Ethanol-induced inhibition of glucose transport across the isolated brush-border membrane of hamster jejunum

Prevalence, sociodemographic, and clinical correlates of underweight in a sample of Chinese male alcohol-dependent patients

BACKGROUND

Underweight is a significant symptom in alcohol-dependent patients, yet few studies have examined underweight in Chinese male patients. The current study aimed to identify the prevalence, sociodemographic, and clinical correlates of underweight in Chinese male patients with alcohol dependency.

METHODS

In this cross-sectional study, 405 male inpatients with alcohol dependence and 383 healthy male controls were recruited. Participants' demographic and clinical data, including anthropometric data, were collected. We first conducted univariate analysis to identify seven variables with significant differences between groups: smoking behavior, hospitalization, alcohol consumption, cerebral infarction, hypertension, Hamilton Depression Scale (HAMD) score, and Scale for Assessment of Negative Symptom (SANS) score. Then, binary logistic regression was used to assess their relationship with underweight, with a significance level of .05.

RESULTS

The prevalence of underweight was significantly higher in the study population than in the control group (2.99% vs. 2.87%; P < .001). Patients with underweight had significantly higher rates of smoking behavior and cerebral infarction, as well as higher scores of SANS and HAMD than non-underweight patients. The non-underweight patients had higher daily alcohol consumption and times of hospitalization. Furthermore, logistic regression analysis showed that smoking behavior [odds ratio (OR) = 2.84, 95% confidence interval (CI) = 1.03-7.80, P = .043)], cerebral infarction (OR = 5.20, 95% CI = 1.13-23.85, P = .036), SANS score (OR = 1.22, 95% CI = 1.16-1.28, P < .001), and HAMD score (OR = 1.06, 95% CI = 1.02-1.11, P = .005) were associated with underweight.

CONCLUSIONS

More than 20% of male alcohol-dependent patients in a Chinese sample were underweight. Some demographic and clinical variables independent correlates for underweight in alcohol-dependent patients. We need to focus on alcohol-dependent patients with smoking, cerebral infarction, depression, and more prominent negative symptoms.

The Influence of Alcohol Consumption on Intestinal Nutrient Absorption: A Comprehensive Review

Chronic alcohol use has been attributed to the development of malnutrition. This is in part due to the inhibitory effect of ethanol on the absorption of vital nutrients, including glucose, amino acids, lipids, water, vitamins, and minerals within the small intestine. Recent advances in research, along with new cutting-edge technologies, have advanced our understanding of the mechanism of ethanol's effect on intestinal nutrient absorption at the brush border membrane (BBM) of the small intestine. However, further studies are needed to delineate how ethanol consumption could have an impact on altered nutrient absorption under various disease conditions. Current research has elucidated the relationship of alcohol consumption on glucose, glutamine, vitamins B1 (thiamine), B2 (riboflavin), B9 (folate), C (ascorbic acid), selenium, iron, and zinc absorption within the small intestine. We conducted systematic computerized searches in PubMed using the following keywords: (1) "Alcohol effects on nutrient transport"; (2) "Alcohol mediated malabsorption of nutrients"; (3) "Alcohol effects on small intestinal nutrient transport"; and (4) "Alcohol mediated malabsorption of nutrients in small intestine". We included the relevant studies in this review. The main objective of this review is to marshal and analyze previously published research articles and discuss, in-depth, the understanding of ethanol's effect in modulating absorption of vital macro and micronutrients in health and disease conditions. This could ultimately provide great insights in the development of new therapeutic strategies to combat malnutrition associated with alcohol consumption.

Moderate Alcohol Consumption Uniquely Regulates Sodium-Dependent Glucose Co-Transport in Rat Intestinal Epithelial Cells In Vitro and In Vivo

BACKGROUND

Chronic alcohol use often leads to malnutrition. However, how the intestinal absorption of nutrients such as glucose may be affected during moderate ethanol use has not been investigated. Glucose is absorbed via sodium (Na)-dependent glucose co-transport (SGLT1; SLC5A1) along the brush border membrane (BBM) of intestinal absorptive villus cells.

