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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. administered 51Cr-ethylenediaminetetraacetate (51Cr-EDTA) and 125I-bovine serum albumin (125I-BSA), and mast cell histamine release was estimated from the histamine concentration of the gut effluent. Ethanol increased 51Cr-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 increased 51Cr-EDTA and 125I-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.

Jejunal intraluminal ethanol causes morphological and mucosal microvascular injury. The purpose of the present study was to understand the mechanism of the morphological alterations caused by ethanol without the influence of ethanol's effect on the microcirculation. Therefore, we have investigated the ethanol-induced morphological changes in the absence of blood flow (i.e., in the jejunum in vitro) and compared these changes with those reported to occur in the presence of microcirculation (i.e., in the jejunum in vivo). The mucosa of jejunal segments was exposed to a control solution and to solutions containing 0.8, 1.6, and 4.8% (w/v) ethanol, using a specially designed apparatus. The morphological response of the mucosa to these solutions was continuously examined employing a video microscopic technique, and the changes were morphometrically evaluated on subsequent playback of videotapes. Ethanol caused a concentration-dependent increase in the number of villi with subepithelial fluid accumulation, i.e., blebs, and a decrease in the height of the villus core (i.e., lamina propria). With 0.8 and 1.6% ethanol, the contracted core remained partially attached to the epithelium and the total villus height (villus core plus epithelial layer) decreased. With 4.8% ethanol, the villus core contraction was so rapid that the stroma fully separated from the epithelium. Thus, among other factors, the rapidity of the villus core contractions appears to play a role in the subepithelial bleb formation and in the appearance of the bleb. The ethanol-induced changes in vitro are similar to those reported to occur in the jejunum in vivo. Therefore, we conclude that the effect of ethanol on morphology is independent of its action on the microcirculation.

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.

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 less than 0.001). This protein loss was depressed by H1 + H2-receptors blockade throughout 90 min (p less than 0.01). H1-receptor blockade caused a similar depression of ethanol effect but only during 20 to 40 min (p less than 0.05). In contrast, H2-receptor blockade aggravated the protein losing effect of ethanol throughout 90 min (p less than 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.

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.

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.

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.

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.

We have investigated the 3-O-methyl-D-glucose (3MG) absorption by jejunal biopsies obtained from a patient with cholera. The absorption of 3MG (as measured from the determination of intracellular accumulation of this sugar) was found to occur against a concentration gradient and to be a saturable process that follows Michaelis-Menten kinetics. There was no appreciable difference in 3MG absorption between the biopsies from the normal volunteers and those from the patient with cholera.

This study was undertaken to investigate the effect of ethanol on the brush-border activity of the small intestine. Brush-border membrane isolated from hamster jejunum was incubated with L-phenylalanylglycine (Phe-Gly), L-leucylglycine (Leu-Gly), or glycyl-L-tyrosine (Gly-Tyr) in the absence and presence of 1-5% (wt/vol) ethanol, and the L-amino acids liberated were determined. Ethanol was found to depress the hydrolysis of all peptides in a dose-dependent manner. The inhibitory effect of ethanol on the peptidases does not appear to be time dependent. The ethanol-induced inhibition of peptidase activity is completely reversible. Kinetic studies indicate that ethanol caused a decrease in the Vmax of the enzymes responsible for the hydrolysis of the Phe-Gly and Gly-Tyr but did not have any effect on their Km. In the hydrolysis of Leu-Gly, two enzymes were involved, and ethanol depressed the Vmax of both without affecting the Km of either. These findings suggest that ethanol produces conformational changes of the peptidases involved in the hydrolysis of these three dipeptides.

