Comparison of insulin and proinsulin storage in an islet adenoma and adjacent pancreas.

Abstract 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.