Division of Gastroenterology, Departments of Internal Medicine, Lund and
1 Malmö University Hospitals, Sweden
Received 26 July 2000; in revised form 3 November 2000; accepted 5 December 2000
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ABSTRACT |
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INTRODUCTION |
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The GI tract has a well-developed neuroendocrine system, including both endocrine cells and peptidergic nerve fibres. The normal occurrence and distribution of the different endocrine cells and peptidergic nerve fibres are well described (Sjölund et al., 1983; Sundler et al., 1991
).
The neuropeptides have different regulatory functions related to motility, absorption, secretion and blood flow in the GI tract. It is thought that the nervous system and the endocrine cells are closely integrated. It has been suggested that vasoactive intestinal peptide (VIP) relaxes smooth muscle cells and has a vasodilator effect in the GI tract. Substance P is thought to constrict the vascular smooth muscle and reduce gastric mucosal blood flow (Grønbech and Lacy, 1995; Hayashi et al., 1996
; Rekik et al., 1998
). Antibodies to protein gene product (PGP) have become established as markers for neurons and cells of the diffuse neuroendocrine system.
Studies of the acute effects of alcohol on the stomach (mostly in experimental animals) indicate an involvement of nerve fibres; both VIP and substance P seem to be involved in ethanol-induced gastric damage (Karmeli et al., 1993; Hayashi et al., 1996
). Another study on gastric blood flow in alcohol-induced mucosal injury has shown vasodilatation with an increased blood flow (Grønbech and Lacy, 1995
). Galanin has been regarded as a modulator of GI motility (Ulman et al., 1995
; Katsoulis et al., 1996
). Pituitary adenylyl cyclase activating peptide (PACAP) occurs in both the central and peripheral nervous systems, but little is known about its functional role in the gut. VIP-like actions have been suggested (Uddman et al., 1991
).
Very little is known about the effects of alcohol on the neuropeptides in the human small intestine, especially in response to chronic alcohol ingestion.
In experimental animals, a relationship between chronic alcohol ingestion and altered VIP activity in the small intestine has been suggested (Jimenez et al., 1992). Karmeli et al. (1994) treated rats with intragastrically supplied 96% alcohol and subcutaneous indomethacin; somatostatin was thought to have a protective effect in both alcohol and indomethacin-induced gastric mucosal injury.
In light of this it was considered of interest to study the neuroendocrine system in chronic alcoholics. We have examined the most frequently occurring peptidergic nerves and some immunoreactive cells in duodenal biopsies from defined chronic alcoholics, and compared the findings with a control group.
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MATERIALS AND METHODS |
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The control group consisted of 25 individuals (five women, 20 men) with a mean age 45 years (range 2376) referred consecutively for upper endoscopy mainly because of dyspepsia (ulcer, reflux type). All the endoscopies thus had clinical indications. The control subjects were subjectively healthy apart from dyspepsia, which was the reason for performing the endoscopy. A careful history was taken of their alcohol consumption, which was below 40 g/week in all cases. In addition, blood measurements for serum CDT (carbohydrate-deficient transferrin) and GGT (gamma-glutamyl transferase) were performed, a normal CDT being required for participation in this study.
The mean (± SEM) value for CDT in the alcohol group was 41.15 ± 9.75 U/l, compared with 15.32 ± 0.97 U/l in the control group (P = 0.0008). (CDT was not available for 10 individuals in the alcoholic group.)
The study protocol was approved by the local ethical committee, and informed consent was obtained from all patients.
Study design
Both groups of patients were examined by upper GI endoscopy, and biopsies were taken with an Olympus FB 24 K forceps. All the endoscopies were performed after fasting for more than 8 h, and by the same endoscopist (T.H.).
The biopsies were taken from the distal part of the descending duodenum, two for immunocytochemistry, and two for tissue pathology. The tissue specimens were stained with haematoxylin and eosin for routine examination using light microscopy. The villus index was examined in all alcoholics and 11 controls. Villus index was determined by adding the height of the villi to the depth of the crypts (from the bottom of the crypts up to the tip of the villi) and dividing by the depth of the crypts.
Blood samples were taken and analysed using standard routines and equipment on the same day as the endoscopy.
Immunocytochemistry
Fresh specimens were quickly immersed in ice-cold 4% buffered formaldehyde solution. After fixation from 1 to 2 days, the specimens were rinsed repeatedly in sucrose-containing buffer, frozen, and sectioned at 15 µm in a cryostat and processed for the immunocytochemical demonstration of cholecystokinin (CCK), galanin, gastrointestinal peptide (GIP), glucagon, motilin, neuropeptide Y (NPY), PACAP, PGP, secretin, serotonin, somatostatin, substance P, and VIP using the indirect immunofluorescence technique (Coons et al., 1955). The sections were exposed to the peptide or amine antiserum for 3 h at room temperature. After thorough rinsing in phosphate buffer, they were incubated with fluorescein-labelled anti-rabbit IgG for 30 min at room temperature. All the solutions contained 0.25% serum albumin and Triton X-100. After another rinsing in phosphate buffer, the sections were mounted in phosphate-buffered glycine and examined in a fluorescence microscope. Controls in the immunocytochemical procedure were run as recommended by Sternberger (1979), and included incubation of sections with peptide antiserum inactivated by addition of antigen in excess (1100 µg per ml of diluted antiserum).