Microspheres of 15 and 9 microns diameter were injected simultaneously into the left ventricle of the dog, and the entrapment of these microspheres in different layers of the gut wall was measured under resting conditions, vasoconstriction, and subsequent vasodilation. Results show that some of the 9-microns spheres passed into the portal blood through all layers of the gut wall, whereas 15-microns spheres were completely entrapped in the tissue. The pattern of entrapment of 15-microns spheres during vasoconstriction and during subsequent vasodilation suggests that these microspheres measure adequately the arteriolar inflow of the muscularis, submucosa, and mucosa (i.e., villus plus crypt) but, due to series arrangement between the arterioles of the villus and the crypt, cannot measure the arteriolar flow of the villus and crypt separately. The entrapment of 9-microns microspheres in the muscularis, submucosa, crypt, and villus that occurred during vasoconstriction did not change during subsequent vasodilation. This suggests that these microspheres became lodged in the precapillary sphincter or capillary and therefore measured the capillary flow of these layers. Accordingly, the difference between the arteriolar (measured by 15 microns) and the capillary (measured by 9 microns) flow of the muscularis, submucosa, and mucosa may provide an estimate of the noncapillary (shunt) flow of these layers.

We studied the effect of ethanol on glucose and water absorption in vivo. In preliminary experiments, using sodium amytal anesthesia, we found that control animals, whose jejunal segment was perfused without ethanol, required more anesthetic agent than those perfused with ethanol. Thus, to allow for unbiased comparison of the absorption data between the two groups of animals, all absorption studies were carried out on conscious restrained hamsters. We found that ethanol did not influence the permeability of the jejunum to polyethylene glycol (PEG) and meglumine diatrizoate. In addition, ethanol did not influence the time required for the onset of steady-state absorption. Using both the gravimetric and the electrical methods, we were unable to show any measurable osmotic pressure exerted by ethanol (150-1050 mM) on the hamster jejunum. In the absorption studies we found that perfusion of the hamster jejunum with five increasing concentration of ethanol (450-1050 mM) appeared to cause a concentration-dependent depression in steady-state glucose transport. Water transport was depressed only when 4.8% (1050 mM) ethanol was perfused.

Acute exposure of jejunal mucosa to ethanol has been reported to produce a depression of transmural glucose transport across this organ in vitro and in vivo. In an attempt to understand the mechanism of action of ethanol on intestinal transport, in the present study we have investigated the effect of ethanol on glucose uptake by purified brush-border membrane vesicles of hamster jejunum. Ethanol, in concentrations found in man after moderate drinking (1-5% w/v), was found to depress glucose uptake by the brush-border membrane in a dose-dependent and time-dependent manner. Mannose was used to measure nonspecific uptake, and we found that the ethanol-induced depression of glucose uptake was not related to an alteration of the nonspecific uptake of this sugar. The inhibition of glucose uptake of the ethanol-treated membranes completely disappeared after repeated washing of the membranes with ethanol-free buffer. Accordingly, the ethanol-induced depression of glucose uptake was not the result of irreversible damage to membrane proteins but was related to a direct effect of ethanol on the brush-border membrane. On the basis of these findings, it is concluded that a direct interference with glucose translocation across the brush border plays an important role in the ethanol-induced depression of transmural jejunal glucose absorption.

To assess the validity of repeated blood flow measurements using the microsphere technique, the apparent blood flows in the anatomic layers of the jejunum were determined from the entrapment of 9-, 11.5-, and 17-micron microspheres at 1.5, 15, 30, and 60 min after their injection. The entrapment of 17-micron spheres in the mucosa plus submucosa and in the muscularis propria remained similar at all times, but these spheres migrated (P less than 0.01) from the submucosa to the mucosa. By 1.5 min, 5 +/- 2% of 11.5-micron spheres had shunted, but no subsequent shunting was observed. No migration of 11.5-micron spheres from the mucosa, submucosa or the muscularis was observed. The shunting of 9-micron spheres from the whole wall increased from 19 +/- 4% at 1.5 min to 40 +/- 4% at 60 min (P less than 0.001). These data suggest that 17-micron spheres can only fractionate the blood flow of the whole wall into that of the mucosa plus submucosa and that of the muscularis propria, while 11.5-micron spheres may measure fractional flow to the submucosa separately. The continued washout of 9-micron microspheres precludes their use for repeated blood flow measurements.

