Elevated Plasma Proglucagon-like Component with a Glucagon-Secreting Tumor

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Abstract
To determine the character of the glucagon secretion and its modification by streptozotocin, we studied the plasma of a patient with recurrent pancreatic alpha-cell carcinoma. The plasma immunoreactive glucagon level before treatment was 4.80 ng per milliliter. Biogel column separation of the plasma immunoreactive glucagon revealed four components; the predominant component had a molecular weight of 9000 daltons and was designated as proglucagon-like. This fraction constituted 60 to 90 per cent of the total circulating immunoreactive glucagon, and had a biologic activity of 32 per cent of that of an immunoequivalent amount of normal (porcine) pancreatic glucagon. After treatment with streptozotocin (1.5 g per square meter) the plasma immunoreactive glucagon level decreased to 0.24 ng per milliliter. Treatment was accompanied by a marked reduction in the proglucagon-like component, and the appearance of pancreatic glucagon (molecular weight of 3500 daltons) as the major post-therapy fraction. These findings support the use of streptozotocin in the management of unresectable glucagon-secreting tumors. (N Engl J Med 295:242–245, 1976