OBJECTIVE

The aim of this study was to investigate how moderate alcohol consumption affects the absorption of glucose via SGLT1.

METHODS

Intestinal epithelial cells (IEC-18; rat) were exposed to 8.64 mM ethanol over 1, 3, 6, and 12 h. Rats (16-wk-old, male, Sprague-Dawley) were administered 2 g/kg ethanol over 1, 3, and 6 h. Na-dependent 3H-O-methyl-d-glucose uptake was measured to assess SGLT1 activity. Na-K-ATPase activity was measured as a function of inorganic phosphate release. Protein expression was analyzed by Western blot analysis and immunohistochemical staining.

RESULTS

Ethanol significantly decreased Na-dependent glucose absorption in enterocytes in vitro (ethanol treatment: 48.4% of controls at 1 h; P < 0.01) and in vivo (ethanol treatment: 60.0% of controls at 1 h; P < 0.01). Na-K-ATPase activity was significantly inhibited in vitro (ethanol treatment: 36.9% of controls at 1 h; P < 0.01) and in vivo (ethanol treatment: 42.1% of controls at 1 h; P < 0.01). Kinetic studies showed that the mechanism of inhibition of Na-glucose co-transport was secondary to a decrease in the affinity (1/Km) of the co-transporter for glucose both in vitro and in vivo. Western blots and immunohistochemistry further demonstrated unaltered amounts of SGLT1 after ethanol treatment.

CONCLUSIONS

Moderate ethanol significantly decreases glucose absorption in IEC-18 cells and in villus cells of Sprague-Dawley rats. The inhibition of SGLT1 is secondary to an altered Na gradient at the cellular level and secondary to diminished affinity of the co-transporter for glucose at the protein level in the BBM. These observations may, at least in part, explain 1 possible mechanism of the onset of malnutrition associated with alcohol consumption.

Moderate Alcohol Consumption Inhibits Sodium-Dependent Glutamine Co-Transport in Rat Intestinal Epithelial Cells in Vitro and Ex Vivo

Malnutrition is present in chronic alcoholics. However, how moderate alcohol consumption affects the absorption of nutrients like glutamine has not been investigated. Glutamine, an amino acid, is vital to gastrointestinal health. Glutamine is absorbed via sodium-dependent glutamine co-transport (B0AT1; SLC6A19) along the brush border membrane of absorptive villus cells. Rat intestinal epithelial cells (IEC-18) and sixteen-week-old Sprague Dawley rats were administered the equivalent of a 0.04% blood alcohol content of ethanol (8.64 mM; 2 g/kg) to investigate the effect of moderate alcohol on sodium-glutamine co-transport. Sodium-dependent ³H-glutamine uptakes were performed to measure B0AT1 activity. Inorganic phosphate was measured as a function of Na-K-ATPase activity. Protein expression was analyzed by immunohistochemical and Western blot analysis. Ethanol significantly inhibited sodium-dependent glutamine absorption and Na-K-ATPase activity in enterocytes in vitro and ex vivo. Kinetic studies suggested that the mechanism of inhibition was due to decreased maximal rate of uptake (V_max) of the B0AT1 co-transporter, corresponding to decreased B0AT1 protein expression and secondary to an inhibited sodium-gradient at the cellular level in vitro and ex vivo. In all, moderate ethanol significantly inhibited glutamine absorption at the level of decreased B0AT1 expression at the brush border membrane and a reduced sodium gradient, which may contribute to malnutrition present in chronic alcoholics.

