EFFECT OF ISLET AMYLOID POLYPEPTIDE ON SOMATOSTATIN INHIBITION OF INSULIN-SECRETION FROM ISOLATED RAT PANCREATIC-ISLETS

In this study, we investigated the presence of islet amyloid polypepti de (IAPP) in somatostatin cells of rat endocrine pancreas and the effe ct of exogenous IAPP and somatostatin, separate or combined, on in vit ro insulin secretion. By immunocytochemistry, LAPP was found in both B and D cells of rat pancreatic islets. Furthermore, the labeling densi ty of IAPP in D cells was nearly four times higher than in B cells. Af ter a 2-day preincubation in RPMI 1640 (11.1 mM glucose), isolated rat pancreatic islets were exposed to IAPP and/or somatostatin for 90 min in modified Krebs-Ringer bicarbonate (KRB) buffers containing 11.1 or 22.2 mM glucose, or 11.1 mM glucose + 10 mM L-arginine, respectively. At 11.1 mM glucose, insulin secretion was not affected by IAPP and/or somatostatin at concentrations investigated. Insulin response to 22.2 mM glucose was inhibited by exogenous somatostatin. Arginine-stimulat ed insulin secretion was also inhibited by somatostatin, and the effec t was significantly potentiated with additional 10(-5) M IAPP. The stu dy shows that rat pancreatic D cells have higher IAPP density than B c ells in the same islets and that IAPP and somatostatin may cooperate o n rat pancreatic B cells to regulate the insulin secretion in response to potent stimulation. (C) 1997 Elsevier Science B.V.