ACVIM consensus statement: Support for rational administration of gastrointestinal protectants to dogs and cats

The stomach consists of 3 topographic (fundus, corpus, and antrum) and 2 functional (oxyntic and pyloric gland) areas. The oxyntic gland area, the hallmark of which is the oxyntic (oxys, Greek for acid) or parietal cell, comprises 80% of the organ. The pyloric gland area, the hallmark of which is the gastrin or G cell, comprises 20% of the organ. The gastric mucosa is a continuous epithelial layer folded into gastric pits. The oxyntic glands contain 7 types of cells: 1) mucous neck cells, which produce mucus and gastric lipase in dogs; and surface mucous cells, which are cytoprotective; 2) chief cells responsible for the secretion of pepsinogen and leptin; 2213) parietal cells, which produce hydrochloric acid (HCl) and intrinsic factor; 4) enterochromaffin-like (ECL) cells that produce histamine; 5) D cells that contain somatostatin and amylin; 6) enterochromaffin (EC) cells that secrete atrial natriuretic peptide [ANP], serotonin, and adrenomedullin; and 7) A-like or Gr cells (ghrelin and obestatin). Fig 1: Model illustrating the neural, paracrine, and hormonal regulation of gastric acid secretion
Histamine released from ECL cells acts via H 3 receptors to inhibit SST secretion.
The principal stimulants of acid secretion at the level of the parietal cell are Ach released from postganglionic enteric neurons (neurocrine); gastrin, released from antral G cells (hormonal); and histamine, released from oxyntic ECL cells (paracrine). Histamine, released from ECL cells, binds to H2 receptors that activate adenylate cyclase and generate adenosine 3 ,5 -cyclic monophosphate (cAMP). Gastrin, released from G cells, binds to cholecystokinin-2 (CCK-2) receptors that activate phospholipase C to induce release of cytosolic calcium (Ca ++ ). [bib_ref] Gastric acid secretion, Hersey [/bib_ref] Gastrin stimulates the parietal cell directly and indirectly by releasing histamine from ECL cells.
Ach, released from intramural neurons, binds to M 3 receptors that are coupled to an increase in intracellular calcium. The intracellular cAMP and calcium-dependent signaling systems activate downstream protein kinases, ultimately leading to fusion and activation of H + , K + ,-ATPase, the proton pump.A decrease of intragastric pH stimulates somatostatin release from oxyntic D cells. Somatostatin, acting via the SSTR2 receptor, inhibits the parietal cell directly as well as indirectly by inhibiting histamine release from ECL cells.

## Supplement 2

## Regulation of gastric mucosal barrier function
Under normal circumstances, gastric mucosal integrity is maintained by defense mechanisms, which include pre-epithelial factors (mucus-bicarbonate-phospholipid "barrier"), an epithelial "barrier" (surface epithelial cells connected by tight junctions and generating bicarbonate, mucus, phospholipids, trefoil peptides, prostaglandins, and heat shock proteins), continuous cell renewal accomplished by proliferation of progenitor cells (regulated by growth factors, PGE 2 , and survivin), continuous blood flow through mucosal microvessels, and endothelial "barrier", sensory innervation, and generation of PGs and nitric oxide. 225,226 Gastric mucosal injury may occur when noxious factors overwhelm an intact mucosal barrier or when the mucosal defense is impaired.

## Local gastric mucosal defense mechanisms
Mucus-bicarbonate-phospholipid "barrier." The mucus-bicarbonate-phospholipid "barrier" is formed by mucus, gel, bicarbonate, and surfactant phospholipids and constitutes the first line of mucosal defense. [bib_ref] Gastroduodenal mucus bicarbonate barrier: protection against acid and pepsin, Allen [/bib_ref] This unstirred layer retains the bicarbonate secreted by surface epithelial cells to maintain a neutral microenvironment (pH ~ 7.0) at the surface epithelial cells and prevents penetration of pepsin and thus proteolytic digestion of the surface epithelium. Mucus gel is cosecreted with low-molecular weight trefoil factor family peptides (TFFs). 228 TFF2
increases the viscosity of gastric mucin and stabilizes the gel network. Ulcerogenic substances such as aspirin and bile salts cause dissipation of the mucus gel and phospholipid layer, leading to acid back-diffusion and mucosal injury. [bib_ref] Gastroduodenal mucus bicarbonate barrier: protection against acid and pepsin, Allen [/bib_ref] The secretion of HCO3into a stable, adherent mucus gel layer creates a pH gradient at the epithelial surface in the stomach and duodenum, and provides the first line of mucosal defense against luminal acid. When the mucus bicarbonate barrier is overwhelmed or breaks down in disease, the next series of protective mechanisms comes into play, including intracellular neutralization of acid, rapid epithelial repair, and maintenance and distribution of mucosal blood flow.
Surface epithelial cells. The next line of mucosal defense is formed by a continuous layer of surface epithelial cells which secrete mucus and bicarbonate and generate PGs, heat shock proteins, TFFs, and cathelocidins. Cathelocidins and  defensins are cationic peptides that play roles in the innate defensive system at mucosal surfaces preventing bacterial colonization.

