Role of mucus and prostaglandins in the gastric mucosal protective actions of sucralfate against ethanol-induced injury in the rat

Nicotinamide alleviates indomethacin-induced gastric ulcers: a novel antiulcer agent

Nicotinamide, a precursor of nicotinamide adenine dinucleotide (NAD(+)), is an essential nutrient for cell growth that participates in DNA repair and energy production. Nonsteroidal anti-inflammatory drugs (NSAIDs)-induced gastropathy is an intricate process involving gastric mucus depletion, increased microvascular permeability, nitric oxide imbalance, as well as free radical production. The present study was conducted to test for the possible gastroprotective effect of nicotinamide utilizing an acute indomethacin-induced gastric ulcer model. Sucralfate possesses antiulcer/antioxidant properties; hence it was used as the reference drug. Indomethacin resulted in hemorrhagic mucosal lesions, increased microvascular permeability, and reduced the gastric mucosal contents of nitric oxide and mucus. Moreover, it produced an imbalance in the mucosal redox state as indicated by a decline of glutathione and glutathione peroxidase, which were associated with increased lipid peroxides. Comparable to sucralfate, nicotinamide markedly decreased the severity of indomethacin-induced gastric lesions and restored the levels of altered biochemical parameters. Gastroprotection afforded by nicotinamide is possibly mediated by conservation of gastric mucus, as well as nitric oxide contents, enhanced gastric microvascular permeability, and its antioxidant properties.

Injurious effect of Helicobacter pylori culture fluid to gastroduodenal mucosa, and its detoxification by sucralfate in the rat

BACKGROUND

Helicobacter pylori plays an important role in the pathogenesis of peptic ulcer. Although several cytotoxins related to H. pylori have been reported, their effects on gastroduodenal mucosa have not been well evaluated in vivo.

AIM

To investigate the effects of the combination of acid and toxic substances derived from H. pylori on gastroduodenal mucosa, and to observe the effect of sucralfate on such factors in the rat.

METHODS

Male Sprague-Dawley rats were fasted overnight and anaesthetized. The pylorus was ligated, and a double-lumen cannula was inserted into the forestomach for gastric luminal perfusion. In other animals, a cannula was inserted to perfuse the proximal duodenum. 51Cr-EDTA was administered intravenously and mucosal integrity was monitored by measuring the blood-to-lumen 51Cr-EDTA clearance. After 72 h of culture of H. pylori (NCTC11637 and Sydney strain 1), Brucella broth containing 3% FBS was filtered to remove the bacteria (supernate of H. pylori culture fluid; HPsup). HPsup was acidified (pH=2.0) with HCl, and tested for its injurious action on gastric or duodenal mucosa by luminal perfusion. HPsup was incubated with sucralfate for 30 min. The supernate was collected by centrifugation and the pH was readjusted to 2.0. This sucralfate-treated HPsup was used to test the effect of sucralfate against H. pylori-related mucosal injurious factors.

RESULTS

Non-acidified and acidified HPsup did not cause any detectable injury to the gastric mucosa. Non-acidified HPsup did not cause injury in the duodenal mucosa. However, acidified HPsup induced a significantly greater increase in 51Cr-EDTA clearance and greater histological damage than in controls. Sucralfate completely reversed this.

CONCLUSION

These results suggest that an H. pylori-related toxic substance may aggravate duodenal acid injury by acting on luminal surfaces, and that the detoxification of this substance by sucralfate may contribute to its anti-ulcer action.

Effects of prostaglandin E1 on cultured dermal fibroblasts from normal and hypertrophic scarred skin

To investigate the role of prostaglandin (PG) E1 in preventing scar formation as well as that of the related cytokines, we culture fibroblasts from hypertrophic scar tissue (SDF) and normal dermis (NDF) collected from patients with scar contracture. We have compared the type I collagen synthesis, type I collagenase activity, and the production of interleukin (IL)-6, IL-8 and transforming growth factor (TGF)-beta(1) in two types of cultured fibroblasts before and after addition of PGE1. Our results demonstrated that levels of type I collagen and TGF-beta(1) production were higher and that type I collagenase activity and IL-8 production were significantly lower in the culture supernatants of SDF. There was no significance difference in IL-6 production between SDF and NDF culture supernatants. On the other hand, PGE1 significantly increased type I collagenase activity and IL-8 production in the SDF culture supernatants and it increased IL-6 and TGF-beta(1) production in both types of fibroblasts. However, there was no effect on synthesis of type I collagen in either group. To further investigate the role of TGF-beta(1) in NDF and SDF, exogenous recombinant human (rh) TGF-beta(1) was added. In NDF group, rhTGF-beta(1) induced a decrease in the type I collagenase/type I collagen ratio, while rhTGF-beta(1) had no effect on the same ratio in the SDF group. These results suggest that PGE1 may have a role in the prevention of hypertrophic scar by increasing the activity of type I collagenase.