Auxotrophic Mutations Reduce Tolerance of Saccharomyces cerevisiae to Very High Levels of Ethanol Stress

Very high ethanol tolerance is a distinctive trait of the yeast Saccharomyces cerevisiae with notable ecological and industrial importance. Although many genes have been shown to be required for moderate ethanol tolerance (i.e., 6 to 12%) in laboratory strains, little is known of the much higher ethanol tolerance (i.e., 16 to 20%) in natural and industrial strains. We have analyzed the genetic basis of very high ethanol tolerance in a Brazilian bioethanol production strain by genetic mapping with laboratory strains containing artificially inserted oligonucleotide markers. The first locus contained the ura3Δ0 mutation of the laboratory strain as the causative mutation. Analysis of other auxotrophies also revealed significant linkage for LYS2, LEU2, HIS3, and MET15. Tolerance to only very high ethanol concentrations was reduced by auxotrophies, while the effect was reversed at lower concentrations. Evaluation of other stress conditions showed that the link with auxotrophy is dependent on the type of stress and the type of auxotrophy. When the concentration of the auxotrophic nutrient is close to that limiting growth, more stress factors can inhibit growth of an auxotrophic strain. We show that very high ethanol concentrations inhibit the uptake of leucine more than that of uracil, but the 500-fold-lower uracil uptake activity may explain the strong linkage between uracil auxotrophy and ethanol sensitivity compared to leucine auxotrophy. Since very high concentrations of ethanol inhibit the uptake of auxotrophic nutrients, the active uptake of scarce nutrients may be a major limiting factor for growth under conditions of ethanol stress.

Morphological, kinetic, membrane biochemical and genetic aspects of intestinal enteroplasticity

The process of intestinal adaptation (“enteroplasticity”) is complex and multifaceted. Although a number of trophic nutrients and non-nutritive factors have been identified in animal studies, successful, reproducible clinical trials in humans are awaited. Understanding mechanisms underlying this adaptive process may direct research toward strategies that maximize intestinal function and impart a true clinical benefit to patients with short bowel syndrome, or to persons in whom nutrient absorption needs to be maximized. In this review, we consider the morphological, kinetic and membrane biochemical aspects of enteroplasticity, focus on the importance of nutritional factors, provide an overview of the many hormones that may alter the adaptive process, and consider some of the possible molecular profiles. While most of the data is derived from rodent studies, wherever possible, the results of human studies of intestinal enteroplasticity are provided.

Intestinal mucosal adaptation

Intestinal failure is a condition characterized by malnutrition and/or dehydration as a result of the inadequate digestion and absorption of nutrients. The most common cause of intestinal failure is short bowel syndrome, which occurs when the functional gut mass is reduced below the level necessary for adequate nutrient and water absorption. This condition may be congenital, or may be acquired as a result of a massive resection of the small bowel. Following resection, the intestine is capable of adaptation in response to enteral nutrients as well as other trophic stimuli. Identifying factors that may enhance the process of intestinal adaptation is an exciting area of research with important potential clinical applications.

Effects of ethanol intoxication on LH receptors and glucose oxidation in Leydig cells of adult albino rats

The present study was designed to assess the dose-dependent effects of ethanol on Leydig cells of adult albino rats of the Wistar strain. Ethanol was given orally through gastric intubation at three different dose levels (0.5, 1 and 3 g/kg body weight) twice daily as 25% (v/v) aqueous solution for 15 days. Ethanol treatment reduced body and testes weights. Serum testosterone registered a decrease while estradiol levels became elevated. Activities of the steroidogenic enzymes 3beta-hydroxysteroid dehydrogenase (3beta-HSD) and 17-ketosteroid reductase (17-KSR) decreased significantly. The glucose oxidative capacity of Leydig cells was impaired by ethanol treatment in a dose-dependent manner. Similarly, ethanol treatment caused significant reduction in LH receptors on the Leydig cell membrane at higher doses (1 and 3 g/kg) whereas no significant change was observed with the lower dose (0.5 g/kg) as compared to controls. The present findings suggest that the decrease in Leydig cellular LH receptors, glucose oxidation and the activities of 3beta-HSD and 17-KSR are possible mechanisms by which ethanol treatment perturbs Leydig cell steroidogenesis.

