Andrew H. Soll

Nonsteroidal Anti-inflammatory Drugs and Peptic Ulcer Disease

Evidence has accumulated that nonsteroidal anti-inflammatory drugs (NSAIDs) cause clinically important gastroduodenal ulcers. The pathogenesis, which involves the impairment of mucosal resistance to injury in an acid-peptic environment, is multifactorial and controversial. Ulcers caused by NSAIDs can occur either in mucosa inflamed because of infection with Helicobacter pylori or in histologically normal mucosa. The use of these drugs has been linked to an unexpectedly high incidence of ulcer complications, and a history of peptic ulcer disease is common in such cases. Nonsteroidal anti-inflammatory drugs thus appear both to exacerbate an underlying peptic diathesis and to cause de novo ulcers. The association between the use of these drugs and ulcer complications is supported by ulcer prevalence data from cross-sectional studies, and by data from case-controlled and cohort studies, and from randomized, experimental trials. Drug-induced gastric ulcers have been prevented by misoprostol, but not by H2 blocker therapy. Several therapies have been reported to promote ulcer healing despite continued use of NSAIDs, but adequate controlled trials have not been done. Small gastric and duodenal ulcers readily heal, whereas larger gastric ulcers require vigorous and prolonged therapy. The relative efficacies of various therapies in preventing ulcers, healing ulcers, or preventing complications remain to be established.

Potentiating Interactions of Gastric Stimulants on 14C Aminopyrine Accumulation by Isolated Canine Parietal Cells

Interactions between secretagogues have been examined by using [14C]aminopyrine accumulation as an index of the response of isolated canine parietal cells to stimulation. Potentiating interactions were found between histamine and gastrin and histamine and carbachol, but not between carbachol and gastrin. When all three agents were present simultaneously, the response was greater than the sum of the three individual responses and satisfied other criteria for a true three-way potentiation. Against this three-way combination, atropine and cimetidine caused 42 ± 4% and 69 ± 7% inhibition, respectively. When both atropine and cimetidine were added to the three-way combination, the response was inhibited by 84 ± 3%, with the residual response equivalent to that produced by gastrin alone. The phosphodiesterase inhibitor isobutyl methyl xanthine (10 μM) markedly potentiated the actions of histamine. At 10-fold higher concentrations, isobutyl methyl xanthine also potentiated the response to carbachol and gastrin; these effects were inhibited by cimetidine, as had been found previously for. the action of isobutyl methyl xanthine alone. Interference with these potentiating interactions may explain the apparent nonspecificity of atropine and cimetidine in vivo. The striking potency of cimetidine in inhibiting all stimulants of acid secretion in vivo may be explained by the observation that histamine is an essential component of potentiating interactions that determine the parietal cell response to other stimulants.

Localization of specific binding sites for bombesin in the canine gastrointestinal tract.

The goal of these studies was to determine the tissue and cell types possessing specific binding sites for bombesin/gastrin-releasing peptide in the canine gastrointestinal tract. Monoiodinated, biologically active (Tyr-4)-bombesin 14 (100 pM) was applied to sections of canine gut and localized using quantitative autoradiography. The highest density of bombesin/gastrin-releasing peptide specific binding sites occurred over endocrine cells in the antral mucosa. Specific binding sites were also found on the circular muscle layer of the gastric fundus, gastric antrum, and ileum, on longitudinal muscle of the gastric fundus and antrum, and on neuronal elements in the myenteric plexus in the gastric fundus, antrum, and small intestine. No evidence for specific binding of 125I-(Tyr-4)-bombesin 14 was found in sections of canine esophagus, gastric cardia, gallbladder, pancreas, or colon. These results suggest sites of direct action of bombesin and endogenous gastrin-releasing peptide for gastrin release and gastrointestinal motility.

Effects of growth factors and trefoil peptides on migration and replication in primary oxyntic cultures.