Short-term sucralfate administration alters potassium diclofenac absorption in healthy male volunteers

AIMS

Since patients who regularly take NSAIDS may use sucralfate because of its cytoprotective properties, we examined the influence of this compound on the pharmacokinetics of diclofenac.

METHODS

Potassium diclofenac (105 mg) was administered orally to eighteen healthy male volunteers with or without a 5-day pre-treatment with sucralfate (2000 mg twice daily). Blood samples were collected at intervals post-dose and serum concentrations of diclofenac were determined by reverse-phase h.p.l.c.

RESULTS

Pre-treatment with sucralfate significantly decreased both the AUC(0,8 h) [2265 ng h ml-1 (geometric mean) (range 1815-2827) vs 1821 ng h ml-1 (1295-2562)] and the Cmax [1135 ng ml-1 (geometric mean) (range 898-1436) 701 ng ml-1 (501-981)] with no significant delay in absorption [tmax 1.0 h (median) (range 0.5-2.0) vs 1.0 h (0.5-4.0)].

CONCLUSIONS

The short-term treatment of healthy male volunteers with sucralfate decreases potassium diclofenac bioavailability. These findings suggest that either an appropriate increase in the diclofenac intake or the use of another gastric mucosa protector must be adopted.

Effect of long-term sucralfate ingestion on antral and fundic epithelial proliferation in the rat

Sucralfate accelerates the healing of chronic gastric ulcers, but its mechanism is not well understood. We studied the effect of long-term administration of sucralfate on gastric epithelial proliferation in the rat by means of tritiated thymidine autoradiography. Rats were treated perorally with 500 mg/kg sucralfate once a day. After 28 days, rats were injected with tritiated thymidine 1 microCi/g body weight and sacrificed 1 hr later. Autoradiographs from antral and fundic mucosae were prepared and a number of proliferative measurements were made. Long-term sucralfate administration produced an increase in tritiated thymidine labeling of epithelial cells and expansion of the proliferative zone in antral mucosa. These results indicate that long-term sucralfate ingestion stimulates gastric antral epithelial proliferation in the rat. In light of the fact that chronic gastric ulcers are usually located in the antral region in humans, this enhanced epithelial proliferation may contribute to the beneficial effect of sucralfate in accelerating the healing of gastric ulcers.

Prostaglandin I1 analogues, SM-10902 and SM-10906, affect human keratinocytes and fibroblasts in vitro in a manner similar to PGE1: therapeutic potential for wound healing

The newly synthesized prostaglandin (PG) I1 analogues, SM-10902 and SM-10906, were compared with PGE1 in terms of their biological effects on cultured normal human keratinocytes (NHKs) and human dermal fibroblasts (HDFs) in order to evaluate their therapeutic potential for cutaneous wound healing. The PGI1 analogues had a direct effect on cell proliferation of HDFs as did PGE1, but inhibited cell growth of NHKs in contrast to the stimulatory effect observed with PGE1. In contrast to NHKs stimulated with PGI1 analogues, which exhibited low levels of adenosine 3,5-cyclic monophosphate (cAMP). HDFs stimulated with these analogues responded in a dose-dependent manner with extremely high levels of cAMP. Conditioned media (CM) derived from media in which HDFs had been incubated with both the PGI1 analogues promoted NHK proliferation. HDF production of interleukin (IL)-6 increased in response to the PGI1 analogues. Since IL-6 was shown to promote cell growth of NHKs, enhancement of NHK proliferation by CM was thought to be due to IL-6 derived from HDFs stimulated with the PGI1 analogues.

