Effect of chronic ethanol ingestion on enterocyte turnover in rat small intestine

Neuropeptide S reduces duodenal bicarbonate secretion and ethanol-induced increases in duodenal motility in rats

Alcohol disrupts the intestinal mucosal barrier by inducing metabolic and functional changes in epithelial cells. Recently, we showed that neuropeptide S (NPS) decreases duodenal motility and increases mucosal paracellular permeability, suggesting a role of NPS in the pathogenesis of disorders and dysfunctions in the small intestine. The aim of the present study was to investigate the effects of NPS on ethanol- and HCl-induced changes of duodenal mucosal barrier function and motility. Rats were anaesthetized with thiobarbiturate, and a 30-mm segment of the proximal duodenum with an intact blood supply was perfused in situ. The effects on duodenal bicarbonate secretion, the blood-to-lumen clearance of 51Cr-EDTA, motility and transepithelial net fluid flux were investigated. Intravenous (i.v.) administration of NPS significantly reduced duodenal mucosal bicarbonate secretion and stimulated mucosal transepithelial fluid absorption, mechanisms dependent on nitrergic signaling. NPS dose-dependently reduced ethanol-induced increases in duodenal motility. NPS (83 pmol·kg-1·min-1, i.v.) reduced the bicarbonate and fluid secretory response to luminal ethanol, whereas a 10-fold higher dose stimulated fluid secretion but did not influence bicarbonate secretion. In NPS-treated animals, duodenal perfusion of acid (pH 3) induced greater bicarbonate secretory rates than in controls. Pre-treating animals with Nω-nitro-L-arginine methyl ester (L-NAME) inhibited the effect of NPS on bicarbonate secretion. In response to luminal acid, NPS-treated animals had significantly higher paracellular permeability compared to controls, an effect that was abolished by L-NAME. Our findings demonstrate that NPS reduces basal and ethanol-induced increases in duodenal motility. In addition, NPS increases luminal alkalinization and mucosal permeability in response to luminal acid via mechanisms that are dependent on nitric oxide signaling. The data support a role for NPS in neurohumoral regulation of duodenal mucosal barrier function and motility.

Effect of alcohol consumption on the gut

Both acute and chronic alcohol consumption have severe effects on the structure and function of the entire gastrointestinal tract (GIT) which result in a vicious cycle. The healthy person who begins to drink heavily, first experiences the toxic effects of high concentrations of ethanol. Mucosal damage compromises the basic functions of the GIT. Suppression of the gastrointestinal immune system and increased transport of toxins across the mucosa result in increased susceptibility to infections. Inhibition of digestion, absorption and secretion cause diarrhea and reduce the transfer of nutrients to the rest of the body. As the individual becomes more dependent on alcohol, the functional reserve and regenerative capacity of the GIT are overwhelmed and malnutrition increases. The rate of progression of this cycle depends on several factors including nutritional intake. Whilst the clinical effects of alcohol are well recognized, more research is required to fully elucidate the underlying mechanisms.

Effect of chronic ethanol consumption on the activities of residual small bowel brush-border enzymes after proximal jejunum resection in the rat

Ethanol consumption has a toxic effect on the epithelium of the small bowel, but enterocyte maturity is very difficult to measure under these circumstances. However, when ethanol intake is combined with enterectomy, enterocyte immaturity is greater, permitting an easier separation of these two effects. In a group of rats (13 male Wistar rats weighing approximately 220 g) fed a liquid diet containing 35% ethanol for 4 weeks after resection of the proximal jejunum, the residual small intestine brush border maltase, sucrase, and lactase activities were similar to those of a pair-fed control group (13 animals). However, alkaline phosphatase activity was decreased in the mucosa and in the enterocyte brush border, probably because of the lower activity of this enzyme in the jejunum-ileum remnant of the alcoholic group.