## Continuous cell renewal from mucosal progenitor cells.
Complete replacement of the gastric surface epithelium usually takes 3-7 days, whereas months are required to replace glandular cells. [bib_ref] Gastric mucosal defense and cytoprotection: bench to bedside, Laine [/bib_ref] An important new finding is the expression of survivin, an antiapoptosis protein, in gastric progenitor cells, which allows these cells to avoid apoptosis and promotes mitosis. [bib_ref] Survivin: a novel target for indomethacininduced gastric injury, Chiou [/bib_ref] Alkaline tide. "Alkaline tide" occurs because stimulated parietal cells secreting HCl into the gastric lumen concurrently secrete bicarbonate into the interstitium and lumen of adjacent capillary blood vessels. The bicarbonate contributes to the unstirred layer of the mucus and bicarbonate. acid, pepsin, bile acids) or deficient mucosal defenses (e.g., gastric mucosal blood flow, mucus production, bicarbonate secretion, epidermal growth hormone, prostaglandins). [bib_ref] Pathophysiology and modern treatment of ulcer disease, Holle [/bib_ref] For example, increased gastric mucosal blood flow can protect against excessive gastric acid secretion, while deficient mucosal blood flow allows otherwise innocuous amounts of acid to produce GUE.
Hence, while gastric pH is a marker for gastroprotection, ignoring the other factors is simplistic and potentially misleading. NSAID-related injury, stress-related mucosal disease (SRMD), and
Helicobacter pylori-associated disease in people are among the most important causes of impaired gastric mucosal barrier function.

# Nsaid-related gastric injury
Gastric mucosal damage associated with NSAID administration has been well documented in many species, including dogs, cats, and humans. 94, [bib_ref] Spontaneous gastrointestinal perforation in cats: a retrospective study of 13 cases, Bernardin [/bib_ref] [bib_ref] Endoscopy of the gastroduodenal mucosa after carprofen, meloxicam and ketoprofen administration in..., Forsyth [/bib_ref] [bib_ref] The effect of tramadol and indomethacin coadministration on gastric barrier function in..., Hill [/bib_ref] [bib_ref] Gastrointestinal tract perforation in dogs treated with a selective cyclooxygenase-2 inhibitor: 29..., Lascelles [/bib_ref] [bib_ref] Evaluation of adverse effects of long-term oral administration of carprofen, etodolac, flunixin..., Luna [/bib_ref] [bib_ref] An overview of history, pathogenesis and treatment of perforated peptic ulcer disease..., Prabhu [/bib_ref] [bib_ref] Nonsteroidal anti-inflammatory drugs and upper and lower gastrointestinal mucosal damage, Sostres [/bib_ref] As many as 25% of people who are chronic NSAID users will develop ulcer disease, and 2-4% will bleed or perforate. [bib_ref] Comparison of upper gastrointestinal toxicity of rofecoxib and naproxen in patients with..., Bombardier [/bib_ref] [bib_ref] Nonsteroidal anti-inflammatory drug gastropathy, Laine [/bib_ref] [bib_ref] Gastroduodenal mucosa and dyspeptic symptoms in arthritic patients during chronic nonsteroidal anti-inflammatory..., Larkai [/bib_ref] [bib_ref] Misoprostol reduces serious gastrointestinal complications in patients with rheumatoid arthritis receiving nonsteroidal..., Silverstein [/bib_ref] Risk factors for GI complications associated with NSAIDs in people include increased age > 65 years (odds ratio 4.7), [bib_ref] Nonsteroidal anti-inflammatory drug use and increased risk for peptic ulcer disease in..., Griffin [/bib_ref] higher doses of NSAIDs (odds ratio 3.9 at 1-1.5 times standard dose), short-term history of NSAID use (< 1 month; odds ratio 12.7), concurrent administration of corticosteroids (odds ratio 4.4), and anticoagulants (odds ratio 12.7). [bib_ref] Nonsteroidal antiinflammatory drugs and acute renal failure in elderly persons, Griffin [/bib_ref] 

## Stress-related mucosal disease (srmd)
Stress-related gastric mucosal injury appears to be related to local ischemia, although progression to significant mucosal injury requires acid as well. Studies in a rat model reveal a significant correlation between blood pressure during hypotension and gastric mucosal blood flow. [bib_ref] Role of blood flow in gastric and duodenal mucosal injury in the..., Leung [/bib_ref] [bib_ref] Risk factors for gastrointestinal bleeding in critically ill patients. Canadian Critical Care..., Cook [/bib_ref] Endoscopic studies generally indicate that approximately 75-100% of critically ill human patients have gross gastric lesions visible when endoscopy is performed within the first 1-3 days of illness. [bib_ref] Natural history and surgical dilemma of "stress" gastric bleeding, Lucas [/bib_ref] Lesions are generally diffuse subepithelial hemorrhage and erosions and occur more commonly in the proximal stomach. [bib_ref] Stress-related mucosal disease: risk factors and prophylactic therapy, Spirt [/bib_ref] Although stress-related bleeding has been calculated to increase hospital stay and mortality, studies of prophylactic therapy have not revealed that decreased bleeding translates into decreased mortality. 262

## Helicobacter
Overwhelming evidence supports a causal relationship between Helicobacter pylori (HP)
infection and the development of gastric ulceration (GU) and duodenal ulceration (DU) in people. [bib_ref] Helicobacter pylori: the missing link in perspective, Hopkins [/bib_ref] [bib_ref] Helicobacter pylori infection as a cause of gastritis, duodenal ulcer, gastric cancer..., Veldhuyzen Van Zanten [/bib_ref] Several studies indicate that 95% of patients with DU and 80% of patients with GU are infected with HP. [bib_ref] Helicobacter pylori infection as a cause of gastritis, duodenal ulcer, gastric cancer..., Veldhuyzen Van Zanten [/bib_ref] The most convincing evidence for a casual association between HP and peptic ulcer disease is derived from studying ulcer recurrence rates in patients treated with antibiotics effective for eradicating HP. Compared with patients whose ulcers were healed by H 2 RAs, the patients in whom HP was eradicated by antibiotics showed much lower rate of DU recurrence. [bib_ref] Efficacy and tolerability of a one-week triple therapy consisting of pantoprazole, clarithromycin..., Labenz [/bib_ref]