Restitution, the lateral migration of cells over an intact basement membrane, maintains mucosal integrity. We studied the regulation of migration and proliferation of enzyme-dispersed canine oxyntic mucosa cells in primary culture. Confluent monolayers were wounded and cultured in serum-free medium, and cells migrating into the wound were counted. [3H]thymidine incorporation into DNA was studied using subconfluent cultures. Considerable migration occurred in untreated monolayers; however, epidermal growth factor (EGF), transforming growth factor (TGF)-alpha, basic fibroblast growth factor (bFGF), insulin-like growth factor I (IGF-I), two trefoil peptides, and interleukin (IL)-1beta further enhanced migration. The specific EGF receptor (EGFR) monoclonal antibody, MAb-528, inhibited both basal and TGF-alpha- or IL-1beta-stimulated migration, but not the response to trefoil peptide, bFGF, or IGF-I. Exogenous TGF-beta inhibited cell proliferation but did not alter migration. Immunoneutralization with anti-TGF-beta blocked the response to exogenous TGF-beta and produced a small enhancement of basal thymidine incorporation but did not attenuate basal or TGF-alpha-stimulated migration. In conclusion, endogenous EGFR ligands regulate proliferation and migration. TGF-beta inhibits mitogenesis; it did not upregulate migration in these cultures. Although bFGF, IGF-I, and IL-1beta enhance gastric epithelial migration, only IL-1beta acted in a TGF-alpha-dependent fashion.Restitution, the lateral migration of cells over an intact basement membrane, maintains mucosal integrity. We studied the regulation of migration and proliferation of enzyme-dispersed canine oxyntic mucosa cells in primary culture. Confluent monolayers were wounded and cultured in serum-free medium, and cells migrating into the wound were counted. [3H]thymidine incorporation into DNA was studied using subconfluent cultures. Considerable migration occurred in untreated monolayers; however, epidermal growth factor (EGF), transforming growth factor (TGF)-α, basic fibroblast growth factor (bFGF), insulin-like growth factor I (IGF-I), two trefoil peptides, and interleukin (IL)-1β further enhanced migration. The specific EGF receptor (EGFR) monoclonal antibody, MAb-528, inhibited both basal and TGF-α- or IL-1β-stimulated migration, but not the response to trefoil peptide, bFGF, or IGF-I. Exogenous TGF-β inhibited cell proliferation but did not alter migration. Immunoneutralization with anti-TGF-β blocked the response to exogenous TGF-β and produced a small enhancement of basal thymidine incorporation but did not attenuate basal or TGF-α-stimulated migration. In conclusion, endogenous EGFR ligands regulate proliferation and migration. TGF-β inhibits mitogenesis; it did not upregulate migration in these cultures. Although bFGF, IGF-I, and IL-1β enhance gastric epithelial migration, only IL-1β acted in a TGF-α-dependent fashion.

Morphologic and physiologic studies of canine ileal enteroglucagon-containing cells in short-term culture

Enteroglucagon-containing cells have been maintained in short-term culture, and the morphologic characteristics of these cells and their response to selected agents have been determined. After 48 h in culture the ultrastructural appearance of the enteroglucagon-immunoreactive cells showed evidence of polarization with re-formation of apical microvilli and the secretory granules concentrated at the opposite pole of the cell. The size of the intracellular secretory granules was 370 +/- 15 nm. The release of enteroglucagonlike immunoreactivity was stimulated in a dose-dependent manner by the adrenergic agonists epinephrine and isoproterenol. The response to epinephrine was competitively inhibited by propranolol, producing a rightward shift of the dose-responsive curve. The alpha-adrenergic agonists methoxamine and clonidine did not stimulate enteroglucagon release above basal. The adenyl cyclase activator forskolin also stimulated release of the peptide in a dose-dependent manner. Carbachol and somatostatin produced a dose-dependent inhibition of epinephrine-stimulated release, indicating direct inhibitory modulation of enteroglucagonlike immunoreactive cells. Somatostatin also inhibited forskolin-stimulated release. These data indicate that canine ileal enteroglucagon cells in short-term culture respond to a number of specific stimuli.

Somatostatin is released in response to cholecystokinin by activation of type A CCK receptors

Cholecystokinin is a principal mediator of intestinal fat-induced inhibition of gastric acid secretion, indicating that it is an important physiological enterogastrone. Cholecystokinin has been shown to inhibit acid secretion by activation of type A CCK receptors and through a mechanism involving somatostatin. In the present study, we investigated the possibility that these two mechanisms are directly related such that activation of type A CCK receptors by CCK causes the release of somatostatin. We tested this hypothesis in vivo in a study of CCK-stimulated release of somatostatin in dogs and in vitro in a study of CCK-stimulated release of somatostatin from an enriched culture of canine fundic D cells. In dogs, IV infusion of CCK (50 pmol/kg/h, IV) significantly increased circulating somatostatin concentrations above basal. Further, systemic administration of somatostatin MAb F(ab)1 fragments of a somatostatin monoclonal antibody prevented most of CCK-induced inhibition of meal-stimulated acid secretion. In canine fundic D cells in culture, CCK-stimulated somatostatin release was blocked in a dose-dependent fashion by application of a type A CCK receptor antagonist. This study indicates that CCK activates type A CCK receptors to release somatostatin from canine fundic mucosal D cells, and accounts for somatostatin-dependent CCK-induced inhibition of acid secretion.

Circadian Variation of Susceptibility to Gastric Mucosal Injury by Acidified Aspirin or Absolute Ethanol in the Rat

Circadian rhythms of physiologic processes allow coordination of interdependent functions and separation of incompatible functions. Several gastrointestinal processes, which potentially alter the balance between gastric mucosal protection and injury, show regular fluctuations. We investigated the possibility that susceptibility to gastric mucosal injury by acidified aspirin and absolute ethanol may vary with phases of the light/dark cycle in the rat. We found that acidified aspirin caused significantly more gastric mucosal lesions when administered early in the light phase compared with administration early in the dark phase. The differences in susceptibility were not altered by pretreatment conditions such as immobilization or length of the fasting period. Absolute ethanol also caused significantly greater gastric mucosal injury when administered in the light than in the dark phase, but this difference was only evident in rats immobilized during the pretreatment fasting period. In contrast to the acidified aspirin group, rats unrestrained during pretreatment fasting did not have light/dark differences in susceptibility to ethanol injury. We concluded that rats show circadian variation in susceptibility to gastric mucosal injury by acidified aspirin.

