HYPERSECRETION OF ISLET AMYLOID POLYPEPTIDE FROM PANCREATIC-ISLETS OF VENTROMEDIAL HYPOTHALAMIC-LESIONED RATS AND OBESE ZUCKER RATS

To investigate the possible role of islet amyloid polypeptide (IAPP) in the development of type 2 diabetes mellitus, we examined the IAPP content and secretion in pancreatic islets isolated from ventromedial hypothalamic (VMH)-lesioned rats and genetically obese Zucker rats, using a specific RIA for IAPP. Obesity and hyperinsulinemia were observed in rats 21 days after VMH lesioning. IAPP content was increased in the islets of VMH-lesioned rats compared with findings in the sham-operated controls (100.9 +/- 6.6 vs. 72.8 +/- 3.85 fmol/islet; P < 0.01). Isolated islets of VMH-lesioned rats secreted larger amounts of IAPP in the presence of 2.8 mM and 16.7 mM glucose (2.99 +/- 0.98 and 11.2 +/- 1.29 fmol.islet-1.3 h-1) than was noted in sham-operated rats (ND and 6.65 +/- 0.78 fmol.islet-1.3 h-1). In the obese Zucker rats, aged 14 weeks, IAPP concentrations in the islets were elevated compared with lean rats (133.3 +/- 10.6 vs. 84.4 +/- 8.5 fmol/islet; P < 0.01). The isolated islets secreted larger amounts of IAPP in response to 2.8 mM and 16.7 mM glucose (2.83 +/- 0.88 and 15.81 +/- 1.35 fmol.islet-1.3 h-1) than did those from lean control rats (0.36 +/- 0.19 and 12.49 +/- 1.20 fmol.islet-1.3 h-1). These results strongly suggest that over-production and hypersecretion of IAPP occur in animals with obesity and hyperinsulinemia.