Gastrin	

Gastrin is produced by G cells in the gastric antrum (from which it was first isolated in 1905) and upper small intestine and exists in a variety of molecular forms. The principal ones are fourteen, seventeen, or thirty-four amino acids in length, the latter being described as ‘big gastrin’. The bioactive part of the molecule is the four amino-acid carboxy terminal sequence, which is common to all. The predominant circulating forms of gastrin are G17 from the stomach and G34 from the small intestine. G17 has a half-life in the circulation of some five minutes, while G34 has a half-life of approximately forty minutes; the two forms, however, are almost equipotent