Localization and biosynthesis of polyamines in insulin-producing cells

Two recently developed fluorescence cytochemical methods, specific for spermidine and spermine, were used to localize polyamines in the endocrine pancreas. The polyamines were restricted to the insulin-producing beta-cells and were mainly associated with the secretory granules. Chemical polyamine determinations carried out on isolated rat and mouse pancreatic islets revealed large amounts of polyamines. Compared with extracts of whole pancreas, the islets contained very high concentrations of spermine relative to spermidine. Biosynthesis of polyamines from [3H]ornithine or from [3H]putrescine in isolated islets was significantly stimulated at high glucose concentrations. Moreover, significant incorporation of label from [3H]putrescine was also detected in gamma-aminobutyric acid. This incorporation, however, was not stimulated by high glucose. Possible roles for polyamines associated with the secretory granules in insulin-producing cells are discussed.