Insulin, Glucagon, and Somatostatin Secretion by Cultured Rat Islet Cell Tumor and Its Clones

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Abstract
Cells derived from rat islet tumor and grown in culture (parent cells-RIN-m) and 2 clones obtained from them were used to study the effect of various secretagogues on insulin, glucagon and somatostatin secretion. Parent cells secreted all 3 hormones in various quantities, while clone 5F secreted predominantly insulin and clone 14B secreted predominantly somatostatin. The secretory behaviors of these cells were compared to each other and to that of normal islets. In general, as in the case of normal islets, insulin secretion was stimulated by Ca, K, tolbutamide, theophylline and glucagon. It was inhibited by somatostatin. Glucagon secretion was stimulated by Ca, arginine, and theophylline. Somatostatin secretion was stimulated in clone 14B by arginine, tolbutamide, theophylline, and insulin. These cells differ from normal islets in that they do not respond to glucose or arginine with increased insulin secretion. Somatostatin failed to inhibit glucagon secretion. The similarity in insulin secretory responses of parent cells and clone 5F suggests that local or paracrine islet hormone secretion plays only a negligible role in the control of other hormone secretion in these cells.