Oxidative and drug-induced alterations in brush border membrane hemileaflet fluidity, functional consequences for glucose transport

Oxidation of biological membranes has been suggested as a major pathological process in a variety of disease states including intestinal ischemia and inflammatory bowel disease. Previous studies on the small intestinal brush border membrane have shown that part of the decrease in the activity of the Na(+)-dependent glucose transporter (SGLT1) observed after oxidation could be secondary to the derangement in membrane fluidity that accompanied oxidative damage. The present study examined the relationship between oxidative-induced hemileaflet fluidity alterations and the resultant change in Na(+)-dependent glucose transport activity. To address this issue, in vitro oxidation of guinea pig brush border membrane vesicles was induced by incubation of the vesicles with ferrous sulfate and ascorbate. We found that oxidation decreased the fluidity of both the outer and inner hemileaflets, the decrease being greater in the outer leaflet. Moreover, the preferential alteration in hemileaflet fluidity was accompanied by a decrease in glucose transport. However, when membrane perturbing agents such as hexanol and A(2)C were used to restore membrane fluidity to levels comparable to controls, rates of glucose transport could not be interpreted in terms of variation of bulk membrane fluidity or variation in fluidity of any specific membrane leaflet. On the basis of these experiments, we propose that previous studies that reported coincidental alteration in membrane fluidity and glucose transport cannot be interpreted on the basis of bulk fluidity or hemileaflet fluidity.

Increased sodium-dependent D-glucose transport in the jejunal brush-border membrane of spontaneously hypertensive rat

The current studies explore the effect of hypertension on D-glucose transport into jejunal brush-border membrane vesicles (BBMV). Spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats, as a control group, were used. The purity of the BBMV from both groups of animals was validated by the finding that the specific activity of brush-border enzyme marker, sucrase, was severalfold greater in membrane vesicles compared with corresponding values in mucosal homogenate. D-glucose uptake was Na+ dependent in both groups of animals, with a transient increase in the intravesicular concentration of D-glucose. However, the initial rate and the magnitude of the accumulation of Na+-dependent D-glucose was significantly higher in SHR compared with WKY rats. In order to investigate the mechanism(s) for the increase in Na+-dependent D-glucose transport in SHR, several experiments were performed: (1) an experiment that indicated 22Na uptake, as an indicator for Na+ permeability, was similar between SHR and WKY rats, (2) kinetic studies that indicated that Vmax values of SHR were significantly greater that those of WKY rats. In contrast, similar Km values for glucose were found between SHR and WKY rats, (3) Na+-dependent phlorizin binding measurements that were not altered by hypertension and (4) a study of the brush-border membrane lipid composition that showed a significant increase in the free cholesterol/phospholipid ratio in SHR. We conclude that altered membrane cholesterol content and consequently altered lipid fluidity could be, at least in part, responsible for the observed increase in Na+-dependent D-glucose transport in SHR.

Ethanol-induced jejunal microvascular and morphological injury in relation to histamine release in rabbits

BACKGROUND

To investigate the relation between ethanol-induced jejunal microvascular injury, morphological changes, and histamine release, the present study examined whether the attenuation of microvascular effect of ethanol by 16,16-dimethyl prostaglandin E2 (dmPGE2) (reported by us previously) was associated with an attenuation of epithelial damage and histamine release.

METHODS

Rabbits were used. Mucosal microvascular injury was assessed by determining jejunal plasma protein loss (JPPL), histamine release by measuring histamine concentration of the gut effluent, and epithelial damage by routine histology.

RESULTS

(1) During 90-minute jejunal ethanol perfusion, there was a direct relation between the time course of histamine release and that of JPPL. (2) dmPGE2 attenuated the ethanol-induced JPPL and histamine release, and the decrease in JPPL was directly proportional to the decrease in histamine release. (3) dmPGE2 did not alleviate ethanol-induced epithelial damage. (4) Ketotifen (a mast cell stabilizer), similar to dmPGE2, attenuated ethanol-induced JPPL and histamine release. (5) Ethanol caused histamine release by the jejunum in vitro; this was attenuated by dmPGE2 and also by phloretin (a mast cell stabilizer).

