Effect of Streptozotocin on Qualitative Aspects of Plasma Insulin in a Patient with a Malignant Islet Cell Tumor

The effect of Streptozotocin on qualitative aspects of insulin secretion was studied in a patient with an islet cell carcinoma. A dramatic clinical response to chemotherapy with regression in liver size and cessation of hypoglycemic attacks was observed in this patient despite minimal change in plasma IRI concentrations. Streptozotocin treatment reduced the unusually large proportion of “big” insulin at 1, 2 and 3 hr after oral glucose. The use of “big” insulin as a marker for abnormal insulin biosynthesis and release is discussed. Abnormal insulins with variable immunoactivity and bioactivity may be formed and might explain both the abnormal glucose tolerance tests and the frequency of hypoglycemia without elevated plasma IRI in patients with islet cell tumors.