individuals with different phenotypic variants, e.g. the beta 1 vs beta 2 isoenzymes, appear to have different rates of ethanol elimination. The cloning of the ADH genes and the availability of molecular hybridization methods now make it possible to genotype individuals and to correlate the genotype with both alcohol elimination rates and with the risk of developing medical complications of alcoholism or even of developing alcoholism itself.

Effect of growth hormone on alcohol dehydrogenase activity in hepatocyte culture

The effect of growth hormone on the activity of alcohol dehydrogenase was determined in hepatocyte culture from normal and hypophysectomized male rats. Alcohol dehydrogenase activity was highest in hepatocytes harvested from hypophysectomized rats. The enzyme activity remained stable in hepatocytes harvested from normal rats during 2 to 6 days of culture but declined steadily in hepatocytes cultured from hypophysectomized rats. The combination of growth hormone (1 microgram per ml) and corticosterone (1 microM) increased alcohol dehydrogenase activity in hepatocytes from normal rats, while neither hormone alone had an effect. Corticosterone (1 microM) prevented the decline of the enzyme activity in hepatocytes from hypophysectomized rats, and the combination of growth hormone (1 microgram per ml) and corticosterone (1 microM) resulted in a further increase in enzyme activity. The increases in alcohol dehydrogenase, due to the exposure of the hepatocytes to the combination of growth hormone and corticosterone, were associated with increases in the rate of ethanol elimination. These observations indicate that growth hormone enhances liver alcohol dehydrogenase activity and ethanol elimination, and that this effect is dependent on the permissive influence of corticosterone.

First pass metabolism of ethanol--a gastrointestinal barrier against the systemic toxicity of ethanol

Both in men and rats, most of the ethanol ingested at a low dose is metabolized before it reaches the systemic circulation. Oxidation of ethanol (mainly in the stomach) accounts for the bulk of this effect. This "first pass" metabolism (FPM) may be viewed as a barrier which protects against the systemic toxicity of ethanol. This barrier can be overcome by large doses of ethanol. Its efficiency is also reduced by a decrease in gastric alcohol dehydrogenase (ADH) activity secondary to chronic alcohol consumption.

First pass metabolism of ethanol: an important determinant of blood levels after alcohol consumption

Alcohol consumption by rats fed ethanol-containing liquid diets is considerably greater than the measured rate of ethanol elimination from the blood, suggesting that a significant fraction of the alcohol ingested does not enter the systemic circulation. To assess the possibility of a first pass metabolism of ethanol, we compared the areas under the blood ethanol concentration curves after administration of various doses through various routes in alcohol-fed and control rats. In both groups, blood ethanol concentrations were significantly lower after intragastric than after intraportal or intravenous (femoral) administrations and, to a lesser extent, than after an intraduodenal dose. By contrast, the rise in blood acetate, a product of ethanol oxidation, was faster after intragastric administration. Moreover, absorption of the ethanol dose was virtually complete at the time of ethanol disappearance from the blood. The fraction of the dose that did not enter the systemic circulation was proportionally greater with the smaller doses. These results indicate that there is a significant first pass metabolism of ethanol which takes place in the gastrointestinal tract and particularly in the stomach, where alcohol dehydrogenase (ADH) activity is the highest. Chronic alcohol administration decreased ADH activity (probably secondary to gastric mucosal injury) and also decreased the magnitude of the first pass metabolism. The amount of ethanol ingested which does not enter the systemic circulation accounts for the apparent dissociation between alcohol consumption, blood ethanol levels and rate of blood ethanol elimination in alcohol-fed animals.

Rat liver alcohol dehydrogenase. II. Quantitative enzyme-linked immunoadsorbent assay

Monospecific rabbit antibodies against purified Fischer-344 rat liver alcohol dehydrogenase were produced and used to develop an enzyme-linked immunoadsorbent assay for alcohol dehydrogenase. The assay is based upon the competitive inhibition of specific antibody binding to antigen (alcohol dehydrogenase adsorbed onto plastic microtiter plates) by soluble alcohol dehydrogenase (contained in unknown sample extracts or in known standard solutions). The amount of bound antibody is determined following incubation with peroxidase-linked second antibody (goat anti-rabbit IgG antibody-peroxidase conjugate) by colorimetric measurements of peroxidase activity at 490 nm in the presence of O-phenylenediamine. The assay is highly sensitive (it detects 10-1000 ng alcohol dehydrogenase/50 microliter) and it offers a precise (interexperimental variations in samples were less than 10%), rapid (6-8 h), and specific method for measurements of alcohol dehydrogenase in tissue homogenates or cultured hepatocytes. The assay was used to study changes in alcohol dehydrogenase levels during the growth cycle of cultured hepatocytes over a 2-week period and in rat liver homogenates after starving the animals for 72 h. In cultured hepatocytes, alcohol dehydrogenase activity and immunoassayable enzyme levels decreased coordinately during lag and early log phase, from 13.2 +/- 1.2 to 5.0 +/- 1.0 micrograms enzyme/mg protein, respectively. In mid-log phase, the enzyme levels were very low (1.3 +/- 0.4 micrograms enzyme/mg protein). During stationary phase, the levels (5.7 +/- 0.6 micrograms enzyme/mg protein) increased to 35% of the levels of freshly isolated hepatocytes (15.6 +/- 1.4 micrograms enzyme/mg protein). In starved animals, the enzyme levels decreased from 7.56 +/- 0.55 to 2.97 +/- 0.27 mg enzyme/liver. These changes also coincided with decreases in activity from 8.84 +/- 0.35 to 6.56 +/- 0.68 microM/min/liver.

Effect of dihydrotestosterone on rat liver alcohol dehydrogenase activity

Castration was previously demonstrated to result in an increase in liver alcohol dehydrogenase and in rates of ethanol elimination in male rats. In this study, the effect of dihydrotestosterone, which is a more potent androgen than testosterone in the rat, was determined on liver alcohol dehydrogenase and ethanol elimination in the castrated rat. Dihydrotestosterone was found to be a substrate of liver alcohol dehydrogenase in the reductive direction and a competitive inhibitor of ethanol oxidation by the enzyme. Also, the administration of a single dose of dihydrotestosterone inhibited liver alcohol dehydrogenase 4 hr after the injection, but this effect was not persistent at later intervals following injection. This transient in vivo inhibition of liver alcohol dehydrogenase was associated with a delay in ethanol elimination. The microsomal ethanol-oxidizing enzyme system was found to play no role in the changes in ethanol elimination observed after castration and dihydrotestosterone administration since its activity remained unchanged. These studies provide further evidence of an effect of androgenic steroids on liver alcohol dehydrogenase activity and ethanol metabolism.