CONCLUSIONS

It appears that (1) ethanol causes JPPL by inducing release of mediators from mucosal mast cells. (2) dmPGE2 attenuates JPPL by stabilizing mast cells. (3) The ethanol-induced mucosal microvascular injury is directly related to histamine release but not to epithelial damage.

Proline transport across the intestinal microvillus membrane may be regulated by membrane physical properties

There is now abundant evidence that integral membrane protein function may be modulated by the physical properties of membrane lipids. The intestinal brush border membrane represents a membrane system highly specialized for nutrient absorption and, thus, provides an opportunity to study the interaction between integral membrane transport proteins and their lipid environment. We have previously demonstrated that alterations in this environment may modulate the function of the sodium-dependent glucose transporter in terms of its affinity for glucose. In this communication we report that membrane lipid-protein interactions are distinctly different for the proline transport proteins. Maximal transport rates for L-proline by either the neutral brush border or imino transport systems are reduced 10-fold when the surrounding membrane environment is made more fluid over the physiological range that exists along the crypt-villus axis. Furthermore, in microvillus membrane vesicles prepared from enterocytes isolated from along the crypt-villus axis a similar gradient exists in the functional activity of these transport systems. This would imply that either the functional activity of these transporters are regulated by membrane physical properties or that the synthesis and insertion of these proteins is coordinated in concert with membrane physical properties as the enterocyte migrates up the crypt-villus axis.

In vitro effect of ethanol on sodium and glucose transport in rabbit renal brush border membrane vesicles

The effect of ethanol on sodium and glucose transport in rabbit renal brush border membrane vesicles was examined. When membrane vesicles were preincubated in the presence of ethanol the sodium-dependent D-glucose uptake was significantly inhibited. This effect, as suggested by O'Neill et al. (1986) FEBS Lett. 194, 183-188, may be due to a faster collapse of the Na+ gradient. As a matter of fact, the amiloride-insensitive sodium pathway was increased by ethanol in our brush border membrane preparation. However, sodium/D-glucose cotransport was inhibited by ethanol, although to a lesser degree, also in the absence of a sodium gradient. In addition, ethanol inhibited glucose-dependent sodium uptake, suggesting that a direct interaction with the translocator was involved. This conclusion was also supported by kinetic measurements showing a decrease of Vmax and an increase in Km for glucose in membrane vesicles treated with ethanol. Moreover, ethanol influenced the interaction of phlorizin with the cotransporter: uptake experiments performed in the presence of the two inhibitors demonstrated that phlorizin and ethanol behave as not mutually exclusive inhibitors of D-glucose transport. These data indicate that in rabbit renal brush border membranes ethanol not only affects the 'passive pathway', i.e. the sodium permeability, but it also directly interferes with carrier functions.

16,16-Dimethyl prostaglandin E2 alleviates jejunal microvascular effects of ethanol but not the ethanol-induced inhibition of water, sodium, and glucose absorption

