Pentagastrin

Pentagastrin is a synthetic pentapeptide containing the C-terminal tetrapeptide sequence of gastrin (Trp-Met-Asp-Phe) linked to a beta-alanine residue with a tert-butyloxycarbonyl (Boc) protecting group. This minimal bioactive fragment retains the full acid-stimulating activity of native gastrin, making pentagastrin a standardized and reproducible diagnostic agent for assessing gastric acid secretory capacity.

The pentagastrin stimulation test was historically the gold standard for measuring maximal gastric acid output (MAO). In this test, pentagastrin is administered subcutaneously, and gastric secretions are collected via nasogastric tube over one hour. The volume and acidity of the collected secretions quantify the stomach's maximal acid-producing capacity. This test was used to diagnose conditions such as Zollinger-Ellison syndrome (gastrinoma), atrophic gastritis, pernicious anemia, and to assess the completeness of vagotomy.

Pentagastrin also plays an important role in thyroid oncology as a provocative test for calcitonin secretion. Medullary thyroid carcinoma (MTC) cells secrete calcitonin, and pentagastrin stimulates calcitonin release from these cells. The pentagastrin-stimulated calcitonin test is used for screening in families with multiple endocrine neoplasia type 2 (MEN 2), for detecting residual or recurrent MTC after surgery, and for evaluating patients with mildly elevated basal calcitonin levels.

The availability of pentagastrin has become increasingly limited in many countries, including the United States, where it has been withdrawn from the market. This has complicated the performance of these diagnostic tests and led to the adoption of alternative provocative agents (such as calcium infusion for calcitonin stimulation testing) and non-invasive diagnostic methods.