We have demonstrated previously that ethanol causes alterations in jejunal morphology and fluid secretion, and that these changes are accompanied by an increase in mucosal arteriolar blood flow, shunting of blood through noncapillary microvessels, hyperemia, hemoconcentration, and an enhanced loss of plasma protein into the gut lumen. All the microcirculatory changes are compatible with an ethanol-induced mucosal microvascular stasis. The present study was undertaken to examine whether these changes are accompanied by an enhanced mucosal microvascular permeability. Using a colloidal carbon vascular labeling technique, we demonstrated that 6% wt/vol intraluminal ethanol caused marked accumulation of carbon particles in the walls of the capillaries and microvenules of the villus tips. The effect of 3% ethanol was much less pronounced, and the extent of carbon entrapment did not significantly differ from microvessels in villi perfused with Krebs-Ringer solution without ethanol. Electron microscopy indicated that the carbon was localized between the endothelial cell and the basal lamina of the microvessels. Because the carbon accumulation was always localized at the vicinity of endothelial cell junctions, the escape of carbon particles from the lumen probably occurred through these cell junctions. This could have been the result of a transient retraction of endothelial cells. Electron microscopic examination also demonstrated that the lumina of some capillaries and venules of the villus tip of jejunal segments perfused with 6% ethanol were clogged with carbon particles. This latter finding indicates that there was stasis in these vessels at the time of carbon injection. Similar intraluminal carbon accumulation was never seen in control jejunum or jejunum perfused with 3% ethanol. Thus the results of this study indicate that 6% (wt/vol) ethanol causes microvascular injury and stasis. The findings with 6% ethanol are reminiscent of those described by others in the early phases of acute inflammation, and thus it is possible that the microvascular changes caused by ethanol may be related to the liberation of some of the chemical mediators of the immediate response to acute injury.

In this study we investigated whether the products of 5-lipoxygenase (5-LO) were involved in the jejunal microvascular injury induced by intraluminal ethanol (ETH). A group of rabbits was given orally a selective inhibitor of 5-LO (L-651,392, Merck Frosst Canada) in two 10-mg doses, 24 and 2 h before the experiments (treated group). Another group received no such treatment (untreated group). In each animal of both groups, a jejunal segment was perfused with a control solution (control segment) and an adjacent segment with an ETH-containing (6% wt/vol) solution (ETH-perfused segment). In a series of experiments, we measured 5-LO activity of the jejunal segments of both groups using the generation of leukotriene B4 (LTB4) as an index. In a second series of experiments, we determined the ETH-induced intraluminal protein loss, which was taken as a measure of mucosal microvascular damage. In the untreated group, LTB4 generation (pg/mg tissue) by the ETH-treated segment (2.49 +/- 0.70) was higher (P less than 0.005) than that by the control segment (0.68 +/- 0.14). In the treated group, the LTB4 generation decreased (P less than 0.05) both in the control (0.15 +/- 0.03) and the ETH-perfused segments (0.44 +/- 0.09), but the difference between the two segments still remained significant. ETH caused a 13-fold increase (P less than 0.01) in jejunal protein loss in the untreated group but only a 5-fold increase (P less than 0.05) in the treated group. The ETH-induced increase in protein loss was significantly lower in the treated than in the untreated group (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Previous light microscopic studies showed that perfusion of the hamster jejunum with 4.8% ethanol (ethanol period) in vivo produced fluid-filled subepithelial blisters (blebs) on the villi. These blebs had virtually disappeared within 45 min after the discontinuation of the ethanol perfusion (recovery period). The present study examined these ethanol-induced changes in the jejunum by scanning (SEM) and transmission (TEM) electron microscopy. TEM revealed that ethanol did not damage epithelial cells in areas where blebs were not present. In these areas the basal surfaces of the epithelial cells were attached to the basal lamina, and the lateral intercellular spaces (LIS) were open. In the areas where blebs formed, the stretched epithelial cells which covered the blebs lost their basal anchoring and so could not maintain their LIS. Both SEM and TEM indicate that there was a decrease in the quantity of glycocalyx at the surfaces of cells which covered blebs. Our findings indicate that ethanol does not directly damage epithelial cells but that the cellular damage is due to detachment over the blebs. It is likely that ethanol at first traverses the epithelial layer and then produces stasis in the villus core. Continued fluid transport by the epithelial layer in the presence of statis results in accumulation of the fluid and widely dilated LIS. With subsequent enlargement of the LIS the bases of the cells detach from the basal lamina and blebs are formed.