Evaluation of mucosal damage of surfactants in rat jejunum and colon

Surfactants are one of the most frequently used adjuvants in oral pharmaceutical preparations, used primarily as solubilizers, stabilizers, emulsifiers, and wetting agents. However, surfactants can disrupt normal membrane structure. In this study, lactate dehydrogenase (LDH) and mucus were evaluated as potential markers of intestinal damage in a single-pass in situ perfusion model in the rat. The release of LDH and mucus into the intestinal lumen of the rat following perfusion of the nonionic surfactants Tween 80 and Triton X-100 was determined. The release rate of LDH increased in the order saline < Tween 80 < Triton X-100 in both jejunum and colon. LDH release rate was approximately three times lower in the colon than in the jejunum, but relative effects of nonionic surfactants were comparable between regions. In addition, the rate of LDH release in the jejunum increased with decreasing perfusion rates for both saline and Tween groups and with increasing Tween 80 concentrations. At each flow rate studied, mucus release rate was greater in the presence of Tween 80 and Triton X-100 than saline, but there was no significant difference between the effect of Tween 80 and Triton X-100 on mucus release rate. When perfusion of Triton X-100 was followed by saline, rates of both mucus and LDH release returned to baseline values, suggesting damage is reversible. Histological damage agreed with trends observed in LDH and mucus release rates. This model allows for early evaluation of intestinal damage due to both excipients and active ingredients and simultaneous measurement of drug absorption.

Effects of prostaglandin E1 on human keratinocytes and dermal fibroblasts: a possible mechanism for the healing of skin ulcers

The effects of prostaglandin E1 (PGE1) on cell growth, cytokine production and interaction of cultured normal human keratinocytes (NHKs) and human dermal fibroblasts (HDFs) were investigated. When NHKs were treated with PGE1 directly, only a slight increase in cell growth and a transient decrease in interleukin 1 alpha (IL-1 alpha) secretion were observed. No IL-6 was detected either before or after PGE1 treatment. In addition, IL-8 and transforming growth factor alpha (TGF alpha) production were uninfluenced by PGE1. The response of HDFs to PGE1 differed from that of NHKs. Following PGE1 treatment, IL-1 alpha and TGF alpha from HDFs remained undetectable while IL-6 production was enhanced markedly. IL-8 production was also slightly enhanced. Exposure of HDFs to PGE1 for 96 hours significantly promoted cell proliferation. Two kinds of conditioned media (CM) were prepared by a brief feeding of HDFs with keratinocyte basic medium or Dulbecco's modified Eagle's medium supplemented with 5% FCS with or without PGE1. NHKs proliferated more rapidly in CM than in corresponding basic medium. Moreover, CM prepared with PGE1 treatment showed a stronger effect in promoting NHK proliferation than CM without PGE1 treatment. This promoting effect was inhibited by anti-human IL-6 monoclonal antibody dose-dependently. These results indicate that fibroblasts are more sensitive than keratinocytes in response to PGE1 and that, upon PGE1 stimulation, HDF-derived IL-6 may play an essential role in NHK cell proliferation which may at least partly account for the beneficial effects of PGE1 in the treatment of cutaneous ulcerations.

Sucralfate induces proliferation of dermal fibroblasts and keratinocytes in culture and granulation tissue formation in full-thickness skin wounds

Sucralfate is used to induce healing of gastrointestinal tract ulcers. We evaluated its potential utility in the healing of skin wounds. Initial experiments examined the effects of the sucralfate on proliferation of cultured dermal fibroblasts and keratinocytes. Sucralfate induced proliferation in quiescent cultures of both cell types. Additionally, sucralfate enhanced prostaglandin E2 synthesis in basal keratinocytes and in interleukin-1-stimulated keratinocytes and dermal fibroblasts. Basal interleukin-1 and 6 release were not affected by sucralfate, but the agent enhanced interleukin-1-stimulated interleukin-6 release from fibroblasts. When applied daily to full-thickness wounds in rats, sucralfate increased the thickness of granulation tissue when assessed at day 12.

The effects of sucralfate and luminal stasis on recovery of the chambered rat gastric mucosa from taurocholate-induced damage

We have previously shown, using a gastric chamber model, that both sucralfate and luminal stasis protected the rat gastric mucosa against the development of hemorrhagic erosions produced by subsequent exposure for 10 minutes to acidified (50 mM HCl) 80 mM sodium taurocholate (NaT). The protection afforded by sucralfate was abolished by inhibition of cyclooxygenase activity but restored by sucralfate. In this study we demonstrate that indomethacin pretreatment decreases both the depth (in microns) and magnitude (in pH units) of the juxtamucosal pH gradient, but that sucralfate restores these parameters to levels characteristic of normal mucosae. The cytoprotective effect of sucralfate is thus prostaglandin-independent and, at least in part, a consequence of sucralfate-induced increases in the thickness of the juxtamucosal pH gradient/unstirred layer. We have also examined the ability of sucralfate to prevent the otherwise inevitable development of hemorrhagic erosions when it was applied after the gastric mucosa was exposed to NaT. When 100 mg sucralfate in 50 mM HCl was applied for 10 minutes, without stirring, subsequent to a 10-minute exposure of the mucosa to NaT, the average lesion area was reduced from about 15% to less than 3%. Unlike its cytoprotective property, the ability of sucralfate to accelerate the recovery process after damage was abolished by indomethacin pretreatment. Studies using antimony microelectrodes revealed that indomethacin pretreatment resulted in reductions in both the depth and magnitude of the pH gradient that resulted from plasma efflux from the mucosa after exposure to the acidified bile salt. These studies demonstrate that sucralfate is capable not only of prevention or attenuation of acute damage when administered prior to damaging agents, but is also capable of arresting the sequence of events that produces hemorrhage in the previously inflamed or damaged stomach.

