progastrin

Progastrin is the peptide precursor of the stomach hormone gastrin. It is produced by the G cells of the gastric antrum and, to a lesser extent, by enteroendocrine cells of the duodenum. The GAST gene encodes a larger precursor that is processed through the secretory pathway to yield progastrin, which is then further cleaved to the mature gastrins, principally gastrin-17 (G-17) and gastrin-34 (G-34).

In normal physiology, progastrin is secreted into the bloodstream as part of prohormone processing, but the biologically active forms responsible for gastric acid secretion and mucosal growth are the mature gastrins. Gastrin-17 and gastrin-34 stimulate parietal cells to secrete acid and promote growth of the gastric mucosa. Progastrin itself has limited direct activity in acid secretion, though certain processing intermediates and fragments may have biological effects in other tissues.

Clinical relevance arises mainly in conditions with gastrin excess, such as gastrin-secreting tumors (gastrinomas). In these cases, elevated levels of both gastrin and gastrin precursors, including progastrin, can be observed. Measurement of circulating progastrin may aid diagnosis or disease monitoring in some settings, particularly when assays distinguish progastrin from mature gastrins. Assay specificity varies, with some tests detecting progastrin, others measuring total gastrin, and some focusing on mature forms.