The storage of insulin and proinsulin in various subcellular compartments of an islet adenoma and islets from the adjacent pancreas was compared. The tumor had a greater concentration of proinsulin relative to insulin in the secretion granule fraction than the adjacent islets. The microsome fraction from both the adenoma and islets had a larger percentage of proinsulin compared to insulin in contrast to other fractions. In a tolbutamide tolerance test before surgery, the percentage of serum proinsulin relative to insulin was 53% before and 17% after tolbutamide. Proinsulin secretion was temporally separated from insulin secretion in the early phase.
Bibliographical noteFunding Information:
From the Endocrinr Section. Departments Minnesota, Minneapolis. Minn. Received-for publication September 5. 1973. Supported by USPHS G-ants AM-II 739. AM-651 7, and RR-400. the Graduate School of the University of Minnesota,a nd the Twin Cities Diabetes Association. Minneapolis, Minn. Arnold W. Lindall. M.D., Ph.D.: Associate Prqfersor qf Medicine and Laboratory Medicine, University o/ Minnesota, and Director, Metropolitan Reference Laboratory. Minneapolis War Mentorial Blood Bank, Minneapolis. Minn. Michael W. Steffes, M.D., Ph.D.: Fellow. Department of Laboratory Medicine. University of Minnesota, Minneapolis. Minn. Edward T. Wong. M.D.: Assistant ProJessor of Medicine, University of Minnesota. and Department of Medicine. Hennepin County General Hospital, Minneapolis. Minn. Reprint requests should be addressed to Dr. Arnold W. Lindall, tory. 2304 Park Avenue South. Minneapolis, Minn. 55404. ? I974 b.1, Grune & Stratton, Inc.