Prostacyclin analogues inhibit canine parietal cell activity and cyclic AMP formation.

To assess further the mechanism by which prostacyclin inhibits acid secretion, the actions of two stable prostacyclin analogues on parietal cell function and cyclic AMP formation were tested using enzymatically dispersed cells from canine fundic mucosa. Accumulation of 14C-aminopyrine (AP) was used as an index of parietal cell response to stimulation. The 16-phenoxy derivative or PGI2 inhibited accumulation of AP stimulated by histamine (10 microM), with 50% inhibition (ID50) at 10 nM. 68-PGI1 also inhibited the action of histamine (ID50 0.5 microM) but failed to block stimulation by carbachol or the dibutyryl derivative of cyclic AMP (dbcAMP). In similar concentrations to those producing inhibition of histamine-stimulated AP accumulation, the 16-phenoxy analogue and 6 beta-PGI1 inhibited histamine-stimulated cyclic AMP generation by parietal cells. At 100 fold higher concentrations, 68-PGI1 stimulated cyclic AMP formation, presumably in non-parietal cells. Even in high concentrations the 16-phenoxy analogue failed to increase cyclic AMP formation by mucosal cells. These data indicate that the stable prostacyclin analogues are potent, direct inhibitors of histamine-stimulated parietal cell function and that it is the inhibition, rather than the stimulation, of cyclic AMP formation that is linked to the antisecretory actions of these prostanoid compounds.

Characterization of bombesin receptors on canine antral gastrin cells

Dispersed canine antral mucosal cells were prepared by sequential steps of collagenase digestion and EDTA treatment. Cell preparations enriched in gastrin cells were made by centrifugal elutriation followed by step density gradient centrifugation. Specific, saturable, and reversible binding of 125I-[Tyr4]-bombesin was found in all preparations. This saturable binding was time, temperature, and cell number dependent. In both velocity (elutriator) and density cell separation experiments, saturable binding of bombesin correlated with the distribution of cells containing gastrin- but not somatostatin-like immunoreactivity. Maximal specific binding to gastrin (G) cell-enriched fractions was reached in 45 min at 37 degrees C and constituted 90% of total binding. Addition of 100 nM nonradioactive bombesin to cells incubated with 50 pM 125I-[Tyr4]-bombesin for 45 min resulted in time-dependent dissociation of specifically bound tracer to about 40% of the maximal equilibrium binding. Analysis of saturable equilibrium binding yielded a best fit to a one-site model of high affinity binding sites with an apparent Kd of 85 +/- 14 pM and a Bmax of 231,000 +/- 71,000 receptors/gastrin cell. Nonradioactive [Tyr4]-bombesin and related analogs inhibited the specific binding of the tracer in a dose-related manner. The rank order of potency, determined at the IC50, of [Tyr4]-bombesin and related analogs for inhibition of specific binding was bombesin greater than [Tyr4]-bombesin = hGRP-27 greater than GRP-10 greater than ranatensin much greater than neuromedin B. Cholecystokinin, somatostatin, substance K, and kassinin each tested at a concentration of 1 microM did not inhibit bombesin binding.(ABSTRACT TRUNCATED AT 250 WORDS)

Gastroesophageal reflux disease: Presentation and assessment of a common, challenging disorder

Although gastroesophageal reflux disease (GERD) is frequently referred to as a continuous spectrum, it is more useful to consider GERD as 2 discrete entities with several subsets that differ in pathophysiology, clinical presentation, natural history, and therapy. One entity is classic severe acid reflux with erosive esophagitis and its complications. Barretts esophagus is an important subset of this group, with markedly increased acid exposure and an increased risk of adenocarcinoma. The second entity is nonerosive reflux disease (NERD) with minimal or no esophagitis. Patients with NERD do not develop local mucosa complications, like stricture or Barretts esophagus, but their symptom severity can equal that of erosive esophagitis. Acid is involved in the symptoms of many but not all NERD patients. This acid dependence is evident either as an increase in esophageal acid reflux or a hypersensitivity to acid, and both generally respond well to proton pump inhibitor (PPI) therapy. NERD patients who are not acid-dependent have what is called functional heartburn; GERD-like symptoms are present, but there is no obvious involvement of refluxed acid. An important subset of GERD is refractory GERD, which consists of patients who fail aggressive PPI therapy. Parallel findings with other refractory syndromes can be anticipated; however, there are indications that psychosocial factors play a major role in refractory GERD, and these patients may benefit more from an integrated biopsychosocial approach. Diagnosis of GERD is usually made on clinical grounds, often supplemented by a therapeutic trial with antisecretory agents. Endoscopy is reserved for patients with alarm symptoms, such as dysphagia, anemia, or weight loss, or to detect Barretts esophagus. Endoscopy is not useful to exclude the diagnosis of GERD because it will be negative in 70% of cases in primary care. Ambulatory 24-hour esophageal pH monitoring is necessary only when the diagnosis is in doubt, the patient fails medical management, or surgery is contemplated.