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 out in 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 of L-leucylglycine (Leu-Gly), glycyl-L-tyrosine (Gly-Tyr), and L-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 the Vmax decreased and the Km increased. In the hydrolysis of Phe-Gly, two enzymes were involved, and ethanol depressed the Vmax of both, without affecting their Km. 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 effects of intraluminal ethanol perfusion (3.0% and 6.0% vt/vol) on mucosal morphology, water transport, and regional blood flow were examined in in vivo jejunal segments of pentobarbital-anesthetized rabbits. Compared with control segments, ethanol-perfused segments exhibited morphological alterations of the mucosa consisting of subepithelial fluid accumulation (bleb formation), exfoliation of enterocytes, and vascular congestion. The prevalence of epithelial damage was significantly increased in the segments perfused with 6% ethanol. Net water transport was significant (p less than 0.025) depressed in segments perfused with 3.0% and 6.0% wt/vol ethanol. In animals in which the control segment was absorbing water, ethanol led to a depression in net water absorption or to the reversal of absorption to net secretion. In animals in which the control segment exhibited secretion, ethanol led to an enhanced net secretion. Blood flow through the total jejunal wall and through the luminal layer (consisting of mucosa plus submucosa) was significantly (p less than 0.05) increased by the presence of 3.0% and 6.0% wt/vol ethanol in the intestinal lumen. Blood flow in the external layer of the jejunum (consisting of muscularis plus serosa) did not change significantly. It therefore appears that the ethanol-induced alterations in jejunal mucosal morphology and water transport are accompanied by a localized mucosal or submucosal hyperemia, or both. However, a direct cause and effect relationship between these remains to be established.

Glucose and water transport is depressed in the hamster jejunum in vivo by ethanol (4.8%) which also produced fluid-filled blebs at the tips of the villi. The epithelial cells over the blebs appeared stretched and cuboidal, the lateral intercellular spaces (LIS) were no longer recognizable, and the lacteals were closed. Forty-five minutes after discontinuation of the ethanol, water transport returned to normal while glucose transport remained depressed. At this time the villus structure had returned to normal. The blebs had disappeared, the LIS were again recognizable, and their appearance and number were similar to those in the control animals. Thus, the depression of water transport correlated with the obvious structural changes caused by ethanol; however, the depression of glucose absorption is associated with some effect of ethanol not evident by routine light microscopy.

In order to study the morphological effects of exposure of the jejunum to low ethanol concentrations, we perfused hamster jejunum with 2.1-4.8% ethanol. Following 45 min exposure, many of the villi developed fluid-filled blisters. To compare these findings to the effect of an inert solute at similar concentrations, we perfused hamster jejuna with mannitol. This caused necrosis of the villus tips but no blister formation. Therefore the blisters were the result of the action of ethanol. The rat jejunum was less resistant to ethanol than that of the hamster. We suggest that the initial insult of the freely permeant ethanol is deep to the epithelium, resulting in accumulation of edema under the epithelium.