Effect of alcohol on gastrointestinal cell regeneration as a possible mechanism in alcohol-associated carcinogenesis

Chronic ethanol consumption is a major risk factor for oropharyngeal, esophageal, and rectal cancer. Because hyperregenerative gastrointestinal mucosa has an increased susceptibility towards chemical carcinogens and thus influences carcinogenesis, various studies have been performed to evaluate the effect of chronic ethanol consumption on mucosal cell turnover. In the rat, morphometric analysis showed that in chronically ethanol-fed rats the size of the basal cell nuclei of the oral mucosa from the floor of the mouth, the edge of the tongue, and the base of the tongue were significantly enlarged. The size of the basal cell layer was increased and the stratification of the cells was altered. The percentage of cells in S-phase of the cell cycle was significantly higher in ethanol-fed rats compared to controls. In addition, mucosal atrophy was found. Similar to the oropharynx, in the esophagus chronic ethanol consumption increased cell proliferation depending on salivary gland function, because only in the presence of the salivary glands was this stimulative effect of alcohol on cell turnover found. Subsequently, chronic ethanol ingestion significantly stimulated crypt cell production rate in the rectum, in an age-dependent manner. This hyperregeneration, which was only observed in the rectum but not in the remaining colon, was associated with an expansion of the proliferative compartment of the crypt. Such an expansion is correlated with increased risk for rectal cancer. In addition, crypt cell production rates in the rectal crypts can be correlated with mucosal acetaldehyde concentrations, underlining a toxic effect of acetaldehyde on the rectal mucosa that is answered by compansatory hyperregeneration. These data from the rat model could be confirmed in humans. In conclusion, chronic ethanol consumption leads to mucosal hyperregeneration in gastrointestinal mucosa associated with a high risk for cancer and may therefore be at least one mechanism by which alcohol exerts its cocarcinogenic effect.

Age related changes in functions and physicochemical properties of rat jejunal brush border membrane after chronic ethanol administration

1. We investigated the chronic effects of a 4 week treatment with ethanol on functions and physicochemical properties of BBM of young and adult rats (2 and 7 months old respectively). 2. In the ethanol treated groups the cholesterol/phospholipid and the protein/lipid ratios as well as the D-glucose uptake and lactase specific activity and Vmax were increased. In spite of a minor alcohol consumption the adult group was the more affected. 3. Membranes from the ethanol fed rats were less fluid and more tolerant to the in vitro addition of ethanol.

Alcohol and the small intestine

Several alterations of the small-intestinal morphology and function have been documented after alcohol ingestion. There are morphologic changes macroscopically and microscopically after acute alcohol administration in the proximal part of the small intestine, which are quickly reversible. There are no macroscopic changes and, in most patients, very discrete light microscopic changes in the small intestine after chronic alcohol ingestion. The ultrastructural changes are, however, profound, as seen by both transmission and scanning electron microscopy. The permeability is probably increased, permitting entrance of possible noxious agents, which may explain some of the extraintestinal tissue damage observed in chronic alcoholism. The transit is increased, at least after acute alcohol administration, perhaps contributing to the diarrhea commonly seen after heavy drinking. Several of the enzymes located in the brush border are affected; lactase activity can be depressed and perhaps result in a transient milk intolerance in predisposed individuals. The activity of GGT is increased and may partly account for the GGT elevation in serum after heavy drinking. Other enzymes, such as Na(+)-K(+)-ATPase, can be inhibited and result in a decreased absorption of substances that require active, energy-dependent transport mechanisms. The secretion of water and electrolytes may be increased (an effect on cAMP?). The absorption of several nutrients, vitamins, and other elements is disturbed. The bacterial flora is increased and changed, which may give rise to symptoms and also increase the production of acetaldehyde by bacterial metabolism of ethanol. Acetaldehyde is more toxic than ethanol, and an increased concentration of acetaldehyde can possibly accentuate the damage to the liver and other organs. The bacterial overgrowth can possibly cause endotoxinemia. Although studies on alcohol-related intestinal alterations have been relatively sparse, the acute and chronic effects of alcohol thus seem to be considerable. From available results it is, however, difficult to draw any definite conclusions about the clinical importance of many of the findings. Future research will need to study the relationship between, for example, the chronic morphologic changes, the absorptive dysfunction, and permeability alterations, on the one hand, and the gastrointestinal symptoms, the extraintestinal damage, and various deficiencies, on the other hand.

