Stimulation of Insulin Release by Glucose in a Transplantable Rat Islet Cell Tumor*

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Abstract
A subline of an x-ray-induced transplantable rat insulinoma has been studied in vivo and in vitro. Tumors grew rapidly after sc transplantation and were rich in insulin, but contained only small amounts of glucagon and somatostatin. Despite marked basal hyperinsulinemia, iv glucose administration caused a further increase in plasma insulin in tumor-bearing rats. When the pancreas was functionally excluded by ligation of supplying arteries, glucose still elicited a clear insulin response. In vitro, insulin release from perifused tumor fragments was stimulated by the combination of glucose and 3-isobutyl-l-methylxanthine, but not by glucose alone. In contrast, there was a clear stimulation of insulin release by glucose in primary monolayer cultures of tumor cells. This suggests a better functional capacity of the cultured cells compared to that of the tumor fragments. The results indicate that this transplantable rat islet cell tumor is a convenient source of large quantities of functional β-cells

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