P. K. Dinda

Effect of Ethanol on Sodium-Dependent Glucose Transport in the Small Intestine of the Hamster

The objective of this study was to investigate the mechanism by which ethanol inhibits intestinal absorption of sugars. In vitro experiments on hamster jejunum have shown that the presence of ethanol in the mucosal solution caused an inhibition of the net transport of water and glucose. There was also a decrease in the intracellular water content and an increase in the intracellular sodium and potassium concentration of the gut tissue. In contrast, the intracellular glucose concentration decreased in the presence of ethanol. These ethanol-induced changes were directly related to the ethanol concentration of the mucosal solution. In the presence of 450 mM (2%) ethanol in the mucosal solution, there was also a significant inhibition of transmural potential difference, estimated glucose metabolism, and both unidirectional fluxes of sodium. The net flux of sodium to the serosal side however did not decrease significantly. These effects of ethanol cannot be fully explained by its osmotic action, and it is suggested that the ethanol-induced reduction in glucose transport could be mainly the result of an interference with the carrier-mediated coupled entrance of glucose and sodium across the brush border. A depression of cellular metabolism could also have played a role in this process.

Histamine Is Involved in Ethanol-Induced Jejunal Microvascular Injury in Rabbits

To examine for the possible involvement of histamine in the jejunal microvascular effects of ethanol, we investigated the effects of (a) intraluminal ethanol on histamine release by the jejunum and (b) simultaneous inhibition of both histamine1 and histamine2 receptors (using promethazine and cimetidine, respectively) on ethanol-induced intestinal plasma protein loss in rabbits. Ethanol increased histamine release by the jejunum both in vivo (p less than 0.01) and in vitro (p less than 0.05). To investigate the effect of antihistamines on ethanol-induced plasma protein loss, we determined the dose of blockers that would completely inhibit the histamine1 and histamine2 receptors. In the absence of antihistamines, ethanol caused a 10-fold increase in jejunal protein loss over the controls (p less than 0.001). Simultaneous inhibition of histamine1 and histamine2 receptors attenuated (p less than 0.025), but did not abolish, the ethanol-induced protein loss. These data are discussed in relation to the literature, and it is concluded that histamine may play a role in the jejunal microvascular effects of ethanol. As the ethanol-induced protein loss was not completely inhibited, other mediators or mechanisms were probably involved.

Mechanism of Ethanol-Induced Jejunal Microvascular and Morphologic Changes in the Dog

To study the mechanism of morphologic and microvascular effects of intraluminal ethanol, we perfused jejunal segments of the dog with 6% (wt/vol) ethanol for 0 (control), 10, 20, 30, 60, and 90 min, and measured the time-dependent changes in (a) the prevalence of villi with epithelial damage (i.e., villi with intact blebs plus those with broken blebs) and those without epithelial damage (undamaged villi), (b) the height of the villus core and the patency of lacteals, (c) jejunal albumin loss, and (d) permeability of microvessels of the villus tip by colloidal carbon vascular labeling. We found that (a) the prevalence of villi with epithelial damage or with intact bleb increased progressively during the first 20 min of ethanol perfusion and then declined gradually; (b) the height of the villus core and the patency of lacteals in the undamaged villi and in those with intact bleb decreased during the first 20 min and then gradually increased; and (c) jejunal albumin loss and the prevalence of villi with carbon labeling increased for the first 30 min, after which the former declined gradually whereas the latter remained at a plateau. These findings suggest that contraction of the villus core and compression of the lymphatics are the primary cause of ethanol-induced epithelial damage, which is accentuated by increased microvascular permeability and consequent protein leakage. The mechanism of recovery of most parameters, in spite of continuous ethanol perfusion, remains to be investigated.

Role of xanthine oxidase-derived oxidants and leukocytes in ethanol-induced jejunal mucosal injury

Previous reports indicate that intestinal intraluminal ethanol increases mucosal permeability (an index of mucosal injury) and histamine release by mast cells, and that the released histamine plays a role in mediating the increased permeability. In the present study, we investigated whether reactive oxygen metabolites and their major sources (xanthine oxidase and leukocytes) were involved in these ethanol effects. In rabbits, segments of the jejunum were perfused with a control solution or with 6% ethanol. In these segments, mucosal permeability was assessed by determining jejunal clearance of i.v. administered51Cr-ethylenediaminetetraacetate (51Cr-EDTA) and125I-bovine serum albumin (125I-BSA), and mast cell histamine release was estimated from the histamine concentration of the gut effluent. Ethanol increased51Cr-EDTA clearance,125I-BSA clearance, and histamine release. These ethanol effects decreased when the animals were given superoxide dismutase plus catalase (scavenger of O2− and H2O2, respectively), allopurinol, or oxypurinol (xanthine oxidase inhibitors). Administration of a monoclonal antibody (R15.7) against leukocyte adhesion molecule, CD18, inhibited completely the ethanol-induced increased51Cr-EDTA and125I-BSA clearances and histamine release. These and supplementary data suggest that (a) ethanol-induced mucosal injury and mast cell histamine release are mediated primarily by leukocytes, and (b) oxy radicals, especially those generated by xanthine oxidase, mediate these ethanol effects mainly by promoting leukocyte infiltration.

