Which Agent Inhibits Gastric Bicarbonate Secretion?
Aspirin (c) inhibits gastric bicarbonate secretion, which is a key protective mechanism of the gastric mucosa. 1
Mechanisms of Gastric Protection and NSAID-Induced Damage
Role of Prostaglandins in Gastric Protection
- Prostaglandins play a crucial protective role in the gastric mucosa by stimulating the synthesis and secretion of mucus and bicarbonate, as well as promoting epithelial proliferation and increasing mucosal blood flow 2
- Prostaglandins found in the stomach have dual protective effects: they inhibit acid secretion and enhance mucosal defensive mechanisms 3
- Endogenous prostaglandins modulate acid secretion and stimulate both mucus and bicarbonate secretion in the stomach and duodenum, serving as key components of the mucosal defense system 3
How Aspirin Inhibits Bicarbonate Secretion
- Aspirin decreases both basal and prostaglandin-stimulated bicarbonate secretion in the duodenum through histamine-dependent and histamine-independent pathways 1
- Aspirin causes topical injury to the mucosa and systemic effects through prostaglandin depletion, which impairs the gastric mucosal protective barrier 2
- The inhibition of prostaglandin synthesis by aspirin leads to reduced bicarbonate secretion, creating an environment more susceptible to acid-peptic damage 1, 4
Effects of Other Agents on Bicarbonate Secretion
Prostaglandins (option a)
- Rather than inhibiting bicarbonate secretion, prostaglandins actually stimulate bicarbonate secretion in the gastroduodenal mucosa 2, 5
- Prostaglandins of the E type have been shown to enhance protective mechanisms including bicarbonate secretion 5
- A prostaglandin-depleted mucosa (as occurs with NSAID use) is more susceptible to damage due to impaired bicarbonate secretion 3
Vagal Stimulation (option b)
- There is no evidence in the provided literature that vagal stimulation inhibits gastric bicarbonate secretion
- The vagus nerve is primarily associated with stimulation of gastric acid secretion, not inhibition of bicarbonate secretion 2
Gastrin (option d)
- None of the evidence provided indicates that gastrin inhibits gastric bicarbonate secretion
- Gastrin is primarily known for its role in stimulating gastric acid secretion 2
Clinical Implications of Aspirin's Effect on Bicarbonate Secretion
- The inhibition of bicarbonate secretion by aspirin contributes to its ulcerogenic potential, especially when used chronically 2
- Even low-dose aspirin (81-325 mg/day) used for cardiovascular protection increases the risk of GI injury through these mechanisms 2
- Attempts to coat or buffer aspirin have not successfully mitigated these GI effects, as the systemic inhibition of prostaglandin synthesis still occurs 2
Protective Strategies
- Proton pump inhibitors (PPIs) can be used as co-therapy to reduce the risk of aspirin-induced gastric damage 2
- H2-receptor antagonists may provide some protection against aspirin-induced duodenal ulcers but are less effective for gastric ulcers 2
- Patients with risk factors such as age over 60-65 years, history of GI bleeding, or concurrent use of multiple antithrombotics should receive gastroprotection when taking aspirin 6
In conclusion, among the options presented, only aspirin (c) inhibits gastric bicarbonate secretion, which is an important mechanism contributing to its potential for causing gastroduodenal injury.