Circulating Proinsulin-like Material in Patients with Functioning Insulinomas

Abstract

Because islet-cell tumors of the pancreas produce proinsulin-like material in vitro, the plasma of 11 patients with functioning insulinomas was studied to determine the immunoreactive insulin proportion contributed by circulating proinsulin-like material. The plasma of nine patients with insulinomas showed on gel filtration an increased proinsulin-like material (28 to 89 per cent) as compared to subjects of normal weight, those who were obese, and those with functional hypoglycemia (less than 20 per cent). Polyacrylamide-gel electrophoresis of serum showed material compatible with proinsulin, insulin and an intermediate component. Considering the data so far reported, any patient with hypoglycemia who shows an elevated percentage of proinsulin-like material should be suspected of having an insulinoma. In one patient, surgical removal of an islet-cell adenoma resulted in a fall of serum proinsulin-like material from 65 to 0 per cent. Determination of plasma proinsulin-like material may provide diagnostic aid and a measure of therapeutic efficacy in patients with islet-cell tumors.