How does Cimetidine work to reduce stomach acid production?

A patient with a duodenal ulcer is treated successfully with the drug cimetidine. The basis for cimetidine’s inhibition of gastric H+ secretion is that it A. Blocks H2 receptors on parietal cells B. Blocks muscarinic receptors on parietal cells C. Enhances the action of acetylcholine (ACh) on parietal cells D. Increases intracellular cyclic adenosine monophosphate (cAMP) levels

A

The correct answer is A. Blocks H2 receptors on parietal cells.

Cimetidine is a drug that belongs to the class of H2 receptor antagonists, which are drugs that work by blocking the histamine H2 receptors on parietal cells in the stomach, thereby reducing the production of acid by these cells. When histamine binds to H2 receptors on parietal cells, it activates a cascade of events that leads to the secretion of acid into the stomach. By blocking these receptors, cimetidine reduces the release of acid, and it is thus effective in treating conditions such as duodenal ulcers, gastroesophageal reflux disease (GERD), and other acid-related disorders.

Options B, C, and D are incorrect because cimetidine does not affect muscarinic receptors, acetylcholine levels, or cAMP levels. Muscarinic receptors are not involved in the secretion of gastric acid; rather, they are involved in the regulation of gastric motility. Acetylcholine can stimulate gastric acid secretion, but cimetidine does not enhance its action. Cyclic AMP is also involved in the regulation of gastric acid secretion, but cimetidine does not increase its levels.

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