Guenther Boden, MD; Erik Murer, MD; Maria Mozzoli, BS
To determine the reason patients with insulinoma are unable to cease insulin secretion during hypoglycemia.
Five patients with insulinoma.
All patients fasted for up to 25 hours, during which blood was obtained serially for determination of glucose and insulin concentrations. Insulinomas were surgically removed from all patients and Glut 1 and Glut 2 transporter proteins were measured in solubilized tumor membranes by immune blotting.
In all patients, serum insulin concentrations failed to decrease to less than 30.0 pmol/L (<5.0 µU/mL) and C-peptide concentrations to less than 0.08 nmol/L during hypoglycemia (glucose concentration, <2.2 mmol/L) that was induced by fasting. The islet cell tumors from all five patients contained Glut 1, a low-Km glucose transporter protein, which is not normally present in β-cells. Glut 2, a high-Km glucose transporter protein, which is normally prevalent in β-cells, was undetectable in one patient and was present in what appeared to be low concentrations in the remaining four patients.
Our data are compatible with the concept that continued glucose transport, mediated by the low-Km Glut 1 glucose transporter, was responsible for continued insulin release during hypoglycemia in these patients.
Boden G, Murer E, Mozzoli M. Glucose Transporter Proteins in Human Insulinoma. Ann Intern Med. ;121:109–112. doi: 10.7326/0003-4819-121-2-199407150-00005
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Published: Ann Intern Med. 1994;121(2):109-112.
Cardiology, Coronary Risk Factors, Diabetes, Endocrine and Metabolism, Gastroenterology/Hepatology.
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