The sucrase-isomaltase complex of the intestinal brush border membrane (BBM) catalyzes the hydrolysis of sucrose. The stereospecificity of this enzyme, however, is not known. To investigate this, BBM of hamster jejunum was incubated with D-sucrose or L-sucrose, and the reaction mixture was analyzed using a gas-liquid chromatograph. It was found that D-sucrose was hydrolyzed to its monomers, but L-sucrose remained unhydrolyzed. It is concluded that the sucrase-isomaltase of intestinal BBM of hamster jejunum does not hydrolyze L-sucrose and therefore this enzyme is stereospecific.

The present study was undertaken to compare the 3-O-methyl-D-glucose (3MG) absorption by jejunal biopsies from normal human subjects (N = 3) with that by the jejunum of the rat (N = 8) and of the hamster (N = 8), and to examine whether jejunal biopsies from normal subjects (N = 3), patients with primary lactase deficiency (N = 5) and from patients with celiac sprue (N = 5) follow the same pattern of sugar absorption as usually observed in vivo. The results indicate that under the conditions of our experiments the estimated affinity of carrier for 3MG (ie, apparent Km) in the biopsies from normal subjects did not differ significantly from that in rat or hamster jejunum. The estimated capacity of carriers for 3MG absorption (ie, Vmax) appeared to be similar in biopsies from normal subjects and in hamster jejunum, but significantly lower in rat jejunum. There was no difference in apparent Km between the biopsies from normal subjects and those from the patients with lactase deficiency. Although the Vmax for the lactase deficient patients was substantially higher than that for the normal subjects, the difference was not statistically significant. The absorption of 3MG by the biopsies from patients with celiac sprue did not follow Michaelis-Menten kinetics and was compatible with that of passive diffusion or low saturation conditions. Since the intracellular concentration of 3MG in all biopsies from celiac patients exceeded the concentration of the media, sugar transport could not have occurred by diffusion, and it is concluded that the absence of Michaelis-Menten kinetics was the result of low saturation conditions. This active transport with low saturation kinetics in patients with celiac disease suggests that in these patients not only the number of functioning carrier molecules is diminished but also the affinity of the existing carrier for sugar molecule is reduced. This situation, at least in some patients, seems to improve after treatment with gluten-free diet.

Experiments were done for indentification and localization of certain structural changes at different levels of jejunal villus of the hamster during positive and negative water transport across the intestine in vivo and in vitro. Positive transport occurred when the mucosal surface of the intestine was bathed (in vitro experiments) or perfused (in vivo experiments) with isotonic Krebs-Ringer bicarbonate solution containing 10 mM glucose, and negative water transport was achieved by rendering this solution hypertonic with 150 mM mannitol. Results indicate that during positive net water transport the intestine in vivo transported more fluid and exhibited a more conspicuous dilatation of the lateral intercellular spaces (L.I.S.) than did the in vitro preparation. Dilatation of the L.I.S. in both preparations was present only in the apical part of the villus, suggesting that this is the principal site of water absorption. When the mucosal solution was made hypertonic with mannitol, the L.I.S. in the in vivo intestine totally collapsed, whereas in the in vitro intestine these spaces remained open very slightly. These morphological changes correspond well with our finding that in the presence of the hypertonic mucosal solution there was a greater net negative water transport in vivo than in vitro. Incubation of the intestine in the isotonic mucosal solution produced subnuclear swelling of the mid-villus epithelial cells, and this morphological change was associated with an increase in the water content of the tissue. Perfusion of the in vivo intestine with the isotonic solution produced neither the swellings nor the increase in water content of the tissue. In the presence of hypertonic mucosal solution there was a water loss from the tissue both in vivo and in vitro, and these swellings were not observed. These results are discussed in relation to intestinal sugar transport and to the maturity of the epithelial cells, and it is concluded that transport studies on in vitro preparations may provide valid information on a qualitative basis, if not on a strictly quantitative basis.