The heterogeneity of gastrin, with reference to conversion of gastrin-17.

High-resolution gel chromatography monitored by a sensitive radioimmunoassay for gastrin has disclosed that gastrin circulates in twenty different components. Since the assay is specific for the biological active sequence of gastrin (-Trp-Met-Asp-PheNH2), we conclude that all the twenty circulating molecular forms of gastrin encountered in this study may participate in the regulation of gastric acid secretion. There are two dominating forms of gastrin in serum: gastrin-34-like components and gastrin-17-like components. The former constituted 60% and the latter constitutes approximately 30% of the immunoreactive gastrins. We suggest that extragastrointestinal conversion of gastrin-17, released from tissue, is an important source of gastric-34-like components. Such conversion has been observed in intact man and pig. Studies with the isolated perfused porcine liver indicate that the liver is important in the metabolism of gastrin-17, and that conversion may be a hepatic function.