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 inin 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-μm microspheres was increased in the mucosa of the ethanol-perfused segments. In contrast to this, shunting of 9-μm microspheres in the submucosa and muscularis was unaffected by intraluminal perfusion with ethanol. It therefore appears that the ethanolinduced 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.

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-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.

Effects of ethanol on cytoplasmic peptidases of the jejunal epithelial cell of the hamster

Although ethanol has been reported to inhibit intestinal amino acid absorption and peptide hydrolysis by the brush border membrane (BBM) peptidases, its effect on other events of protein absorption (such as peptide hydrolysis by cytosol peptidases, absorption of peptides across the BBM, and translocation of amino acids across the basolaterial membrane) has not yet been reported. To obtain a better understanding of the overall effect of ethanol on intestinal protein absorption, in the present study we have investigated the influence of ethanol on the cytosol peptidases. In order to examine the activity of these enzymes, without the influence of brush border digestion and translocation of peptides, the present study was carried outin vitro using a preparation of cytosol peptidases. Results show that exposure of the enzymes to 1–5% (w/v) ethanol caused a dose-dependent inhibition of hydrolysis ofl-leucylglylcine (Leu-Gly), glycyl-l-tyrosine (Gly-Tyr), andl-phenylalanylglycine (Phe-Gly) by the cytosol peptidases. These inhibitions were completely reversible. Kinetic studies indicated that ethanol depressed the hydrolysis of Leu-Gly and Gly-Tyr by a mixed type of inhibition, in which theVmax decreased and theKm increased. In the hydrolysis of Phe-Gly, two enzymes were involved, and ethanol depressed theVmax of both, without affecting theirKm. These findings suggest that ethanol alters only the catalytic center of both enzymes involved in the hydrolysis of Phe-Gly and alters both the catalytic center and the substrate binding site of the enzymes involved in the hydrolysis of Leu-Gly and Gly-Tyr. The results of this study together with those of our previous investigation on BBM peptidases indicate that ethanol interferes with the intestinal hydrolysis of peptides and, therefore, probably with the absorption of protein.

The role of histamine1 and histamine2 receptors in the ethanol-induced jejunal plasma protein loss

Histamine and other mediators have been shown to be involved in the ethanol-induced jejunal plasma protein loss. In this study we have investigated whether the histamine (H)-related component of this protein loss is mediated by H1-receptors, H2-receptors or both. Four groups of dogs (n=12 in each) were studied. They were: untreated, H1+H2-receptor blockade, H1-receptor blockade and H2-receptor blockade. Chlorpheniramine and ranitidine were used to block H1 and H2-receptor blockade. Chlorpheniramine and ranitidine were used to block H1 and H2-receptors respectively. In all animals, jejunal protein loss was measured over 10 min periods for 90 min. Ethanol increased protein loss in all time periods (p<0.001). This protein loss was depressed by H1+H2-receptors blockade throughout 90 min (p<0.01). H1-receptor blockade caused a similar depression of ethanol effect but only during 20 to 40 min (p<0.05). In contrast, H2-receptor blockade aggravated the protein losing effect of ethanol throughout 90 min (p<0.01). Analyses of data tend to suggest that the ethanol-induced protein loss is mediated principally by H1-receptors, and that a complete inhibition of the histamine-related ethanol-induced protein loss can be achieved only by a simultaneous blockade of both H1 and H2- receptors, and not by H1- or H2-receptor blockade alone.

Chemical Mediators in Ethanol-Induced Increased Jejunal Microvascular Permeability

The intraluminal ethanol concentration in the jejunum of man varies between 2% and 9% w/v [1] in the course of moderate drinking. This concentration is 15–100 times higher than that which occurs in the blood (0.08%–0.15%) during mild inebriation. Ethanol is transferred across the epithelial layer of the jejunum by simple diffusion [2]. The capillaries and postcapillary venules of the jejunal villus lie in close proximity to the epithelium. They are separated from the lumen only by a sheet of epithelial cells, the basal lamina of the villous core, and a very thin and loose connective tissue layer. Because of this, ethanol can reach the microvessels in high concentrations and could initiate microvascular damage.