To examine the relation between ethanol-induced microvascular and absorptive changes, we have investigated the effect of 16,16-dimethyl prostaglandin E2 on the jejunal intraluminal plasma albumin loss (which was taken as a measure of microvascular changes) and the inhibition of water, sodium, and glucose transport caused by intraluminal ethanol. A group of 8 dogs received intravenously 16,16-dimethyl prostaglandin E2 at a dose of 0.1 microgram/kg as a bolus followed by 0.05 microgram/kg.hour for 2 h (prostaglandin-treated group). A second group of 8 dogs received no 16,16-dimethyl prostaglandin E2 (untreated group). In each dog of both groups, one jejunal segment was perfused with an ethanol-free solution (control segment) and an adjacent segment was perfused with the same solution containing 6% (wt/vol) ethanol (ethanol-perfused segment). The albumin loss (mg/g dry gut wt.90 min, mean +/- SE) by the control and the ethanol-perfused segments was 0.76 +/- 0.23 and 8.29 +/- 1.27, respectively, in the untreated group, and 0.66 +/- 0.23 and 4.81 +/- 0.67, respectively, in the prostaglandin-treated group. The ethanol-induced increase in albumin loss was significant in both groups, but was significantly lower (p less than 0.05) in the prostaglandin-treated group than in the untreated group. Intraluminal ethanol depressed net water, sodium, and glucose transport by 74%, 52%, and 22%, respectively, in the untreated group, and by 92%, 65%, and 38%, respectively, in the prostaglandin-treated group. The magnitude of this depression did not differ significantly between the two groups. As 16,16-dimethyl prostaglandin E2 attenuated the ethanol-induced plasma albumin loss, but not the inhibition of water, sodium, or glucose transport, we conclude that the microvascular and the absorptive changes produced by ethanol are not mediated by the same mechanism.

Ethanol inhibits Na+-gradient-dependent uptake of L-amino acids into intestinal brush border membrane vesicles

Brush border membrane vesicles from hamster jejunum were used to investigate the effects of ethanol on Na+-dependent transport of amino acids. Imposition of an inwardly directed gradient of NaCl resulted in transient accumulation of L-alanine and L-phenylalanine, followed by a gradual decline to equilibrium levels. Ethanol reduced both the rate of uptake and the maximum accumulation of these amino acids without altering the final equilibrium level. The inhibitory effects of ethanol on L-alanine uptake were dose dependent and reversible. On the other hand, ethanol had no effect on the rate of uptake of L-alanine or the final equilibrium level attained when vesicles were incubated with a KCl gradient or when NaCl was equilibrated across the vesicle membrane. These results suggest that ethanol does not inhibit Na+-dependent uptake of neutral amino acids by direct inhibition of the Na+-dependent transport systems for these solutes.

Sensitivity of Na+-coupled D-glucose uptake, Mg2+-ATPase and sucrase to perturbations of the fluidity of brush-border membrane vesicles induced by n-aliphatic alcohols

The aim of our work is to show the importance of the role of hydrophobic bonds in maintaining Mg2+-ATPase or sucrase activity and Na+-coupled D-glucose uptake normal for the brush border of rat enterocytes. The activity of the two enzymes and the D-glucose uptake were therefore measured under the action of n-aliphatic alcohols and related to the fluidity determined by ESR. Three concentrations were used for the first eight alcohols, those of octanol being about 1500-times lower than those of methanol. For each alcohol the D-glucose uptake and the fluidity were linear functions of the logarithm of the concentration, the linear regressions being practically parallel and equidistant. The concentrations (C) of the eight alcohols inhibiting the D-glucose uptake by 80% were similar to those increasing the membrane fluidity by 3%. The linear relationship which existed in both cases between log 1/C and log P, P being octanol/water partition coefficients of the alcohols, was evidence of great sensitivity to the hydrophobic effect of the alcohols. Only the first alcohols, however, produced any notable inhibition of Mg2+-ATPase and sucrase. Hydrophobic bonds are thus shown to have little influence in maintaining the activity of Mg2+-ATPase and sucrase, but they modulate the Na+-coupled D-glucose uptake.

Effect of ethanol on morphology and total, capillary, and shunted blood flow of different anatomical layers of dog jejunum

