Preservation of urinary postprandial alkaline tide despite inhibition of gastric acid secretion.

Ingestion of food leads to a rise in urinary pH. This phenomenon is commonly known as "postprandial alkaline tide" and is generally attributed to acid secretion in the stomach. To examine this hypothesis, we studied the changes of urinary pH, H+ concentration, PCO2, and bicarbonate in nine healthy volunteers with and without histamine H2 receptor blockade, using cimetidine and placebo medication. Postprandial alkaline tide persisted and was even exaggerated during treatment with cimetidine. Preservation of postprandial urinary alkaline tide, despite the expected inhibition of gastric acid secretion by cimetidine, tends to exclude a causal relation between alkaline tide and gastric acid secretion.