Proinsulin Secretion by a Pancreatic Beta-Cell Adenoma

Abstract

In a patient with a pancreatic islet-cell adenoma, fasting serum immunoreactive insulin was 114 to 372 μU per milliliter, about five to 20 times the normal value, but 77 per cent of this "insulin" was found to be proinsulin. After intravenous administration of 1 g of tolbutamide an increase in absolute proinsulin concentration was observed. By means of a specific immunoassay, human C-peptide was detected in the expected elution position after gel filtration of serum extracts.