On the basis of previous studies in our laboratory we postulated that the ethanol-induced alteration in jejunal morphology was the result of its effect on the microcirculation. The present study was undertaken to examine the validity of this hypothesis. Accordingly, the effects of intraluminal ethanol perfusion (3.0 and 6.0% w/v) on mucosal morphology; water, glucose, and sodium transport; and regional blood flow were examined in in vivo jejunal segments of pentobarbital-anesthetized dogs. Compared to control segments, those perfused with ethanol exhibited a significant increase in the prevalence of morphological alterations of the mucosa, consisting of subepithelial fluid accumulation (bleb formation) and exfoliation. Those villi with epithelial damage exhibited villus cores significantly shorter than those with a normal, undamaged epithelium. Segments perfused with ethanol exhibited a depressed net water absorption, to the point that net secretion occurred in the segments perfused with 6% ethanol. Net absorption of glucose was similarly depressed by intraluminal perfusion with ethanol, whereas net absorption of sodium was unaffected. Regional jejunal blood flows were estimated using a dual, radiolabeled microsphere technique. Both total jejunal wall and total mucosal blood flow (in ml/min/100 g dry tissue) in the ethanol-perfused segments were significantly increased over control. Similarly, jejunal wall and mucosal capillary blood flows were increased by ethanol perfusion. Neither submucosal nor muscularis blood flows were affected by intraluminal perfusion with ethanol. Compared to control, shunting or nonentrapment of 9-micron microspheres was increased in the mucosa of the ethanol-perfused segments. In contrast to this, shunting of 9-micron microspheres in the submucosa and muscularis was unaffected by intraluminal perfusion with ethanol. It therefore appears that the ethanol-induced mucosal morphological alterations are accompanied by a localized mucosal hyperemia, and an increased shunting of blood through the mucosa. Based on the results of this and other studies, a microvascular mechanism was tentatively proposed to explain the pathogenesis of the ethanol-induced morphological changes.

Effects of ethanol in vitro on rat intestinal brush-border membranes

Ethanol, at concentrations found in the intestinal lumen after moderate drinking, has been shown to inhibit carrier-mediated intestinal transport processes. This inhibition could occur by direct interaction with membrane transporters, dissipation of the energy producing Na+ electrochemical gradient and/or nonspecific alteration of membrane integrity. The latter alteration may be reflected by changes in membrane fluidity, chemical composition or vesicular size. These possibilities were examined with studies in purified brush border membrane vesicles of rat intestine. Ethanol inhibited concentrative Na+-dependent D-glucose uptake in a dose-dependent manner. In contrast, ethanol did not inhibit concentrative D-glucose uptake under conditions of D-glucose trans-stimulation in the absence of a Na+ electrochemical gradient. Ethanol also inhibited initial, concentrative Na+-dependent taurocholic acid uptake, as well as equilibrium uptake. That ethanol exerted a dual effect on transport by increasing membrane conductance for Na+ while decreasing intravesicular space was supported by direct studies of Na+ uptake. Morphometric analysis confirmed that ethanol-treated membranes had a decreased intravesicular size when compared to untreated membranes. Finally, membrane fluidity measured by EPR showed that ethanol had a significant fluidizing effect without producing qualitative changes in membrane proteins, as determined by SDS gel electrophoresis. These results suggest that ethanol inhibits carrier-mediated transport by dissipation of the Na+ electrochemical gradient and alteration of membrane integrity rather than by direct interaction with membrane transporter.

Effects of ethanol on cultured human fibroblasts

The effects of ethanol on cellular functions of growth and low density lipoprotein uptake were studied with cultured human fibroblasts, WI-38. Cells were grown in basal medium for 24 hr, then incubated in medium containing 0, 100, or 500 mM ethanol for various times. Growth in 100 mM ethanol had little effect, but growth in 500 mM ethanol for 24 or more hours significantly decreased the number of cells per dish and increased the protein, but not the DNA, content, per cell. Exposure to 500 mM ethanol had little effect on protein synthesis but significantly depressed DNA synthesis. It was also evident from microscopy that fewer but larger cells were present. There appeared to be no consistent acute effects of 500 mM ethanol on the uptake of lipoproteins by confluent monolayers of cells. After chronic exposure, uptake was comparable to that of 0 or 100 mM ethanol when expressed as nanogram of lipoprotein/mg of cell protein but higher when expressed as picograms/cell. The results suggest that 500 mM ethanol decreased the rate of cell division but resulted in enlargement of cells.