Protein synthesis of muscle fractions from the small intestine in alcohol fed rats

The effects of chronic ethanol feeding on the amounts and synthesis rates of cytoplasmic, contractile, and stromal protein fractions were investigated in the small intestine of eight pairs of immature and seven pairs of mature rats. Treated rats were fed ethanol as 36% of total energy in a nutritionally adequate liquid diet. Paired controls were fed isovolumetric amounts of the same diet in which ethanol was substituted by isocaloric glucose. After six weeks the total cytoplasmic and contractile protein content in immature rats was reduced by 18% and 31%, respectively (p less than or equal to 0.007). The decline in the stromal protein content (26%) was not statistically significant (p = 0.130). In mature rats the protein contents were also reduced in the cytoplasmic (25%, p = 0.035) and contractile (27%, p = 0.005) protein fractions, though the stromal protein fraction was unaltered (p = 0.913). In immature rats fractional rates of protein synthesis in cytoplasmic and contractile protein fractions of the small intestine were unaltered by chronic ethanol feeding (p less than or equal to 0.853). In mature rats, the synthesis rates of corresponding fractions declined, by 18% and 31%, respectively, but were also not statistically significant (p less than or equal to 0.369). Absolute rates of protein synthesis in immature rats fell by 6% (p = 0.549) in the cytoplasmic and 31% in the contractile protein fraction (p = 0.045). In mature rats, the corresponding reductions were 38% (p = 0.106) and 48% (p = 0.033), respectively. Virtually no radioactivity could be detected in the stromal fraction, signifying very low synthesis rates. Chronic ethanol feeding reduces the amount of protein in the small intestine of the immature and mature rat with the contractile protein fraction showing the greatest decrease. In the absence of statistically significant reductions in fractional synthesis rates a partial adaptation in turnover rates may have occurred.

Morphologic changes in the small intestine after chronic alcohol consumption

The morphology of the small-intestinal mucosa was studied in 11 alcoholic patients admitted to hospital for detoxification. A first biopsy specimen from the small intestine was taken as soon as possible after admission and a second specimen after about 6 weeks of abstinence. The specimens were studied in the light microscope, in the scanning electron microscope, and by immunohistochemistry. Morphometrically, a slight reduction in villus height in relation to crypt depth was observed. One patient had a subtotal villus atrophy. After abstinence the villus height was increased in five of the six patients who accepted a second biopsy. No obvious changes were seen in the frequency and appearance of peptidergic nerves or endocrine cells. Ultrastructurally, pronounced alterations were seen in the surface ultrastructure of the enterocytes. In two specimens bacterial adhesion to the mucosal surface was also found. The ultrastructural changes were unaltered after abstinence. In serum the concentrations of zinc were reduced, and the levels of copper were elevated compared with a group of teetotallers. A recently developed marker of high alcohol consumption, carbohydrate-deficient transferrin, was as good an indicator as the other conventional biochemical markers.

Effects of ethanol on rat Schwann cell proliferation and myelination in culture

It is possible to treat dissociated embryonic rat dorsal root ganglia in culture to inhibit proliferation of all nonneuronal cells except Schwann cells. Neurons have been shown to produce a mitogenic stimulus for Schwann cells under these conditions. Additionally, myelin-competent neurons induce Schwann cells to elaborate myelin sheaths. Groups of sibling cultures were exposed to various nonlethal concentrations of ethanol (0, 43, 86, or 172 mM) for 4 wk. Cultures were assessed weekly by light microscopy in a blind fashion for evidence of Schwann cell proliferation and myelin formation. Ethanol adversely affected both Schwann cell proliferation and myelin formation in culture. No obvious differences in neuronal morphology were observed among the various groups of cultures by light or electron microscopy. These observations suggest that ethanol might interfere with Schwann cell proliferation and myelin formation in culture by one or both of the following means: a) inhibit neuronal production of signals for Schwann cell proliferation and myelination or b) impede Schwann cell responses to neuronal signals. Investigation of these possibilities in culture may provide insight into neuropathologic mechanisms operative in the fetal alcohol syndrome or alcohol-associated peripheral neuropathy in humans.