Treatment of duodenal ulcer with sucralfate

Sucralfate attains a healing rate of about 79% for duodenal ulcer in 4 weeks, which is similar to the effects of cimetidine and ranitidine. Whereas cigarette smoking significantly affects duodenal ulcer healing by acid-reducing agents, the healing rates of smokers and non-smokers treated with sucralfate or colloidal bismuth are indistinguishable, suggesting an inherent advantage through the cytoprotective mechanisms of these agents. The 12-month relapse curves for duodenal ulcers initially healed with sucralfate and colloidal bismuth subcitrate closely overlap each other and are significantly lower than the curves for the histamine H2-receptor antagonists. These findings cannot be accounted for by clearance of Helicobacter pylori, on which sucralfate has little effect. Preliminary evidence suggests that the use of acid-reducing agents results in up-regulation of the parietal cells and may help to explain the differences in relapse rates. Sucralfate is superior to placebo and comparable to H2 antagonists in the prevention of duodenal ulcer recurrence.

The effect of misoprostol, omeprazole and sucralfate on nicotine- and ethanol-induced gastric injury and gastric mucosal blood flow: a comparative study

Nicotine, which is thought to be responsible for part of the pharmacological effect of smoking, exacerbates gastric mucosal injury in rats. The effects of misoprostol (12.5 micrograms to 100 micrograms), omeprazole (12.5 mg to 100 mg) and sucralfate (50 to 400 mg) on gastric mucosal blood flow and mucosal injury induced by nicotine were studied in an ex vivo gastric chamber preparation in rats. Rats were pretreated with nicotine (25 micrograms/mL orally) for 10 days and ethanol was added to the gastric chamber preparation. Laser Doppler flowmetry was used to measure the gastric mucosal blood flow and mucosal damage (ulcer index) was assessed by the area of haemorrhagic lesions. The ulcer index was significantly higher in rats pretreated with nicotine. Treatment with misoprostol and omeprazole lowered the ulcer index significantly compared with controls. The peak and summation blood flows were lower in nicotine-treated rats but failed to reach statistical significance. The peak blood flow (blood flow at 45 min) and the summation blood flow were significantly higher with all doses of sucralfate, misoprostol and omeprazole than in controls (P less than 0.05). The increase in gastric mucosal blood flow was significantly higher with sucralfate and misoprostol than with omeprazole. We conclude that sucralfate, misoprostol and omeprazole prevent nicotine- and ethanol-induced gastric mucosal damage and are accompanied by an increase in gastric mucosal blood flow. This indicates that smoking exacerbates gastric mucosal injury and that cytoprotective and site-protective agents can reduce injury by these noxious agents.

Stress bleeding prophylaxis with sucralfate. Pathophysiologic basis and clinical use

The development of acute stress bleeding in intensive-care patients occurs on a multifactorial basis. The basic mechanism lies in the imbalance between aggressive and protective factors. Most intensive care patients show a reduced acid secretion, a reduction of the gastric mucosal blood flow, and a decreased mucus and bicarbonate secretion. Sucralfate enhances most of the defensive mechanisms. These actions are the pathophysiologic basis of the efficacy of sucralfate in the prevention of stress bleeding. Because sucralfate has only a minor influence on the gastric pH and at the same time has proven bactericidal effects, gastric and gut bacterial overgrowth is significantly reduced. These effects explain the observed differences in mortality between sucralfate and alkalinizing drugs like antacids or H2-antagonists. The indications and limits of sucralfate in stress bleeding prophylaxis are pointed out.

Why do ulcers heal with sucralfate?