The tissue specimens were stained with different antisera (Table 1).
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The different endocrine cell types were counted per unit length of mucosa (0.32 mm) in sections cut perpendicularly to the mucosal surface and arranged so that the entire mucosal height was visible in each section. Five to ten visual fields in three to six sections from each of two specimens taken from each location and each patient were examined.
Statistics
The results are presented as arithmetic means, means, and standard errors of the mean (SEM). Tests for statistical significance were made using the non-parametric MannWhitney two-sample test.
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RESULTS |
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The semi-quantitative evaluation of the peptidergic nerves is shown in Table 3. There was a moderate to rich supply of both substance P and VIP in the mucosa and submucosa, but no significant statistical difference between the two groups. Few or moderate numbers of PACAP-containing nerve fibres were seen in both groups. Only very few nerve fibres containing galanin were seen in the submucosa in the alcoholic group. As regards NPY, we saw no or very few nerves in the mucosa, but more in the submucosa. All the single different peptidergic nerve fibres in the alcoholic group showed higher mean values, but not statistically significantly different from the controls (Fig. 2
). For nine performed examinations of PGP in alcoholics and controls, there was no difference between the groups (data not shown). Figure 3
shows pictures of VIP and PGP peptidergic nerves in the duodenum of an alcoholic and a control patient, respectively.
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If the density for all the different peptidergic nerves in the mucosa and submucosa respectively are seen together, there were obvious statistical differences between the alcoholics and controls (P < 0.0001), with a higher density of peptidergic nerves in both mucosa and submucosa in the alcoholic group (Fig. 2).
A similar examination of all the different endocrine cells (seen together) showed a mean value in the alcohol group of 15.5 ± 1.6 cells/unit length compared with 13.9 ± 1.6 cells/unit length in the controls (P = NS). However, there was an increased number of GIP and glucagon immunoreactive cells in the alcohol group (P = 0.02 for both) (see Table 4). The mean values for CCK, motilin and somatostatin were slightly but not significantly higher in the alcohol group.
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DISCUSSION |
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With regard to endocrine cells, there was a significantly increased number of GIP and glucagon cells per unit length of mucosa, which may indicate that alcohol interacts with the glucoseinsulin axis in the gut.
In a previous small study from our department, some of the peptidergic nerves and immunoreactive cells were examined in biopsies obtained with a Watson capsule from the distal duodenum and proximal jejunum. In this study, the villus height was increased in five of six patients who accepted a second biopsy after 6 weeks of abstinence. With regard to peptidergic nerve fibres and immunoreactive cells, there was no obvious difference (Persson et al., 1990). Gut neuropeptides seem to be involved in different morphological alterations in the small intestine, which can also be related to alcohol, for example an altered microcirculation and motility.
Alcohol abuse leads to altered motility in the small intestine (Persson, 1991; Feinman et al., 1992
; Papa et al., 1998
). Regulatory functions in intestinal motility have been proposed for at least VIP, galanin, and substance P, and possibly also PACAP (Sundler et al., 1991
; Rekik et al., 1998
). A mucosal microvascular stasis is considered to be central in the pathogenesis of alcohol-related morphological alterations in the small intestine (Beck et al., 1986
; Ray et al., 1989
). Different pathogenetic mechanisms leading to a disturbance in the villus drainage have been described (Beck and Dinda, 1981
; Dinda et al., 1988
). An initial action of alcohol in the disruption of the normal drainage can be related to a direct effect on the microcirculation or by inducing contraction on the villus core (Beck and Dinda, 1981
). In the case of neuropeptides, substance P and VIP may affect local mucosal blood flow via mast cell mediators (Karmeli et al., 1993
; Hayashi et al., 1996
). Increased mucosal levels of both VIP and substance P were also found in the stomach after alcohol ingestion. Somatostatin was able to prevent both an alteration in these neuropeptides and the alcohol-related mucosal injury (Karmeli et al., 1994
). The present study did not show any difference between alcoholics and controls concerning the number of somatostatin immunoreactive cells.
It is possible that the effects related to chronic alcohol ingestion differ from those found after acute ingestion, and that the small intestine adapts to noxious substances. In our study, upper GI endoscopy was performed 4 days after admission. However, a more recently published clinical study using intragastric application of alcohol and alcoholic beverages did not show any macroscopic lesions in the duodenum on endoscopy (Knoll et al., 1998).
In conclusion, we have performed an extensive evaluation of the neuroendocrine system in the duodenal mucosa in a group of chronic alcoholics having high alcohol consumption. The findings suggest that chronic alcohol consumption in man may have a general effect on the peptidergic nerve system and on some endocrine cell types in the duodenal mucosa.
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FOOTNOTES |
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