It is unknown why ulcers in general heal. Some clues are worth considering. What is known is (i) that ulcer healing occurs spontaneously, (ii) that ulcers heal more quickly in the duodenum than in the stomach, (iii) that mucosal blood flow at ulcer edge improves with healing, and (iv) that healing can be speeded up by (a) not smoking, (b) removing acid from the stomach, and (c) using non-antisecretory mucosal protective agents such as sucralfate and colloidal bismuth. The difference in healing rates between duodenal and gastric ulcers may be related to ulcer size, duodenal alkalinity due to the secretion of the Brunner's glands, and other uninvestigated factors such as epidermal growth factor and mucosal blood flow. The difference between smokers and non-smokers may be related to inhibition of prostaglandin synthesis and impairment of mucosal blood flow due to smoking and to higher acid secretion in smokers. The success with antisecretory agents indicates that acid inhibits the healing process. The success of sucralfate and bismuth indicates that cytoprotective mechanisms play a role in ulcer healing. The literature also shows that ulcer healing is less affected by smoking in patients treated with sucralfate than in those treated with antisecretory agents, suggesting that cytoprotective mechanisms play a more important part than acid inhibition in counteracting the adverse effects of smoking on healing. Furthermore, ulcer relapse occurs sooner in patients treated with antisecretory agents than in those treated with sucralfate or bismuth, suggesting that withdrawal of antisecretory agents speeds up relapse and/or that cytoprotective mechanisms are associated with longer-lasting remission. It is concluded that sucralfate healing involves cytoprotective mechanisms and that these cannot be ignored in the planning of any anti-ulcer therapy. Despite the understanding of the various site-protective and cytoprotective mechanisms, as discussed in the previous article, it is not clear why ulcers heal with sucralfate. In fact, there is no clear answer to the fundamental question as to why ulcers in general heal with the known therapeutic agents, including H2-receptor antagonists, antacids, proton pump inhibitors, anticholinergics, site-protective agents, and cytoprotective agents. This review examines this question, using sucralfate as a model.

Effect of sucralfate on gastric mucosal blood flow in rats

Sucralfate possesses site protective and cytoprotective actions and heals ulcers effectively, but its effect on gastric mucosal blood flow is unknown. Using an ex vivo gastric chamber preparation, we studied the effect of sucralfate on gastric mucosal blood flow in rats by laser doppler flowmetry. Under both fasting and fed states, measurements of gastric mucosal blood flow and damage were made in rats after topical application of absolute ethanol alone or after pretreatment with sucralfate. Gastric mucosal damage was assessed by measuring the total area of haemorrhagic mucosal lesions. Ethanol induced gastric mucosal lesions were significantly less with sucralfate pretreatment than without (p less than 0.008). Mucosal blood flow significantly fell after ethanol application (p less than 0.001). The fall was significantly less in fed than in fasted rats (p less than 0.05), and after pretreatment with sucralfate 100 mg or 200 mg than without in both fasted (p less than 0.0008 and 0.00001, respectively) and fed (p less than 0.002 and 0.001, respectively) rats. Graded doses of sucralfate (25-400 mg) resulted in an increase in gastric mucosal blood flow in a dose dependent manner (r = 0.731, p less than 0.001). In conclusion that sucralfate increases gastric mucosal blood flow in rats and lessens the fall in blood flow in rats treated with ethanol, and this action may contribute to its protection against the vascular damage of mucosa by ethanol.

Na+/H+ ion-exchange property of postmortem human gastric mucus. The effects of Campylobacter pylori infection and sucralfate

The effect of Campylobacter pylori infection and sucralfate treatment on the ion-exchange property of human gastric mucus from 17 human postmortem stomachs was investigated in an in vitro chamber. Of the 10 stomachs not infected with C. pylori mucus from 4 stomachs had a 'normal' Na+/H+ exchange capacity, whereas 6 were without a Na+/H+ exchange capacity. The Na+/H+ exchange capacity of the seven stomachs infected with C. pylori was half that of the four 'normal' uninfected stomachs. Sucralfate significantly improved the Na+/H+ exchange capacity of mucus from C. pylori-infected stomachs and from the uninfected stomachs without Na+/H+ exchange. This study shows that impairment of the Na+/H+ exchange capacity of gastric mucus is associated with C. pylori infection and that sucralfate improves the Na+/H+ exchange capacity of gastric mucus.

Effect of sucralfate and cimetidine on rheumatoid patients with active gastroduodenal lesions who are taking nonsteroidal anti-inflammatory drugs. A pilot study

In a pilot study, 26 rheumatoid arthritic patients taking continuous, stable dosage regimens of nonsteroidal anti-inflammatory drugs and with developed gastric and duodenal lesions were administered sucralfate 1 g four times per day (14 patients) or cimetidine 400 mg twice daily (12 patients) in a single-blind regimen for six weeks. Eleven of the patients given sucralfate and eight of the patients taking cimetidine had improved lesion scores. The lesion score of 10 of the 14 patients taking sucralfate and four of the 12 patients taking cimetidine improved by 50 percent or better (not significant). The antrum and body of the gastric mucosa and the mucosa of the duodenum synthesized prostanoids and thromboxane A2, and there was no significant difference in the synthesis of individual prostanoids at entry to the trial in the groups assigned to sucralfate or cimetidine. After six weeks of administration of sucralfate, prostaglandin E2 (PGE2) synthesis by the antrum and body, but not the duodenum, was significantly greater than observed in the biopsy specimens at entry despite continuation of non-steroidal anti-inflammatory drug therapy. After six weeks of cimetidine treatment, no change in PGE2 synthesis was noted in any biopsy specimens when compared with the synthesis at entry. No change in the synthesis of PGF2 alpha, 6-oxo-PGF1 alpha, or thromboxane B2 was noted in gastric or duodenal biopsy specimens in any treatment group. Sucralfate and cimetidine administration resulted in improved gastroduodenal lesion scores in rheumatoid arthritic patients continuing with nonsteroidal anti-inflammatory drug therapy.

Protection of rat gastric mucosa by sucralfate. Effects of luminal stasis and of inhibition of prostaglandins synthesis

Studies using a gastric chamber model demonstrated that sucralfate protected the rat gastric mucosa against hemorrhagic erosions induced by 40 percent ethanol and by acidified 80 mM sodium taurocholate. Protection required continuous contact of sucralfate with the gastric mucosa but it occurred without the production, by sucralfate alone, of significant damage to the luminal epithelium. Ultrastructural examination indicated that sucralfate stimulated mucus secretion by surface epithelial cells. Furthermore, sucralfate was "cytoprotective" in that, in addition to its anti-ulcer effects, it significantly reduced the damaging effects of luminal ethanol on the surface epithelium. Luminal stasis also significantly reduced the extent of hemorrhagic erosions produced by both ethanol and sodium taurocholate, but the most effective reduction in erosions occurred when sucralfate and luminal stasis were combined. Pretreatment with indomethacin abolished the protection provided by luminal stasis, but this protection was restored by sucralfate. Thus, these studies suggest that protection of the gastric mucosa by sucralfate results in part from effects on the unstirred layer. Sucralfate or its products also interact with the epithelial cells and stimulate mucus release and synthesis or release of inflammatory mediators.

Pathways of gastrointestinal protection and repair: mechanisms of action of sucralfate

Protection, i.e., prevention of major lesions and the mechanisms of repair/healing of major tissue loss in the gastrointestinal mucosa, are multifactorial processes. Conceptually, it is useful to categorize the components and mechanisms of gastroprotection and distinguish between: (1) Preservation of existing cells either by enhanced resistance of cells or by decreased exposure to damaging agents that can be achieved by maintenance of proper blood flow, vascular permeability, motility, mucus and bicarbonate secretion. If these mechanisms fail and tissue necrosis ensues, (2) replacement of lost tissue is achievable by either the original cells (e.g., epithelia), by cell migration (restitution) and proliferation (regeneration), and/or by connective tissue repair (e.g., fibroblasts, collagen) through cell proliferation and production of extracellular matrix. For acute gastroprotection ("cytoprotection"), maintenance of blood flow in the upper mucosa and epithelial restitution are listed as key mechanisms. For the long-term safeguarding of the mucosa, proper mucus and bicarbonate secretion, as well as ability to respond by cell proliferation, are the proposed key mechanisms of mucosal defense. The mechanisms of action of sucralfate are also multifactorial. The acute gastroprotection by sucralfate is a prostaglandin- and sulfhydryl-sensitive process: after early protection of microvasculature and maintenance of blood flow, along with direct or indirect preservation of the proliferative zone, rapid restitution repairs the initial epithelial defect. The mechanisms of accelerated healing by sucralfate of chronic ulcers include enhanced mucus and bicarbonate secretion, increased ability of mucus to maintain pH gradient, stimulated binding of epidermal growth factor and other growth factors, and maintained or enhanced blood flow resulting in increased cell proliferation leading to granulation tissue formation and re-epithelialization. The slight direct antipeptic and bile-acid binding property of sucralfate might also contribute to its ability to accelerate ulcer healing.